Electrochemical behavior of bis(cyclopentadienylnickel)-alkyne derivatives

The electrochemical behavior of dimetallic [Ni(2)Cp(2)](RC=CR') (Cp = pi-cyclopentadienyl; R = R' = Ph; COOMe; R = H, R' = Ph; R = Me, R' = Ph; R = Ph, R' = -C=CPh) and tetrametallic M(2)M(2)'(PhC=CC=CPh) (M(2) = M(2)' = Ni(2)Cp(2); M(2) = Ni(2)Cp(2), M(2)' = Co-2(CO)(6)) derivatives has been investigated. All dinickel compounds undergo an electrochemically and chemically reversible le (metal-centered) reduction followed by further ligand-based reductions. The tetrametallic complex [Ni(2)Cp(2)](2)(PhC=CC=CPh) shows two fully reversible le (metal-centered) reductions, indicating a strong electronic communication between the two redox units (Delta E(o) = 670 mV). The mixed-metal [Ni(2)Cp(2)][Co-2(CO)(6)](PhC=CC=CPh) derivative exhibits a 1e (Co-2-centered) reduction at first, followed by a further 1e (Ni-2-centered) reduction; such an electrochemical scenario is complicated by a fast decomposition following the first reduction, which produces some amount of [Ni(2)Cp(2)](PhC=CC=CPh) compound, having a dangling (uncoordinated) triple bond.