CAN ORGANOMETALLIC NOBLE-GAS COMPOUNDS BE OBSERVED IN SOLUTION AT ROOM-TEMPERATURE - A TIME-RESOLVED INFRARED (TRIR) AND UV SPECTROSCOPIC STUDY OF THE PHOTOCHEMISTRY OF M(CO)(6) (M=CR, MO, AND W) IN SUPERCRITICAL NOBLE-GAS AND CO2 SOLUTION

The first systematic TRIR study of the photolysis of M(CO)(6) in super critical Ar, Kr, Xe, and CO2 permits the observation of M(CO)(5)L (M = Cr, Mo, and W; L = Ar (W only), Kr, Xe, and CO2). The second-order ra te constants for the reaction of M(CO)(5)L with CO have been evaluated and the reactivity for each metal is Kr > Xe approximate to CO2. For M(CO)(5)Kr, M(CO)(5)Xe, or M(CO)(5)(CO2) the reactivity is Cr approxim ate to Mo > W. In supercritical Kr doped with either Xe or CO2, the M( CO)(5) moiety interacts with Xe or CO2 in preference to Kr. The effect of solvent density on the rate of the reaction of W(CO)(5)(CO2) with CO has been investigated. This is the first time that the density depe ndence of any dissociative reaction has been followed in this way in s upercritical solution. Our observations demonstrate that the reaction of W(CO)(5)(CO2) with CO in scCO(2) is predominantly a dissociative pr ocess. The activation energies for the reaction of W(CO)(5)Xe and W(CO )(5)(CO2) with CO and the relative wavelength of the visible absorptio n maxima for Cr(CO)(5)Xe and Cr(CO)(5)(CO2) all indicate a similar str ength of interaction for Xe and CO2 with the M(CO)(5) moiety.