Mechanism of interconversion of the silica-supported tin alkyl complexes (ΞSiO)3-nSn (n-C4H9)n+1, n = 0, 1, 2. Synthesis and characterization of the tin-containing polyhedral oligo-silsesquioxanes [(c-C5H9)7 Si8O12(CH3)2Sn(n-C4H9)3], [(c-C5H9)7Si7O11(OH)Sn(n-C4H9)2] and [(c-C5H9)7Si7 O12Sn(n-C4H9)] as possible models for the expected surface structures

Thermolysis of the organometallic complex ΞSiOSn(n-C₄H₉)₃ 1 grafted on silica dehydroxylated either at 200 (silica₍₂₀₀₎) or 500 °C (silica₍₅₀₀₎) can be interpreted by assuming two decomposition pathways: (i) hydrolysis of the butyl groups by silanols, leading to n-butane and their stepwise substitution by surface siloxy ligands, and (ii) β-H elimination, followed by a reductive elimination of butane and formation of tin(II) surface species. In order to have further evidences of these two decomposition pathways on the two types of silica, both the thermolysis of (ΞSiO)₂Sn(n-C₄H₉)₂ 2 supported on silica₍₂₀₀₎ and silica₍₅₀₀₎ (which is assumed to be formed during the thermolysis of 1) and the synthesis of molecular models with a silsesquioxane ligand were undertaken. It has been shown that on silica₍₂₀₀₎ the major decomposition pathway of 2 is the hydrolysis by remaining hydroxyl groups, leading to (ΞSiO)₃Sn(n-C₄H₉) 3 and finally to dealkylated species, while on silica₍₅₀₀₎ the major decomposition pathway is the β-H elimination, leading to (ΞSiO)₂Sn^II. Molecular models of 1, 2 and 3 were synthesized by reaction of oligo-silsesquioxanes with butyltin chlorides in presence of triethylamine. We chose this way instead to the direct reaction with tin hydrides simply for commodity and because butyltin trihydride is not known. [(c-C₅H₉)₇Si₇O₁₁ (OH)Sn(n-C₄H₉)₂] 2′ and [(c-C₅H₉)₇Si₇O₁₂ Sn(n-C₄H₉)] 3′, which can be considered as molecular models of 2 and 3, were synthesized by reaction of (c-C₅H₉)₇Si₇O₉ (OH)₃ with Cl₂Sn(n-C₄ H₉)₂ and Cl₃Sn(n-C₄ H₉) respectively. [(c-C₅ H₉)₇Si₈O₁₂ Sn(n-C₄H₉)₃ (CH₃)₂] 1′, which can be considered as a molecular model of 1, was synthesized by reaction of (c-C₅H₉)₇Si₈O₉ (CH₃)₂(OH) with ClSn(n-C₄H₉)₃. The ¹³C and ¹¹⁹Sn NMR chemical shifts of these compounds, both in solution and in the solid state, compared well with those of the surface organometallic species.