Kinetics of some Reactions of Ru 3(CO) 10(μ-bisdiphenylphosphinomethane)

Abstract

The kinetics of substitution of Ru 3(CO) 10(dppm) with several relatively weak nucleophiles to form Ru 3(CO) 9(dppm)(L) in benzene have been studied over the temperature fange 30–60°C. At lower temperatures the observed first order rate constants for reaction under N 2 or air are independent of the nature or concentration of the nucleophile but reactions are retarded by CO in a way characteristic of a simple CO dissociative mechanism. It is, however, also possible that the rate determining step is a form of isomerization of the cluster and some possibilities are discussed. In terms of △ H * the dppm substituent is found to be more labilizing than two PPh 3 substitutents, possibly because of a greater strain in the cluster caused by the bridging dppm ligand. At higher temperatures another reaction path appears to be available for reaction with PPh 3, and this accounts for ca. 30% of the rate at 50 °C. A similar path has been reported for reaction with dppm but some difficulties arise which suggest that the mechanism proposed for that reaction is at least oversimplified.