REDOX-INDUCED ACTIVATION OF C-H BONDS IN 1,2,3,4,5-PENTAMETHYLCYCLOPENTADIENE PLATINUM COMPLEXES

The electrochemical behaviour of the platinum complexes [Pt(eta(4)-C(5)Me(5)H)(eta(5)-C5H5)](BF4-)-B-+ (1(+)) and [Pt(eta(4)-diene)(eta(5)- C(5)Me(5))](BF4-)-B-+ (diene = C(5)Me(5)H (2(+)) or 1,3-cyclohexadiene; (3(+)) 1,5-cyclooctadiene(4(+))) has been studied by cyclic voltammetry. The complexes 1(+)-4(+) are capable of both oxidation and reduction. The bulk electrolysis of 2(+) at the potential of its reduction gives a mixture of two neutral isomeric complexes 5a and 5b. These are assigned structures with eta(3)-allylic and of sigma, pi-bonding methylene cyclopentenyl Me(3)C(5)H(=CH2) ligand. This is the proposed result from methyl C-H bond breakage in pentamethylcyclopentadiene ligand of an intermediate 19-electron complex [Pt(eta(4)-C(5)Me(5)H)(eta(5)-C(5)Me(5))](.) (2(.)). The same mixture of isomers 5a and 5b forms in interaction of 2(+) and (t)-BuOK in tetrahydrofuran. The preparative electrochemical oxidation of 2(+) proceeds with C-H bond scission at the pentamethylcyclopentadiene sp(3)-hybridized carbon in an intermediate 17-electron dication radical [Pt(eta(4)-C(5)Me(5)H)(eta(5)-C(5)Me(5))](.2+) (2(.2+)) to give decamethylplatinacene dication [Pt(eta(5)-C(5)Me(5))(2)](2+)(BF4-)(2) (7(2+)). The one-electron reduction of 7(2+) regenerates 2(+).