Redox Chemistry of Nickelocene-Based Monomers and Polymers
journal contribution
posted on 2021-06-18, 13:04 authored by Rebecca A. Musgrave, Andrew D. Russell, Paul R. Gamm, Rebekah L. N. Hailes, Kevin Lam, Hazel
A. Sparkes, Jennifer C. Green, William E. Geiger, Ian MannersThe
oxidation of [<i>n</i>]nickelocenophanes [Ni(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(CH<sub>2</sub>)<sub>3</sub>] (<b>3</b>), [Ni(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>] (<b>10</b>), [Ni(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(SiMe<sub>2</sub>)<sub>2</sub>O] (<b>11</b>), [Ni(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(CH<sub>2</sub>)<sub>4</sub>] (<b>12</b>), and poly(nickelocenylpropylene) [Ni(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(CH<sub>2</sub>)<sub>3</sub>]<sub><i>n</i></sub> (<b>4</b>) 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 <b>3</b> in dichloromethane
was also investigated by CV. The [<i>n</i>]nickelocenophanes <b>3</b> and <b>10</b>–<b>12</b> exhibited
two single-electron Nernstian redox
processes, and the monocations <b>[3]</b><sup><b>+</b></sup>, <b>[10]</b><sup><b>+</b></sup>, <b>[11]</b><sup><b>+</b></sup>, and <b>[12]</b><sup><b>+</b></sup> were isolable as [B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sup>−</sup> salts after chemical oxidation, and were structurally
characterized. Ni–Cp<sub>cent</sub> 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(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>(CH<sub>2</sub>)<sub>3</sub>]<sup>+</sup>}<sub><i>n</i></sub> (<b>[4]</b><sup><b><i>n</i>+</b></sup>) were used to estimate
the molecular weight of the polymeric material (<i>M</i><sub>w</sub> = 5300 g mol<sup>–1</sup>) by comparing its diffusion
coefficient with that of a monomeric analogue, and the second electrochemical
oxidation of polymer <b>4</b> was found to be only partially
chemically reversible.
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