1
|
van der Zee LJC, Hofman J, van Gaalen JM, Slootweg JC. Mechanistic studies on single-electron transfer in frustrated Lewis pairs and its application to main-group chemistry. Chem Soc Rev 2024; 53:4862-4876. [PMID: 38623621 PMCID: PMC11104263 DOI: 10.1039/d4cs00185k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Indexed: 04/17/2024]
Abstract
Advances in the field of frustrated Lewis pair (FLP) chemistry have led to the discovery of radical pairs, obtained by a single-electron transfer (SET) from the Lewis base to the Lewis acid. Radical pairs are intriguing for their potential to enable cooperative activation of challenging substrates (e.g., CH4, N2) in a homolytic fashion, as well as the exploration of novel radical reactions. In this review, we will cover the two known mechanisms of SET in FLPs-thermal and photoinduced-along with methods (i.e., CV, DFT, UV-vis) to predict the mechanism and to characterise the involved electron donors and acceptors. Furthermore, the available techniques (i.e., EPR, UV-vis, transient absorption spectroscopy) for studying the corresponding radical pairs will be discussed. Initially, two model systems (PMes3/CPh3+ and PMes3/B(C6F5)3) will be reviewed to highlight the difference between a thermal and a photoinduced SET mechanism. Additionally, three cases are analysed to provide further tools and insights into characterizing electron donors and acceptors, and the associated radical pairs. Firstly, a thermal SET process between LiHMDS and [TEMPO][BF4] is discussed. Next, the influence of Lewis acid complexation on the electron acceptor will be highlighted to facilitate a SET between (pBrPh)3N and TCNQ. Finally, an analysis of sulfonium salts as electron acceptors will demonstrate how to manage systems with rapidly decomposing radical species. This framework equips the reader with an expanded array of tools for both predicting and characterizing SET events within FLP chemistry, thereby enabling its extension and application to the broader domain of main-group (photo)redox chemistry.
Collapse
Affiliation(s)
- Lars J C van der Zee
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, PO box 94157, 1090 GD Amsterdam, The Netherlands.
| | - Jelle Hofman
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, PO box 94157, 1090 GD Amsterdam, The Netherlands.
| | - Joost M van Gaalen
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, PO box 94157, 1090 GD Amsterdam, The Netherlands.
| | - J Chris Slootweg
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, PO box 94157, 1090 GD Amsterdam, The Netherlands.
| |
Collapse
|
2
|
Helling C, van der Zee LJC, Hofman J, de Zwart FJ, Mathew S, Nieger M, Slootweg JC. Homolytic C-H Bond Activation by Phosphine-Quinone-Based Radical Ion Pairs. Angew Chem Int Ed Engl 2023; 62:e202313397. [PMID: 37831966 DOI: 10.1002/anie.202313397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Revised: 10/04/2023] [Accepted: 10/13/2023] [Indexed: 10/15/2023]
Abstract
Herein, we present the formation of transient radical ion pairs (RIPs) by single-electron transfer (SET) in phosphine-quinone systems and explore their potential for the activation of C-H bonds. PMes3 (Mes=2,4,6-Me3 C6 H2 ) reacts with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) with formation of the P-O bonded zwitterionic adduct Mes3 P-DDQ (1), while the reaction with the sterically more crowded PTip3 (Tip=2,4,6-iPr3 C6 H2 ) afforded C-H bond activation product Tip2 P(H)(2-[CMe2 (DDQ)]-4,6-iPr2 -C6 H2 ) (2). UV/Vis and EPR spectroscopic studies showed that the latter reaction proceeds via initial SET, forming RIP [PTip3 ]⋅+ [DDQ]⋅- , and subsequent homolytic C-H bond activation, which was supported by DFT calculations. The isolation of analogous products, Tip2 P(H)(2-[CMe2 {TCQ-B(C6 F5 )3 }]-4,6-iPr2 -C6 H2 ) (4, TCQ=tetrachloro-1,4-benzoquinone) and Tip2 P(H)(2-[CMe2 {oQtBu -B(C6 F5 )3 }]-4,6-iPr2 -C6 H2 ) (8, oQtBu =3,5-di-tert-butyl-1,2-benzoquinone), from reactions of PTip3 with Lewis-acid activated quinones, TCQ-B(C6 F5 )3 and oQtBu -B(C6 F5 )3 , respectively, further supports the proposed radical mechanism. As such, this study presents key mechanistic insights into the homolytic C-H bond activation by the synergistic action of radical ion pairs.
Collapse
Affiliation(s)
- Christoph Helling
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090, GD Amsterdam, The Netherlands
| | - Lars J C van der Zee
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090, GD Amsterdam, The Netherlands
| | - Jelle Hofman
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090, GD Amsterdam, The Netherlands
| | - Felix J de Zwart
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090, GD Amsterdam, The Netherlands
| | - Simon Mathew
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090, GD Amsterdam, The Netherlands
| | - Martin Nieger
- Department of Chemistry, University of Helsinki, A. I. Virtasen aukio 1, P.O. Box 55, FIN-00014, Helsinki, Finland
| | - J Chris Slootweg
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090, GD Amsterdam, The Netherlands
| |
Collapse
|
3
|
Wang M, Shanmugam M, McInnes EJL, Shaver MP. Light-Induced Polymeric Frustrated Radical Pairs as Building Blocks for Materials and Photocatalysts. J Am Chem Soc 2023; 145:24294-24301. [PMID: 37890166 PMCID: PMC10636756 DOI: 10.1021/jacs.3c09075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2023] [Revised: 10/06/2023] [Accepted: 10/11/2023] [Indexed: 10/29/2023]
Abstract
Polymeric frustrated Lewis pairs, or poly(FLP)s, have served to bridge the gap between functional polymer science and main group catalysis, pairing the uniqueness of sterically frustrated Lewis acids and bases with a polymer scaffold to create self-healing gels and recyclable catalysts. However, their utilization in radical chemistry is unprecedented. In this paper, we disclose the synthesis of polymeric frustrated radical pairs, or poly(FRP)s, by in situ photoinduction of FLP moieties, where their Lewis acidic and basic centers are tuned to promote single electron transfer (SET). Through systematic manipulation of the chemical structure, we demonstrate that inclusion of ortho-methyl groups on phosphine monomers is crucial to enable SET. The generation of radicals is evidenced by monitoring the stable polymeric phosphine radical cations via UV/vis and EPR spectroscopy. These new poly(FRP)s enable both catalytic hydrogenation and radical-mediated photocatalytic perfluoroalkylations. These polymeric radical systems open new avenues to design novel functional polymers for catalysis and photoelectrical chemistry.
Collapse
Affiliation(s)
- Meng Wang
- Department
of Materials, School of Natural Sciences, University of Manchester, Manchester M13 9PL, U.K.
- Sustainable
Materials Innovation Hub, Henry Royce Institute, University of Manchester, Manchester M13 9PL, U.K.
| | - Muralidharan Shanmugam
- Photon
Science Institute, Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
| | - Eric J. L. McInnes
- Photon
Science Institute, Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
| | - Michael P. Shaver
- Department
of Materials, School of Natural Sciences, University of Manchester, Manchester M13 9PL, U.K.
- Sustainable
Materials Innovation Hub, Henry Royce Institute, University of Manchester, Manchester M13 9PL, U.K.
| |
Collapse
|
4
|
Ju M, Lu Z, Novaes LFT, Alvarado JIM, Lin S. Frustrated Radical Pairs in Organic Synthesis. J Am Chem Soc 2023; 145:19478-19489. [PMID: 37656899 PMCID: PMC10625356 DOI: 10.1021/jacs.3c07070] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/03/2023]
Abstract
Frustrated radical pairs (FRPs) describe the phenomenon that two distinct radicals─which would otherwise annihilate each other to form a closed-shell covalent adduct─can coexist in solution, owing to steric repulsion or weak bonding association. FRPs are typically formed via spontaneous single-electron transfer between two sterically encumbered precursors─an oxidant and a reductant─under ambient conditions. The two components of a FRP exhibit orthogonal chemical properties and can often act in cooperativity to achieve interesting radical reactivities. Initially observed in the study of traditional frustrated Lewis pairs, FRPs have recently been shown to be capable of homolytically activating various chemical bonds. In this Perspective, we will discuss the discovery of FRPs, their fundamental reactivity in chemical bond activation, and recent developments of their use in synthetic organic chemistry, including in C-H bond functionalization. We anticipate that FRPs will provide new reaction strategies for solving challenging problems in modern organic synthesis.
Collapse
Affiliation(s)
| | | | - Luiz F. T. Novaes
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | | | - Song Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| |
Collapse
|
5
|
van der Zee LJ, Pahar S, Richards E, Melen RL, Slootweg JC. Insights into Single-Electron-Transfer Processes in Frustrated Lewis Pair Chemistry and Related Donor-Acceptor Systems in Main Group Chemistry. Chem Rev 2023; 123:9653-9675. [PMID: 37431868 PMCID: PMC10416219 DOI: 10.1021/acs.chemrev.3c00217] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Indexed: 07/12/2023]
Abstract
The activation and utilization of substrates mediated by Frustrated Lewis Pairs (FLPs) was initially believed to occur solely via a two-electron, cooperative mechanism. More recently, the occurrence of a single-electron transfer (SET) from the Lewis base to the Lewis acid was observed, indicating that mechanisms that proceed via one-electron-transfer processes are also feasible. As such, SET in FLP systems leads to the formation of radical ion pairs, which have recently been more frequently observed. In this review, we aim to discuss the seminal findings regarding the recently established insights into the SET processes in FLP chemistry as well as highlight examples of this radical formation process. In addition, applications of reported main group radicals will also be reviewed and discussed in the context of the understanding of SET processes in FLP systems.
