201
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Lee E, Kamlet AS, Powers DC, Neumann CN, Boursalian GB, Furuya T, Choi DC, Hooker JM, Ritter T. A fluoride-derived electrophilic late-stage fluorination reagent for PET imaging. Science 2011; 334:639-42. [PMID: 22053044 PMCID: PMC3229297 DOI: 10.1126/science.1212625] [Citation(s) in RCA: 317] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The unnatural isotope fluorine-18 ((18)F) is used as a positron emitter in molecular imaging. Currently, many potentially useful (18)F-labeled probe molecules are inaccessible for imaging because no fluorination chemistry is available to make them. The 110-minute half-life of (18)F requires rapid syntheses for which [(18)F]fluoride is the preferred source of fluorine because of its practical access and suitable isotope enrichment. However, conventional [(18)F]fluoride chemistry has been limited to nucleophilic fluorination reactions. We report the development of a palladium-based electrophilic fluorination reagent derived from fluoride and its application to the synthesis of aromatic (18)F-labeled molecules via late-stage fluorination. Late-stage fluorination enables the synthesis of conventionally unavailable positron emission tomography (PET) tracers for anticipated applications in pharmaceutical development as well as preclinical and clinical PET imaging.
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Affiliation(s)
- Eunsung Lee
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
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202
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Racowski JM, Ball ND, Sanford MS. C-H bond activation at palladium(IV) centers. J Am Chem Soc 2011; 133:18022-5. [PMID: 22017502 DOI: 10.1021/ja2051099] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
This communication describes the first observation and study of C-H activation at a Pd(IV) center. This transformation was achieved by designing model complexes in which the rate of reductive elimination is slowed relative to that of the desired C-H activation process. Remarkably, the C-H activation reaction can proceed under mild conditions and with complementary site selectivity to analogous transformations at Pd(II). These results provide a platform for incorporating this new reaction as a step in catalytic processes.
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Affiliation(s)
- Joy M Racowski
- University of Michigan, Department of Chemistry, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
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203
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Maimone TJ, Milner PJ, Kinzel T, Zhang Y, Takase MK, Buchwald SL. Evidence for in situ catalyst modification during the Pd-catalyzed conversion of aryl triflates to aryl fluorides. J Am Chem Soc 2011; 133:18106-9. [PMID: 21999801 DOI: 10.1021/ja208461k] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
A mechanistic investigation of the Pd-catalyzed conversion of aryl triflates to fluorides is presented. Studies reveal that C-F reductive elimination from a LPd(II)(aryl)F complex (L = t-BuBrettPhos or RockPhos) does not occur when the aryl group is electron rich. Evidence is presented that a modified phosphine, generated in situ, serves as the actual supporting ligand during catalysis with such substrates. A preliminary study of the reactivity of a LPd(II)(aryl)F complex based on this modified ligand is reported.
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Affiliation(s)
- Thomas J Maimone
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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204
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Mankad NP, Toste FD. C(sp(3))-F reductive elimination from alkylgold(iii) fluoride complexes. Chem Sci 2011; 3:72-76. [PMID: 23087810 DOI: 10.1039/c1sc00515d] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Rare examples of C(sp(3))-F reductive elimination were observed from several cis-F(2)Au(R)(IPr) intermediates generated by oxidation of (IPr)AuR complexes with XeF(2). For R groups bearing β-hydrogens, β-hydride elimination was competitive with C(sp(3))-F reductive elimination. For strained cyclic R groups and most acyclic R groups lacking β-hydrogens, carbocation-like rearrangements occurred prior to C(sp(3))-F reductive elimination. Kinetics of the decay of one cis-F(2)Au(R)(IPr) species, stereochemical analysis of reductive elimination with a chiral R group, and DFT analysis collectively suggest C(sp(3))-F reductive elimination proceeding through transient cationic [(IPr)Au(F)(R)](+) intermediates with significant ionization of the Au-alkyl bonds.
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Affiliation(s)
- Neal P Mankad
- Department of Chemistry, University of California-Berkeley, Berkeley, CA, 94720, USA
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205
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Noël T, Maimone TJ, Buchwald SL. Accelerating palladium-catalyzed C-F bond formation: use of a microflow packed-bed reactor. Angew Chem Int Ed Engl 2011; 50:8900-3. [PMID: 21837710 PMCID: PMC3339491 DOI: 10.1002/anie.201104652] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Indexed: 11/11/2022]
Abstract
A flow process for Pd-catalyzed carbon fluorine bond formation is described. A microreactor using a packed-bed design allows for easy handling of large quantities of insoluble CsF with precise control over reaction times, efficient mixing, and the ability to safely handle elevated temperatures and pressures. A variety of aryl triflates, including heteroaryl ones, were converted to their corresponding aryl fluoride in short reaction times that would be difficult to achieve in a typical batch process.
