Cobalt-Catalyzed Hydrogenations via Olefin Cobaltate and Hydride Intermediates

Redox
noninnocent ligands are a promising tool to moderate electron transfer
processes within base-metal catalysts. This report introduces bis­(imino)­acenaphthene
(BIAN) cobaltate complexes as hydrogenation catalysts. Sterically
hindered trisubstituted alkenes, imines, and quinolines underwent
clean hydrogenation under mild conditions (2–10 bar, 20–80
°C) by use of the stable catalyst precursor [(DippBIAN)­CoBr2] and the cocatalyst LiEt3BH. Mechanistic
studies support a homogeneous catalysis pathway involving alkene and
hydrido cobaltates as active catalyst species. Furthermore, considerable
reaction acceleration by alkali cations and Lewis acids was observed.
The dinuclear hydridocobaltate anion with bridging hydride ligands
was isolated and fully characterized.