EXTRUSION OF ALKENES FROM RHENIUM(V) DIOLATES - ENERGETICS AND MECHANISM

The kinetics of extrusion of ethylene, 2-butene, and bicyclo[2.2.2]oct -2-ene from CpRe(O)(OCH(R)CH(R)O) (Cp* = eta-C-5(CH3)(5)) are measure d, as are the kinetics bf oxidation of norbornene, norbornadiene,and t rans-cyclooctene by CpReO3. Activation parameters calculated from the data show that strain in the double bond has a large effect on the en thalpy of activation for alkene oxidation but little or no effect on t he enthalpy of activation for alkene extrusion. Entropies of activatio n for alkene extrusion are less than zero. A secondary deuterium isoto pe effect of 1.3 at 99.5 degrees C is measured for extrusion of ethyle ne-d(4). Taken together, this data is inconsistent with a concerted me chanism for interaction of alkenes with CpReO3 but consistent with a stepwise mechanism with a metallaoxetane intermediate.