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Pu M, Nielsen CDT, Senol E, Sperger T, Schoenebeck F. Post-Transition-State Dynamic Effects in the Transmetalation of Pd(II)-F to Pd(II)-CF 3. JACS AU 2024; 4:263-275. [PMID: 38274253 PMCID: PMC10806791 DOI: 10.1021/jacsau.3c00724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Revised: 12/11/2023] [Accepted: 12/12/2023] [Indexed: 01/27/2024]
Abstract
The observation of post-transition-state dynamic effects in the context of metal-based transformation is rare. To date, there has been no reported case of a dynamic effect for the widely employed class of palladium-mediated coupling reactions. We performed an experimental and computational study of the trifluoromethylation of Pd(II)F, which is a key step in the Pd(0)/Pd(II)-catalyzed trifluoromethylation of aryl halides or acid fluorides. Our experiments show that the cis/trans speciation of the formed Pd(II)CF3 is highly solvent- and transmetalation reagent-dependent. We employed GFN2-xTB- and B3LYP-D3-based molecular dynamics trajectory calculations (with and without explicit solvation) along with high-level QM calculations and found that depending on the medium, different transmetalation mechanisms appear to be operative. A statistically representative number of Born-Oppenheimer molecular dynamics (MD) simulations suggest that in benzene, a difluorocarbene is generated in the transmetalation with R3SiCF3, which subsequently recombines with the Pd via two distinct pathways, leading to either the cis- or trans-Pd(II)CF3. Conversely, GFN2-xTB simulations in MeCN suggest that in polar/coordinating solvents an ion-pair mechanism is dominant. A CF3 anion is initially liberated and then rebinds with the Pd(II) cation to give a cis- or trans-Pd(II). In both scenarios, a single transmetalation transition state gives rise to both cis- and trans-species directly, owing to bifurcation after the transition state. The potential subsequent cis- to trans isomerization of the Pd(II)CF3 was also studied and found to be strongly inhibited by free phosphine, which in turn was experimentally identified to be liberated through displacement by a polar/coordinating solvent from the cis-Pd(II)CF3 complex. The simulations also revealed how the variation of the Pd-coordination sphere results in divergent product selectivities.
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Affiliation(s)
- Maoping Pu
- Institute of Organic Chemistry,
RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | | | - Erdem Senol
- Institute of Organic Chemistry,
RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Theresa Sperger
- Institute of Organic Chemistry,
RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
| | - Franziska Schoenebeck
- Institute of Organic Chemistry,
RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany
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2
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Minshull H, Lloyd-Jones GC. TMSCF 3-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism. J Org Chem 2023; 88:17450-17460. [PMID: 38041656 PMCID: PMC10729029 DOI: 10.1021/acs.joc.3c02219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 11/13/2023] [Accepted: 11/15/2023] [Indexed: 12/03/2023]
Abstract
As reported by Zhao, the TBAT ([Ph3SiF2]-[Bu4N]+)-initiated reaction of ethyl salicylate with TMSCF3 in THF generates α,α-difluoro-3-coumaranones via the corresponding O-silylated ethoxy ketals. The mechanism has been investigated by in situ 19F and 29Si NMR spectroscopy, CF2-trapping, competition, titration, and comparison of the kinetics with the 3-, 4-, 5-, and 6-fluoro ethyl salicylate analogues and their O-silylated derivatives. The process evolves in five distinct stages, each arising from a discrete array of anion speciations that modulate a sequence of silyl-transfer chain reactions. The deconvolution of coupled equilibria between salicylate, [CF3]-, and siliconate [Me3Si(CF3)2]- anions allowed the development of a kinetic model that accounts for the first three stages. The model provides valuable practical insights. For example, it explains how the initial concentrations of the TMSCF3 and salicylate and the location of electron-withdrawing salicylate ring substituents profoundly impact the overall viability of the process, how stoichiometric CF3H generation can be bypassed by using the O-silylated salicylate, and how the very slow liberation of the α,α-difluoro-3-coumaranone can be rapidly accelerated by evaporative or aqueous workup.
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Affiliation(s)
- Hannah
B. Minshull
- School of Chemistry, University of Edinburgh, Joseph Black Building, Edinburgh EH9 3FJ, U.K.
| | - Guy C. Lloyd-Jones
- School of Chemistry, University of Edinburgh, Joseph Black Building, Edinburgh EH9 3FJ, U.K.
