Reaction mechanisms of metal–metal bonded carbonyls. Part XI. Reactions of nonacarbonyl(triphenylphosphine)dirhenium and octacarbonylbis(triphenylphosphine)dirhenium

Abstract

The Kinetics of the reversible reaction [Re₂(CO)₉(PPh₃)]+ PPh₃⇌[Re₂(CO)₈(PPh₃)₂]+ CO in decalin have been studied in each direction and activation parameters obtained. The Kinetic behaviour is quite simple and is consistent with a ligand-dissociative mechanism. However, it is also consistent with metal migration and homolytic-fission mechanisms. The reaction of [Re₂(CO)₉(PPh₃)] with carbon monoxide has quite different activation parameters from the reaction with triphenylphosphine and these reactions cannot, therefore, both go via simple rate-determining homolytic fission. Reaction of [Re₂(CO)₈(PPh₃)₂] with PPh₃ leads to mononuclear carbonylphosphine products and is half order in [Re₂(CO)₈(PPh₃)₂]. This reaction most probably does go via reversible homolytic fission. Reactions with oxygen, nitrogen monoxide, and iodine are also described.