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 2a−2f 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.