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

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High Resolution Image Download MS PowerPoint Slide The hexahydride complex OsH 6 (P i Pr 3 ) 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)(P i Pr 3 ) 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 .