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Affiliation(s)
| | | | - Stephen L. Buchwald
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (USA)
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206
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Huang C, Liang T, Harada S, Lee E, Ritter T. Silver-mediated trifluoromethoxylation of aryl stannanes and arylboronic acids. J Am Chem Soc 2011; 133:13308-10. [PMID: 21827148 PMCID: PMC3218431 DOI: 10.1021/ja204861a] [Citation(s) in RCA: 164] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A silver-mediated cross-coupling of trifluoromethoxide with aryl stannanes and arylboronic acids to give aryl trifluoromethyl ethers is reported. This is the first report of a transition-metal-mediated C(aryl)-OCF(3) bond formation.
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Affiliation(s)
- Chenghong Huang
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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207
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Vigalok A. Electrophilic Fluorination of Group 10 Organometallic Complexes: Chemistry beyond Oxidative Addition. Organometallics 2011. [DOI: 10.1021/om200507g] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Arkadi Vigalok
- School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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208
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Noël T, Maimone TJ, Buchwald SL. Accelerating Palladium-Catalyzed CF Bond Formation: Use of a Microflow Packed-Bed Reactor. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201104652] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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209
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Abstract
An operationally simple ipso fluorination of phenols with a new deoxyfluorination reagent is presented.
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Affiliation(s)
- Pingping Tang
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Weike Wang
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Tobias Ritter
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
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210
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Chan KSL, Wasa M, Wang X, Yu JQ. Palladium(II)-catalyzed selective monofluorination of benzoic acids using a practical auxiliary: a weak-coordination approach. Angew Chem Int Ed Engl 2011; 50:9081-4. [PMID: 21748831 DOI: 10.1002/anie.201102985] [Citation(s) in RCA: 185] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2011] [Indexed: 11/11/2022]
Affiliation(s)
- Kelvin S L Chan
- Department of Chemistry, The Scripps Research Institute (TSRI), 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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211
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Chan KSL, Wasa M, Wang X, Yu JQ. Palladium(II)-Catalyzed Selective Monofluorination of Benzoic Acids Using a Practical Auxiliary: A Weak-Coordination Approach. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102985] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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212
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Choi J, Wang DY, Kundu S, Choliy Y, Emge TJ, Krogh-Jespersen K, Goldman AS. Net oxidative addition of C(sp3)-F bonds to iridium via initial C-H bond activation. Science 2011; 332:1545-8. [PMID: 21700870 DOI: 10.1126/science.1200514] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Carbon-fluorine bonds are the strongest known single bonds to carbon and as a consequence can prove very hard to cleave. Alhough vinyl and aryl C-F bonds can undergo oxidative addition to transition metal complexes, this reaction has appeared inoperable with aliphatic substrates. We report the addition of C(sp(3))-F bonds (including alkyl-F) to an iridium center via the initial, reversible cleavage of a C-H bond. These results suggest a distinct strategy for the development of catalysts and promoters to make and break C-F bonds, which are of strong interest in the context of both pharmaceutical and environmental chemistry.
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Affiliation(s)
- Jongwook Choi
- Department of Chemistry and Chemical Biology, Rutgers, State University of New Jersey, New Brunswick, NJ 08903, USA
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213
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Zhao SB, Becker JJ, Gagné MR. Steric Crowding Makes Challenging C(sp3)-F Reductive Eliminations Feasible. Organometallics 2011; 30:3926-3929. [PMID: 21869853 DOI: 10.1021/om200515f] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A high-yielding fluorination of (triphos)Pt-R(+) has been achieved using an array of F(+) sources, with XeF(2) yielding R-F in minutes. The C-F coupling proved to be a stereoretentive process that proceeds via a concerted reductive elimination from a putative dicationic Pt(IV) center. The larger the steric congestion of the (triphos)Pt-C(sp3) (+) complexes, the more efficient the fluorination, seemingly a result of sterically accelerated C-F reductive elimination along with simultaneous deceleration of its competing processes (β-H elimination).
