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 alpha-[Os(CO)(3)Cl-2](2) and working in ethylene glycol solution

New high yield routes to the high nuclearity hydrido carbonyl clusters [H5OS10(CO)24]- and [H4OS10(CO)24]2-, model systems for the chemisorption of CO and H2 on metal surfaces, are reported. [H5OS10(CO)24]- is obtained in good yields by hydrogenation (1 atm) at 200°C of physisorbed [Os(CO)3(OH)2]n whereas in refluxing ethylene glycol solution, that is less acidic than the silica surface, [H4OS10(CO)24]2- is obtained in high yield start-ing from [Os(CO)3(OH)2]n or, more conveniently, from α-[Os(CO)3Cl2]2 in the presence of the stoichiometric amount of sodium carbonate. The quantitative equilibrium [H4OS10(CO)24]2- +OH-⇄+H+ [H5OS10(CO)24]- is confirmed.