Collapse
Affiliation(s)
- Lars J.
C. van der Zee
- Van
’t Hoff Institute for Molecular Sciences, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands
| | - Sanjukta Pahar
- Cardiff
Catalysis Institute, Cardiff University, Translational Research Hub, Maindy
Road, Cathays, Cardiff, CF24 4HQ Wales, United Kingdom
| | - Emma Richards
- Cardiff
Catalysis Institute, Cardiff University, Translational Research Hub, Maindy
Road, Cathays, Cardiff, CF24 4HQ Wales, United Kingdom
| | - Rebecca L. Melen
- Cardiff
Catalysis Institute, Cardiff University, Translational Research Hub, Maindy
Road, Cathays, Cardiff, CF24 4HQ Wales, United Kingdom
| | - J. Chris Slootweg
- Van
’t Hoff Institute for Molecular Sciences, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands
| |
Collapse
|
6
|
Lu Z, Ju M, Wang Y, Meinhardt JM, Martinez Alvarado JI, Villemure E, Terrett JA, Lin S. Regioselective aliphatic C-H functionalization using frustrated radical pairs. Nature 2023; 619:514-520. [PMID: 37407819 PMCID: PMC10530363 DOI: 10.1038/s41586-023-06131-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 04/25/2023] [Indexed: 07/07/2023]
Abstract
Frustrated Lewis pairs (FLPs) are well documented for the activation of small molecules such as dihydrogen and carbon dioxide1-4. Although canonical FLP chemistry is heterolytic in nature, recent work has shown that certain FLPs can undergo single-electron transfer to afford radical pairs5. Owing to steric encumbrance and/or weak bonding association, these radicals do not annihilate one another, and they have thus been named frustrated radical pairs (FRPs). Notable preliminary results suggest that FRPs may be useful reagents in chemical synthesis6-8, although their applications remain limited. Here we demonstrate that the functionalization of C(sp3)-H bonds can be accomplished using a class of FRPs generated from disilazide donors and an N-oxoammonium acceptor. Together, these species undergo single-electron transfer to generate a transient and persistent radical pair capable of cleaving unactivated C-H bonds to furnish aminoxylated products. By tuning the structure of the donor, it is possible to control regioselectivity and tailor reactivity towards tertiary, secondary or primary C-H bonds. Mechanistic studies lend strong support for the formation and involvement of radical pairs in the target reaction.
Collapse
Affiliation(s)
- Zhipeng Lu
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Minsoo Ju
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Yi Wang
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Jonathan M Meinhardt
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | | | - Elisia Villemure
- Department of Discovery Chemistry, Genentech, Inc., South San Francisco, CA, USA
| | - Jack A Terrett
- Department of Discovery Chemistry, Genentech, Inc., South San Francisco, CA, USA
| | - Song Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA.
| |
Collapse
|
7
|
Cooperative Bond Activation and Catalytic CO 2 Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene. J Am Chem Soc 2023; 145:7011-7020. [PMID: 36939300 DOI: 10.1021/jacs.3c00949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/21/2023]
Abstract
Metal-ligand cooperativity has emerged as an important strategy to tune the reactivity of transition-metal complexes for the catalysis and activation of small molecules. Studies of main-group compounds, however, are scarce. Here, we report the synthesis, structural characterization, and reactivity of a geometrically constrained bis(silylene)-stabilized borylene. The one-pot reaction of [(SiNSi)Li(OEt2)] (SiNSi = 4,5-bis(silylene)-2,7,9,9-tetramethyl-9H-acridin-10-ide) with 1 equiv of [BBr3(SMe2)] in toluene at room temperature followed by reduction with 2 equiv of potassium graphite (KC8) leads to borylene [(SiNSi)B] (1), isolated as blue crystals in 45% yield. X-ray crystallography shows that borylene (1) has a tricoordinate boron center with a distorted T-shaped geometry. Computational studies reveal that the HOMO of 1 represents the lone pair orbital on the boron center and is delocalized over the Si-B-Si unit, while the geometric perturbation significantly increases its energy. Borylene (1) shows single electron transfer reactivity toward tris(pentafluorophenyl)borane (B(C6F5)3), forming a frustrated radical pair [(SiNSi)B]•+[B(C6F5)3]•-, which can be trapped by its reaction with PhSSPh, affording an ion pair [(SiNSi)BSPh][PhSB(C6F5)3] (3). Remarkably, the cooperation between borylene and silylene allows the facile cleavage of the N-H bond of aniline, the P-P bond in white phosphorus, and the C═O bond in ketones and carbon dioxide, thus representing a new type of main-group element-ligand cooperativity for the activation of small molecules. In addition, 1 is a strikingly effective catalyst for carbon dioxide reduction. Computational studies reveal that the cooperation between borylene and silylene plays a key role in the catalytic chemical bond activation process.
Collapse
|
8
|
Song H, Lee E. Revisiting the Reaction of IPr with Tritylium: An Alternative Mechanistic Pathway. Chemistry 2023; 29:e202203364. [PMID: 36445754 DOI: 10.1002/chem.202203364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 11/29/2022] [Accepted: 11/29/2022] [Indexed: 11/30/2022]
Abstract
Despite a recent proposal on the mechanism of a single-electron transfer (SET) process between tritylium and 2,6-bis(diisopropylphenyl)imidazol-2-ylidene (IPr) based on evidence of transient IPr radical cation intermediate ([IPr]⋅+ ) formation, such oxidation is still contentious because of the high oxidation potential of N-heterocyclic carbenes. Our experimental analysis indicates that the appearance of deep purple color, previously considered to be from transient [IPr]⋅+ , originates from a zwitterionic intermediate (3 a), not a radical cation. Here, we propose an alternative mechanism for the reaction involving tritylium and IPr. This mechanism is noteworthy for explaining how [NHC-H]+ can be generated without the formation of transient [NHC]⋅+ , which has been frequently proposed as an intermediate for the reaction between NHC and oxidants. These results also show that a transient strong single-electron donor (3 a) could be generated by the alternative mechanism for oxidants using NHCs, which is a more feasible explanation for the reactivity of NHCs with oxidants.
Collapse
Affiliation(s)
- Hayoung Song
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 37673, Republic of Korea
| | - Eunsung Lee
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 37673, Republic of Korea.,Division of Advanced Materials Science, Pohang University of Science and Technology, Pohang, 37673, Republic of Korea
| |
Collapse
|
9
|
Tan CY, Kim M, Park I, Kim Y, Hong S. Site-Selective Pyridine C-H Alkylation with Alcohols and Thiols via Single-Electron Transfer of Frustrated Lewis Pairs. Angew Chem Int Ed Engl 2022; 61:e202213857. [PMID: 36314414 DOI: 10.1002/anie.202213857] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Indexed: 11/07/2022]
Abstract
A unified strategy for the deoxygenative or desulfurative pyridylation of various alcohols and thiols has been developed through a single-electron transfer (SET) process of frustrated Lewis pairs (FLPs) derived from pyridinium salts and PtBu3 . Mechanistic studies revealed that N-amidopyridinium salts serve as effective Lewis acids for the formation of FLPs with PtBu3 , and the generated phosphine radical cation ionically couples with the in situ generated xanthate, eventually affording the alkyl radical through facile β-scission under photocatalyst-free conditions. The reaction efficiency was further accelerated by visible-light irradiation. This method is conceptually appealing by using encounter complexes in FLP chemistry to promote SET, which provides a previously unrecognized opportunity for the selective heteroarylation of a diverse range of alcohols and thiols with various functional groups, even in complex settings under mild reaction conditions.
Collapse
Affiliation(s)
- Chang-Yin Tan
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea.,Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Myojeong Kim
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea.,Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Inyoung Park
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea.,Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Yuhyun Kim
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea.,Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Sungwoo Hong
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea.,Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| |
Collapse
|
10
|
Falk A, Bauer JO. Structural and Electronic Effects on Phosphine Chalcogenide Stabilized Silicon Centers in Four-Membered Heterocyclic Cations. Inorg Chem 2022; 61:15576-15588. [PMID: 36130169 DOI: 10.1021/acs.inorgchem.2c02360] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Understanding the interplay of structural and electronic parameters in the stabilization of Lewis acidic silicon centers is crucial for stereochemical questions and applications in bond activation and catalytic transformations. Phosphine chalcogenide functionalized (Ch = O, S, and Se) hydrosilanes having tert-butyl and 2,4,6-trimethoxyphenyl (TMP) substituents on the silicon atom were synthesized, and the ring-closing reactions to afford the heterocyclic four-membered CPChSi cations were investigated. Synthetic access was only achieved for the sulfur- and selenium-based cations. A thorough study by means of single-crystal X-ray structure determination, NMR spectroscopic data, and density functional theory (DFT) calculations provided insight into important electronic and structural parameters affecting the stability of the intramolecularly stabilized cations. Detailed structural considerations were made on the contributions to the ring strain (angular strain and steric repulsion). Thermochemical investigations showed that the substituents on the silicon and phosphorus atoms play an important role for the stability of the cationic heterocycles. In the absence of large steric repulsions through bulky substituents (methyl groups on silicon and tert-butyl groups on phosphorus), an intrinsic stability sequence of the intramolecular Ch-Si coordination depending on the chalcogen atom in the direction Se ≤ S < O can be observed. However, the order is reversed (O < S < Se) in the case of strong repulsions between sterically demanding substituents (tert-butyl groups on both silicon and phosphorus atoms). Natural bond orbital (NBO) analysis supported the explanations for the observed deshielding trends in 31P NMR spectroscopy and revealed that the O-Si bond is more ionic in nature compared to the S-Si and Se-Si bonds, with the latter exhibiting higher covalent character due to a more efficient charge transfer through a σ-type nCh → pSi interaction.
