Redox chemistry of nickelocene-based monomers and polymers

The oxidation of [n]nickelocenophanes [Ni(η5-C5H4)2(CH2)3] (3), [Ni(η5-C5H4)2(SiMe2)2] (10), [Ni(η5-C5H4)2(SiMe2)2O] (11), [Ni(η5-C5H4)2(CH2)4] (12), and poly(nickelocenylpropylene) [Ni(η5-C5H4)2(CH2)3]n (4) to both the monocationic and dicationic species was investigated in dichloromethane by cyclic voltammetry (CV) and square-wave voltammetry. The presence of acetonitrile on the oxidation potentials of 3 in dichloromethane was also investigated by CV. The [n]nickelocenophanes 3 and 10–12 exhibited two single-electron Nernstian redox processes, and the monocations [3]+, [10]+, [11]+, and [12]+ were isolable as [B(C6F5)4]− salts after chemical oxidation, and were structurally characterized. Ni–Cpcent distances in all four monomers decreased upon oxidation, with a structural distortion manifested in the ring-tilt angle, α, among other angles. CV studies of the reversible first oxidation process to the polyelectrolyte {[Ni(η5-C5H4)2(CH2)3]+}n ([4]n+) were used to estimate the molecular weight of the polymeric material (Mw = 5300 g mol–1) by comparing its diffusion coefficient with that of a monomeric analogue, and the second electrochemical oxidation of polymer 4 was found to be only partially chemically reversible.