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Affiliation(s)
- Shu-Bin Zhao
- Caudill Laboratories, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
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214
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Abstract
A regiospecific silver-mediated fluorination of aryl silanes is reported. The reaction is operationally simple, and employs Ag(2)O as readily available, inexpensive silver source, which can be recovered.
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Affiliation(s)
- Pingping Tang
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
| | - Tobias Ritter
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
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215
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Vicente J, Arcas A, Juliá-Hernández F, Bautista D. Synthesis of a Palladium(IV) Complex by Oxidative Addition of an Aryl Halide to Palladium(II) and Its Use as Precatalyst in a CC Coupling Reaction. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102214] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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216
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Vicente J, Arcas A, Juliá-Hernández F, Bautista D. Synthesis of a Palladium(IV) Complex by Oxidative Addition of an Aryl Halide to Palladium(II) and Its Use as Precatalyst in a CC Coupling Reaction. Angew Chem Int Ed Engl 2011; 50:6896-9. [DOI: 10.1002/anie.201102214] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Revised: 05/12/2011] [Indexed: 11/11/2022]
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217
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Furuya T, Kamlet AS, Ritter T. Catalysis for fluorination and trifluoromethylation. Nature 2011; 473:470-7. [PMID: 21614074 PMCID: PMC3119199 DOI: 10.1038/nature10108] [Citation(s) in RCA: 1748] [Impact Index Per Article: 134.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 04/07/2011] [Indexed: 01/23/2023]
Abstract
Recent advances in catalysis have made the incorporation of fluorine into complex organic molecules easier than ever before, but selective, general and practical fluorination reactions remain sought after. Fluorination of molecules often imparts desirable properties, such as metabolic and thermal stability, and fluorinated molecules are therefore frequently used as pharmaceuticals or materials. But the formation of carbon-fluorine bonds in complex molecules is a significant challenge. Here we discuss reactions to make organofluorides that have emerged within the past few years and which exemplify how to overcome some of the intricate challenges associated with fluorination.
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Affiliation(s)
- Takeru Furuya
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA
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218
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Vicente J, Arcas A, Juliá-Hernández F, Bautista D. Synthesis, Isolation, and Characterization of an Organometallic Triiodopalladium(IV) Complex. Quantitative and Regioselective Synthesis of Two C–I Reductive Elimination Products. Inorg Chem 2011; 50:5339-41. [DOI: 10.1021/ic2006869] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- José Vicente
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, and ‡SAI, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
| | - Aurelia Arcas
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, and ‡SAI, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
| | - Francisco Juliá-Hernández
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, and ‡SAI, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
| | - Delia Bautista
- Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, and ‡SAI, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
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219
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Clot E, Eisenstein O, Jasim N, Macgregor SA, McGrady JE, Perutz RN. C-F and C-H bond activation of fluorobenzenes and fluoropyridines at transition metal centers: how fluorine tips the scales. Acc Chem Res 2011; 44:333-48. [PMID: 21410234 DOI: 10.1021/ar100136x] [Citation(s) in RCA: 391] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
In this Account, we describe the transition metal-mediated cleavage of C-F and C-H bonds in fluoroaromatic and fluoroheteroaromatic molecules. The simplest reactions of perfluoroarenes result in C-F oxida tive addition, but C-H activation competes with C-F activation for partially fluorinated molecules. We first consider the reactivity of the fluoroaromatics toward nickel and platinum complexes, but extend to rhenium and rhodium where they give special insight. Sections on spectroscopy and molecular structure are followed by discussions of energetics and mechanism that incorporate experimental and computational results. We highlight special characteristics of the metal-fluorine bond and the influence of the fluorine substituents on energetics and mechanism. Fluoroaromatics reacting at an ML(2) center initially yield η(2)-arene complexes, followed usually by oxidative addition to generate MF(Ar(F))(L)(2) or MH(Ar(F))(L)(2) (M is Ni, Pd, or Pt; L is trialkylphosphine). The outcome of competition between C-F and C-H bond activation is strongly metal dependent and regioselective. When C-H bonds of fluoroaromatics are