PRESSURE ACCELERATION OF [2 + 2] CYCLOADDITION REACTIONS ON THE COORDINATED LIGAND OF CHROMIUM AND TUNGSTEN PENTACARBONYL CARBENE COMPLEXES

The influence of pressure on [2 + 2] cycloaddition reactions of alpha,beta-unsaturated Fischer carbene complexes (M = Cr, W) with 3,4-dihydro-2H-pyran was studied. The cycloaddition was found to be sensitive toward pressure and showed a remarkable rate acceleration independent of the metal center. The temperature, pressure, and solvent dependence of these reactions was studied, and the corresponding activation parameters are reported. These data are used to discuss the intimate nature of the cycloaddition process in comparison to related data reported for organic reactions in the literature. The data are consistent with a nonpolar concerted, synchronous one-step mechanism.