Osmium−Allenylidene Complexes Containing an N-Heterocyclic Carbene Ligand

Complex [(η6-p-cymene)OsCl(IPr)]OTf (1) reacts with 1,1-diphenyl-2-propyn-1-ol to afford the hydroxyvinylidene derivative [(η6-p-cymene)OsCl{CCHC(OH)Ph2}(IPr)]OTf (2), which dehydrates to form [(η6-p-cymene)OsCl(CCCPh2)(IPr)]OTf (3). Treatment in acetonitrile under reflux of the BF4-salt of 3 with AgBF4 leads to the tetrakis(solvento) derivative [Os(CCCPh2)(CH3CN)4(IPr)][BF4]2 (4). At 95 °C, the addition of PiPr3 to an acetonitrile solution of 4 yields the dicationic mixed PiPr3-IPr osmium−allenylidene complex [Os(CCCPh2)(CH3CN)3(IPr)(PiPr3)][BF4]2 (5), which in 2-propanol and in the presence of NaCl evolves into the five-coordinate hydride−alkenylcarbyne [OsHCl(CCHCPh2)(IPr)(PiPr3)][BF4] (6). The X-ray structures of 2, 5, and 6 are also reported.