1
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Barakat M, Elhajj S, Yazji R, Miller AJM, Hasanayn F. Kinetic Isotope Effects and the Mechanism of CO 2 Insertion into the Metal-Hydride Bond of fac-(bpy)Re(CO) 3H. Inorg Chem 2024; 63:12133-12145. [PMID: 38901030 DOI: 10.1021/acs.inorgchem.4c01246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/22/2024]
Abstract
The 1,2-insertion reaction of CO2 into metal-hydride bonds of d6-octahedral complexes to give κ1-O-metal-formate products is the key step in various CO2 reduction schemes and as a result has attracted extensive mechanistic investigations. For many octahedral catalysts, CO2 insertion follows an associative mechanism in which CO2 interacts directly with the coordinated hydride ligand instead of the more classical dissociative mechanism that opens an empty coordination site to bind the substrate to the metal prior to a hydride migration step. To better understand the associative mechanism, we conducted a systematic quantum chemical investigation on the reaction between CO2 and fac-(bpy)Re(CO)3H (1-Re-H; bpy = 2,2'-bipyridine) starting with the gas phase and then moving to THF and other solvents with increased dielectric constants. Detailed analyses of the potential energy surfaces (PESs) and intrinsic reaction coordinates (IRCs) reveal that the reaction is enabled in all media by an initial stage of making a 3c-2e bond between the carbon of CO2 and the metal-hydride bond that is most consistent with an organometallic bridging hydride Re-H-CO2 species. Once CO2 is bent and anchored to the metal-hydride bond, the reaction proceeds by a rotation motion via a cyclic transition state TS2 that interchanges Re-H-CO2 and Re-O-CHO coordination. The combined stages provide an asynchronous-concerted pathway for CO2 insertion on the Gibbs free energy surface with TS2 as the highest energy point. Consideration of TS2 as a rate-determining TS gives activation barriers, inverse KIEs, substituent effects, and solvent effects that agree with the experimental data available in this system. An important new insight revealed by the analyses of the results is that the initial stage of the reaction is not a hydride transfer step as has been assumed in some studies. In fact, the loose vibration of the TS that can be identified for the first stage of the reaction in solution (TS1) does not involve the Re-H stretching vibrational mode. Accordingly, the imaginary frequency of TS1 is insensitive to deuteration, and therefore, TS1 leads to no significant KIE.
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Affiliation(s)
- Mariam Barakat
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Sarah Elhajj
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Riyad Yazji
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Alexander J M Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
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2
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Echeverría J, Alvarez S. The borderless world of chemical bonding across the van der Waals crust and the valence region. Chem Sci 2023; 14:11647-11688. [PMID: 37920358 PMCID: PMC10619631 DOI: 10.1039/d3sc02238b] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Accepted: 07/01/2023] [Indexed: 11/04/2023] Open
Abstract
The definition of the van der Waals crust as the spherical section between the atomic radius and the van der Waals radius of an element is discussed and a survey of the application of the penetration index between two interacting atoms in a wide variety of covalent, polar, coordinative or noncovalent bonding situations is presented. It is shown that this newly defined parameter permits the comparison of bonding between pairs of atoms in structural and computational studies independently of the atom sizes.
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Affiliation(s)
- Jorge Echeverría
- Instituto de Síntesis Química y Catalisis Homogénea (ISQCH) and Departmento de Química Inorgánica, Facultad de Ciencias, Universidad de Zaragoza Pedro Cerbuna 12 50009 Zaragoza Spain
| | - Santiago Alvarez
- Department de Química Inorgànica i Orgànica, Secció de Química Inorgànica, e Institut de Química Teòrica i Computacional, Universitat de Barcelona Martí i Franquès 1-11 08028 -Barcelona Spain
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3
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Sajjad MA, Macgregor SA, Weller AS. A comparison of non-covalent interactions in the crystal structures of two σ-alkane complexes of Rh exhibiting contrasting stabilities in the solid state. Faraday Discuss 2023; 244:222-240. [PMID: 37096331 DOI: 10.1039/d3fd00009e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Non-covalent interactions surrounding the cationic Rh σ-alkane complexes within the crystal structures of [(Cy2PCH2CH2PCy2)Rh(NBA)][BArF4], [1-NBA][BArF4] (NBA = norbornane, C7H12; ArF = 3,5-(CF3)2C6H3), and [1-propane][BArF4] are analysed using Quantum Theory of Atoms in Molecules (QTAIM) and Independent Gradient Model approaches, the latter under a Hirshfeld partitioning scheme (IGMH). In both structures the cations reside in an octahedral array of [BArF4]- anions within which the [1-NBA]+ cation system exhibits a greater number of C-H⋯F contacts to the anions. QTAIM and IGMH analyses indicate these include the strongest individual atom-atom non-covalent interactions between the cation and the anion in these systems. The IGMH approach highlights the directionality of these C-H⋯F contacts that contrasts with the more diffuse C-H⋯π interactions. The accumulative effects of the latter lead to a more significant stabilizing contribution. IGMH %δGatom plots provide a particularly useful visual tool to identify key interactions and highlight the importance of a -{C3H6}- propylene moiety that is present within both the propane and NBA ligands (the latter as a truncated -{C3H4}- unit) and the cyclohexyl rings of the phosphine substituents. The potential for this to act as a privileged motif that confers stability on the crystal structures of σ-alkane complexes in the solid-state is discussed. The greater number of C-H⋯F inter-ion interactions in the [1-NBA][BArF4] system, coupled with more significant C-H⋯π interactions are all consistent with greater non-covalent stabilisation around the [1-NBA]+ cation. This is also supported by larger computed δGatom indices as a measure of cation-anion non-covalent interaction energy.