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Ex-situ generation and synthetic utilization of bare trifluoromethyl anion in flow via rapid biphasic mixing. Nat Commun 2023; 14:1231. [PMID: 36869027 PMCID: PMC9984407 DOI: 10.1038/s41467-022-35611-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 12/13/2022] [Indexed: 03/05/2023] Open
Abstract
Fluoroform (CF3H) is the simplest reagent for nucleophilic trifluoromethylation intermediated by trifluoromethyl anion (CF3-). However, it has been well-known that CF3- should be generated in presence of a stabilizer or reaction partner (in-situ method) due to its short lifetime, which results in the fundamental limitation on its synthetic utilization. We herein report a bare CF3- can be ex-situ generated and directly used for the synthesis of diverse trifluoromethylated compounds in a devised flow dissolver for rapid biphasic mixing of gaseous CF3H and liquid reagents that was designed and structurally optimized by computational fluid dynamics (CFD). In flow, various substrates including multi-functional compounds were chemoselectively reacted with CF3-, extending to the multi-gram-scale synthesis of valuable compounds by 1-hour operation of the integrated flow system.
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García-Domínguez A, Leach AG, Lloyd-Jones GC. In Situ Studies of Arylboronic Acids/Esters and R 3SiCF 3 Reagents: Kinetics, Speciation, and Dysfunction at the Carbanion-Ate Interface. Acc Chem Res 2022; 55:1324-1336. [PMID: 35435655 PMCID: PMC9069690 DOI: 10.1021/acs.accounts.2c00113] [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] [Indexed: 01/06/2023]
Abstract
Reagent instability reduces the efficiency of chemical processes, and while much effort is devoted to reaction optimization, less attention is paid to the mechanistic causes of reagent decomposition. Indeed, the response is often to simply use an excess of the reagent. Two reaction classes with ubiquitous examples of this are the Suzuki-Miyaura cross-coupling of boronic acids/esters and the transfer of CF3 or CF2 from the Ruppert-Prakash reagent, TMSCF3. This Account describes some of the overarching features of our mechanistic investigations into their decomposition. In the first section we summarize how specific examples of (hetero)arylboronic acids can decompose via aqueous protodeboronation processes: Ar-B(OH)2 + H2O → ArH + B(OH)3. Key to the analysis was the development of a kinetic model in which pH controls boron speciation and heterocycle protonation states. This method revealed six different protodeboronation pathways, including self-catalysis when the pH is close to the pKa of the boronic acid, and protodeboronation via a transient aryl anionoid pathway for highly electron-deficient arenes. The degree of "protection" of boronic acids by diol-esterification is shown to be very dependent on the diol identity, with six-membered ring esters resulting in faster protodeboronation than the parent boronic acid. In the second section of the Account we describe 19F NMR spectroscopic analysis of the kinetics of the reaction of TMSCF3 with ketones, fluoroarenes, and alkenes. Processes initiated by substoichiometric "TBAT" ([Ph3SiF2][Bu4N]) involve anionic chain reactions in which low concentrations of [CF3]- are rapidly and reversibly liberated from a siliconate reservoir, [TMS(CF3)2][Bu4N]. Increased TMSCF3 concentrations reduce the [CF3]- concentration and thus inhibit the rates of CF3 transfer. Computation and kinetics reveal that the TMSCF3 intermolecularly abstracts fluoride from [CF3]- to generate the CF2, in what would otherwise be an endergonic α-fluoride elimination. Starting from [CF3]- and CF2, a cascade involving perfluoroalkene homologation results in the generation of a hindered perfluorocarbanion, [C11F23]-, and inhibition. The generation of CF2 from TMSCF3 is much more efficiently mediated by NaI, and in contrast to TBAT, the process undergoes autoacceleration. The process involves NaI-mediated α-fluoride elimination from [CF3][Na] to generate CF2 and a [NaI·NaF] chain carrier. Chain-branching, by [(CF2)3I][Na] generated in situ (CF2 + TFE + NaI), causes autoacceleration. Alkenes that efficiently capture CF2 attenuate the chain-branching, suppress autoacceleration, and lead to less rapid difluorocyclopropanation. The Account also highlights how a collaborative approach to experiment and computation enables mechanistic insight for control of processes.
