Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition.
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)(PH...
| Main Authors: | , , , , , , |
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| Format: | Journal article |
| Language: | English |
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2008
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| _version_ | 1797064409445564416 |
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| author | Nova, A Erhardt, S Jasim, N Perutz, R Macgregor, SA McGrady, J Whitwood, A |
| author_facet | Nova, A Erhardt, S Jasim, N Perutz, R Macgregor, SA McGrady, J Whitwood, A |
| author_sort | Nova, A |
| collection | OXFORD |
| description | 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)}(P iPr3)2] shows planar coordination at Pt with r(F-Pt) = 2.029(3) A 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) A. |
| first_indexed | 2024-03-06T21:13:53Z |
| format | Journal article |
| id | oxford-uuid:3f1a9716-b6bf-4c80-88bb-2048a57aec6f |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T21:13:53Z |
| publishDate | 2008 |
| record_format | dspace |
| spelling | oxford-uuid:3f1a9716-b6bf-4c80-88bb-2048a57aec6f2022-03-26T14:29:52ZCompeting C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition.Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:3f1a9716-b6bf-4c80-88bb-2048a57aec6fEnglishSymplectic Elements at Oxford2008Nova, AErhardt, SJasim, NPerutz, RMacgregor, SAMcGrady, JWhitwood, AA 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)}(P iPr3)2] shows planar coordination at Pt with r(F-Pt) = 2.029(3) A 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) A. |
| spellingShingle | Nova, A Erhardt, S Jasim, N Perutz, R Macgregor, SA McGrady, J Whitwood, A Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition. |
| title | Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition. |
| title_full | Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition. |
| title_fullStr | Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition. |
| title_full_unstemmed | Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition. |
| title_short | Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition. |
| title_sort | competing c f activation pathways in the reaction of pt 0 with fluoropyridines phosphine assistance versus oxidative addition |
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