Mechanistic and thermodynamic aspects of methylene transfer from CH2N2 to MHCl(CO)L2 (M=Ru, Os; L=tertiary phosphine): non-least motion behavior and extreme dependence on phosphine identity

Abstract

Reaction of MHCl(CO)(PBut2Me)2 (M=Ru and Os) with CH2N2 was studied from -78 to 25°C, revealing first the formation of MHCl(CH2)(CO)(PBut2Me)2, where the carbene ligand CH2 occupies what was the open coordination site of MHCl(CO)(PBut2Me)2, which lies trans to the hydride. This intermediate then isomerizes to M(CH3)Cl(CO)(PBut2Me)2, below 25°C for each metal. The analogous reaction of MHCl(CO)(PPri3)2 with CH2N2 does indeed give MHCl(CH2)(CO)(PPri3)2, which then ‘decomposes’ unselectively; when M=Os, C2H4 and OsHCl(CO)(PPri3)2 are among the products. This extreme phosphine dependence is attributed to the H–MCH2 to M(CH3) isomerization requiring phosphine dissociation; the smaller PPri3 fails to dissociate at a rate competitive with alternative decomposition reactions.