The role of SO2 as a ligand to mediate associative substitution reactions of some 18-electron molybdenum complexes

Article abstract of DOI:10.1016/0022-328X(94)00018-8

Results of kinetic studies are reported for intramolecular PPh3 substitution reactions of Mo(CO)2(η¹-L)(PPh3)2(SO2) to form Mo(CO)2(η²-L)(PPh3)(SO2) (L = dmpe=(Me)2PC2H4P(Me)2 and dppe=Ph2PC2H4PPh2) in THF as solvent.Activation parameters for the reactions are: ΔH^<*> values 12.3 kcal mol^-1 for dmpe and 16.7 kcal mol^-1 for dppe; and ΔS^<*> values -30.3 cal mol^-1 K for dmpe and -16.4 cal mol^-1 K for dppe.These results are consistent with an intramolecular associative mechanism.The facile associative pathway for the reaction is discussed in terms of the ability of SO2 to accept a pair of electrons from the metal, with a bonding transformation of η²-SO2 to η¹-pyramidal SO2, so maintaining a stable 18-electron count for the complex in the transition state.Keywords: Molybdenum; Sulfur dioxide; Ligand substitution; Kinetics; Mechanism