Collapse
Affiliation(s)
- Alexander Falk
- Institut für Anorganische Chemie, Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Jonathan O Bauer
- Institut für Anorganische Chemie, Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| |
Collapse
|
11
|
Maiti A, Elvers BJ, Bera S, Lindl F, Krummenacher I, Ghosh P, Braunschweig H, Yildiz CB, Schulzke C, Jana A. Disclosing Cyclic(Alkyl)(Amino)Carbenes as One-Electron Reductants: Synthesis of Acyclic(Amino)(Aryl)Carbene-Based Kekulé Diradicaloids. Chemistry 2022; 28:e202104567. [PMID: 35262232 PMCID: PMC9321839 DOI: 10.1002/chem.202104567] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Indexed: 11/10/2022]
Abstract
Herein, we disclose cyclic(alkyl)(amino)carbenes (CAACs) to be one-electron reductants under the formation of a transient radical cation as indicated by EPR spectroscopy. The disclosed CAAC reducing reactivity was used to synthesize acyclic(amino)(aryl)carbene-based Thiele and Chichibabin hydrocarbons, a new class of Kekulé diradicaloids. The results demonstrate CAACs to be potent organic reductants. Notably, the acyclic(amino)(aryl)carbene-based Chichibabin's hydrocarbon shows an appreciable population of the triplet state at room temperature, as evidenced by both variable-temperature NMR and EPR spectroscopy.
Collapse
Affiliation(s)
- Avijit Maiti
- Tata Institute of Fundamental Research Hyderabad GopanpallyHyderabad500046, TelanganaIndia
| | - Benedict J. Elvers
- Institut für BiochemieUniversität GreifswaldFelix-Hausdorff-Straße 417489GreifswaldGermany
| | - Sachinath Bera
- Department of ChemistryRamakrishna Mission Residential College NarendrapurKolkata700103India
- Shahid Matangini Hazra Govt General Degree College for Women TamlukPurba Medinipur721649India
| | - Felix Lindl
- Institute of Inorganic Chemistry and Institute for Sustainable Chemistry & Catalysis with Boron (ICB)Julius-Maximilians-Universität WürzburgAm Hubland97074WürzburgGermany
| | - Ivo Krummenacher
- Institute of Inorganic Chemistry and Institute for Sustainable Chemistry & Catalysis with Boron (ICB)Julius-Maximilians-Universität WürzburgAm Hubland97074WürzburgGermany
| | - Prasanta Ghosh
- Department of ChemistryRamakrishna Mission Residential College NarendrapurKolkata700103India
| | - Holger Braunschweig
- Institute of Inorganic Chemistry and Institute for Sustainable Chemistry & Catalysis with Boron (ICB)Julius-Maximilians-Universität WürzburgAm Hubland97074WürzburgGermany
| | - Cem B. Yildiz
- Department of Aromatic and Medicinal PlantsAksaray UniversityAksaray68100Turkey
| | - Carola Schulzke
- Institut für BiochemieUniversität GreifswaldFelix-Hausdorff-Straße 417489GreifswaldGermany
| | - Anukul Jana
- Tata Institute of Fundamental Research Hyderabad GopanpallyHyderabad500046, TelanganaIndia
| |
Collapse
|
12
|
Böttcher T, Schmidlin NMC, Radtke V, Schmidt A, Lökov M, Leito I. Electronic Modification of a Sterically Demanding Anionic Pyridine Ligand. Z Anorg Allg Chem 2022. [DOI: 10.1002/zaac.202200136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Tobias Böttcher
- Universität Freiburg Institut für Anorganische und Analytische Chemie Albertstr. 21 79104 Freiburg i.Br. GERMANY
| | | | | | | | | | | |
Collapse
|
13
|
Fontana N, Espinosa-Jalapa NA, Seidl M, Bauer JO. Hidden silylium-type reactivity of a siloxane-based phosphonium-hydroborate ion pair. Chem Commun (Camb) 2022; 58:2144-2147. [PMID: 35050278 DOI: 10.1039/d1cc07016a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new class of siloxane-based cations with hidden silylium-type reactivity is provided, which, in combination with an arylborate counteranion, initiates a highly selective para-C(sp2)-F defunctionalization of a perfluorinated aryl group. The hydrodefluorinated aryl borane is obtained as a crystalline solid via continuous sublimation during the reaction. The heterocyclic six-membered cation could be obtained single-crystalline after dehydrogenative anion exchange. DFT calculations give insight into the bonding within the siloxane-based cation and the mechanism of the ion pair reaction.
Collapse
Affiliation(s)
- Nicolò Fontana
- Institut für Anorganische Chemie, Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, Regensburg D-93053, Germany.
| | - Noel Angel Espinosa-Jalapa
- Institut für Anorganische Chemie, Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, Regensburg D-93053, Germany.
| | - Michael Seidl
- Institut für Anorganische Chemie, Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, Regensburg D-93053, Germany.
| | - Jonathan O Bauer
- Institut für Anorganische Chemie, Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, Regensburg D-93053, Germany.
| |
Collapse
|
14
|
Li S, Hu C, Cui X, Zhang J, Liu LL, Wu L. Site‐Fixed Hydroboration of Terminal and Internal Alkenes using BX
3
/
i
Pr
2
NEt**. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202111978] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Sida Li
- State Key Laboratory for Oxo Synthesis and Selective Oxidation Suzhou Research Institute of LICP Lanzhou Institute of Chemical Physics (LICP) Chinese Academy of Sciences Lanzhou 730000 China
- University of Chinese Academy of Sciences Beijing 100049 China
| | - Chenyang Hu
- Shenzhen Grubbs Institute and Department of Chemistry Southern University of Science and Technology Shenzhen 518055 China
| | - Xin Cui
- State Key Laboratory for Oxo Synthesis and Selective Oxidation Suzhou Research Institute of LICP Lanzhou Institute of Chemical Physics (LICP) Chinese Academy of Sciences Lanzhou 730000 China
| | - Jiong Zhang
- State Key Laboratory for Oxo Synthesis and Selective Oxidation Suzhou Research Institute of LICP Lanzhou Institute of Chemical Physics (LICP) Chinese Academy of Sciences Lanzhou 730000 China
- University of Chinese Academy of Sciences Beijing 100049 China
| | - Liu Leo Liu
- Shenzhen Grubbs Institute and Department of Chemistry Southern University of Science and Technology Shenzhen 518055 China
| | - Lipeng Wu
- State Key Laboratory for Oxo Synthesis and Selective Oxidation Suzhou Research Institute of LICP Lanzhou Institute of Chemical Physics (LICP) Chinese Academy of Sciences Lanzhou 730000 China
| |
Collapse
|
15
|
Chen Y, Chen Z, Jiang L, Li J, Zhao Y, Zhu H, Roesky HW. One- and Two-Electron Transfer Oxidation of 1,4-Disilabenzene with Formation of Stable Radical Cations and Dications. Chemistry 2021; 28:e202103715. [PMID: 34837718 PMCID: PMC9299862 DOI: 10.1002/chem.202103715] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Indexed: 11/24/2022]
Abstract
Electron‐transferable oxidants such as B(C6F5)3/nBuLi, B(C6F5)3/LiB(C6F5)4, B(C6F5)3/LiHBEt3, Al(C6F5)3/(o‐RC6H4)AlH2 (R=N(CMe2CH2)2CH2), B(C6F5)3/AlEt3, Al(C6F5)3, Al(C6F5)3/nBuLi, Al(C6F5)3/AlMe3, (CuC6F5)4, and Ag2SO4, respectively were employed for reactions with (L)2Si2C4(SiMe3)2(C2SiMe3)2 (L=PhC(NtBu)2, 1). The stable radical cation [1]+. was formed and paired with the anions [nBuB(C6F5)3]− (in 2), [B(C6F5)4]− (in 3), [HB(C6F5)3]− (in 4), [EtB(C6F5)3]− (in 5), {[(C6F5)3Al]2(μ‐F)]− (in 6), [nBuAl(C6F5)3]− (in 7), and [Cu(C6F5)2]− (in 8), respectively. The stable dication [1]2+ was also generated with the anions [EtB(C6F5)3]− (9) and [MeAl(C6F5)3]− (10), respectively. In addition, the neutral compound [(L)2Si2C4(SiMe3)2(C2SiMe3)2][μ‐O2S(O)2] (11) was obtained. Compounds 2–11 are characterized by UV‐vis absorption spectroscopy, X‐ray crystallography, and elemental analysis. Compounds 2–8 are analyzed by EPR spectroscopy and compounds 9–11 by NMR spectroscopy. The structure features are discussed on the central Si2C4‐rings of 1, [1]+., [1]2+, and 11, respectively.