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Affiliation(s)
- M Arif Sajjad
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Stuart A Macgregor
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Andrew S Weller
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
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4
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Samudrala KK, Conley MP. Effects of surface acidity on the structure of organometallics supported on oxide surfaces. Chem Commun (Camb) 2023; 59:4115-4127. [PMID: 36912586 DOI: 10.1039/d3cc00047h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
Abstract
Well-defined organometallics supported on high surface area oxides are promising heterogeneous catalysts. An important design factor in these materials is how the metal interacts with the functionalities on an oxide support, commonly anionic X-type ligands derived from the reaction of an organometallic M-R with an -OH site on the oxide. The metal can either form a covalent M-O bond or form an electrostatic M+⋯-O ion-pair, which impacts how well-defined organometallics will interact with substrates in catalytic reactions. A less common reaction pathway involves the reaction of a Lewis site on the oxide with the organometallic, resulting in abstraction to form an ion-pair, which is relevant to industrial olefin polymerization catalysts. This Feature Article views the spectrum of reactivity between an organometallic and an oxide through the prism of Brønsted and/or Lewis acidity of surface sites and draws analogies to the molecular frame where Lewis and Brønsted acids are known to form reactive ion-pairs. Applications of the well-defined sites developed in this article are also discussed.
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Affiliation(s)
| | - Matthew P Conley
- Department of Chemistry, University of California, Riverside, California 92521, USA.
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5
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Royle CG, Sotorrios L, Gyton MR, Brodie CN, Burnage AL, Furfari SK, Marini A, Warren MR, Macgregor SA, Weller AS. Single-Crystal to Single-Crystal Addition of H 2 to [Ir( iPr-PONOP)(propene)][BAr F4] and Comparison Between Solid-State and Solution Reactivity. Organometallics 2022; 41:3270-3280. [DOI: 10.1021/acs.organomet.2c00274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Indexed: 11/30/2022]
Affiliation(s)
- Cameron G. Royle
- Department of Chemistry, University of York, Heslington YO10 5DD, York, U.K
- Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K
| | - Lia Sotorrios
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K
| | - Matthew R. Gyton
- Department of Chemistry, University of York, Heslington YO10 5DD, York, U.K
| | - Claire N. Brodie
- Department of Chemistry, University of York, Heslington YO10 5DD, York, U.K
| | - Arron L. Burnage
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K
| | | | - Anna Marini
- Diamond Light Source Ltd, Didcot OX11 0DE, U.K
- Department of Chemistry, University of Southampton, Southampton SO17 1BJ, U.K
| | | | - Stuart A. Macgregor
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, U.K
| | - Andrew S. Weller
- Department of Chemistry, University of York, Heslington YO10 5DD, York, U.K
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6
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Fazlur-Rahman A, Bennett MA. Activation of Carbon-Carbon bonds in d9 (Co, Rh, Ir) and d8 (Ru) Metal Coordinated Bicyclo[3.2.1]octa-2,6-diene via agostic M-H-C and M-H Interactions. J Organomet Chem 2022. [DOI: 10.1016/j.jorganchem.2022.122349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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7
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Doyle LR, Galpin MR, Furfari SK, Tegner BE, Martínez-Martínez AJ, Whitwood AC, Hicks SA, Lloyd-Jones GC, Macgregor SA, Weller AS. Inverse Isotope Effects in Single-Crystal to Single-Crystal Reactivity and the Isolation of a Rhodium Cyclooctane σ-Alkane Complex. Organometallics 2022; 41:284-292. [PMID: 35273423 PMCID: PMC8900153 DOI: 10.1021/acs.organomet.1c00639] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Indexed: 12/15/2022]
Abstract
![]()
The
sequential solid/gas single-crystal to single-crystal reaction
of [Rh(Cy2P(CH2)3PCy2)(COD)][BArF4] (COD = cyclooctadiene) with H2 or
D2 was followed in situ by solid-state 31P{1H} NMR spectroscopy (SSNMR) and ex situ by solution quenching
and GC-MS. This was quantified using a two-step Johnson–Mehl–Avrami–Kologoromov
(JMAK) model that revealed an inverse isotope effect for the second
addition of H2, that forms a σ-alkane complex [Rh(Cy2P(CH2)3PCy2)(COA)][BArF4]. Using D2, a temporal window is determined
in which a structural solution for this σ-alkane complex is
possible, which reveals an η2,η2-binding mode to the Rh(I) center, as supported by periodic density
functional theory (DFT) calculations. Extensive H/D exchange occurs
during the addition of D2, as promoted by the solid-state
microenvironment.
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Affiliation(s)
- Laurence R. Doyle
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Martin R. Galpin
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford OX1 3QZ, United Kingdom
| | - Samantha K. Furfari
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Bengt E. Tegner
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, Scotland EH14 4AS, United Kingdom
| | | | - Adrian C. Whitwood
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Scott A. Hicks
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Guy C. Lloyd-Jones
- Department of Chemistry, University of Edinburgh, Edinburgh, Scotland EH9 3FJ, United Kingdom
| | - Stuart A. Macgregor
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, Scotland EH14 4AS, United Kingdom
| | - Andrew S. Weller
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
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8
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Abstract
X-ray crystallography is an invaluable tool in design and development of organometallic catalysis, but application typically requires species to display sufficiently high solution concentrations and lifetimes for single crystalline samples to be obtained. In crystallo organometallic chemistry relies on chemical reactions that proceed within the single-crystal environment to access crystalline samples of reactive organometallic fragments that are unavailable by alternate means. This highlight describes approaches to in crystallo organometallic chemistry including (a) solid-gas reactions between transition metal complexes in molecular crystals and diffusing small molecules, (b) reactions of organometallic complexes within the extended lattices of metal-organic frameworks (MOFs), and (c) intracrystalline photochemical transformations to generate reactive organometallic fragments. Application of these methods has enabled characterization of catalytically important transient species, including σ-alkane adducts of transition metals, metal alkyl intermediates implicated in metal-catalyzed carbonylations, and reactive M-L multiply bonded species involved in C-H functionalization chemistry. Opportunities and challenges for in crystallo organometallic chemistry are discussed.
