Ligand Effect on the Insertion Reactions of Allenes with MHCl(CO)(PPh₃)₃ and MHCl(PPh₃)₃ (M = Ru, Os)

Treatment of RuHCl(CO)(PPh₃)₃ with CH₂CCHCO₂Me gives the allyl complex Ru(η³-CH₂CHCHCO₂Me)Cl(CO)(PPh₃)₂. The analogous allyl complexes Os(η³-CH₂CHCHR)Cl(CO)(PPh₃)₂ (R = Ph, CH₂Ph) are also produced from the reactions of OsHCl(CO)(PPh₃)₃ with CH₂CCHR. In contrast, MHCl(PPh₃)₃ (M = Ru, Os) react with CH₂CCHR to give the vinyl complexes MCl(C(CH₃)CHR)(CH₂CCHR)(PPh₃)₂ (M = Ru, R = CMe₃, M = Os, R = CMe₃, Ph, CO₂Et). The difference in the reaction pathways for the reactions of allenes with MHCl(CO)(PPh₃)₃ and MHCl(PPh₃)₃ (M = Ru, Os) has been studied by computational chemistry. The theoretical study shows that the observed different reactivity can be related to the significant difference in the electron density increase at the central carbon of the allene ligand upon coordination to the metal fragments.