Pal S. Cp* non-innocence and the implications of (η
4-Cp*H)Rh intermediates in the hydrogenation of CO
2, NAD
+, amino-borane, and the Cp* framework - a computational study.
Dalton Trans 2023;
52:1182-1187. [PMID:
36648493 DOI:
10.1039/d2dt03611h]
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Abstract
In hydrogenation mediated by half-sandwich complexes of Rh, Cp*Rh(III)-H intermediates are critical hydride-delivery agents. For bipyridine-supported complexes, a unique transformation named 'Cp* non-innocence' leads to the appearance of (Cp*H)Rh(I) intermediates, which are purported to exhibit enhanced hydride-delivery capabilities. In this work, DFT calculations performed to compare the role of these complexes in hydrogenation reveal that (Cp*H)Rh(I) intermediates do not compete with the conventional pathway (involving Cp*Rh(III)-H); instead they can lead to sequential hydrogenation of the Cp* framework, and potentially, catalyst degradation. Thus, caution is warranted when invoking the truly homogeneous nature of hydrogenation catalysis mediated by this popular class of complexes.
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