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Affiliation(s)
- Kaleb A Reid
- Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, TX 77843, USA.
| | - David C Powers
- Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, TX 77843, USA.
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9
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Carlsen R, Maley SM, Ess DH. Timing and Structures of σ-Bond Metathesis C–H Activation Reactions from Quasiclassical Direct Dynamics Simulations. Organometallics 2021. [DOI: 10.1021/acs.organomet.1c00102] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ryan Carlsen
- Department of Chemistry and Biochemistry, Brigham Young University, Provo 84602, Utah, United States
| | - Steven M. Maley
- Department of Chemistry and Biochemistry, Brigham Young University, Provo 84602, Utah, United States
| | - Daniel H. Ess
- Department of Chemistry and Biochemistry, Brigham Young University, Provo 84602, Utah, United States
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10
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Bukvic A, Burnage AL, Tizzard GJ, Martínez-Martínez AJ, McKay AI, Rees NH, Tegner BE, Krämer T, Fish H, Warren MR, Coles SJ, Macgregor SA, Weller AS. A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane. J Am Chem Soc 2021; 143:5106-5120. [PMID: 33769815 PMCID: PMC8154534 DOI: 10.1021/jacs.1c00738] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Indexed: 12/12/2022]
Abstract
Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to single-crystal reactivity, a series of σ-alkane complexes of the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF = 3,5-(CF3)2C6H3). These new complexes have been characterized using single crystal X-ray diffraction, solid-state NMR spectroscopy and DFT computational techniques and present a variety of Rh(I)···H-C binding motifs at the metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), and 1,4-η1:η2 (3-methylpentane). For the linear alkanes propane and hexane, some additional Rh(I)···H-C interactions with the geminal C-H bonds are also evident. The stability of these complexes with respect to alkane loss in the solid state varies with the identity of the alkane: from propane that decomposes rapidly at 295 K to 2-methylbutane that is stable and instead undergoes an acceptorless dehydrogenation to form a bound alkene complex. In each case the alkane sits in a binding pocket defined by the {Rh(Cy2PCH2CH2PCy2)}+ fragment and the surrounding array of [BArF4]- anions. For the propane complex, a small alkane binding energy, driven in part by a lack of stabilizing short contacts with the surrounding anions, correlates with the fleeting stability of this species. 2-Methylbutane forms more short contacts within the binding pocket, and as a result the complex is considerably more stable. However, the complex of the larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears to be an optimal fit between the size and shape of the alkane and overall stability. Such observations are related to guest/host interactions in solution supramolecular chemistry and the holistic role of 1°, 2°, and 3° environments in metalloenzymes.
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Affiliation(s)
- Alexander
J. Bukvic
- Department
of Chemistry, University of York, Heslington, York YO10
5DD, U.K.
- Department
of Chemistry, Chemistry Research Laboratories, University of Oxford, Oxford OX1 3TA, U.K.
| | - Arron L. Burnage
- Institute
of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS. U.K.
| | - Graham J. Tizzard
- UK
National Crystallography Service, University
of Southampton, Highfield, Southampton SO17 1BJ, U.K.
| | | | - Alasdair I. McKay
- Department
of Chemistry, Chemistry Research Laboratories, University of Oxford, Oxford OX1 3TA, U.K.
| | - Nicholas H. Rees
- Department
of Chemistry, Chemistry Research Laboratories, University of Oxford, Oxford OX1 3TA, U.K.
| | - Bengt E. Tegner
- Institute
of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS. U.K.
| | - Tobias Krämer
- Institute
of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS. U.K.
| | - Heather Fish
- Department
of Chemistry, University of York, Heslington, York YO10
5DD, U.K.
| | - Mark R. Warren
- Diamond
Light Source Ltd., Diamond House,
Harwell Science and Innovation Campus, Didcot OX11 0DE, U.K.
| | - Simon J. Coles
- UK
National Crystallography Service, University
of Southampton, Highfield, Southampton SO17 1BJ, U.K.
| | - Stuart A. Macgregor
- Institute
of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS. U.K.
| | - Andrew S. Weller
- Department
of Chemistry, University of York, Heslington, York YO10
5DD, U.K.
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11
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Furfari SK, Tegner BE, Burnage AL, Doyle LR, Bukvic AJ, Macgregor SA, Weller AS. Selectivity of Rh⋅⋅⋅H-C Binding in a σ-Alkane Complex Controlled by the Secondary Microenvironment in the Solid State. Chemistry 2021; 27:3177-3183. [PMID: 33112000 PMCID: PMC7898853 DOI: 10.1002/chem.202004585] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Revised: 10/27/2020] [Indexed: 12/13/2022]
Abstract
Single-crystal to single-crystal solid-state molecular organometallic (SMOM) techniques are used for the synthesis and structural characterization of the σ-alkane complex [Rh(tBu2 PCH2 CH2 CH2 PtBu2 )(η2 ,η2 -C7 H12 )][BArF 4 ] (ArF =3,5-(CF3 )2 C6 H3 ), in which the alkane (norbornane) binds through two exo-C-H⋅⋅⋅Rh interactions. In contrast, the bis-cyclohexyl phosphine analogue shows endo-alkane binding. A comparison of the two systems, supported by periodic DFT calculations, NCI plots and Hirshfeld surface analyses, traces this different regioselectivity to subtle changes in the local microenvironment surrounding the alkane ligand. A tertiary periodic structure supporting a secondary microenvironment that controls binding at the metal site has parallels with enzymes. The new σ-alkane complex is also a catalyst for solid/gas 1-butene isomerization, and catalyst resting states are identified for this.
