Surface organometallic chemistry of tin: Controlled thermal transformation in vacua of Sn(n-C₄H₉)₃ fragments grafted on the surface of alumina

The thermal transformation in vacuo of the well defined surface organometallic fragments [AlO]_xSn(H-C₄H₉)₃ (x = 1, 2) 1 grafted on various partially dehydroxylated aluminas (α, γ, η) has been investigated. The surface reactions were followed by qualitative and quantitative determination of the evolved gases including IR spectroscopy, ¹³C cross-polarisation magic angle spinning and ¹¹⁹Sn magic angle spinning NMR studies. On all aluminas, comparable transformations of 1 were identified showing that the ratio of octahedral : tetrahedral aluminium sites in the aluminas is not an important parameter. Solvolysis reactions of 1 led to the formation of the surface multigrafted species (AlO)_x+zSnBu_3-z (x = 1, 2; z = 1, 2, 3), while β-H elimination of but-1-ene followed by reductive elimination led to inorganic tin(II) compounds on the surface of the alumina. These transformations occur at temperatures lower than those observed with ≡SiOSnBu₃ grafted on the surface of silica. This is possibly related to the more acidic properties of alumina or to the higher concentration and/or mobility of Al hydroxy groups with respect to Si hydroxy groups.