Surface-mediated organometallic synthesis: Preparation of (Os sub 5 C(CO) sub 14 ) sup 2 minus and (Os sub 10 C(CO) sub 24 ) sup 2 minus on the basic magnesium oxide surface

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 + H{sub 2}. Control of the product distributions was exerted by choice of the temperature, pressure, gas-phase composition, and metal compound precursor. (Os{sub 10}C(CO){sub 24}){sup 2{minus}} was prepared from (H{sub 2}OsCl{sub 6}) adsorbed on MgO treated in equimolar CO + H{sub 2} at 275{degree}C and 1 atm, and (Os{sub 5}C(CO){sub 14}){sup 2{minus}} was prepared from (Os{sub 3}(CO){sub 12}) adsorbed on MgO treated in CO at 275{degree}C and 1 atm. These syntheses are more efficient than the best known solution syntheses; the results suggest a more general applicability of surface-mediated synthesis.