activated, there is a preference for the remaining C-F bonds to lie ortho to the metal. An unusual feature of metal-fluorine bonds is their response to replacement of nickel by platinum. The Pt-F bonds are weaker than their nickel counterparts; the opposite is true for M-H bonds. Metal-fluorine bonds are sufficiently polar to form M-F···H-X hydrogen bonds and M-F···I-C(6)F(5) halogen bonds. In the competition between C-F and C-H activation, the thermodynamic product is always the metal fluoride, but marked differences emerge between metals in the energetics of C-H activation. In metal-fluoroaryl bonds, ortho-fluorine substituents generally control regioselectivity and make C-H activation more energetically favorable. The role of fluorine substituents in directing C-H activation is traced to their effect on bond energies. Correlations between M-C and H-C bond energies demonstrate that M-C bond energies increase far more on ortho-fluorine substitution than do H-C bonds. Conventional oxidative addition reactions involve a three-center triangular transition state between the carbon, metal, and X, where X is hydrogen or fluorine, but M(d)-F(2p) repulsion raises the activation energies when X is fluorine. Platinum complexes exhibit an alternative set of reactions involving rearrangement of the phosphine and the fluoroaromatics to a metal(alkyl)(fluorophosphine), M(R)(Ar(F))(PR(3))(PR(2)F). In these phosphine-assisted C-F activation reactions, the phosphine is no spectator but rather is intimately involved as a fluorine acceptor. Addition of the C-F bond across the M-PR(3) bond leads to a metallophosphorane four-center transition state; subsequent transfer of the R group to the metal generates the fluorophosphine product. We find evidence that a phosphine-assisted pathway may even be significant in some apparently simple oxidative addition reactions. While transition metal catalysis has revolutionized hydrocarbon chemistry, its impact on fluorocarbon chemistry has been more limited. Recent developments have changed the outlook as catalytic reactions involving C-F or C-H bond activation of fluorocarbons have emerged. The principles established here have several implications for catalysis, including the regioselectivity of C-H activation and the unfavorable energetics of C-F reductive elimination. Palladium-catalyzed C-H arylation is analyzed to illustrate how ortho-fluorine substituents influence thermodynamics, kinetics, and regioselectivity.
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Affiliation(s)
- Eric Clot
- Institut Charles Gerhardt, Université Montpellier 2, CNRS UMR 5253, cc 1501 Place Eugène Bataillon, 34000 Montpellier, France
| | - Odile Eisenstein
- Institut Charles Gerhardt, Université Montpellier 2, CNRS UMR 5253, cc 1501 Place Eugène Bataillon, 34000 Montpellier, France
| | - Naseralla Jasim
- Department of Chemistry, University of York, York YO10 5DD, United Kingdom
| | - Stuart A. Macgregor
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - John E. McGrady
- Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom
| | - Robin N. Perutz
- Department of Chemistry, University of York, York YO10 5DD, United Kingdom
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220
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Maestri G, Motti E, Della Ca' N, Malacria M, Derat E, Catellani M. Of the ortho effect in palladium/norbornene-catalyzed reactions: a theoretical investigation. J Am Chem Soc 2011; 133:8574-85. [PMID: 21563760 DOI: 10.1021/ja110988p] [Citation(s) in RCA: 159] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mechanistic questions concerning palladium and norbornene catalyzed aryl-aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the "ortho effect" (caused by an ortho substituent in the starting aryl halide), which leads to aryl-aryl coupling with a second molecule of aryl halide rather than to aryl-norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading to Pd(IV). The unselective sp(2)-sp(2) and sp(2)-sp(3) coupling, experimentally observed in this case, can be explained in the framework of the transmetalation pathway since the energetic difference between aryl attack onto the aryl or norbornyl carbon of the palladacycle intermediate is quite small. On the other hand, according to the experimentally observed "ortho effect", selective aryl-aryl coupling only occurs in the reactions of ortho-substituted metallacycles. The present work offers the first possible rationalization of this finding. These in situ formed palladacycles containing an ortho substituent could more easily undergo oxidative addition of an aryl halide rather than reductive elimination from the transmetalation intermediate as a result of a steric clash in the transition state of the latter. The now energetically accessible Pd(IV) intermediate, featuring a Y-distorted trigonal bipyramidal structure, can account for the reported selective aryl-aryl coupling through a reductive elimination which is easier than aryl-norbornyl coupling. Thus, the steric effect represents the main factor that dictates the energetic convenience of the system to follow the Pd(IV) or the transmetalation pathway. Ortho substituents cause a higher energy transition state for reductive elimination from the transmetalation intermediate than for oxidative addition to the metallacycle palladium(II) and the pathway based on the latter predominates.
