Mechanisms of organometallic substitution reactions. Part 4. Kinetics of replacement of dimethyl sulphoxide (dmso) from [RuX2(η-C6H6)(dmso)](X = Cl or Br) complexes by triphenylphosphine

Abstract

A kinetic study has been undertaken of the replacement of dimethyl sulphoxide (dmso) in [RuX₂(η-C₆H₆)(dmso)](X = Cl or Br) by triphenylphosphine in both dmso and 1,2-dichloroethane as solvent [equation (1)]. For the [RuX₂(η-C₆H₆)(dmso)]+ PPh₃→[RuX₂(η-C₆H₆)(PPh₃)]+ dmso (1) relatively slow reactions in dmso the rate law, rate =K[complex][PPh₃], is observed. However, a stopped-flow kinetic investigation of the rapid reactions in 1,2-dichloroethane supports a rate law of the form: rate =k₁k₂-[complex][PPh₃]/(k_–1[dmso]+k₂[PPh₃]). For both solvents a mechanism is proposed involving initial dissociation (k₁) of the dmso ligand generating the co-ordinatively unsaturated intermediates, [RuX₂(η-C₆H₆)], which may then either recombine (k_–1) with dmso to regenerate the starting complexes or add a PPh₃ ligand irreversibly (k₂) to yield the observed products.