Collapse
Affiliation(s)
- Yilin Chen
- State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Zhikang Chen
- State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Liuyin Jiang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Jiancheng Li
- State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Yiling Zhao
- State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Hongping Zhu
- State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China
| | - Herbert W Roesky
- Institut für Anorganische Chemie, Georg-August-Universität, 37077, Göttingen, Germany
| |
Collapse
|
16
|
Li S, Hu C, Cui X, Zhang J, Liu LL, Wu L. Site-Fixed Hydroboration of Terminal and Internal Alkenes using BX 3 / i Pr 2 NEt*. Angew Chem Int Ed Engl 2021; 60:26238-26245. [PMID: 34536251 DOI: 10.1002/anie.202111978] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Indexed: 12/27/2022]
Abstract
An unprecedented and general hydroboration of alkenes with BX3 (X=Br, Cl) as the boration reagent in the presence of i Pr2 NEt is reported. The addition of i Pr2 NEt not only suppresses alkene polymerization and haloboration side reactions but also provides an "H" source for hydroboration. More importantly, the site-fixed installation of a boryl group at the original position of the internal double bond is readily achieved in contrast to conventional transition-metal-catalyzed hydroboration processes. Further application to the synthesis of 1,n-diborylalkanes (n=3-10) is also demonstrated. Preliminary mechanistic studies reveal a major reaction pathway that involves radical species and operates through a frustrated Lewis pair type single-electron-transfer mechanism.
Collapse
Affiliation(s)
- Sida Li
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou, 730000, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Chenyang Hu
- Shenzhen Grubbs Institute and Department of Chemistry, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Xin Cui
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou, 730000, China
| | - Jiong Zhang
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou, 730000, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Liu Leo Liu
- Shenzhen Grubbs Institute and Department of Chemistry, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Lipeng Wu
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou, 730000, China
| |
Collapse
|
17
|
Xie C, Smaligo AJ, Song XR, Kwon O. Phosphorus-Based Catalysis. ACS CENTRAL SCIENCE 2021; 7:536-558. [PMID: 34056085 PMCID: PMC8155461 DOI: 10.1021/acscentsci.0c01493] [Citation(s) in RCA: 129] [Impact Index Per Article: 43.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Indexed: 05/08/2023]
Abstract
Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.
Collapse
Affiliation(s)
- Changmin Xie
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
| | - Andrew J. Smaligo
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
| | | | - Ohyun Kwon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, United States
| |
Collapse
|
18
|
Klare HFT, Albers L, Süsse L, Keess S, Müller T, Oestreich M. Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts. Chem Rev 2021; 121:5889-5985. [PMID: 33861564 DOI: 10.1021/acs.chemrev.0c00855] [Citation(s) in RCA: 107] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The history of silyl cations has all the makings of a drama but with a happy ending. Being considered reactive intermediates impossible to isolate in the condensed phase for decades, their actual characterization in solution and later in solid state did only fuel the discussion about their existence and initially created a lot of controversy. This perception has completely changed today, and silyl cations and their donor-stabilized congeners are now widely accepted compounds with promising use in synthetic chemistry. This review provides a comprehensive summary of the fundamental facts and principles of the chemistry of silyl cations, including reliable ways of their preparation as well as their physical and chemical properties. The striking features of silyl cations are their enormous electrophilicity and as such reactivity as super Lewis acids as well as fluorophilicity. Known applications rely on silyl cations as reactants, stoichiometric reagents, and promoters where the reaction success is based on their steady regeneration over the course of the reaction. Silyl cations can even be discrete catalysts, thereby opening the next chapter of their way into the toolbox of synthetic methodology.
Collapse
Affiliation(s)
- Hendrik F T Klare
- Institut für Chemie, Technische Universität Berlin, Strasse des 17 Juni 115, 10623 Berlin, Germany
| | - Lena Albers
- Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky-Strasse 9-11, 26129 Oldenburg, Germany
| | - Lars Süsse
- Institut für Chemie, Technische Universität Berlin, Strasse des 17 Juni 115, 10623 Berlin, Germany
| | - Sebastian Keess
- Institut für Chemie, Technische Universität Berlin, Strasse des 17 Juni 115, 10623 Berlin, Germany
| | - Thomas Müller
- Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky-Strasse 9-11, 26129 Oldenburg, Germany
| | - Martin Oestreich
- Institut für Chemie, Technische Universität Berlin, Strasse des 17 Juni 115, 10623 Berlin, Germany
| |
Collapse
|
19
|
Shaikh AC, Veleta JM, Moutet J, Gianetti TL. Trioxatriangulenium (TOTA +) as a robust carbon-based Lewis acid in frustrated Lewis pair chemistry. Chem Sci 2021; 12:4841-4849. [PMID: 34168760 PMCID: PMC8179643 DOI: 10.1039/d0sc05893a] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 02/07/2021] [Indexed: 12/15/2022] Open
Abstract
We report the reactivity between the water stable Lewis acidic trioxatriangulenium ion (TOTA+) and a series of Lewis bases such as phosphines and N-heterocyclic carbene (NHC). The nature of the Lewis acid-base interaction was analyzed via variable temperature (VT) NMR spectroscopy, single-crystal X-ray diffraction, UV-visible spectroscopy, and DFT calculations. While small and strongly nucleophilic phosphines, such as PMe3, led to the formation of a Lewis acid-base adduct, frustrated Lewis pairs (FLPs) were observed for sterically hindered bases such as P( t Bu)3. The TOTA+-P( t Bu)3 FLP was characterized as an encounter complex, and found to promote the heterolytic cleavage of disulfide bonds, formaldehyde fixation, dehydrogenation of 1,4-cyclohexadiene, heterolytic cleavage of the C-Br bonds, and interception of Staudinger reaction intermediates. Moreover, TOTA+ and NHC were found to first undergo single-electron transfer (SET) to form [TOTA]·[NHC]˙+, which was confirmed via electron paramagnetic resonance (EPR) spectroscopy, and subsequently form a [TOTA-NHC]+ adduct or a mixture of products depending the reaction conditions used.
Collapse
Affiliation(s)
- Aslam C Shaikh
- University of Arizona, Department of Chemistry and Biochemistry Tucson AZ USA
| | - José M Veleta
- University of Arizona, Department of Chemistry and Biochemistry Tucson AZ USA
| | - Jules Moutet
- University of Arizona, Department of Chemistry and Biochemistry Tucson AZ USA
| | - Thomas L Gianetti
- University of Arizona, Department of Chemistry and Biochemistry Tucson AZ USA
| |
Collapse
|
20
|
Fontana N, Espinosa‐Jalapa NA, Seidl M, Bauer JO. Easy Access to Enantiomerically Pure Heterocyclic Silicon-Chiral Phosphonium Cations and the Matched/Mismatched Case of Dihydrogen Release. Chemistry 2021; 27:2649-2653. [PMID: 33264430 PMCID: PMC7898527 DOI: 10.1002/chem.202005171] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Indexed: 11/17/2022]
Abstract
Phosphonium ions are widely used in preparative organic synthesis and catalysis. The provision of new types of cations that contain both functional and chiral information is a major synthetic challenge and can open up new horizons in asymmetric cation-directed and Lewis acid catalysis. We discovered an efficient methodology towards new Si-chiral four-membered CPSSi* heterocyclic cations. Three synthetic approaches are presented. The stereochemical sequence of anchimerically assisted cation formation with B(C6 F5 )3 and subsequent hydride addition was fully elucidated and proceeds with excellent preservation of the chiral information at the stereogenic silicon atom. Also the mechanism of dihydrogen release from a protonated hydrosilane was studied in detail by the help of Si-centered chirality as stereochemical probe. Chemoselectivity switch (dihydrogen release vs. protodesilylation) can easily be achieved through slight modifications of the solvent. A matched/mismatched case was identified and the intermolecularity of this reaction supported by spectroscopic, kinetic, deuterium-labeling experiments, and quantum chemical calculations.