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Affiliation(s)
- Giovanni Maestri
- Dipartimento di Chimica Organica e Industriale, Università degli Studi di Parma, Parco Area delle Scienze, 17/A, 43124 Parma, Italy
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221
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Ball ND, Gary JB, Ye Y, Sanford MS. Mechanistic and computational studies of oxidatively-induced aryl-CF3 bond-formation at Pd: rational design of room temperature aryl trifluoromethylation. J Am Chem Soc 2011; 133:7577-84. [PMID: 21513271 DOI: 10.1021/ja201726q] [Citation(s) in RCA: 185] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This article describes the rational design of first generation systems for oxidatively induced Aryl-CF(3) bond-forming reductive elimination from Pd(II). Treatment of (dtbpy)Pd(II)(Aryl)(CF(3)) (dtbpy = di-tert-butylbipyridine) with NFTPT (N-fluoro-1,3,5-trimethylpyridinium triflate) afforded the isolable Pd(IV) intermediate (dtbpy)Pd(IV)(Aryl)(CF(3))(F)(OTf). Thermolysis of this complex at 80 °C resulted in Aryl-CF(3) bond-formation. Detailed experimental and computational mechanistic studies have been conducted to gain insights into the key reductive elimination step. Reductive elimination from this Pd(IV) species proceeds via pre-equilibrium dissociation of TfO(-) followed by Aryl-CF(3) coupling. DFT calculations reveal that the transition state for Aryl-CF(3) bond formation involves the CF(3) acting as an electrophile with the Aryl ligand serving as a nucleophilic coupling partner. These mechanistic considerations along with DFT calculations have facilitated the design of a second generation system utilizing the tmeda (N,N,N',N'-tetramethylethylenediamine) ligand in place of dtbpy. The tmeda complexes undergo oxidative trifluoromethylation at room temperature.
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Affiliation(s)
- Nicholas D Ball
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, USA
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222
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Sun AD, Love JA. Nickel-Catalyzed Selective Defluorination to Generate Partially Fluorinated Biaryls. Org Lett 2011; 13:2750-3. [DOI: 10.1021/ol200860t] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alex D. Sun
- Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Jennifer A. Love
- Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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223
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John A, Nicholas KM. Copper-Catalyzed Amidation of 2-Phenylpyridine with Oxygen as the Terminal Oxidant. J Org Chem 2011; 76:4158-62. [DOI: 10.1021/jo200409h] [Citation(s) in RCA: 178] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Alex John
- Department of Chemistry & Biochemistry, Stephenson Life Sciences Research Center, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, United States
| | - Kenneth M. Nicholas
- Department of Chemistry & Biochemistry, Stephenson Life Sciences Research Center, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, United States
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224
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Engle KM, Mei TS, Wang X, Yu JQ. Bystanding F+ oxidants enable selective reductive elimination from high-valent metal centers in catalysis. Angew Chem Int Ed Engl 2011; 50:1478-91. [PMID: 21264991 PMCID: PMC3094160 DOI: 10.1002/anie.201005142] [Citation(s) in RCA: 341] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Indexed: 11/06/2022]
Abstract
Reductive elimination from partially or completely oxidized metal centers is a vital step in a myriad of carbon-carbon and carbon-heteroatom bond-forming reactions. One strategy for promoting otherwise challenging reductive elimination reactions is to oxidize the metal center using a two-electron oxidant (that is, from M((n)) to M((n+2))). However, many of the commonly used oxidants for this type of transformation contain oxygen, nitrogen, or halogen moieties that are subsequently capable of participating in reductive elimination, thus leading to a mixture of products. In this Minireview, we examine the use of bystanding F(+) oxidants for addressing this widespread problem in organometallic chemistry and describe recent applications in Pd(II) /Pd(IV) and Au(I) /Au(III) catalysis. We then briefly discuss a rare example in which one-electron oxidants have been shown to promote selective reductive elimination in palladium(II)-catalyzed C-H functionalization, which we view as a promising future direction in the field.
