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.