Reactions of Osmium–Pinacolboryl Complexes: Preparation of the First Vinylideneboronate Esters
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The reactions of OsHCl(CO)(PR3)2 (PR3 = PiPr3 (1a), PCy3 (1b)) with pinacolborane (HBpin) afford the boryl–dihydrogen derivatives Os(Bpin)Cl(η2-H2)(CO)(PR3)2 (PR3 = PiPr3 (2a), PCy3 (2b)), which lose the H2 ligand to give the five-coordinate boryl complexes Os(Bpin)Cl(CO)(PR3)2 (PR3 = PiPr3 (3a), PCy3 (3b)). Treatment of 3a,b with LiCCPh leads to the five-coordinate alkynyl–boryl derivatives Os(Bpin)(CCPh)(CO)(PR3)2 (PR3 = PiPr3 (4a), PCy3 (4b)), which under a carbon monoxide atmosphere evolve into the vinylideneboronate esters Os{CC(Bpin)Ph}(CO)2(PR3)2 (PR3 = PiPr3 (5a), PCy3 (5b)). Complex 5a is also prepared by stirring of a toluene solution of 3a under CO and subsequent reaction of the resulting cis-dicarbonyl compound Os(Bpin)Cl(CO)2(PiPr3)2 (6) with LiCCPh. The X-ray structures of 3a, 4a, and 5b are also reported.
