Surface mediated organometallic synthesis:: Formation of [H5Os10(CO)24]- by hydrogenation of silica-supported [Os(CO)3(OH)2]n as a springboard for a high-yield synthesis of [H4Os10(CO)24]2- starting from α-[Os(CO)3Cl2]2 and working in ethylene glycol solution

New high yield routes to the high nuclearity hydride carbonyl clusters [H5Os10(CO)(24)](-) and [H2Os10(CO)(24)](2-), model systems for the chemisorption of CO and H, on metal surfaces, are reported. [H5Os10(CO)(24)](-) is obtained in good yields by hydrogenation (1 atm) at 200 degreesC of physisorbed [Os(CO)(3)(OH)(2)](n) whereas in refluxing ethylene glycol solution, that is less acidic than thr silica surface, [H4Os10(CO)(24)](2-) is obtained in high yield starting from [Os(CO),(OH),I, or, more conveniently, from alpha-[Os(CO)(3)Cl-2](2) in the presence of the stoichiometric amount of sodium carbonate. The quantitative equilibrium [H4Os10(CO)(24)](2-) reversible arrow (+OH-)(+H+) [H5Os10(CO)(24)](-) is confirmed.