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Affiliation(s)
- Keary M. Engle
- Department of Chemistry, The Scripps Research Institute (TSRI), 10550 N. Torrey Pines Road, La Jolla, CA 92037 (USA)
| | - Tian-Sheng Mei
- Department of Chemistry, The Scripps Research Institute (TSRI), 10550 N. Torrey Pines Road, La Jolla, CA 92037 (USA)
| | - Xisheng Wang
- Department of Chemistry, The Scripps Research Institute (TSRI), 10550 N. Torrey Pines Road, La Jolla, CA 92037 (USA)
| | - Jin-Quan Yu
- Department of Chemistry, The Scripps Research Institute (TSRI), 10550 N. Torrey Pines Road, La Jolla, CA 92037 (USA)
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225
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[Ru(NHC)(P–P)(CO)HF] (NHC = N-heterocyclic carbene; P–P = xantphos, dppf) complexes: Efforts to prepare new hydrodefluorination catalysts. J Organomet Chem 2011. [DOI: 10.1016/j.jorganchem.2010.09.077] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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226
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Engle KM, Mei TS, Wang X, Yu JQ. Passive F+-Oxidationsmittel ermöglichen die selektive reduktive Eliminierung hochvalenter Metallzentren in der Katalyse. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201005142] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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227
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Ye Y, Ball ND, Kampf JW, Sanford MS. Oxidation of a cyclometalated Pd(II) dimer with "CF3+": formation and reactivity of a catalytically competent monomeric Pd(IV) aquo complex. J Am Chem Soc 2011; 132:14682-7. [PMID: 20866077 DOI: 10.1021/ja107780w] [Citation(s) in RCA: 217] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The reaction of [(bzq)Pd(OAc)](2) (bzq = benzo[h]quinoline) with "CF(3)(+)" reagents to afford the monomeric Pd(IV) aquo complex (bzq)Pd(CF(3))(OAc)(2)(OH(2)) is demonstrated. Heating this Pd(IV) adduct at 60 °C for 12 h leads to highly chemoselective aryl-CF(3) bond-forming reductive elimination. The rate and yield of this transformation are both significantly enhanced by the addition of Brønsted and Lewis acidic additives. The mechanism of C-CF(3) bond formation from (bzq)Pd(CF(3))(OAc)(2)(OH(2)) has been studied, and the major pathway is proposed to involve pre-equilibrium acetate dissociation followed by C-CF(3) coupling. Finally, this monomeric Pd(IV) complex is shown to be a kinetically competent intermediate for C-H trifluoromethylation with "CF(3)(+)" reagents. Collectively, these studies provide valuable insights about the speciation, nuclearity, and reactivity of Pd intermediates in catalytic C-H trifluoromethylation reactions.
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Affiliation(s)
- Yingda Ye
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, USA
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228
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Powers DC, Xiao DY, Geibel MAL, Ritter T. On the mechanism of palladium-catalyzed aromatic C-H oxidation. J Am Chem Soc 2011; 132:14530-6. [PMID: 20873835 DOI: 10.1021/ja1054274] [Citation(s) in RCA: 164] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The mechanism of Pd-catalyzed aromatic C-H oxidation chemistry continues to be vigorously discussed. Historically, Pd(II)/Pd(IV) catalysis cycles have been proposed. Herein, we present a detailed study of Pd(OAc)(2)-catalyzed aromatic C-H chlorination and propose dinuclear Pd(III) complexes as intermediates. We have identified a succinate-bridged dinuclear Pd(II) complex, which self-assembles during catalysis, as the catalyst resting state. In situ monitoring of catalysis has revealed that chlorination proceeds with turnover-limiting oxidation of a dinuclear resting state, and that acetate ions, liberated during the formation of the catalyst resting state, catalyze the bimetallic oxidation. Informed by reaction kinetics analysis, relevant dinuclear Pd(III) complexes have been prepared and observed to undergo selective C-Cl reductive elimination. Based on the combination of kinetic data obtained during catalysis and explicit structural information of relevant intermediates, we propose a Pd(II)(2)/Pd(III)(2) catalysis cycle for Pd(OAc)(2)-catalyzed aromatic C-H chlorination.
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Affiliation(s)
- David C Powers
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA
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229
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Powers DC, Benitez D, Tkatchouk E, Goddard WA, Ritter T. Bimetallic reductive elimination from dinuclear Pd(III) complexes. J Am Chem Soc 2011; 132:14092-103. [PMID: 20858006 DOI: 10.1021/ja1036644] [Citation(s) in RCA: 210] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In 2009, we reported C-halogen reductive elimination reactions from dinuclear Pd(III) complexes and implicated dinuclear intermediates in Pd(OAc)(2)-catalyzed C-H oxidation chemistry. Herein, we report results of a thorough experimental and theoretical investigation of the mechanism of reductive elimination from such dinuclear Pd(III) complexes, which establish the role of each metal during reductive elimination. Our results implicate reductive elimination from a complex in which the dinuclear core is intact and suggest that redox synergy between the two metals is responsible for the facile reductive elimination reactions observed.