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Affiliation(s)
| | - Bengt E. Tegner
- Institute of Chemical SciencesHeriot-Watt UniversityEdinburghEH14 4ASUK
| | - Arron L. Burnage
- Institute of Chemical SciencesHeriot-Watt UniversityEdinburghEH14 4ASUK
| | | | - Alexander J. Bukvic
- Department of ChemistryUniversity of YorkYorkYO10 5DDUK
- Department of ChemistryUniversity of OxfordMansfield RoadOxfordOX1 3TAUK
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12
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Storey CM, Gyton MR, Andrew RE, Chaplin AB. Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity. Chemistry 2020; 26:14715-14723. [PMID: 32677713 PMCID: PMC7756505 DOI: 10.1002/chem.202002962] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Revised: 07/15/2020] [Indexed: 01/11/2023]
Abstract
Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincer ligands-which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC-n)(C2 H4 )][BArF 4 ] (n=12, 14, 16; ArF =3,5-(CF3 )2 C6 H3 )-have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr' (Ar'=3,5-tBu2 C6 H3 ) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3-enynes by C-C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E-alkenyl complexes derived from HC≡CtBu and gem-alkenyl complexes derived from HC≡CAr', and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E-tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E-alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH2 )Ar' is encumbered relative to head-to-head coupling of HC≡CAr' and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC-Me)(C2 H4 )][BArF 4 ] and solvent effects.
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Affiliation(s)
- Caroline M. Storey
- Department of ChemistryUniversity of WarwickGibbet Hill RoadCoventryCV4 7ALUK
| | - Matthew R. Gyton
- Department of ChemistryUniversity of WarwickGibbet Hill RoadCoventryCV4 7ALUK
| | - Rhiann E. Andrew
- Department of ChemistryUniversity of WarwickGibbet Hill RoadCoventryCV4 7ALUK
| | - Adrian B. Chaplin
- Department of ChemistryUniversity of WarwickGibbet Hill RoadCoventryCV4 7ALUK
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13
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Peralta RA, Huxley MT, Evans JD, Fallon T, Cao H, He M, Zhao XS, Agnoli S, Sumby CJ, Doonan CJ. Highly Active Gas Phase Organometallic Catalysis Supported Within Metal-Organic Framework Pores. J Am Chem Soc 2020; 142:13533-13543. [PMID: 32650640 DOI: 10.1021/jacs.0c05286] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Metal-organic frameworks (MOFs) can act as a platform for the heterogenization of molecular catalysts, providing improved stability, allowing easy catalyst recovery and a route toward structural elucidation of the active catalyst. We have developed a MOF, 1, possessing vacant N,N-chelating sites which are accessible via the porous channels that penetrate the structure. In the present work, cationic rhodium(I) norbornadiene (NBD) and bis(ethylene) (ETH) complexes paired with both noncoordinating and coordinating anions have been incorporated into the N,N-chelation sites of 1 via postsynthetic metalation and facile anion exchange. Exploiting the crystallinity of the host framework, the immobilized Rh(I) complexes were structurally characterized using X-ray crystallography. Ethylene hydrogenation catalysis by 1·[Rh(NBD)]X and 1·[Rh(ETH)2]X (X = Cl and BF4) was studied in the gas phase (2 bar, 46 °C) to reveal that 1·[Rh(ETH)2](BF4) was the most active catalyst (TOF = 64 h-1); the NBD materials and the chloride salt were notably less active. On the basis of these observations, the activity of the Rh(I) bis(ethylene) complexes, 1·[Rh(ETH)2]BF4 and 1·[Rh(ETH)2]Cl, in butene isomerization was also studied using gas-phase NMR spectroscopy. Under one bar of butene at 46 °C, 1·[Rh(ETH)2]BF4 rapidly catalyzes the conversion of 1-butene to 2-butene with a TOF averaging 2000 h-1 over five cycles. Notably, the chloride derivative, 1 [Rh(ETH)2]Cl displays negligible activity in comparison. XPS analysis of the postcatalysis sample, supported by DFT calculations, suggest that the catalytic activity is inhibited by the strong interactions between a Rh(III) allyl hydride intermediate and the chloride anion.