Collapse
Affiliation(s)
- Nicolò Fontana
- Institut für Anorganische ChemieFakultät für Chemie und PharmazieUniversität RegensburgUniversitätsstraße 3193053RegensburgGermany
| | - Noel Angel Espinosa‐Jalapa
- Institut für Anorganische ChemieFakultät für Chemie und PharmazieUniversität RegensburgUniversitätsstraße 3193053RegensburgGermany
| | - Michael Seidl
- Institut für Anorganische ChemieFakultät für Chemie und PharmazieUniversität RegensburgUniversitätsstraße 3193053RegensburgGermany
| | - Jonathan O. Bauer
- Institut für Anorganische ChemieFakultät für Chemie und PharmazieUniversität RegensburgUniversitätsstraße 3193053RegensburgGermany
| |
Collapse
|
21
|
Dasgupta A, Richards E, Melen RL. Frustrated Radical Pairs: Insights from EPR Spectroscopy. Angew Chem Int Ed Engl 2021; 60:53-65. [PMID: 32931604 PMCID: PMC7883636 DOI: 10.1002/anie.202010633] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Indexed: 12/29/2022]
Abstract
Progress in frustrated Lewis pair (FLP) chemistry has revealed the importance of the main group elements in catalysis, opening new avenues in synthetic chemistry. Recently, new reactivities of frustrated Lewis pairs have been uncovered that disclose that certain combinations of Lewis acids and bases undergo single-electron transfer (SET) processes. Here an electron can be transferred from the Lewis basic donor to a Lewis acidic acceptor to generate a reactive frustrated radical pair (FRP). This minireview aims to showcase the recent advancements in this emerging field covering the synthesis and reactivities of frustrated radical pairs, with extensive highlights of the results from Electron Paramagnetic Resonance (EPR) spectroscopy to explain the nature and stability of the different radical species observed.
Collapse
Affiliation(s)
- Ayan Dasgupta
- School of ChemistryCardiff Catalysis InstituteCardiff UniversityMain Building, Park PlaceCardiffCF10 3ATUK
| | - Emma Richards
- School of ChemistryCardiff Catalysis InstituteCardiff UniversityMain Building, Park PlaceCardiffCF10 3ATUK
| | - Rebecca L. Melen
- School of ChemistryCardiff Catalysis InstituteCardiff UniversityMain Building, Park PlaceCardiffCF10 3ATUK
| |
Collapse
|
22
|
Pan Y, Cui J, Wei Y, Xu Z, Wang T. B-H and O-H bonds activation via a single electron transfer of frustrated radical pairs. Dalton Trans 2021; 50:8947-8954. [PMID: 34109966 DOI: 10.1039/d1dt01169c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The rare examples of B-H bond activation in a frustrated radical pair regime have been observed by treatment of TEMPO radicals with Piers' borane HB(C6F5)2 or bis-borane, respectively. The resulting concomitant formation of zwitterionic products and geminal N/B frustrated Lewis pairs implied a one electron process. In addition, the reaction of a TEMPO/B(C6F5)3 pair with H2O·B(C6F5)3 was assumed to involve one-electron reduction of water. Our results provide insights into chemical bond (e.g. B-H and O-H) activation via a single electron transfer.
Collapse
Affiliation(s)
- Yanlin Pan
- Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, P. R. China.
| | - Jie Cui
- Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, P. R. China.
| | - Yongliang Wei
- Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, P. R. China.
| | - Zhaochao Xu
- Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, P. R. China. and CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Tongdao Wang
- Zhang Dayu School of Chemistry, Dalian University of Technology, Dalian 116024, P. R. China.
| |
Collapse
|
23
|
Holtrop F, Jupp AR, Kooij BJ, van Leest NP, de Bruin B, Slootweg JC. Single-Electron Transfer in Frustrated Lewis Pair Chemistry. Angew Chem Int Ed Engl 2020; 59:22210-22216. [PMID: 32840947 PMCID: PMC7756365 DOI: 10.1002/anie.202009717] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Indexed: 02/05/2023]
Abstract
Frustrated Lewis pairs (FLPs) are well known for their ability to activate small molecules. Recent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride, or tetrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events; that is, being direct SET to B(C6 F5 )3 or not. The reactions of H2 and Ph3 SnH with archetypal P/B FLP systems do not proceed via a radical mechanism. In contrast, reaction with TCQ proceeds via SET, which is only feasible by Lewis acid coordination to the substrate. Furthermore, SET from the Lewis base to the Lewis acid-substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical main-group chemistry.
Collapse
Affiliation(s)
- Flip Holtrop
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Andrew R. Jupp
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Bastiaan J. Kooij
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Nicolaas P. van Leest
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Bas de Bruin
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - J. Chris Slootweg
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| |
Collapse
|
24
|
Hirakawa F, Nakagawa H, Honda S, Ishida S, Iwamoto T. Trialkylphosphines Having a Bulky Phosphacyclopentane Backbone: Structural and Redox Properties Depending on the Exocyclic Alkyl Groups and EPR Observation of a Persistent Trialkylphosphine Radical Cation. J Org Chem 2020; 85:14634-14642. [PMID: 32700539 DOI: 10.1021/acs.joc.0c01393] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bulky phosphines and their redox properties have received increased attention in the view of useful auxiliary ligands for transition metal catalysts and Lewis-base components of frustrated Lewis pairs for chemical transformations. Herein we report the synthesis, structure, and properties of a series of trialkylphosphines 2R (R = methyl, ethyl, isopropyl, tert-butyl, 1-adamantyl) that possess the bulky 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane as a structural backbone. Among these phosphines, 2Ad, which contains an adamantyl moiety, has a very large buried volume (%Vbur) for a trialkylphosphine (62.0) and shows a quasi-reversible oxidative wave at a lower oxidation potential (-0.12 V in CH2Cl2, vs ferrocene/ferrocenium couple) by cyclic voltammetry. The reaction of 2Ad with AgPF6 afforded a cationic silver aquo complex [Ag(2Ad)(H2O)]+[PF6]-, whereas the reaction with NOSbF6 gave a persistent phosphine radical cation [2Ad]•+. Based on the EPR spectra and DFT studies, the spin and positive charge of [2Ad]•+ are localized on the phosphorus atom.
Collapse
Affiliation(s)
- Fumiya Hirakawa
- Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| | - Hiroshi Nakagawa
- Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| | - Shunya Honda
- Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| | - Shintaro Ishida
- Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| | - Takeaki Iwamoto
- Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
| |
Collapse
|
25
|
Dasgupta A, Richards E, Melen RL. Frustrated Radical Pairs: Insights from EPR Spectroscopy. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202010633] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Ayan Dasgupta
- School of Chemistry Cardiff Catalysis Institute Cardiff University Main Building, Park Place Cardiff CF10 3AT UK
| | - Emma Richards
- School of Chemistry Cardiff Catalysis Institute Cardiff University Main Building, Park Place Cardiff CF10 3AT UK
| | - Rebecca L. Melen
- School of Chemistry Cardiff Catalysis Institute Cardiff University Main Building, Park Place Cardiff CF10 3AT UK
| |
Collapse
|
26
|
Horstmann JS, Klabunde S, Hepp A, Layh M, Hansen MR, Eckert H, Würthwein E, Uhl W. Reactions of Al‐N Based Active Lewis Pairs with Ketones and 1,2‐Diketones: Insertion into Al‐N Bonds, C‐C and C‐N Bond Formation and a Tricyclic Saturated Tetraaza Compound. Eur J Inorg Chem 2020. [DOI: 10.1002/ejic.202000570] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Julia Silissa Horstmann
- Institut für Anorganische und Analytische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| | - Sina Klabunde
- Institut für Physikalische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| | - Alexander Hepp
- Institut für Anorganische und Analytische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| | - Marcus Layh
- Institut für Anorganische und Analytische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| | - Michael Ryan Hansen
- Institut für Physikalische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| | - Hellmut Eckert
- Institut für Physikalische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| | - Ernst‐Ulrich Würthwein
- Organisch‐chemisches Institut and Center for Multiscale Theory and Computation (CMTC) Universität Münster Corrensstrasse 40 48149 Münster Germany
| | - Werner Uhl
- Institut für Anorganische und Analytische Chemie Universität Münster Corrensstraße 30 48149 Münster Germany
| |
Collapse
|
27
|
Holtrop F, Jupp AR, Kooij BJ, Leest NP, Bruin B, Slootweg JC. Single‐Electron Transfer in Frustrated Lewis Pair Chemistry. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202009717] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Flip Holtrop
- Van't Hoff Institute for Molecular Sciences University of Amsterdam PO Box 94157 1090 GD Amsterdam The Netherlands
| | - Andrew R. Jupp
- Van't Hoff Institute for Molecular Sciences University of Amsterdam PO Box 94157 1090 GD Amsterdam The Netherlands
| | - Bastiaan J. Kooij
- Van't Hoff Institute for Molecular Sciences University of Amsterdam PO Box 94157 1090 GD Amsterdam The Netherlands
| | - Nicolaas P. Leest
- Van't Hoff Institute for Molecular Sciences University of Amsterdam PO Box 94157 1090 GD Amsterdam The Netherlands
| | - Bas Bruin
- Van't Hoff Institute for Molecular Sciences University of Amsterdam PO Box 94157 1090 GD Amsterdam The Netherlands
| | - J. Chris Slootweg
- Van't Hoff Institute for Molecular Sciences University of Amsterdam PO Box 94157 1090 GD Amsterdam The Netherlands
| |
Collapse
|
28
|
Lange H, Schröder H, Oberem E, Villinger A, Rabeah J, Ludwig R, Neymeyr K, Seidel WW. Facile Synthesis of a Stable Side-on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation. Chemistry 2020; 26:11492-11502. [PMID: 32181544 PMCID: PMC7540294 DOI: 10.1002/chem.201905750] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 03/08/2020] [Indexed: 11/23/2022]
Abstract
Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ5 -phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31 P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations.
