SYNTHESIS, CHARACTERIZATION, REACTIVITY, AND CATALYTIC-HYDROGENATION ACTIVITY OF THE HEXANUCLEAR HEXAHYDRIDO CARBONYL CLUSTER COMPOUND [RU-6(MU-H)(6)(MU(3),ETA(2)-AMPY)(2)(CO)(14)] (HAMPY=2-AMINO-6-METHYLPYRIDINE)

The reaction of the 48-electron complex [Ru-3(mu-H)(mu(3),eta(2)-ampy) (CO)(9)] (1) (Hampy = 2-amino-6-methylpyridine) with molecular hydroge n (1 atm, toluene, 110 degrees C) gives the 99-electron hexanuclear he xahydrido derivative [Ru-6(mu-H)(6)(mu(3),eta(2)-ampy)(2)(CO)(14)] (2) . This hexanuclear compound regenerates complex 1 when exposed to carb on monoxide. However, it undergoes CO substitution instead of ligand a ddition when treated with PR(3) to give (mu-H)(6)(mu(3),eta(2)-ampy)(2 )(PR(3))(2)(CO)(12)] (R=4-tolyl (3a) or Ph (3b)). The X-ray diffractio n structure of 3a indicates that it consists of two trinuclear fragmen ts connected to each other through two bridging hydrides, and two weak metal-metal bonds. NMR experiments (H-1, C-13, homonuclear H-1 NOE, a nd heteronuclear indirect C-13-H-1 correlations) indicate that 2 is is ostructural with 3a. Complex 2 is an efficient catalyst precursor for the homogeneous hydrogenation of unsaturated organic molecules. A kine tic analysis of the hydrogenation of diphenylacetylene under very mild conditions (T = 323 K, P(H-2) < 1 atm) has shown that the reaction is first-order in the concentration of 2, first-order in hydrogen pressu re and zero-order in substrate concentration, suggesting that the acti ve catalytic species are hexanuclear.