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Affiliation(s)
- Ricardo A Peralta
- Centre for Advanced Nanomaterials and Department of Chemistry, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia
| | - Michael T Huxley
- Centre for Advanced Nanomaterials and Department of Chemistry, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia
| | - Jack D Evans
- Department of Inorganic Chemistry, Technische Universität Dresden, Bergstraße 66, 01062 Dresden, Germany
| | - Thomas Fallon
- Centre for Advanced Nanomaterials and Department of Chemistry, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia
| | - Haijie Cao
- Institute of Materials for Energy and Environment, College of Materials Science and Engineering, Qingdao University, Qingdao 266071, PR China
| | - Maoxia He
- Environment Research Institute, Shandong University, Qingdao 266237, PR China
| | - Xiu Song Zhao
- Institute of Materials for Energy and Environment, College of Materials Science and Engineering, Qingdao University, Qingdao 266071, PR China.,School of Chemical Engineering, The University of Queensland, St Lucia,Brisbane 4072, Australia
| | - Stefano Agnoli
- Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Christopher J Sumby
- Centre for Advanced Nanomaterials and Department of Chemistry, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia
| | - Christian J Doonan
- Centre for Advanced Nanomaterials and Department of Chemistry, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia
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14
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Eastwood JB, Hammarback LA, McRobie MT, Clark IP, Towrie M, Fairlamb IJS, Lynam JM. Time-resolved infra-red spectroscopy reveals competitive water and dinitrogen coordination to a manganese(i) carbonyl complex. Dalton Trans 2020; 49:5463-5470. [PMID: 32255172 DOI: 10.1039/c9dt04878b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Time-resolved infra-red (TRIR) spectroscopy has been used to demonstrate that photolysis of [Mn(C^N)(CO)4] (C^N = bis-(4-methoxyphenyl)methanimine) in heptane solution results in ultra-fast CO dissociation and ultimate formation of a rare Mn-containing dinitrogen complex fac-[Mn(C^N)(CO)3(N2)] with a diagnostic stretching mode for a terminal-bound N[triple bond, length as m-dash]N ligand at 2249 cm-1. An isotopic shift to 2174 cm-1 was observed when the reaction was performed under 15N2 and the band was not present when the experiment was undertaken under an atmosphere of argon, reinforcing this assignment. An intermediate solvent complex fac-[Mn(C^N)(CO)3(heptane)] was identified which is formed in less than 2 ps, indicating that CO-release occurs on an ultra-fast timescale. The heptane ligand is labile and is readily displaced by both N2 and water to give fac-[Mn(C^N)(CO)3(N2)] and fac-[Mn(C^N)(CO)3(OH2)] respectively. The fac-[Mn(C^N)(CO)3(heptane)] framework showed a significant affinity for N2, as performing the reaction under air produced significant amounts of fac-[Mn(C^N)(CO)3(N2)]. Kinetic analysis reveals that the substitution of heptane by N2 (k = (1.028 ± 0.004) × 109 mol-1 dm3 s-1), and H2O is competitive on fast (<1 μs) time scales. The binding of water is reversible and, under an atmosphere of N2, some fac-[Mn(C^N)(CO)3(OH2)] converts to fac-[Mn(C^N)(CO)3(N2)].
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Affiliation(s)
- Jonathan B Eastwood
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
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15
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Boyd TM, Tegner BE, Tizzard GJ, Martínez‐Martínez AJ, Neale SE, Hayward MA, Coles SJ, Macgregor SA, Weller AS. A Structurally Characterized Cobalt(I) σ-Alkane Complex. Angew Chem Int Ed Engl 2020; 59:6177-6181. [PMID: 31943626 PMCID: PMC7187152 DOI: 10.1002/anie.201914940] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Indexed: 11/11/2022]
Abstract
A cobalt σ-alkane complex, [Co(Cy2 P(CH2 )4 PCy2 )(norbornane)][BArF 4 ], was synthesized by a single-crystal to single-crystal solid/gas hydrogenation from a norbornadiene precursor, and its structure was determined by X-ray crystallography. Magnetic data show this complex to be a triplet. Periodic DFT and electronic structure analyses revealed weak C-H→Co σ-interactions, augmented by dispersive stabilization between the alkane ligand and the anion microenvironment. The calculations are most consistent with a η1 :η1 -alkane binding mode.
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Affiliation(s)
- Timothy M. Boyd
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of OxfordOxfordOX1 3TAUK
- Department of ChemistryUniversity of YorkYorkYO10 5DDUK
| | - Bengt E. Tegner
- Institute of Chemical SciencesHeriot-Watt UniversityEdinburghEH14 4ASUK
| | - Graham J. Tizzard
- UK National Crystallography ServiceChemistryFaculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonSO17 1BJUK
| | | | - Samuel E. Neale
- Institute of Chemical SciencesHeriot-Watt UniversityEdinburghEH14 4ASUK
| | - Michael A. Hayward
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of OxfordOxfordOX1 3TAUK
| | - Simon J. Coles
- UK National Crystallography ServiceChemistryFaculty of Engineering and Physical SciencesUniversity of SouthamptonSouthamptonSO17 1BJUK
| | | | - Andrew S. Weller
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of OxfordOxfordOX1 3TAUK
- Department of ChemistryUniversity of YorkYorkYO10 5DDUK
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16
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Young RJ, Huxley MT, Pardo E, Champness NR, Sumby CJ, Doonan CJ. Isolating reactive metal-based species in Metal-Organic Frameworks - viable strategies and opportunities. Chem Sci 2020; 11:4031-4050. [PMID: 34122871 PMCID: PMC8152792 DOI: 10.1039/d0sc00485e] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 03/19/2020] [Indexed: 02/01/2023] Open
Abstract
Structural insight into reactive species can be achieved via strategies such as matrix isolation in frozen glasses, whereby species are kinetically trapped, or by confinement within the cavities of host molecules. More recently, Metal-Organic Frameworks (MOFs) have been used as molecular scaffolds to isolate reactive metal-based species within their ordered pore networks. These studies have uncovered new reactivity, allowed observation of novel metal-based complexes and clusters, and elucidated the nature of metal-centred reactions responsible for catalysis. This perspective considers strategies by which metal species can be introduced into MOFs and highlights some of the advantages and limitations of each approach. Furthermore, the growing body of work whereby reactive species can be isolated and structurally characterised within a MOF matrix will be reviewed, including discussion of salient examples and the provision of useful guidelines for the design of new systems. Novel approaches that facilitate detailed structural analysis of reactive chemical moieties are of considerable interest as the knowledge garnered underpins our understanding of reactivity and thus guides the synthesis of materials with unprecedented functionality.
