HAMMETT STUDIES ON ALKENE EXTRUSION FROM RHENIUM(V) DIOLATES AND AN MO DESCRIPTION OF METAL ALKOXIDE-ALKYL METAL OXO INTERCONVERSION

Rates of cycloreversion of phenyl-substituted diolates of the type Cp Re(O)(diolate), where diolate = phenylethane-1,2-diolate, exhibited a linear relationship with Hammett sigma(-) constants, with rho = 0.42. This suggests a slight buildup of electron density but little charge d evelopment in the transition state. The better fit with sigma(-) const ants suggests a resonance interaction between the phenyl ring and the breaking C-O bond. On the other hand, similar 1,2-diphenylethane-1,2-d iolates showed curved Hammett behavior, with acceleration by electron- donating and electron-withdrawing groups. Such behavior offers more ev idence for a nonsymmetric transition state and stepwise cleavage of th e C-O bonds. Molecular orbital calculations suggest a rationale for bo nding changes in these systems.