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Affiliation(s)
- Andrés García-Domínguez
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Andrew G. Leach
- School of Health Sciences, Stopford Building, The University of Manchester, Oxford Road, Manchester M13 9PT, U.K
| | - Guy C. Lloyd-Jones
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
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Fujihira Y, Liang Y, Ono M, Hirano K, Kagawa T, Shibata N. Synthesis of trifluoromethyl ketones by nucleophilic trifluoromethylation of esters under a fluoroform/KHMDS/triglyme system. Beilstein J Org Chem 2021; 17:431-438. [PMID: 33633811 PMCID: PMC7884878 DOI: 10.3762/bjoc.17.39] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 02/02/2021] [Indexed: 12/29/2022] Open
Abstract
A straightforward method that enables the formation of biologically attractive trifluoromethyl ketones from readily available methyl esters using the potent greenhouse gas fluoroform (HCF3, HFC-23) was developed. The combination of fluoroform and KHMDS in triglyme at −40 °C was effective for this transformation, with good yields as high as 92%. Substrate scope of the trifluoromethylation procedure was explored for aromatic, aliphatic, and conjugated methyl esters. This study presents a straightforward trifluoromethylation process of various methyl esters that convert well to the corresponding trifluoromethyl ketones. The tolerance of various pharmacophores under the reaction conditions was also explored.
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Affiliation(s)
- Yamato Fujihira
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-5888, Japan
| | - Yumeng Liang
- Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-5888, Japan
| | - Makoto Ono
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-5888, Japan
| | - Kazuki Hirano
- Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-5888, Japan
| | - Takumi Kagawa
- Tosoh Finechem Corporation, 4988, Kaiseicho, Shunan, 746-0006, Japan
| | - Norio Shibata
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-5888, Japan.,Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-5888, Japan.,Institute of Advanced Fluorine-Containing Materials, Zhejiang Normal University, 688 Yingbin Avenue, 321004 Jinhua, China
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6
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Mechanism of Anion-Catalyzed C–H Silylation Using TMSCF3: Kinetically-Controlled CF3-Anionoid Partitioning As a Key Parameter. ACS Catal 2021. [DOI: 10.1021/acscatal.1c00033] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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7
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García-Domínguez A, West TH, Primozic JJ, Grant KM, Johnston CP, Cumming GG, Leach AG, Lloyd-Jones GC. Difluorocarbene Generation from TMSCF3: Kinetics and Mechanism of NaI-Mediated and Si-Induced Anionic Chain Reactions. J Am Chem Soc 2020; 142:14649-14663. [DOI: 10.1021/jacs.0c06751] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Andrés García-Domínguez
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Thomas H. West
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Johann J. Primozic
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Katie M. Grant
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Craig P. Johnston
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Grant G. Cumming
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
| | - Andrew G. Leach
- School of Health Sciences, Stopford Building, The University of Manchester, Oxford Road, Manchester M13 9PT, U.K
| | - Guy C. Lloyd-Jones
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, U.K
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Viesser RV, Tormena CF. Counterintuitive deshielding on the 13 C NMR chemical shift for the trifluoromethyl anion. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2020; 58:540-547. [PMID: 31705544 DOI: 10.1002/mrc.4958] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 10/18/2019] [Indexed: 06/10/2023]
Abstract
The trifluoromethyl anion (CF3 - ) displays 13 C NMR chemical shift (175.0 ppm) surprisingly larger than neutral (CHF3 , 122.2 ppm) and cation (CF3 + , 150.7 ppm) compounds. This unexpected deshielding effect for a carbanion is investigated by density functional theory calculations and decomposition analyses of the 13 C shielding tensor into localized molecular orbital contributions. The present work determines the shielding mechanisms involved in the observed behaviour of the fluorinated anion species, shedding light on the experimental NMR data and demystify the classical correlation between electron density and NMR chemical shift. The presence of fluorine atoms induces the carbon lone pair to create a paramagnetic shielding on the carbon nucleus.