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Affiliation(s)
- Rosemary J Young
- Department of Chemistry, Centre for Advanced Nanomaterials, The University of Adelaide Adelaide Australia
- School of Chemistry, The University of Nottingham Nottingham UK
| | - Michael T Huxley
- Department of Chemistry, Centre for Advanced Nanomaterials, The University of Adelaide Adelaide Australia
| | - Emilio Pardo
- Institute of Molecular Science, University of Valencia Valencia Spain
| | | | - Christopher J Sumby
- Department of Chemistry, Centre for Advanced Nanomaterials, The University of Adelaide Adelaide Australia
| | - Christian J Doonan
- Department of Chemistry, Centre for Advanced Nanomaterials, The University of Adelaide Adelaide Australia
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17
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Boyd TM, Tegner BE, Tizzard GJ, Martínez‐Martínez AJ, Neale SE, Hayward MA, Coles SJ, Macgregor SA, Weller AS. A Structurally Characterized Cobalt(I) σ‐Alkane Complex. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201914940] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Timothy M. Boyd
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of Oxford Oxford OX1 3TA UK
- Department of ChemistryUniversity of York York YO10 5DD UK
| | - Bengt E. Tegner
- Institute of Chemical SciencesHeriot-Watt University Edinburgh EH14 4AS UK
| | - Graham J. Tizzard
- UK National Crystallography ServiceChemistryFaculty of Engineering and Physical SciencesUniversity of Southampton Southampton SO17 1BJ UK
| | | | - Samuel E. Neale
- Institute of Chemical SciencesHeriot-Watt University Edinburgh EH14 4AS UK
| | - Michael A. Hayward
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of Oxford Oxford OX1 3TA UK
| | - Simon J. Coles
- UK National Crystallography ServiceChemistryFaculty of Engineering and Physical SciencesUniversity of Southampton Southampton SO17 1BJ UK
| | | | - Andrew S. Weller
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of Oxford Oxford OX1 3TA UK
- Department of ChemistryUniversity of York York YO10 5DD UK
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18
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Martínez-Martínez AJ, Royle CG, Furfari SK, Suriye K, Weller AS. Solid-State Molecular Organometallic Catalysis in Gas/Solid Flow (Flow-SMOM) as Demonstrated by Efficient Room Temperature and Pressure 1-Butene Isomerization. ACS Catal 2020; 10:1984-1992. [PMID: 32296595 PMCID: PMC7147255 DOI: 10.1021/acscatal.9b03727] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 01/05/2020] [Indexed: 02/06/2023]
Abstract
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The
use of solid–state molecular organometallic chemistry
(SMOM–chem) to promote the efficient double bond isomerization
of 1-butene to 2-butenes under flow–reactor conditions is reported.
Single crystalline catalysts based upon the σ-alkane complexes
[Rh(R2PCH2CH2PR2)(η2η2-NBA)][BArF4] (R
= Cy, tBu; NBA = norbornane; ArF = 3,5-(CF3)2C6H3) are prepared by hydrogenation
of a norbornadiene precursor. For the tBu-substituted system
this results in the loss of long-range order, which can be re-established
by addition of 1-butene to the material to form a mixture of [Rh(tBu2PCH2CH2PtBu2)(cis-2-butene)][BArF4] and [Rh(tBu2PCH2CH2PtBu2)(1-butene)][BArF4], in an order/disorder/order phase change. Deployment under flow-reactor
conditions results in very different on-stream stabilities. With R
= Cy rapid deactivation (3 h) to the butadiene complex occurs, [Rh(Cy2PCH2CH2PCy2)(butadiene)][BArF4], which can be reactivated by simple addition
of H2. While the equivalent butadiene complex does not
form with R = tBu at 298 K and on-stream conversion
is retained up to 90 h, deactivation is suggested to occur via loss
of crystallinity of the SMOM catalyst. Both systems operate under
the industrially relevant conditions of an isobutene co-feed. cis:trans
selectivites for 2-butene are biased in favor of cis for the tBu system and are more leveled for Cy.
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Affiliation(s)
| | - Cameron G. Royle
- Department of Chemistry, Chemistry Research Laboratories, University of Oxford, Oxford OX1 3TA, United Kingdom
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingsdom
| | - Samantha K. Furfari
- Department of Chemistry, Chemistry Research Laboratories, University of Oxford, Oxford OX1 3TA, United Kingdom
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingsdom
| | - Kongkiat Suriye
- SCG Chemicals, 1 Siam Cement Road, Bangsue, Bangkok 10800, Thailand
| | - Andrew S. Weller
- Department of Chemistry, Chemistry Research Laboratories, University of Oxford, Oxford OX1 3TA, United Kingdom
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingsdom
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19
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Alharis RA, McMullin CL, Davies DL, Singh K, Macgregor SA. Understanding electronic effects on carboxylate-assisted C-H activation at ruthenium: the importance of kinetic and thermodynamic control. Faraday Discuss 2019; 220:386-403. [PMID: 31528900 DOI: 10.1039/c9fd00063a] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Meta- and para-substituted 1-phenylpyrazoles (R-phpyz-H) react with [RuCl2(p-cymene)]2 in the presence of NaOAc to form cyclometallated complexes [M(R-phpyz)Cl(p-cymene)] (where R = NMe2, OMe, Me, H, F, CF3 and NO2). Experimental and DFT studies indicate that product formation can be reversible or irreversible depending on the substituents and the reaction conditions. Competition experiments show that the kinetic selectivity favours electron-donating substituents and correlate well with the Hammett parameter, giving a negative slope (ρ = -2.4) that is consistent with a cationic transition state. However, surprisingly, the thermodynamic selectivity is completely opposite, with substrates featuring electron-withdrawing groups being favoured. These trends are reproduced with DFT calculations that locate a rate-limiting transition state dominated by Ru-O bond dissociation and minimal C-H bond elongation. Detailed computational analysis of these transition states shows that C-H activation proceeds by an AMLA/CMD mechanism through a synergic combination of a C-H→Ru agostic interaction and C-HO H-bonding. NBO calculations also highlight a syndetic bonding term, and the relative weights of these three components vary in a complementary fashion depending on the nature of the substituent. With meta-substituted ligands H/D exchange experiments signal kinetically accessible ortho-C-H activation when R = NMe2, OMe and Me. This is also modelled computationally and the calculations highlight the kinetic relevance of the HOAc/Cl exchange that occurs post C-H bond cleavage, in particular with the bulkier NMe2 and Me substituents. Our study highlights that the experimental substituent effects are dependent on the reaction conditions and so using such studies to assign the mechanism of C-H activation in either stoichiometric or catalytic reactions may be misleading.
