Effect of Substituents on the Formation of Vinylideneruthenium(II) Complexes. X-ray Structures of RuCl2{CC(Z)Ph}(dcpmp) (Z = H, SiMe3; dcpmp = C5H3N(CH2PCy2)2)

Kinetic studies have been carried out for the formation of vinylideneruthenium(II) complexes RuCl2{CC(Z)R}(dcpmp) [Z = H, R = p-MeOC6H4 (2a), p-MeC6H4 (2b), Ph (2c), p-BrC6H4 (2d), t-Bu (2e), ferrocenyl (2f); Z = SiMe3, R = Ph (5a), SiMe3 (5b); dcpmp = 2,6-bis{(dicyclohexylphosphino)methyl}pyridine] from RuCl2(NCMe)(dcpmp) (1) and alkynes (RC⋮CZ). The reactions with terminal alkynes proceed via preliminary dissociation of the MeCN ligand from 1, giving vinylidene complexes 2a2f in quantitative yields. More electron-rich and less sterically demanding alkynes tend to provide higher reaction rates. On the other hand, the reactions with silylalkynes afford equilibrium mixtures of 1 and β-silylvinylidene complexes 5. The X-ray structures of 2c and 5a are reported.