Collapse
Affiliation(s)
- Helge Lange
- Institut für ChemieUniversität RostockAlbert-Einstein-Str. 3a18059RostockGermany
| | - Henning Schröder
- Institut für MathematikUniversität RostockUlmenstraße 6918057RostockGermany
| | - Elisabeth Oberem
- Institut für ChemieUniversität RostockAlbert-Einstein-Str. 3a18059RostockGermany
| | - Alexander Villinger
- Institut für ChemieUniversität RostockAlbert-Einstein-Str. 3a18059RostockGermany
| | - Jabor Rabeah
- Leibniz-Institut für Katalyse e.V.Albert-Einstein-Straße 29a18059RostockGermany
| | - Ralf Ludwig
- Institut für ChemieUniversität RostockAlbert-Einstein-Str. 3a18059RostockGermany
- Leibniz-Institut für Katalyse e.V.Albert-Einstein-Straße 29a18059RostockGermany
| | - Klaus Neymeyr
- Institut für MathematikUniversität RostockUlmenstraße 6918057RostockGermany
- Leibniz-Institut für Katalyse e.V.Albert-Einstein-Straße 29a18059RostockGermany
| | - Wolfram W. Seidel
- Institut für ChemieUniversität RostockAlbert-Einstein-Str. 3a18059RostockGermany
| |
Collapse
|
29
|
Holtrop F, Jupp AR, van Leest NP, Paradiz Dominguez M, Williams RM, Brouwer AM, de Bruin B, Ehlers AW, Slootweg JC. Photoinduced and Thermal Single-Electron Transfer to Generate Radicals from Frustrated Lewis Pairs. Chemistry 2020; 26:9005-9011. [PMID: 32259331 PMCID: PMC7496419 DOI: 10.1002/chem.202001494] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 04/06/2020] [Indexed: 12/17/2022]
Abstract
Archetypal phosphine/borane frustrated Lewis pairs (FLPs) are famed for their ability to activate small molecules. The mechanism is generally believed to involve two-electron processes. However, the detection of radical intermediates indicates that single-electron transfer (SET) generating frustrated radical pairs could also play an important role. These highly reactive radical species typically have significantly higher energy than the FLP, which prompted this investigation into their formation. Herein, we provide evidence that the classical phosphine/borane combinations PMes3 /B(C6 F5 )3 and PtBu3 /B(C6 F5 )3 both form an electron donor-acceptor (charge-transfer) complex that undergoes visible-light-induced SET to form the corresponding highly reactive radical-ion pairs. Subsequently, we show that by tuning the properties of the Lewis acid/base pair, the energy required for SET can be reduced to become thermally accessible.
Collapse
Affiliation(s)
- Flip Holtrop
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Andrew R. Jupp
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Nicolaas P. van Leest
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | | | - René M. Williams
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Albert M. Brouwer
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Bas de Bruin
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| | - Andreas W. Ehlers
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
- Department of ChemistryScience FacultyUniversity of JohannesburgPO Box 254, Auckland ParkJohannesburgSouth Africa
| | - J. Chris Slootweg
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamPO Box 941571090 GDAmsterdamThe Netherlands
| |
Collapse
|
30
|
Wong A, Chu J, Wu G, Telser J, Dobrovetsky R, Ménard G. Redox-Controlled Reactivity at Boron: Parallels to Frustrated Lewis/Radical Pair Chemistry. Inorg Chem 2020; 59:10343-10352. [PMID: 32643930 DOI: 10.1021/acs.inorgchem.0c01464] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report the synthesis of new Lewis-acidic boranes tethered to redox-active vanadium centers, (Ph2N)3V(μ-N)B(C6F5)2 (1a) and (N(CH2CH2N(C6F5))3)V(μ-N)B(C6F5)2 (1b). Redox control of the VIV/V couple resulted in switchable borane versus "hidden" boron radical reactivity, mimicking frustrated Lewis versus frustrated radical pair (FLP/FRP) chemistry, respectively. Whereas heterolytic FLP-type addition reactions were observed with the VV complex (1b) in the presence of a bulky phosphine, homolytic peroxide, or Sn-hydride bond cleavage reactions were observed with the VIV complex, [CoCp2*][(N(CH2CH2N(C6F5))3)V(μ-N)B(C6F5)2] (3b), indicative of boron radical anion character. The extent of radical character was probed by spectroscopic and computational means. Together, these results demonstrate that control of the VIV/V oxidation states allows these compounds to access reactivity observed in both FLP and FRP chemistry.
Collapse
Affiliation(s)
- Anthony Wong
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Jiaxiang Chu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States.,School of Chemical Science, University of Chinese Academy of Sciences, Huaibei hen, Huairou District, Beijing 101408, China
| | - Guang Wu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Joshua Telser
- Department of Biological, Chemical, and Physical Sciences, Roosevelt University, Chicago, Illinois 60605, United States
| | - Roman Dobrovetsky
- School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Gabriel Ménard
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| |
Collapse
|
31
|
Sapsford JS, Csókás D, Scott DJ, Turnell-Ritson RC, Piascik AD, Pápai I, Ashley AE. Establishing the Role of Triflate Anions in H 2 Activation by a Cationic Triorganotin(IV) Lewis Acid. ACS Catal 2020; 10:7573-7583. [PMID: 32905389 PMCID: PMC7469243 DOI: 10.1021/acscatal.0c02023] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Revised: 06/05/2020] [Indexed: 12/13/2022]
Abstract
![]()
Cationic
Lewis acids (LAs) are gaining interest as targets for
frustrated Lewis pair (FLP)-mediated catalysis. Unlike neutral boranes,
which are the most prevalent LAs for FLP hydrogenations, the Lewis
acidity of cations can be tuned through modulation of the counteranion;
however, detailed studies on such anion effects are currently lacking
in the literature. Herein, we present experimental and computational
studies which probe the mechanism of H2 activation using iPr3SnOTf (1-OTf) in conjunction
with a coordinating (quinuclidine; qui) and noncoordinating (2,4,6-collidine;
col) base and compare its reactivity with {iPr3Sn·base}{Al[OC(CF3)3]4} (base = qui/col) systems which lack a coordinating anion to investigate
the active species responsible for H2 activation and hence
resolve any mechanistic roles for OTf– in the iPr3SnOTf-mediated pathway.
Collapse
Affiliation(s)
- Joshua S. Sapsford
- Molecular Sciences Research Hub, Imperial College, White City Campus, 80 Wood Lane, London W12 0BZ, U.K
| | - Dániel Csókás
- Institute of Organic Chemistry, Research Center for Natural Sciences, Magyar tudósok körútja 2, Budapest H-1117, Hungary
| | - Daniel J. Scott
- Institute of Inorganic Chemistry, University of Regensburg, Universitätsstraße 31, Regensburg 93051, Germany
| | - Roland C. Turnell-Ritson
- Molecular Sciences Research Hub, Imperial College, White City Campus, 80 Wood Lane, London W12 0BZ, U.K
| | - Adam D. Piascik
- Molecular Sciences Research Hub, Imperial College, White City Campus, 80 Wood Lane, London W12 0BZ, U.K
| | - Imre Pápai
- Institute of Organic Chemistry, Research Center for Natural Sciences, Magyar tudósok körútja 2, Budapest H-1117, Hungary
| | - Andrew E. Ashley
- Molecular Sciences Research Hub, Imperial College, White City Campus, 80 Wood Lane, London W12 0BZ, U.K
| |
Collapse
|
32
|
Andrews RJ, Stephan DW. Isolable Anionic, Neutral and Cationic Radicals from Reactions of N,N'-Dimesityldiamidocarbene and Lewis Acids. Chemistry 2020; 26:7194-7198. [PMID: 32149432 DOI: 10.1002/chem.202001191] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Indexed: 01/04/2023]
Abstract
B(C6 F5 )3 undergoes nucleophilic attack by N,N'-dimesityldiamidocarbene (DAC) with fluoride transfer to the boron center, resulting in a new zwitterion (1). This B-F fluoride can be replaced or abstracted to give the corresponding hydride (2) or triflate (3) derivatives or the corresponding cation (4). These species are reduced with KC8 or Cp2 Co to give isolable anionic and neutral radicals (5-8). Similarly, the [Ph3 C] cation undergoes nucleophilic attack by DAC resulting in the spontaneous formation of the radical cation (9).
Collapse
Affiliation(s)
- Ryan J Andrews
- Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON, M5S 3H4, Canada
| | - Douglas W Stephan
- Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON, M5S 3H4, Canada
| |
Collapse
|
33
|
Dong Z, Pezzato C, Sienkiewicz A, Scopelliti R, Fadaei-Tirani F, Severin K. SET processes in Lewis acid-base reactions: the tritylation of N-heterocyclic carbenes. Chem Sci 2020; 11:7615-7618. [PMID: 34094138 PMCID: PMC8159480 DOI: 10.1039/d0sc01278e] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Reactions between N-heterocyclic carbenes (NHCs) and the trityl cation, [Ph3C]+, give covalent adducts of type [NHC-CPh3]+ and/or [NHC-C6H5-CPh2]+. EPR spectroscopy, UV-Vis analyses, and trapping experiments imply that adduct formation involves carbene radical cations and the trityl radical. The results demonstrate that single electron transfer (SET) processes should be considered for reaction of NHCs with oxidizing Lewis acids.