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Affiliation(s)
- Raed A Alharis
- Department of Chemistry, University of Leicester, Leicester, LE1 7RH, UK.
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20
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Martínez‐Martínez AJ, Rees NH, Weller AS. Reversible Encapsulation of Xenon and CH
2
Cl
2
in a Solid‐State Molecular Organometallic Framework (Guest@SMOM). Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201910539] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Antonio J. Martínez‐Martínez
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of Oxford Oxford OX1 3TA UK
- Current Address: CIQSO-Centre for Research in Sustainable Chemistry and Department of ChemistryUniversity of Huelva Campus El Carmen 21007 Huelva Spain
| | - Nicholas H. Rees
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of Oxford Oxford OX1 3TA UK
| | - Andrew S. Weller
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of Oxford Oxford OX1 3TA UK
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21
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Martínez‐Martínez AJ, Rees NH, Weller AS. Reversible Encapsulation of Xenon and CH 2 Cl 2 in a Solid-State Molecular Organometallic Framework (Guest@SMOM). Angew Chem Int Ed Engl 2019; 58:16873-16877. [PMID: 31539184 PMCID: PMC6899477 DOI: 10.1002/anie.201910539] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2019] [Indexed: 12/22/2022]
Abstract
Reversible encapsulation of CH2 Cl2 or Xe in a non-porous solid-state molecular organometallic framework of [Rh(Cy2 PCH2 PCy2 )(NBD)][BArF4 ] occurs in single-crystal to single-crystal transformations. These processes are probed by solid-state NMR spectroscopy, including 129 Xe SSNMR. Non-covalent interactions with the -CF3 groups, and hydrophobic channels formed, of [BArF4 ]- anions are shown to be important, and thus have similarity to the transport of substrates and products to and from the active site in metalloenzymes.
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Affiliation(s)
- Antonio J. Martínez‐Martínez
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of OxfordOxfordOX1 3TAUK
- Current Address: CIQSO-Centre for Research in Sustainable Chemistry and Department of ChemistryUniversity of HuelvaCampus El Carmen21007HuelvaSpain
| | - Nicholas H. Rees
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of OxfordOxfordOX1 3TAUK
| | - Andrew S. Weller
- Chemistry Research LaboratoriesDepartment of ChemistryUniversity of OxfordOxfordOX1 3TAUK
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22
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Schmitz D, Kalter M, Dunbar AC, Vöst M, Fischer A, Batke K, Eickerling G, Ruhland K, Ebad‐Allah J, Kuntscher C, Scherer W. Pressure‐Enhanced C–H Bond Activation in Chloromethane Platinum(II) Complexes. Eur J Inorg Chem 2019. [DOI: 10.1002/ejic.201901117] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Dominik Schmitz
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Marcel Kalter
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Andrew C. Dunbar
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Marcel Vöst
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Andreas Fischer
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Kilian Batke
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Georg Eickerling
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Klaus Ruhland
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Jihaan Ebad‐Allah
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
- Department of Physics Tanta University 31527 Tanta Egypt
| | - Christine Kuntscher
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
| | - Wolfgang Scherer
- Institut für Physik Universität Augsburg Universitätsstr. 1 86135 Augsburg Germany
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23
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Spearing-Ewyn EAK, Beattie NA, Colebatch AL, Martinez-Martinez AJ, Docker A, Boyd TM, Baillie G, Reed R, Macgregor SA, Weller AS. The role of neutral Rh(PONOP)H, free NMe 2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η 2-H 2)] + catalyst. Dalton Trans 2019; 48:14724-14736. [PMID: 31538996 DOI: 10.1039/c9dt03358k] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ, but this undergoes dehydrocoupling to reform 1 and give the aminoborane dimer [H2BNMe2]2. NMR studies on this system reveal an intermediate neutral hydride forms, Rh(PONOP)H, 4, that has been prepared independently. 1 is a competent catalyst (2 mol%, ∼30 min) for the dehydrocoupling of H3B·Me2H. Kinetic, mechanistic and computational studies point to the role of NMe2H in both forming the neutral hydride, via deprotonation of a σ-amine-borane complex and formation of aminoborane, and closing the catalytic cycle by reprotonation of the hydride by the thus-formed dimethyl ammonium [NMe2H2]+. Competitive processes involving the generation of boronium [H2B(NMe2H)2]+ are also discussed, but shown to be higher in energy. Off-cycle adducts between [NMe2H2]+ or [H2B(NMe2H)2]+ and amine-boranes are also discussed that act to modify the kinetics of dehydrocoupling.
