The Homogeneous Reduction of Co? by [Ni(cyclam)]+: Increased Catalytic Rates with the Addition of a CO Scavenger

By Froehlich, Jesse D. & Kubiak, Clifford P.
Published in Journal of the American Chemical Society NULL 2015

Abstract

The homogeneous electrochemical reduction of Co? by the molecular catalyst [Ni(cyclam)]2+ is studied by electrochemistry and infrared spectroelectrochemistry. The electrochemical kinetics are probed by varying Co? substrate and proton concentrations. Products of Co? reduction are observed in infrared spectra obtained from spectroelectrochemical experiments. The two major species observed are a Ni(I) carbonyl, [Ni(cyclam)(CO)]+, and a Ni(II) coordinated bicarbonate, [Ni(cyclam)(Co?OH)]+. The rate-limiting step during electrocatalysis is determined to be CO loss from the deactivated species, [Ni(cyclam)(CO)]+, to produce the active catalyst, [Ni(cyclam)]+. Another macrocyclic complex, [Ni(TMC)]+, is deployed as a CO scavenger in order to inhibit the deactivation of [Ni(cyclam)]+ by CO. Addition of the CO scavenger is shown to dramatically increase the catalytic current observed for Co? reduction. Evidence for the [Ni(TMC)]+ acting as a CO scavenger includes the observation of [Ni(TMC)(CO)]+ by IR. Density functional theory (DFT) calculations probing the optimized geometry of the [Ni(cyclam)(CO)]+ species are also presented.

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