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Affiliation(s)
- Renan V Viesser
- Institute of Chemistry, University of Campinas-UNICAMP, P.O. Box 6154, Campinas, SP, 13083-970, Brazil
| | - Cláudio F Tormena
- Institute of Chemistry, University of Campinas-UNICAMP, P.O. Box 6154, Campinas, SP, 13083-970, Brazil
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9
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Johnston C, West TH, Dooley RE, Reid M, Jones AB, King EJ, Leach AG, Lloyd-Jones GC. Anion-Initiated Trifluoromethylation by TMSCF 3: Deconvolution of the Siliconate-Carbanion Dichotomy by Stopped-Flow NMR/IR. J Am Chem Soc 2018; 140:11112-11124. [PMID: 30080973 PMCID: PMC6133236 DOI: 10.1021/jacs.8b06777] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Indexed: 12/25/2022]
Abstract
The mechanism of CF3 transfer from R3SiCF3 (R = Me, Et, iPr) to ketones and aldehydes, initiated by M+X- (<0.004 to 10 mol %), has been investigated by analysis of kinetics (variable-ratio stopped-flow NMR and IR), 13C/2H KIEs, LFER, addition of ligands (18-c-6, crypt-222), and density functional theory calculations. The kinetics, reaction orders, and selectivity vary substantially with reagent (R3SiCF3) and initiator (M+X-). Traces of exogenous inhibitors present in the R3SiCF3 reagents, which vary substantially in proportion and identity between batches and suppliers, also affect the kinetics. Some reactions are complete in milliseconds, others take hours, and others stall before completion. Despite these differences, a general mechanism has been elucidated in which the product alkoxide and CF3- anion act as chain carriers in an anionic chain reaction. Silyl enol ether generation competes with 1,2-addition and involves protonation of CF3- by the α-C-H of the ketone and the OH of the enol. The overarching mechanism for trifluoromethylation by R3SiCF3, in which pentacoordinate siliconate intermediates are unable to directly transfer CF3- as a nucleophile or base, rationalizes why the turnover rate (per M+X- initiator) depends on the initial concentration (but not identity) of X-, the identity (but not concentration) of M+, the identity of the R3SiCF3 reagent, and the carbonyl/R3SiCF3 ratio. It also rationalizes which R3SiCF3 reagent effects the most rapid trifluoromethylation, for a specific M+X- initiator.
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Affiliation(s)
- Craig
P. Johnston
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K.
| | - Thomas H. West
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K.
| | - Ruth E. Dooley
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K.
| | - Marc Reid
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K.
| | - Ariana B. Jones
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K.
| | - Edward J. King
- TgK
Scientific Limited, 7
Long’s Yard, St Margaret’s Street, Bradford-on-Avon, BA15 1DH, U.K.
| | - Andrew G. Leach
- School
of Pharmacy and Biomolecular Sciences, Liverpool
John Moores University, Byrom Street, Liverpool, L3 3AF, U.K.
| | - Guy C. Lloyd-Jones
- EaStChem, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, U.K.
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Saito T, Wang J, Tokunaga E, Tsuzuki S, Shibata N. Direct nucleophilic trifluoromethylation of carbonyl compounds by potent greenhouse gas, fluoroform: Improving the reactivity of anionoid trifluoromethyl species in glymes. Sci Rep 2018; 8:11501. [PMID: 30065282 PMCID: PMC6068191 DOI: 10.1038/s41598-018-29748-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 07/18/2018] [Indexed: 01/19/2023] Open
Abstract
A simple protocol to overcome the problematic trifluoromethylation of carbonyl compounds by the potent greenhouse gas "HFC-23, fluoroform" with a potassium base is described. Simply the use of glymes as a solvent or an additive dramatically improves the yields of this transformation. Experimental results and DFT calculations suggest that the beneficial effect deals with glyme coordination to the K+ to produce [K(polyether)n]+ whose diminished Lewis acidity renders the reactive anionoid CF3 counterion species more 'naked', thereby slowing down its undesirable decomposition to CF2 and F- and simultaneously increasing its reactivity towards the organic substrate.
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Affiliation(s)
- Takuya Saito
- Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya, 466-5888, Japan
| | - Jiandong Wang
- Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya, 466-5888, Japan
| | - Etsuko Tokunaga
- Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya, 466-5888, Japan
| | - Seiji Tsuzuki
- Research Center for Computational Design of Advanced Functional Materials, AIST, Tsukuba, Ibaraki, 305-8568, Japan
| | - Norio Shibata
- Department of Nanopharmaceutical Sciences, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya, 466-5888, Japan.
- Institute of Advanced Fluorine-Containing Materials, Zhejiang Normal University, 688 Yingbin Avenue, 321004, Jinhua, China.
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