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24
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McKay AI, Bukvic AJ, Tegner BE, Burnage AL, Martı Nez-Martı Nez AJ, Rees NH, Macgregor SA, Weller AS. Room Temperature Acceptorless Alkane Dehydrogenation from Molecular σ-Alkane Complexes. J Am Chem Soc 2019; 141:11700-11712. [PMID: 31246012 PMCID: PMC7007236 DOI: 10.1021/jacs.9b05577] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The non-oxidative catalytic dehydrogenation of light alkanes via C-H activation is a highly endothermic process that generally requires high temperatures and/or a sacrificial hydrogen acceptor to overcome unfavorable thermodynamics. This is complicated by alkanes being such poor ligands, meaning that binding at metal centers prior to C-H activation is disfavored. We demonstrate that by biasing the pre-equilibrium of alkane binding, by using solid-state molecular organometallic chemistry (SMOM-chem), well-defined isobutane and cyclohexane σ-complexes, [Rh(Cy2PCH2CH2PCy2)(η:η-(H3C)CH(CH3)2][BArF4] and [Rh(Cy2PCH2CH2PCy2)(η:η-C6H12)][BArF4] can be prepared by simple hydrogenation in a solid/gas single-crystal to single-crystal transformation of precursor alkene complexes. Solid-gas H/D exchange with D2 occurs at all C-H bonds in both alkane complexes, pointing to a variety of low energy fluxional processes that occur for the bound alkane ligands in the solid-state. These are probed by variable temperature solid-state nuclear magnetic resonance experiments and periodic density functional theory (DFT) calculations. These alkane σ-complexes undergo spontaneous acceptorless dehydrogenation at 298 K to reform the corresponding isobutene and cyclohexadiene complexes, by simple application of vacuum or Ar-flow to remove H2. These processes can be followed temporally, and modeled using classical chemical, or Johnson-Mehl-Avrami-Kologoromov, kinetics. When per-deuteration is coupled with dehydrogenation of cyclohexane to cyclohexadiene, this allows for two successive KIEs to be determined [kH/kD = 3.6(5) and 10.8(6)], showing that the rate-determining steps involve C-H activation. Periodic DFT calculations predict overall barriers of 20.6 and 24.4 kcal/mol for the two dehydrogenation steps, in good agreement with the values determined experimentally. The calculations also identify significant C-H bond elongation in both rate-limiting transition states and suggest that the large kH/kD for the second dehydrogenation results from a pre-equilibrium involving C-H oxidative cleavage and a subsequent rate-limiting β-H transfer step.
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Affiliation(s)
- Alasdair I McKay
- Chemistry Research Laboratories, University of Oxford , Oxford OX1 3TA , United Kingdom
| | - Alexander J Bukvic
- Chemistry Research Laboratories, University of Oxford , Oxford OX1 3TA , United Kingdom
| | - Bengt E Tegner
- Institute of Chemical Sciences, Heriot Watt University , Edinburgh EH14 4AS , United Kingdom
| | - Arron L Burnage
- Institute of Chemical Sciences, Heriot Watt University , Edinburgh EH14 4AS , United Kingdom
| | | | - Nicholas H Rees
- Chemistry Research Laboratories, University of Oxford , Oxford OX1 3TA , United Kingdom
| | - Stuart A Macgregor
- Institute of Chemical Sciences, Heriot Watt University , Edinburgh EH14 4AS , United Kingdom
| | - Andrew S Weller
- Chemistry Research Laboratories, University of Oxford , Oxford OX1 3TA , United Kingdom
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25
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Carlsen R, Jenkins JR, Huang TCJ, Pugh SL, Ess DH. Paddle Ball Dynamics during Conversion of a Rh–Methyl Hydride Complex to a Rh–Methane σ-Complex through Reductive Coupling. Organometallics 2019. [DOI: 10.1021/acs.organomet.8b00936] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ryan Carlsen
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
| | - Jordan R. Jenkins
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
| | - Tsung-Chiang Johnny Huang
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
| | - Samuel L. Pugh
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
| | - Daniel H. Ess
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
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26
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Martínez-Martínez AJ, Weller AS. Solvent-free anhydrous Li+, Na+ and K+ salts of [B(3,5-(CF3)2C6H3)4]−, [BArF4]−. Improved synthesis and solid-state structures. Dalton Trans 2019; 48:3551-3554. [DOI: 10.1039/c9dt00235a] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report an alternative, improved, multigram scale (∼20 g, 60–70% yield) preparation of solvent-free anhydrous Li[BArF4], Na[BArF4] and K[BArF4], and the corresponding single-crystal X-ray characterisation of [Li(H2O)][BArF4], Na[BArF4]˙ and K[BArF4].
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Affiliation(s)
| | - Andrew S. Weller
- Department of Chemistry
- Chemistry Research Laboratories
- Mansfield Road
- University of Oxford
- Oxford
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27
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Johnson A, Martínez-Martínez AJ, Macgregor SA, Weller AS. A d 10 Ag(i) amine-borane σ-complex and comparison with a d 8 Rh(i) analogue: structures on the η 1 to η 2:η 2 continuum. Dalton Trans 2019; 48:9776-9781. [PMID: 31012457 DOI: 10.1039/c9dt00971j] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
H3B·NMe3 σ-complexes of d8 [(L1)Rh][BArF4] and d10 [(L1)Ag][BArF4] (where L1 = 2,6-bis-[1-(2,6-diisopropylphenylimino)ethyl]pyridine) have been prepared and structurally characterised. Analysis of the molecular and electronic structures reveal important but subtle differences in the nature of the bonding in these σ-complexes, which differ only by the identity of the metal centre and the d-electron count. With Rh the amine-borane binds in an η2:η2 fashion, whereas at Ag the unsymmetrical {AgH3B·NMe3} unit suggests a structure lying between the η2:η2 and η1 extremes.
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Affiliation(s)
- Alice Johnson
- Chemistry Research Laboratories, Department of Chemistry, University of Oxford, Oxford, OX1 3TA, UK.
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