Chemical and Thermal Behavior of the Molecular Models [Os₃(CO)₁₀(μ-H)(μ-OSiR₂R‘)] (R = Et, Ph; R‘ = Et, Ph, OH, OSiPh₂OH):  Molecular Approach to the Clarification of the Surface Chemistry of the Silica-Anchored Cluster [Os₃(CO)₁₀(μ-H)(μ-OSi⋮)]

Abstract

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.

Well-defined silica supported aluminum hydride: another step towards the utopian single site dream?

“…There is a tendency to rationalize the understanding of heterogeneous catalysis by making well-dened model compounds. [1][2][3][4][5][6][7][8] The study of the reactivity of these models allows the identication of some elementary steps of heterogeneous catalysis. [9][10][11][12][13][14] One of the simplest ways to make such models compounds is to react the surface silanols (^Si-OH) of partially dehydroxylated silica with a metal-alkyl to obtain in principle well dened graed complexes.…”

Surface Organometallic Chemistry: Synthesis and X-ray Characterization of Novel Silanolate Surface Models [Re2(CO)8(μ-H)(μ-OSiR2R‘)] and of the First Models with Two Homo and Hetero Metal Carbonyl Fragments Linked to Vicinal or Geminal Silanols

“…It can be better understood from the structure and reactivity of molecular organometallic compounds bearing silanolate ligands to mimic the functional groups of the silica surface. These models are an important tool not only to define structural aspects but also to clarify by a molecular approach the chemical behavior of organometallic species bound to silica . Although models of silica- anchored carbonyl species of various metals (e.g.…”

“…Although models of silica- anchored carbonyl species of various metals (e.g. Rh, Os, , Ru 5 ) have been prepared and characterized, in the case of Re only recently has the anionic species [Re 2 (CO) 6 (μ-OH) 3 - x (μ-OSiEt 3 ) x ] - ( x = 1−3) been obtained …”

Surface Organometallic Chemistry: A New Synthesis of [Re2(CO)6(μ-OH)3]-from [Re(CO)3OH]4Supported on a Silica Surface Added with K2CO3; Evidence of Its Thermal Binding to the Surface via Re−O−Si⋮ Bonds Confirmed by the Synthesis of the Molecular Models [Re2(CO)6(μ-OH)x(μ-OSiEt3)3-x]-(x= 0, 1, or 2) by Reaction of [Re2

“…The bottom of the vessel (about half of the cylinder) was put in an oven and heated at 200 °C. After 20 h, the solution was evaporated to dryness and washed with pentane, to remove minor amounts of Et 3 SiOSiEt 3 and traces of Et 3 SiOSiEt 2 OSiEt 3 formed at this temperature, affording [NEt 4 ][Re 2 (CO) 6 (μ-OSiEt 3 ) 3 ] (65 mg; 0.061 mmol; 89% yield). The product was characterized by elemental analysis (Calcd: C, 38.09; H, 6.45; N, 1.40.…”