Reduction–oxidation properties of organotransition-metal complexes. Part 25. The one-electron reduction of cationic cyclopentadienyl–cobalt and –rhodium nitrosyl derivatives

Abstract

The complexes [ML(NO)(η-C5R5)][PF6][M = Co or Rh, R = H, L = PPh3; R = Ph, L = P(OMe)3 or P(OPh)3] undergo diffusion-controlled, one-electron reduction at a platinum-based electrode in CH2Cl2 or tetrahydrofuran (thf). Reduction of the cobalt complexes either chemically with [Co(η-C5H5)2] or by controlled potential electrolysis leads to P-donor ligand elimination, and dimerisation, to give [{Co(µ-NO)(η-C5R5)}2](R = H or Ph). The primary reduction products, namely [CoL(NO)(η-C5Ph5)][L = P(OMe)3 or P(OPh)3], have been detected by e.s.r. spectroscopy at –196 °C; the rhodium analogues, [RhL(NO)(η-C5Ph5)][L = P(OMe)3 or P(OPh)3] are stable at room temperature and have been isolated from the reaction between [RhL(NO)(η-C5Ph5)][PF6] and [Co(η-C5H5)2]. The dimer [{Co(µ-NO)(η-C5Ph5)}2] undergoes two reversible, one-electron oxidations and one irreversible, one-electron reduction; the paramagnetic salt [{Co(µ-NO)(η-C5Ph5)}2][PF6] has been isolated via[N2C6H4F-p][PF6] oxidation of the neutral precursor. The rhodium dimer [{Rh(µ-NO)(η-C5Ph5)}2], prepared by the reductive nitrosylation of [{RhBr2-(η-C5Ph5)}2] with NO gas and [Co(η-C5H5)2] in thf, or by the [Co(η-C5H5)2] reduction of [RhI(NO)(η-C5Ph5)], undergoes reversible one-electron oxidation and reduction and a second, irreversible, one-electron oxidation.