Mechanism of interconversion of the silica-supported tin alkyl complexes (SiO) 3- nSn( n-C 4H 9) n+1, n = 0, 1, 2. Synthesis and characterization of the tin-containing polyhedral oligo-silsesquioxanes [( c-C 5H 9) 7Si 8O 12(CH 3) 2Sn( n-C 4H 9) 3], [( c-C 5H 9) 7Si 7O 11 (OH)Sn( n-C 4H 9) 2] and [( c-C 5H 9) 7Si

Abstract

Thermolysis of the organometallic complex SiOSn( n-C 4H 9) 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 (SiO) 2Sn( n-C 4H 9) 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 (SiO) 3Sn( n-C 4H 9) 3 and finally to dealkylated species, while on silica (500) the major decomposition pathway is the β-H elimination, leading to (SiO) 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-C 5H 9) 7Si 7O 11(OH)Sn( n-C 4H 9) 2] 2′ and [( c-C 5H 9) 7Si 7O 12Sn( n-C 4H 9)] 3′, which can be considered as molecular models of 2 and 3, were synthesized by reaction of ( c-C 5H 9) 7Si 7O 9(OH) 3 with Cl 2Sn( n-C 4H 9) 2 and Cl 3Sn( n-C 4H 9) respectively. [( c-C 5H 9) 7Si 8O 12Sn( n-C 4H 9) 3(CH 3) 2] 1′, which can be considered as a molecular model of 1, was synthesized by reaction of ( c-C 5H 9) 7Si 8O 9(CH 3) 2(OH) with ClSn( n-C 4H 9) 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. To cite this article: C. Nédez et al., C. R. Chimie 7 (2004).