Kinetics and Mechanism of the Acetate-Catalyzed Heterolysis of the Metal-Carbon σ Bond of (α-Hydroxyalkyl)Chromium(III) Complexes. Effects of Nonparticipating Ligands, Temperature, and Pressure

The acetate-catalyzed heterolysis reaction of two (a-hydroxyalkyl)chromium(III) complexes, Cr^III-CH₂OH and Cr^III-C(CH₃)₂OH, with three types of nonparticipating ligands (H₂O)₅Cr-R²⁺, irons-([15]aneN₄)(H₂O)Cr-R²⁺, and cis-(nta)(H₂O)Cr-R^-, has been studied as a function of acetate concentration, temperature, and pressure. The reported rate and activation parameters demonstrate that the catalytic effect results from a trans-labilization effect by coordinated acetate and involves the attack by a solvent water molecule on the metal-carbon bond. The positive volumes of activation support the operation of a dissociatively activated heterolysis mechanism, which is in line with the suggested labilization effect by coordinated acetate.