Mechanistic differences between "reductive" and "oxidative" heterolysis ofmetal-carbon sigma bonds

Volumes of activation, Delta V double dagger, for the heterolysis reactions of copper complexes with metal-carbon sigma bonds, viz. [(H2O)(5)Cu-III-R] (2+) (R = CH2CO2- or CHCl2-) and [LCuII-R](+) (L = 2,5,8,11-tetramethyl-2,5 ,8,11-tetraazadodecane; R = CH2CO2-), were determined using high pressure p ulse-radiolysis techniques. In addition, the volume of activation for the b imolecular decomposition of [LCuII-CH3](+) was determined. The results reve al the different roles of the solvent (water) in the transition states for oxidative and reductive heterolysis reactions.