Benzene C-D bond activation by free vanadium cluster cations

Reaction of free V{sub x}{sup +} (x < 20) with C{sub 6}D{sub 6} is found to proceed via facile initial chemisorption followed by activated C-D cleavage and D{sub 2} elimination. Species with varying deuterium content V{sub x}C{sub 6}D{sub m}{sup +} (m = 0, 2, 4, 6) are produced, whose relative abundances in turn vary considerably with cluster size. Further, sequential dehydrogenation channels are observed for several of the clusters. In contrast to the reaction of C{sub 6}D{sub 6} with Nb{sub x}, Nb{sub x}{sup +}, Pt{sub x}, and Rh{sub x}, for which primarily m = 0 and m = 6 are formed, all V{sub x}{sup +} larger than the trimer also give rise to partially dehydrogenated species with m = 2 or 4. A global correlation between the probability of V{sub x}C{sub 6}D{sub m}{sup +} formation and the rate of activated D{sub 2} chemisorption by V{sub x}{sup +} implicates cluster valence electronic structure in the C-D activation process. Deviations from this correlation exhibited by V{sub 13}{sup +} and V{sub 14}{sup +} are interpreted as evidence for a relatively compact and/or symmetric structure for these two clusters.