Synthesis, characterization, reactivity, and catalytic hydrogenation activity of the hexanuclear hexahydrido carbonyl cluster compound 3,η2-ampy)2(CO)14> (Hampy = 2-amino-6-methylpyridine)

Article abstract of DOI:10.1016/0022-328X(94)05372-I

The reaction of the 48-electron complex 3,η²-ampy)(CO)9> (1) (Hampy = 2-amino-6-methylpyridine) with molecular hydrogen (1 atm, toluene, 110 deg C) gives the 92-electron hexanuclear hexahydrido derivative 3,η²-ampy)2(CO)14> (2).This hexanuclear compound regenerates complex 1 when exposed to carbon monoxide.However, it undergoes CO substitution instead of ligand addition when treated with PR3 to give 3,η²-ampy)2(PR3)2(CO)12> (R = 4-tolyl (3a) or Ph (3b)).The X-ray diffraction structure of 3a indicates that it consists of two trinuclear fragments connected to each other through two bridging hydrides, and two weak metal-metal bonds.NMR experiments (1H, 13C, homonuclear 1H NOE, and heteronuclear indirect 13C-1H correlations) indicate that 2 is isostructural with 3a.Complex 2 is an efficient catalyst precursor for the homogeneous hydrogenation of unsaturated organic molecules.A kinetic analysis of the hydrogenation of diphenylacetylene under very mild conditions (T = 323 K, P(H2)<1 atm) has shown that the reaction is first-order in the concentration of 2, first-order in hydrogen pressure and zero-order in substrate concentration, suggesting that the active catalytic species are hexanuclear.Keywords: Ruthenium; Hydride; Cluster; X-ray structure; Catalytic hydrogenation; Alkyne hydrogenation kinetics