KINETICS AND MECHANISM OF THE ACETATE-CATALYZED HETEROLYSIS OF THE METAL-CARBON SIGMA-BOND OF (ALPHA-HYDROXYALKYL)CHROMIUM(III) COMPLEXES - EFFECTS OF NONPARTICIPATING LIGANDS, TEMPERATURE, AND PRESSURE

The acetate-catalyzed heterolysis reaction of two (alpha-hydroxyalkyl)chromium(III) complexes, Cr(III)-CH2OH and Cr(III)-C(CH3)2OH, with three types of nonparticipating ligands (H2O)5Cr-R2+, trans-([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.