Osmium-allenylidene complexes containing an N-heterocyclic carbene ligand

Complex [(eta(6)-p-cymene)OsCl(IPr)]OTf (1) reacts with 1,1-diphenyl-2-propyn-1-ol to afford the hydroxyvinylidene derivative [(eta(6)-p-cymene)OsCl{=C=CHC(OH)Ph-2}(IPr)]OTf (2), which dehydrates to form [(eta(6)-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 degrees C, the addition of (PPr3)-Pr-i to an acetonitrile solution of 4 yields the dicationic mixed (PPr3)-Pr-i-IPr osmium-allenylidene complex [Os(=C=C=CPh2)(CH3CN)(3)(IPr)((PPr3)-Pr-i)][BF4](2) (5), which in 2-propanol and in the presence of NaCl evolves into the five-coordinate hydride-alkenylcarbyne [OsHCl(equivalent to CCH= CPh2)(IPr)((PPr3)-Pr-i)1[BF4] (6). The X-ray structures of 2, 5, and 6 are also reported.