Coordinatively unsaturated 16-electron ruthenium allenylidene complexes : synthetic, structural, and catalytic studies

The one-pot reactions of [(p-cymene)RuCl2](2) (1) or (PPh3)(4)RuCl2 (2) with 2 equiv of PCy3 and 3,3-diphenylpropyn-3-ol afford the novel 16-electron ruthenium allenylidene complex (PCy3)(2)Cl2Ru(=C=C=CPh2) (3) in high yields. Substitution of one PCy3 ligand in 3 for one nucleophilic carbene ligand, IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], affords the novel complex (PCy3)(IMes)Cl2Ru(=C=C=CPh2) (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