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 H2) of various [Os3(CO)10(μ-H) (μ-OSiPh2R′)] (R′ = Ph, OH, OSiPh2OH) clusters and the thermal behavior of [Os3(CO)10(μ-H)(μ-OSiEt3)] have been studied with the aim of clarifying by a molecular approach some aspects of the surface chemistry of silica-anchored [Os3(CO)10(μ-H)(μ-OSi≡)]. Their easy and selective reduction to [Os3(CO)12] (under CO) and to [H4Os4(CO)12] (under H2) suggests that [Os3(CO)10(μ-H)(μ-OSi≡)] does not require, as a reactive intermediate, a previous hydrolysis to the more reactive molecular species [Os3(CO)10(μ-H)(μ-OH)] in order to generate different osmium carbonyl clusters in their silica-mediated synthesis starting from OsCl3 or [Os(CO)3Cl2]2. The thermal behavior of [Os3(CO)10(μ-H)(μ-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 surface of [Os3(CO)10(μ-H)(μ-OSi≡)]. In triethylsilanol, oxidation occurs to give a Os(II) hydrido carbonyl species which, on the basis of chemical and spectroscopic evidence, we suggest to be [Os(CO)3(μ-OSiEt3)2(OSiEt3) (H)Os(CO)2]n (n = probably 2), whereas in triglyme an aggregation to high-nuclearity clusters such as [H4Os10(CO)24]2- and [H5Os10(CO)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 the reactivity of organometallic species on the silica surface.