A Cobalt Hydride Catalyst for the Hydrogenation of
CO<sub>2</sub>: Pathways for Catalysis and Deactivation
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Abstract
The
complex Co(dmpe)<sub>2</sub>H catalyzes the hydrogenation of
CO<sub>2</sub> at 1 atm and 21 °C with significant improvement
in turnover frequency relative to previously reported second- and
third-row transition-metal complexes. New studies are presented to
elucidate the catalytic mechanism as well as pathways for catalyst
deactivation. The catalytic rate was optimized through the choice
of the base to match the p<i>K</i><sub>a</sub> of the [Co(dmpe)<sub>2</sub>(H)<sub>2</sub>]<sup>+</sup> intermediate. With a strong enough
base, the catalytic rate has a zeroth-order dependence on the base
concentration and the pressure of hydrogen and a first-order dependence
on the pressure of CO<sub>2</sub>. However, for CO<sub>2</sub>:H<sub>2</sub> ratios greater than 1, the catalytically inactive species
[(μ-dmpe)(Co(dmpe)<sub>2</sub>)<sub>2</sub>]<sup>2+</sup> and
[Co(dmpe)<sub>2</sub>CO]<sup>+</sup> were observed
