Reduction–oxidation properties of organotransition-metal complexes. Part 15. Synthesis, electrochemistry, and reactivity of the radical cations [Co(CO)2–nLn(η-C5R5)]+(n= 1 or 2, L = phosphine, R = H or Me)

Abstract

Cyclic voltammetric studies show that the complexes [Co(CO)L(η-C₅H₅)][1; L = P(C₆H₁₁)₃ or PPh₃] undergo one-electron oxidation to the radical cations [Co(CO)L(η-C₅H₅)]⁺. Chemical oxidation of (1) with [Fe(η-C₅H₅)₂][PF₆] gives [Co(CO){P(C₆H₁₁)₃}(η-C₅H₅)][PF₆](2) and the bis(phosphine) salt [Co(PPh₃)₂(η-C₅H₅)][PF₆](3). The latter is also prepared directly from [Co(CO)₂(η-C₅H₅)] and PPh₃ in the presence of [Fe(η-C₅H₅)₂][PF₆], but [Co(CO)₂(η-C₅Me₅)] gives [Co(CO)(PPh₃)(η-C₅Me₅)][PF₆](4). Complex (2) undergoes substitution reactions to give paramagnetic [CoL{P(C₆H₁₁)₃}(η-C₅H₅)][PF₆](L = PPh₃ or pyridine) and diamagnetic [Co{P(OMe)₃}₃(η-C₅H₅)][PF₆]₂. With halogens, X₂, with Me₂NC(S)SSC(S)NMe₂, and with NO gas, (2)–(4) undergo radical-coupling reactions to give [CoX(CO){P(C₆H₁₁)₃}(η-C₅H₅)][PF₆](X = Br or I), [CoL(S₂CNMe₂)(η-C₅H₅)][PF₆][L = P(C₆H₁₁)₃ or PPh₃], and [Co(NO)(PPh₃)(η-C₅R₅)][PF₆](R = H or Me) respectively. With ortho-quinones, (2) gives [Co(O–O){P(C₆H₁₁)₃}(η-C₅H₅)][PF₆](5; O–O =o-chloranil, 1,2-naphthoquinone, or phenanthrenequinone) the e.s.r. spectra of which suggest the unpaired electron to be localised mainly on the quinone ligand.