Redox behaviour of triangular platinum–cobalt clusters. Electrochemically induced generation of the tetranuclear cluster [Pt2Co2(µ-Co)3(CO)5(PPh3)2]

Abstract

The redox behaviour of two trimetallic platinum–cobalt clusters [PtCo₂(µ-CO)(CO)₆(dppe)](1)[dppe = 1,2-bis(diphenylphosphino)ethane] and [PtCo₂(µ-CO)(CO)₇(PPh₃)](2) was studied on both solid and mercury electrodes in aprotic medium by polarography, cyclic voltammetry, and potentiostatic coulometry. The reduction of the two clusters occurs via a one-electron irreversible step which further results in the release of one [Co(CO)₄]^– anion per mol of cluster. The cluster [Pt₂Co₂(µ-CO)₃(CO)₅(PPh₃)₂](3) was isolated in good yield from the reduction of (2). Each of the clusters (1) and (2) undergoes two one-electron oxidation steps. The first oxidation step is reversible at high potential scans, whereas the second step leads to electrode passivation. The redox potentials corresponding to the studied reactions are compared with those previously obtained for the linear trimetallic complex [(OC)₄Co(PtL₂)Co(CO)₄](4)(L =cyclo-CNC₆H₁₁).