High-nuclearity osmium carbonyl clusters have been synthesized by simple means and in high yields on the surface of porous, high surface area magnesium oxide in the presence of CO and CO + H2. Control of the product distributions was exerted by choice of the temperature, pressure, gas-phase composition, and metal compound precursor. [Os10C(CO)24]2™ was prepared from [H20sCl6] adsorbed on MgO treated in equimolar CO + H2 at 275 °C and 1 atm, and [Os5C(CO)14]2™ was prepared from [Os3(CO)12] adsorbed on MgO treated in CO at 275 °C and 1 atm. These cluster anions were isolated from the MgO in 65% yield by cation metathesis with [PPN] [Cl] in acetone. These syntheses are more efficient than the best known solution syntheses; the results suggest a more general applicability of surface-mediated synthesis.

The catalytic reduction of aldehydes and ketones to alcohols has been successfully effected through the use of M(CO)SB-(M = Cr, W, Mo; B = Bransted base) under hydrogen pressure in THF or MeOH. Both organic (CH,CO;) and inorganic [Mn(CO)S-] Bransted bases have been utilized for these reactions. Mechanistic models of this process include the ligand-assisted heterolytic cleavage of H2, an alkoxide-stabilized oxidative-addition dihydride, or an s2-Ht group 6 metal carbonyl as intermediates which are expected to produce a highly reactive group 6 anionic hydride. Subsequent steps involve hydride attack on the carbonyl carbon followed by protonation to produce the alcohol.The use of main group metal hydrides, such as LiAlH4, for the reduction of aldehydes and ketones suffers from the drawback that stoichiometric quantities of these reagents are required.Ia Transition-metal hydrides may serve as attractive alternatives, rendering these reduction processes involving less active substrates catalytic in metal. For example, cationic RhH2(PMe3)2L2+ complexes have been found to catalyze the reduction of ketones under mild conditions in the presence of small quantities of water.IbIn addition, the anionic hydride complex, R u H~( P P~~)~-~~ ~ (3) Darensbourg, D. J.; Ovalles, C. J . Am. Chem. SOC. 1984, 106, 3750. (4) (a) Kubas, G. J.; Ryan, R. R.; Swanson, B. 1.; Vergamini, P. J.; Wasserman, H. J. J . Am. Chem. Soc. 1984, 106,451. (b) Upmacis, R. K.; Gadd, G. E.; Poliakoff, M.; Simpson, M. B.; Turner, J. J.; Whyman, R.; Simpson, A. F.

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