Chemical and thermal behavior of the molecular models [Os-3(CO)(10)(mu-H)(mu-OSiR2R ')] (R = Et, Ph; R ' = Et, Ph, OH, OSiPh2OH): Molecular approach to the clarification of the surface chemistry of the silica-anchored cluster [Os-3(CO)(10)(mu-H)(mu-OSi )]

The reactivity (e.g., toward hydrolysis, alcoholysis, reduction by CO or H- 2) of various [Os-3-(CO)(10)(mu -H)(mu -OSiPh2R')](R' = Ph, OH, OSiPh2OH) c lusters and the thermal behavior of [Os-3(CO)(10)(mu -H)(mu -OSiEt3)] have been studied with the aim of clarifying by a molecular approach some aspect s of the surface chemistry of silica-anchored [Os-3(CO)(10)(mu -H)(mu -OSi drop)] Their easy and selective reduction to [Os-3(CO)(12)] (under CO) and tb [H4Os4(CO)(12)] (under H-2) suggests that [Os-3(CO)(10)(mu -H)(mu -OSi d rop)] does not require, as a reactive intermediate, a previous hydrolysis t o the more reactive molecular species [Os-3(CO)(10)(mu -H)(mu -OH)] in orde r to generate different osmium carbonyl clusters in their silica-mediated s ynthesis starting from OsCl3 or [Os(CO)(3)Cl-2](2) The thermal behavior of [Os-3(CO)(10)(mu -H)(mu -OSiEt3)] dissolved in triethylsilanol (to mimic a silica surface with many available surface silanols) or triglyme (to mimic a highly dehydroxylated silica surface) gives an answer to the controversy on the nature of the products formed by thermal degradation on the silica s urface of [Os-3(CO)(10)(mu -H)(mu -OSi drop)]. In triethylsilanol, oxidatio n occurs to give a Os(II) hydride carbonyl species which, on the basis of c hemical and spectroscopic evidence, we suggest to be [OS(CO)(3)(mu -OSiEt3) (2)(OSiEt3)(H)OS(CO)(2)](n) (n = probably 2), whereas in triglyme an aggreg ation to high-nuclearity clusters such as [H4Os10(C)(24)](2-) and [H5OS10(C O)(24)](-) occurs. Therefore, it is shown for the first time that molecular models not only are a tool to define structural aspects but also may be a springboard to understand and clarify by a molecular approach aspects of th e reactivity of organometallic species on the silica surface.