An Acyl-NHC Osmium Cooperative System: Coordination of Small Molecules and Heterolytic B–H and O–H Bond Activation

The
hexahydride complex OsH6(PiPr3)2 (1) activates the
C–OMe bond of 1-(2-methoxy-2-oxoethyl)-3-methylimidazolium
chloride (2), in addition to promoting the direct metalation
of the imidazolium group, to afford a five-coordinate OsCl­(acyl-NHC)­(PiPr3)2 (3) compound. The latter coordinates carbon monoxide, oxygen, and molecular
hydrogen to give the corresponding carbonyl (4), dioxygen
(5), and dihydrogen (6) derivatives. Complex 3 also promotes the heterolytic bond activation of pinacolborane
(HBpin), using the acyl oxygen atom as a pendant Lewis base. The hydride
ligand and the Bpin substituent of the Fischer-type carbene of the
resulting complex 7 activate the O–H bond of alcohols
and water. As a consequence, complex 3 is a metal ligand
cooperating catalyst for the generation of molecular hydrogen, by
means of both the alcoholysis and hydrolysis of pinacolborane, via
the intermediates 7 and 6.