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Affiliation(s)
- David C Powers
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA
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230
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McCall AS, Wang H, Desper JM, Kraft S. Bis-N-heterocyclic carbene palladium(IV) tetrachloride complexes: synthesis, reactivity, and mechanisms of direct chlorinations and oxidations of organic substrates. J Am Chem Soc 2011; 133:1832-48. [PMID: 21247150 DOI: 10.1021/ja107342b] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This Article describes the preparation and isolation of novel octahedral CH(2)-bridged bis-(N-heterocyclic carbene)palladium(IV) tetrachlorides of the general formula LPd(IV)Cl(4) [L = (NHC)CH(2)(NHC)] from LPd(II)Cl(2) and Cl(2). In intermolecular, nonchelation-controlled transformations LPd(IV)Cl(4) reacted with alkenes and alkynes to 1,2-dichlorination adducts. Aromatic, benzylic, and aliphatic C-H bonds were converted into C-Cl bonds. Detailed mechanistic investigations in the dichlorinations of alkenes were conducted on the 18VE Pd(IV) complex. Positive solvent effects as well as kinetic measurements probing the impact of cyclohexene and chloride concentrations on the rate of alkene chlorination support a Pd(IV)-Cl ionization in the first step. Product stereochemistry and product distributions from various alkenes also support Cl(+)-transfer from the pentacoordinated Pd(IV)-intermediate LPd(IV)Cl(3)(+) to olefins. 1-Hexene/3-hexene competition experiments rule out both the formation of π-complexes along the reaction coordinate as well as in situ generated Cl(2) from a reductive elimination process. Instead, a ligand-mediated direct Cl(+)-transfer from LPd(IV)Cl(3)(+) to the π-system is likely to occur. Similarly, C-H bond chlorinations proceed via an electrophilic process with in situ formed LPd(IV)Cl(3)(+). The presence of a large excess of added Cl(-) slows cyclohexene chlorination while the presence of stoichiometric amounts of chloride accelerates both Pd(IV)-Cl ionization and Cl(+)-transfer from LPd(IV)Cl(3)(+). (1)H NMR titrations, T1 relaxation time measurements, binding isotherms, and Job plot analysis point to the formation of a trifurcated Cl(-)···H-C bond in the NHC-ligand periphery as a supramolecular cause for the accelerated chemical events involving the metal center.
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Affiliation(s)
- A Scott McCall
- Department of Chemistry, Kansas State University, 213 CBC Building, Manhattan, Kansas 66506-0401, United States
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231
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de Haro T, Nevado C. Flexible Gold-Catalyzed Regioselective Oxidative Difunctionalization of Unactivated Alkenes. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201005763] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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232
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de Haro T, Nevado C. Flexible gold-catalyzed regioselective oxidative difunctionalization of unactivated alkenes. Angew Chem Int Ed Engl 2011; 50:906-10. [PMID: 21246688 DOI: 10.1002/anie.201005763] [Citation(s) in RCA: 180] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 12/01/2010] [Indexed: 01/08/2023]
Affiliation(s)
- Teresa de Haro
- Organic Chemistry Institute, Universität Zürich, Switzerland
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233
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Braun T, Wehmeier F. C–F Bond Activation of Highly Fluorinated Molecules at Rhodium: From Model Reactions to Catalysis. Eur J Inorg Chem 2011. [DOI: 10.1002/ejic.201001184] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Thomas Braun
- Humboldt‐Universität zu Berlin, Institut für Chemie, Brook‐Taylor‐Str. 2 12489 Berlin, Germany, Fax: +49‐30‐2093‐6966
| | - Falk Wehmeier
- Humboldt‐Universität zu Berlin, Institut für Chemie, Brook‐Taylor‐Str. 2 12489 Berlin, Germany, Fax: +49‐30‐2093‐6966
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234
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Abstract
While the organometallic chemistry of Pd in its (0), (+II), and (+IV) oxidation states is well-established, organometallic Pd(III) chemistry remains widely unexplored. Few characterized Pd(III) complexes are known, which has inhibited detailed study of the organometallic chemistry of Pd(III). In this review, the potential roles of both mono- and dinuclear Pd(III) complexes in organometallic chemistry will be discussed. While not widely recognized, Pd in the (+III) oxidation state may play a significant role in a variety of known Pd-catalyzed reactions.
