Competing C-F Activation Pathways in the Reaction of Pt(0) with Fluoropyridines: Phosphine-Assistance versus Oxidative Addition

Nova, A., Erhardt, S., Jasim, N. A., Perutz, R. N., Macgregor, S. A., McGrady, J. E. and Whitwood, A. C. (2008) Competing C-F Activation Pathways in the Reaction of Pt(0) with Fluoropyridines: Phosphine-Assistance versus Oxidative Addition. Journal of the American Chemical Society, 130(46), pp. 15499-15511. (doi: 10.1021/ja8046238)

Abstract

A survey of computed mechanisms for C-F bond activation at the 4-position of pentafluoropyridine by the model zero-valent bis-phosphine complex, [Pt(PH3)(PH2Me)], reveals three quite distinct pathways leading to square-planar Pt(II) products. Direct oxidative addition leads to cis-[Pt(F)(4-C5NF4)(PH3)(PH2Me)] via a conventional 3-center transition state. This process competes with two different phosphine-assisted mechanisms in which C-F activation involves fluorine transfer to a phosphorus center via novel 4-center transition states. The more accessible of the two phosphine-assisted processes involves concerted transfer of an alkyl group from phosphorus to the metal to give a platinum(alkyl)(fluorophosphine), trans-[Pt(Me) (4-C5NF4)(PH3)(PH2F)], analogues of which have been observed experimentally. The second phosphine-assisted pathway sees fluorine transfer to one of the phosphine ligands with formation of a metastable metallophosphorane intermediate from which either alkyl or fluorine transfer to the metal is possible. Both Pt-fluoride and Pt(alkyl)(fluorophosphine) products are therefore accessible via this route. Our calculations highlight the central role of metallophosphorane species, either as intermediates or transition states, in aromatic C-F bond activation. In addition, the similar computed barriers for all three processes suggest that Pt-fluoride species should be accessible. This is confirmed experimentally by the reaction of [Pt(PR3)(2)] species (R = isopropyl (iPr), cyclohexyl (Cy), and cyclopentyl (Cyp)) with 2,3,5-trifluoro-4-(trifluoromethyl)pyridine to give cis-[Pt(F){2-C5NHF2(CF3)}(PR3)(2)]. These species subsequently convert to the trans-isomers, either thermally or photochemically. The crystal structure of cis-[Pt(F){2-C5NHF2(CF3)}(PiPr(3))(2)] shows planar coordination at Pt with r(F-Pt) = 2.029(3) angstrom and P(1)-Pt-P(2) = 109.10(3)degrees. The crystal structure of trans-[Pt(F){2-C5NHF2(CF3)}(PCYP3)(2)] shows standard square-planar coordination at Pt with r(F-Pt) = 2.040(19) angstrom .

• Item Type: Articles
• Keywords: (FLUOROARENE)TRICARBONYLCHROMIUM(0) COMPLEXES ACTIVATION ARYL FLUORIDES BOND BOND ACTIVATION COMPLEX COMPLEXES COORDINATION CROSS-COUPLING REACTIONS CRYSTAL Crystal structure CRYSTAL-STRUCTURE FLUORINE BOND ACTIVATION GRIGNARD-REAGENTS H BONDS LIGAND LIGANDS MECHANISM METAL-COMPLEXES MODEL ORGANOMETALLIC FLUORIDES PATHWAY PHOSPHORUS PYRIMIDINONE DERIVATIVES REDUCTIVE ELIMINATION STATE Structure TRANSITION TRANSITION-STATE
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: McGrady, Prof John
• Authors: Nova, A., Erhardt, S., Jasim, N. A., Perutz, R. N., Macgregor, S. A., McGrady, J. E., and Whitwood, A. C.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of the American Chemical Society
• ISSN: 0002-7863