Carbonylic-Carbon-Centered Mechanism for Catalytic α‑Methylation

The
multicarbonyl manganese pincer complex-catalyzed α-methylation
reaction is studied. In this theoretical work, an unprecedented carbonylic-carbon-centered
mechanism is discovered. That is, the catalytic center is on the carbonyl
ligand instead of the metal atom, such as the common aromatization/dearomatization
metal–ligand cooperation mechanism. Further, the origins of
chemoselectivity of enone hydrogenation are addressed with the $DEL-type
NBO analyses. With a manganese pincer catalyst, the donor–acceptor
electron transfer is found from the CC bond to the CO
antibond, which can be regarded as the original driving force for
the enone CC hydrogenation. In contrast, the Noyori-type RuH2(diphosphine)­(diamine) catalysts favor the CO hydrogenation,
where the driving force is the donor–acceptor interaction associated
with the O···H–N hydrogen bond.