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235
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236
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237
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Zhao X, Dong VM. Carbon-Sulfur Reductive Elimination from Palladium(IV) Sulfinate Complexes. Angew Chem Int Ed Engl 2010; 50:932-4. [DOI: 10.1002/anie.201005489] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2010] [Indexed: 11/08/2022]
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238
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Zhao X, Dong VM. Carbon-Sulfur Reductive Elimination from Palladium(IV) Sulfinate Complexes. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201005489] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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239
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Katcher MH, Doyle AG. Palladium-catalyzed asymmetric synthesis of allylic fluorides. J Am Chem Soc 2010; 132:17402-4. [PMID: 21087003 DOI: 10.1021/ja109120n] [Citation(s) in RCA: 164] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The enantioselective fluorination of readily available cyclic allylic chlorides with AgF has been accomplished using a Pd(0) catalyst and Trost bisphosphine ligand. The reactions proceed with unprecedented ease of operation for Pd-mediated nucleophilic fluorination, allowing access to highly enantioenriched cyclic allylic fluorides that bear diverse functional groups. Evidence that supports a mechanism in which C-F bond formation occurs by an S(N)2-type attack of fluoride on a Pd(II)-allyl intermediate is presented.
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Affiliation(s)
- Matthew H Katcher
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
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240
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Hughes RP. Fluorine as a ligand substituent in organometallic chemistry: A second chance and a second research career. J Fluor Chem 2010. [DOI: 10.1016/j.jfluchem.2010.06.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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241
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242
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Abstract
Carbon-fluorine bond formation by transition metal catalysis is difficult, and only a few methods for the synthesis of aryl fluorides have been developed. All reported transition-metal-catalyzed fluorination reactions for the synthesis of functionalized arenes are based on palladium. Here we present silver catalysis for carbon-fluorine bond formation. Our report is the first example of the use of the transition metal silver to form carbon-heteroatom bonds by cross-coupling catalysis. The functional group tolerance and substrate scope presented here have not been demonstrated for any other fluorination reaction to date.
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Affiliation(s)
- Pingping Tang
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Takeru Furuya
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
| | - Tobias Ritter
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138
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243
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Coleman KS, Fawcett J, Harding DAJ, Hope EG, Singh K, Solan GA. Routes to Ruthenium-Fluoro Cations of the Type [RuL2(CO)nF]+ (n = 2,3; L = PR3, NHC): A Play-Off between Solvent, L and Weakly Coordinating Anion. Eur J Inorg Chem 2010. [DOI: 10.1002/ejic.201000410] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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244
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Higgs AT, Zinn PJ, Sanford MS. Synthesis and Reactivity of NiII(Phpy)2 (Phpy = 2-Phenylpyridine). Organometallics 2010. [DOI: 10.1021/om100387z] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Andrew T. Higgs
- Department of Chemistry, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109
| | - Paul J. Zinn
- Department of Chemistry, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109
| | - Melanie S. Sanford
- Department of Chemistry, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109
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245
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Furuya T, Klein JEMN, Ritter T. C-F Bond Formation for the Synthesis of Aryl Fluorides. SYNTHESIS-STUTTGART 2010; 2010:1804-1821. [PMID: 20953341 PMCID: PMC2953275 DOI: 10.1055/s-0029-1218742] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
A selection of carbon-fluorine bond-forming reactions is presented with particular focus on transition metal-mediated fluorination. A brief summary of conventional fluorination reactions is followed by a discussion of fluorination reactions mediated by palladium and silver. Investigations into the mechanism as well as the conceptual difficulty associated with transition metal-mediated carbon-fluorine bond formation are presented.
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Affiliation(s)
- Takeru Furuya
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA, Fax: +1(617)4964591
| | - Johannes E. M. N. Klein
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA, Fax: +1(617)4964591
| | - Tobias Ritter
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA, Fax: +1(617)4964591
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246
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Sun AD, Love JA. Cross coupling reactions of polyfluoroarenes via C–F activation. Dalton Trans 2010; 39:10362-74. [DOI: 10.1039/c0dt00540a] [Citation(s) in RCA: 200] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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