THE INITIAL PHOTOCHEMICAL PROCESS OF TRIOSMIUMDODECACARBONYL ADSORBEDON THE SURFACE OF SILICA AS STUDIED BY PICOSECOND DIFFUSE-REFLECTANCELASER PHOTOLYSIS AND MATRIX-ISOLATION

The transient absorption spectrum of the coordinatively unsaturated tr inuclear osmium carbonyl cluster Os-3(CO)(11) adsorbed on the surface of silica was observed for the first time by the ps time-resolved diff use reflectance laser photolysis of Os-3(CO)(12). The present results demonstrated that Os-3(CO)(11) is the photoprimary product responsible for the net oxidative addition of surface hydroxyls to Os-3(CO)(12) a dsorbed on the surface of silica to form the surface attached trinucle ar species HOs3(CO)(10)-OSi=. It was revealed that the addition of sur face hydroxyls to Os-3(CO)(11) is completed within the time of our ins trumental response (less than or equal to 35 ps), which is comparable to the coordination of solvent to coordinatively unsaturated metal car bonyls.