The stereochemistry of alkyne insertion into Ru–H and Ru–Cl bonds

Abstract

Proton-coupled ¹³C NMR studies of vinyl complexes obtained by insertion of MeO₂CCCCO₂Me into the Ru–H bond of [Ru(CO)₂Cl(H)L₂](L = PMe₂Ph or AsMe₂Ph) or one Ru–H bond of [Ru(CO)₂H₂L₂] have shown that the reactions involve trans addition of Ru–H to the alkyne. For the PMe₂Ph complexes, selective deuteriation was required to simplify the spectra. In contrast, [Ru(CO)Cl(H)(PMe₂Ph)₃] reacts by cis addition of Ru–H to the alkyne. Carbonyl substitution in [Ru(CO)₂{C(CO₂Me)C(CO₂Me)H}Cl(PMe₂Ph)₂] by PMe₂Ph leaves the geometry of the vinyl ligand unchanged, so that two (non-interconverting) isomers of [Ru(CO){C(CO₂Me)=C(CO₂Me)H}Cl(PMe₂Ph)₃] can be obtained. Whereas trans-[Ru(CO)₂Cl₂(PMe₂Ph)₂] combines with MeO₂CCCCO₂Me by cis addition of Ru–Cl to the alkyne, [Ru(CO)(η²-C₂H₄)Cl₂(PMe₂Ph)₂] apparently reacts by trans addition, yielding [[graphic omitted]OMe)Cl}Cl(PMe₂Ph)₂]. Since, however, both reactions appear to involve the same ruthenium intermediate, [Ru(CO)Cl₂(PMe₂Ph)₂], it is possible that the direction of addition is the same in both cases, but that the vinyl ligand can isomerize.