σ-Bonded organotransition-metal ions. Part X. Kinetics and mechanism of the unimolecular hydrolysis of some pyridiomethyl metal carbonyl compounds in aqueous acid

Abstract

The rate of decomposition of the 4-pyridiomethyl-pentacarbonylmanganese, -π-cyclopentadienyltricarbonyl-molybdenum and -π-cyclopentadienyltricarbonyltungsten ions in aqueous acidic solution is independent of acid and halide ion concentration except for a small, positive specific salt effect. The kinetics and products of these reactions show that they involve the unimolecular heterolysis of the saturated carbon to metal bond (S_E1 at carbon, S_N1 at metal). The decomposition of the 3-pyridiomethylpentacarbonyl-manganese and -π-cyclopentadienyl-tricarbonylmolybdenum ions is also independent of acid and halide ion concentration, and is believed to involve and initial unimolecular homolysis of the saturated carbon–metal bond. The 3- and 4-pyridiomethyl-π-cyclopentadienyldicarbonyliron ions are extremely stable, but, as their decomposition is influenced by the presence of oxygen, good kinetics were not observed.