Surface Organometallic Chemistry of Tin: Reactivity of Tetraalkyltin Complexes and Tributyltin Hydride toward Silica

Tetraalkyltin complexes, SnR₄ (R = Me, Et, i-Pr, Bu), and tributylhydridotin were reacted with the surface of partially dehydroxylated silica. Interaction between the complexes and the silica surface was followed by IR and ¹³C and ¹¹⁹Sn MAS NMR spectroscopies and analysis of the evolved gases. At room temperature, all the studied complexes are physisorbed: a hydrogen-type bonding between the terminal methyl group of the alkyl ligands and/or the hydride ligand and the surface silanol groups is evidenced. Above 100 °C, with silica dehydroxylated at 500 °C (SiO₂(500)), a reaction occurs, leading to the formation at 200 °C of essentially one surface complex, ⪫SiO-SnR₃ (1) with evolution of 1 mol of alkane per mol of surface tin. 1 is already formed at room temperature by reaction of silica with Bu₃SnH; the reaction is slow and liberates 1 mol of H₂/mol of surface Sn. At low surface coverage, and for R ≠ Me, the alkyl ligands of 1 are folded toward the surface, interacting with it via hydrogen-type bonding. The same interaction and reaction are observed when the surface of silica is less dehydroxylated, SiO₂(200): nevertheless 1 is less stable, probably due to the availability of surface silanol groups in the neighborhood of 1.