Collapse
Affiliation(s)
- Zhaowen Dong
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Cristian Pezzato
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | | | - Rosario Scopelliti
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Farzaneh Fadaei-Tirani
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Kay Severin
- Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| |
Collapse
|
34
|
Aramaki Y, Imaizumi N, Hotta M, Kumagai J, Ooi T. Exploiting single-electron transfer in Lewis pairs for catalytic bond-forming reactions. Chem Sci 2020; 11:4305-4311. [PMID: 34122888 PMCID: PMC8152713 DOI: 10.1039/d0sc01159b] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
A single-electron transfer (SET) between tris(pentafluorophenyl)borane (B(C6F5)3) and N,N-dialkylanilines is reported, which is operative via the formation of an electron donor–acceptor (EDA) complex involving π-orbital interactions as a key intermediate under dark conditions or visible-light irradiation depending on the structure of the aniline derivatives. This inherent SET in the Lewis pairs initiates the generation of the corresponding α-aminoalkyl radicals and their additions to electron-deficient olefins, revealing the ability of B(C6F5)3 to act as an effective one-electron redox catalyst. Radical–ion pair generation from common Lewis pairs and its application to catalytic carbon–carbon bond formation.![]()
Collapse
Affiliation(s)
- Yoshitaka Aramaki
- Institute of Transformative Bio-Molecules (WPI-ITbM), Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University Nagoya 464-8601 Japan
| | - Naoki Imaizumi
- Institute of Transformative Bio-Molecules (WPI-ITbM), Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University Nagoya 464-8601 Japan
| | - Mao Hotta
- Institute of Transformative Bio-Molecules (WPI-ITbM), Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University Nagoya 464-8601 Japan
| | - Jun Kumagai
- Institute of Materials and Systems for Sustainability, Nagoya University Nagoya 464-8601 Japan
| | - Takashi Ooi
- Institute of Transformative Bio-Molecules (WPI-ITbM), Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University Nagoya 464-8601 Japan .,CREST, Japan Science and Technology Agency (JST), Nagoya University Nagoya 464-8601 Japan
| |
Collapse
|
35
|
|
36
|
Dong Z, Albers L, Müller T. Trialkylsilyl-Substituted Silole and Germole Dianions as Precursors for Unusual Silicon and Germanium Compounds. Acc Chem Res 2020; 53:532-543. [PMID: 32031772 DOI: 10.1021/acs.accounts.9b00636] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Group 14 element heteroles are the heavier analogues of cyclopentadienes in which a heavier group 14 element atom replaces the sp3 carbon atom. In particular siloles and, to a somewhat smaller degree, germoles attracted considerable attention since the early 1990s due to their favorable photophysical properties which allowed the construction of OLEDs using group 14 element heteroles as emissive or electron-transport layers. Anions and in particular dianions derived from group 14 element heteroles have been of substantial interest due to the possible occurrence of Hückel aromaticity involving the heavier main group atom. Aromaticity is not the only notable electronic feature of silole and germole dianions; the spatial and energetic alignment of their frontier orbitals is equally remarkable. With a high lying lone pair at the heteroatom, which is orthogonal to a delocalized π-system, their frontier orbital sequence closely resembles that of N-heterocyclic carbene analogues. Despite these intriguing parallels between carbene analogues and silole and germole dianions, disappointingly little is known about their reactivity. The installation of trialkylsilyl substituents in the 2,5-positions of the heterocyclopentadiene ring as in K2[I] has a remarkable effect on the stability of silole and germole dianions and allows us to study their reactivity and to evaluate their synthetic potential in detail. Simple double salt metathesis reactions with different dihalides provided heterofulvenes. These were detected either as intermediates or, in the case of carbon dihalides, isolated in the form of their ylidic isomers II. In other cases, the heterofulvenes were the starting point for complex reaction sequences leading to novel binuclear complexes of titanium and zirconium III or for simple isomerization reactions that lead to bicyclohexene-type tetrylenes (BCH-tetrylenes) IV, a novel class of heavier carbenes. These bicyclic carbene analogues are significantly stabilized by homoconjugation between the electron deficient tetrel atom and the remote C═C double bond. Compound IV with E'R2═SiR2 and E = Si is a valence isomer of disilabenzene and is a stable derivative of the global minimum of the Si2C4H6 potential energy surface. With group 13 dihalides, as for example with boron dichlorides, topological closely related compounds V were isolated. These Ge(II) complexes of borole dianions are isolobal to half-sandwich complexes of main group elements such as aluminum(I) cyclopentadienide or can be viewed as nido-type clusters. These analogies already open a broad field for future investigations of their reactivity. Trialkylsilyl-substituted heterole dianions I provide a facile synthetic approach to several novel intriguing compound classes with the tetrel element in unusual coordination states. The reactivity and the synthetic potential of these new compounds is however widely unexplored and calls for future systematic studies. Gratifyingly, the periodic table of the elements stills holds a lot of potential for future research on the reactivity of silole and germole dianions.
Collapse
Affiliation(s)
- Zhaowen Dong
- Institute of Chemistry, Carl von Ossietzky University Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Germany, European Union
| | - Lena Albers
- Institute of Chemistry, Carl von Ossietzky University Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Germany, European Union
| | - Thomas Müller
- Institute of Chemistry, Carl von Ossietzky University Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Germany, European Union
| |
Collapse
|
37
|
Sampani SI, Zdorichenko V, Danopoulou M, Leech MC, Lam K, Abdul-Sada A, Cox B, Tizzard GJ, Coles SJ, Tsipis A, Kostakis GE. Shedding light on the use of Cu(ii)-salen complexes in the A 3 coupling reaction. Dalton Trans 2020; 49:289-299. [PMID: 31750481 DOI: 10.1039/c9dt04146j] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
One Cu(ii) complex, {Cu(ii)L} (1S), has been synthesised, in two high yielding steps under ambient conditions, and characterised by single-crystal X-Ray diffraction (SXRD), IR, UV-Vis, circular dichroism (CD), elemental analysis, thermogravimetric analysis (TGA) and electron spray ionization mass spectroscopy (ESI-MS). This air-stable compound enables the generation, at room temperature and in open-air, of twenty propargylamines, nine new, from secondary amines, aliphatic aldehydes and alkynes with a broad scope with yields up to 99%. Catalyst loadings can be as low as 1 mol%, while the recovered material retains its structural integrity and can be used up to 5 times without loss of its activity. Control experiments, SXRD, cyclic voltammetry and theoretical studies shed light on the mechanism revealing that the key to success is the use of phenoxido salen based ligands. These ligands orchestrate topological control permitting alkyne binding with concomitant activation of the C-H bond and simultaneously acting as a template temporarily accommodating the abstracted acetylenic proton, and continuously generating, via in situ formed radicals and a Single Electron Transfer (SET) mechanism, a transient Cu(i) active site to facilitate this transformation. The scope and limitations of this protocol are discussed and presented.
Collapse
Affiliation(s)
- Stavroula I Sampani
- Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ, UK.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
38
|
Radius M, Sattler E, Berberich H, Breher F. Reactivity of a Sterically Unencumbered α-Borylated Phosphorus Ylide towards Small Molecules. Chemistry 2019; 25:12206-12213. [PMID: 31355482 PMCID: PMC6771871 DOI: 10.1002/chem.201902681] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 07/19/2019] [Indexed: 01/06/2023]
Abstract
The influence of substituents on α-borylated phosphorus ylides (α-BCPs) has been investigated in a combined experimental and quantum chemical approach. The synthesis and characterization of Me3 PC(H)B(iBu)2 (1), consisting of small Me substituents on phosphorous and iBu residues on boron, is reported. Compound 1 is accessible through a novel synthetic approach, which has been further elucidated through DFT studies. The reactivity of 1 towards various small molecules was probed and compared with that of a previously published derivative, Ph3 PC(Me)BEt2 (2). Both α-BCPs react with NH3 to undergo heterolytic N-H bond cleavage. Different di- and trimeric ring structures were observed in the reaction products of 1 with CO and CO2 . With PhNCO and PHNCS, the expected insertion products [Me3 PC(H)(PhNCO)B(iBu)2 ] and [Me3 PC(H)(PhNCS)B(iBu)2 ], respectively, were isolated.
Collapse
Affiliation(s)
- Michael Radius
- Institute of Inorganic ChemistryDivision Molecular ChemistryKarlsruhe Institute of Technology (KIT)Engesserstr. 1576131KarlsruheGermany
| | - Ewald Sattler
- Institute of Inorganic ChemistryDivision Molecular ChemistryKarlsruhe Institute of Technology (KIT)Engesserstr. 1576131KarlsruheGermany
| | - Helga Berberich
- Institute of Inorganic ChemistryDivision Molecular ChemistryKarlsruhe Institute of Technology (KIT)Engesserstr. 1576131KarlsruheGermany
| | - Frank Breher
- Institute of Inorganic ChemistryDivision Molecular ChemistryKarlsruhe Institute of Technology (KIT)Engesserstr. 1576131KarlsruheGermany
| |
Collapse
|
39
|
Bennett EL, Lawrence EJ, Blagg RJ, Mullen AS, MacMillan F, Ehlers AW, Scott DJ, Sapsford JS, Ashley AE, Wildgoose GG, Slootweg JC. A New Mode of Chemical Reactivity for Metal-Free Hydrogen Activation by Lewis Acidic Boranes. Angew Chem Int Ed Engl 2019; 58:8362-8366. [PMID: 30968535 PMCID: PMC6594078 DOI: 10.1002/anie.201900861] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 04/09/2019] [Indexed: 12/13/2022]
Abstract
We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H2 outside of the usual Lewis acid/base chemistry described by the concept of frustrated Lewis pairs (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly hindered boranes: tris(3,5-dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway. This radical-based, redox pathway involves the homolytic cleavage of H2 , in contrast to conventional models of FLP chemistry, which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids.
