Reactions of Osmium–Pinacolboryl Complexes: Preparation of the First Vinylideneboronate Esters

The reactions of OsHCl­(CO)­(PR₃)₂ (PR₃ = PⁱPr₃ (<b>1a</b>), PCy₃ (<b>1b</b>)) with pinacolborane (HBpin) afford the boryl–dihydrogen derivatives Os­(Bpin)­Cl­(η²-H₂)­(CO)­(PR₃)₂ (PR₃ = PⁱPr₃ (<b>2a</b>), PCy₃ (<b>2b</b>)), which lose the H₂ ligand to give the five-coordinate boryl complexes Os­(Bpin)­Cl­(CO)­(PR₃)₂ (PR₃ = PⁱPr₃ (<b>3a</b>), PCy₃ (<b>3b</b>)). Treatment of <b>3a</b>,<b>b</b> with LiCCPh leads to the five-coordinate alkynyl–boryl derivatives Os­(Bpin)­(CCPh)­(CO)­(PR₃)₂ (PR₃ = PⁱPr₃ (<b>4a</b>), PCy₃ (<b>4b</b>)), which under a carbon monoxide atmosphere evolve into the vinylideneboronate esters Os­{CC­(Bpin)­Ph}­(CO)₂(PR₃)₂ (PR₃ = PⁱPr₃ (<b>5a</b>), PCy₃ (<b>5b</b>)). Complex <b>5a</b> is also prepared by stirring of a toluene solution of <b>3a</b> under CO and subsequent reaction of the resulting <i>cis</i>-dicarbonyl compound Os­(Bpin)­Cl­(CO)₂(PⁱPr₃)₂ (<b>6</b>) with LiCCPh. The X-ray structures of <b>3a</b>, <b>4a</b>, and <b>5b</b> are also reported