The reactions of OsHCl(CO)(PR 3) 2 (PR 3 = P iPr 3 (1a), PCy 3 (1b)) with pinacolborane (HBpin) afford the boryl-dihydrogen derivatives Os(Bpin)Cl(η 2- H 2)(CO)(PR 3) 2 (PR 3 = P iPr 3 (2a), PCy 3 (2b)), which lose the H 2 ligand to give the five-coordinate boryl complexes Os(Bpin)Cl(CO)(PR 3) 2 (PR 3 = P iPr 3 (3a), PCy 3 (3b)). Treatment of 3a,b with LiC≡CPh leads to the five-coordinate alkynyl-boryl derivatives Os(Bpin)(C≡CPh)(CO)(PR 3) 2 (PR 3 = P iPr 3 (4a), PCy 3 (4b)), which under a carbon monoxide atmosphere evolve into the vinylideneboronate esters Os{CC(Bpin)Ph}(CO) 2(PR 3) 2 (PR 3 = P iPr 3 (5a), PCy 3 (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(P iPr 3) 2 (6) with LiC≡CPh. The X-ray structures of 3a, 4a, and 5b are also reported. © 2011 American Chemical Society.

Financial support from the Spanish MICINN (Projects CTQ2008-00810, Consolider Ingenio 2010 CSD2007-00006, and FR2009-0024), Departamento de Ciencia, Tecnología y Universidad del Gobierno de Aragón (E35), and the European Social Fund is acknowledged. M.M. thanks the Spanish MEC for her FPU grant.

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