Collapse
Affiliation(s)
- Elliot L. Bennett
- School of ChemistryUniversity of East AngliaNorwich Research ParkNorwichNR4 7TJUK
| | - Elliot J. Lawrence
- School of ChemistryUniversity of East AngliaNorwich Research ParkNorwichNR4 7TJUK
| | - Robin J. Blagg
- School of ChemistryUniversity of East AngliaNorwich Research ParkNorwichNR4 7TJUK
| | - Anna S. Mullen
- School of ChemistryUniversity of East AngliaNorwich Research ParkNorwichNR4 7TJUK
| | - Fraser MacMillan
- School of ChemistryUniversity of East AngliaNorwich Research ParkNorwichNR4 7TJUK
| | - Andreas W. Ehlers
- Van 't Hoff Institute for Molecular SciencesUniversity of AmsterdamScience Park 904, PO Box 941571090 GDAmsterdamThe Netherlands
- Department of Chemistry, Science FacultyUniversity of JohannesburgPO Box 254, Auckland ParkJohannesburgSouth Africa
| | - Daniel J. Scott
- Molecular Sciences Research HubImperial College White City Campus80 Wood LaneLondonW12 0BZUK
| | - Joshua S. Sapsford
- Molecular Sciences Research HubImperial College White City Campus80 Wood LaneLondonW12 0BZUK
| | - Andrew E. Ashley
- Molecular Sciences Research HubImperial College White City Campus80 Wood LaneLondonW12 0BZUK
| | - Gregory G. Wildgoose
- School of ChemistryUniversity of East AngliaNorwich Research ParkNorwichNR4 7TJUK
| | - J. Chris Slootweg
- Van 't Hoff Institute for Molecular SciencesUniversity of AmsterdamScience Park 904, PO Box 941571090 GDAmsterdamThe Netherlands
| |
Collapse
|
40
|
Kim Y, Liu LL, Stephan DW. N-Heterocyclic Carbene Derived 3-Azabutadiene as a π-Base in Classic and Frustrated Lewis Pair Chemistry. Chemistry 2019; 25:7110-7113. [PMID: 30968983 DOI: 10.1002/chem.201901609] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Indexed: 11/05/2022]
Abstract
N-Heterocyclic carbene (NHC) derived 3-azabutadienes 1 and 2 have been prepared by a single-step reaction of the corresponding NHC with cyclohexyl isocyanide. Compound 1 features π-basic, delocalized nucleophilic sites over the 3-azabutadiene moiety, therefore allowing for coordinating with small Lewis acids, such as AlCl3 , GaCl3 , and Me2 SAuCl, to form diverse classic Lewis adducts 3-5. Combination of 1 with B(C6 F5 )3 or [Ph3 C][B(C6 F5 )4 ] resulted in single-electron transfer and the obtained radical cation was detected by EPR. In addition, a frustrated Lewis pair comprised of the π-basic 1 and BPh3 effects the splitting of the O-H bond of phenol and the N-H bond of imidazole to give 7 and 8, respectively. An intrinsic bond orbital (IBO) analysis of the pathway leading to 8 showcases the transformation of the delocalized π-electrons of 1 to a newly formed C-H localized σ-bond.
Collapse
Affiliation(s)
- Youngsuk Kim
- Department of Chemistry, University of Toronto, 80 St. George St. Toronto, Ontario, M5S3H6, Canada.,Department of Chemistry, Pohang University of Science and Technology, Pohang, 37673, Korea
| | - Liu Leo Liu
- Department of Chemistry, University of Toronto, 80 St. George St. Toronto, Ontario, M5S3H6, Canada
| | - Douglas W Stephan
- Department of Chemistry, University of Toronto, 80 St. George St. Toronto, Ontario, M5S3H6, Canada
| |
Collapse
|
41
|
Bennett EL, Lawrence EJ, Blagg RJ, Mullen AS, MacMillan F, Ehlers AW, Scott DJ, Sapsford JS, Ashley AE, Wildgoose GG, Slootweg JC. A New Mode of Chemical Reactivity for Metal‐Free Hydrogen Activation by Lewis Acidic Boranes. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201900861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Elliot L. Bennett
- School of ChemistryUniversity of East Anglia Norwich Research Park Norwich NR4 7TJ UK
| | - Elliot J. Lawrence
- School of ChemistryUniversity of East Anglia Norwich Research Park Norwich NR4 7TJ UK
| | - Robin J. Blagg
- School of ChemistryUniversity of East Anglia Norwich Research Park Norwich NR4 7TJ UK
| | - Anna S. Mullen
- School of ChemistryUniversity of East Anglia Norwich Research Park Norwich NR4 7TJ UK
| | - Fraser MacMillan
- School of ChemistryUniversity of East Anglia Norwich Research Park Norwich NR4 7TJ UK
| | - Andreas W. Ehlers
- Van 't Hoff Institute for Molecular SciencesUniversity of Amsterdam Science Park 904, PO Box 94157 1090 GD Amsterdam The Netherlands
- Department of Chemistry, Science FacultyUniversity of Johannesburg PO Box 254, Auckland Park Johannesburg South Africa
| | - Daniel J. Scott
- Molecular Sciences Research HubImperial College White City Campus 80 Wood Lane London W12 0BZ UK
| | - Joshua S. Sapsford
- Molecular Sciences Research HubImperial College White City Campus 80 Wood Lane London W12 0BZ UK
| | - Andrew E. Ashley
- Molecular Sciences Research HubImperial College White City Campus 80 Wood Lane London W12 0BZ UK
| | - Gregory G. Wildgoose
- School of ChemistryUniversity of East Anglia Norwich Research Park Norwich NR4 7TJ UK
| | - J. Chris Slootweg
- Van 't Hoff Institute for Molecular SciencesUniversity of Amsterdam Science Park 904, PO Box 94157 1090 GD Amsterdam The Netherlands
| |
Collapse
|
42
|
Dong Z, Albers L, Schmidtmann M, Müller T. A Germacalicene: Synthesis, Structure, and Reactivity. Chemistry 2018; 25:1098-1105. [PMID: 30450653 DOI: 10.1002/chem.201805258] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Indexed: 11/11/2022]
Abstract
The synthesis of the germacalicene 7 from the reaction of the dipotassium germole dianion K2 [6] with 1,2-bis-diisopropylamino-3-chlorocyclopropenyl perchlorate is reported. Based on the crystal structure analysis and the results of DFT calculations, the germacalicene 7 can be viewed as a cyclopropenium germacyclopentadienide ylide that is isoelectronic to α-cationic phosphanes. First reactivity studies revealed its nucleophilic character and resulted in the isolation of the air- and moisture-stable carbonyl iron complex 15 and the cationic silver complex 20. One-electron oxidation of the germacalicene 7 was achieved by its reaction with [Ph3 C][B(C6 F5 )4 ] and the bis-cationic Ge-Ge-bonded dimer 22 was isolated.
Collapse
Affiliation(s)
- Zhaowen Dong
- Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky-Str. 9-11, 26129, Oldenburg, Germany
| | - Lena Albers
- Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky-Str. 9-11, 26129, Oldenburg, Germany
| | - Marc Schmidtmann
- Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky-Str. 9-11, 26129, Oldenburg, Germany
| | - Thomas Müller
- Institut für Chemie, Carl von Ossietzky Universität Oldenburg, Carl von Ossietzky-Str. 9-11, 26129, Oldenburg, Germany
| |
Collapse
|
43
|
Dong Z, Cramer HH, Schmidtmann M, Paul LA, Siewert I, Müller T. Evidence for a Single Electron Shift in a Lewis Acid–Base Reaction. J Am Chem Soc 2018; 140:15419-15424. [DOI: 10.1021/jacs.8b09214] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Zhaowen Dong
- Institute of Chemistry, Carl von Ossietzky University of Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Federal Republic of Germany, European Union
| | - Hanna H. Cramer
- Institute of Chemistry, Carl von Ossietzky University of Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Federal Republic of Germany, European Union
| | - Marc Schmidtmann
- Institute of Chemistry, Carl von Ossietzky University of Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Federal Republic of Germany, European Union
| | - Lucas A. Paul
- Institute of Inorganic Chemistry, Göttingen University, Tammannstr. 4, D-37077 Göttingen, Federal Republic of Germany, European Union
| | - Inke Siewert
- Institute of Inorganic Chemistry, Göttingen University, Tammannstr. 4, D-37077 Göttingen, Federal Republic of Germany, European Union
| | - Thomas Müller
- Institute of Chemistry, Carl von Ossietzky University of Oldenburg, Carl von Ossietzky-Str. 9-11, D-26129 Oldenburg, Federal Republic of Germany, European Union
| |
Collapse
|
44
|
|