Coordinatively Unsaturated 16-Electron Ruthenium Allenylidene Complexes:  Synthetic, Structural, and Catalytic Studies

The one-pot reactions of [( p -cymene)RuCl 2 ] 2 ( 1 ) or (PPh 3 ) 4 RuCl 2 ( 2 ) with 2 equiv of PCy 3 and 3,3-diphenylpropyn-3-ol afford the novel 16-electron ruthenium allenylidene complex (PCy 3 ) 2 Cl 2 Ru( C C CPh 2 ) ( 3 ) in high yields. Substitution of one PCy 3 ligand in 3 for one nucleophilic carbene ligand, IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], affords the novel complex (PCy 3 )(IMes)Cl 2 Ru( C C CPh 2 ) ( 4 ). Single-crystal X-ray structure analyses of complexes 3 and 4 were performed. Thermal stability of complexes 3 and 4 was investigated, and their catalytic activity promoting ring-closing metathesis (RCM) of various substrates was tested.