LASER FLASH-PHOTOLYSIS STUDIES OF METAL-CARBONYLS IN SUPERCRITICAL CO2 AND ETHANE

The ring-closure reaction of M(CO)(5)L-L (M = W, Mo) where L-L denotes a bidentate ligand was chosen for its comparative independence of solvent properties to demonstrate the repulsive (or intrinsic) part of the activation volume. The ring-closure reaction rate constant was determined in supercritical CO2 and in supercritical ethane over the range between 1000 and 3500 psi at several temperatures (35, 42, 48, and 60 degrees C). The activation volume was observed to be as high as +7000 cm(3)/mol just above the critical point in each of these solvents. The ring-closure activation volume was also determined in liquid CO2 and in several other liquid solvents for comparison. These studies demonstrate a huge repulsive contribution to the activation volume in these two supercritical fluids.