SURFACE ORGANOMETALLIC CHEMISTRY OF TIN - THERMAL TRANSFORMATION, UNDER VACUUM, OF SI-O-SN(N-BU)(3) SUPPORTED ON SILICA

The reactivity of the well-defined surface organometallic fragment dro p Si-O-Sn(n-C4H9)(3) 1 grafted on silica(200) and on silica(500) has b een studied by thermal treatment of 1 at increasing temperatures in va cuo. The surface reactions have been followed by quantitative measurem ents of the evolved gases, infrared and Mossbauer spectroscopies, C-13 CP-MAS and Sn-119 NMR spectroscopy, XPS measurements, and electron mi croscopy (CTEM and STEM EDAX). On both types of silicas, the surface r eactions are similar in nature, although differences are noticeable. F irst, there is formation of (drop Si-O)(2)(Sn(n-C4H9)(2)) 2, which und ergoes a second solvolysis process by silanols leading to (drop Si-O)( 3)Sn(n-C4H9) 3 and finally surface Sn(II) and Sn(IV) atoms (as determi ned by XPS and Mossbauer experiments). Although the well-defined surfa ce organometallic compound (drop Si-O)(2)Sn(n-C4H9)(2) can be prepared on silica by another route, no unique surface compound can be obtaine d during the thermal decomposition which transforms progressively 1 in to 2 and 3. A mechanism of decomposition of the various surface organo metallic complexes has been deduced from a comparison of the results o btained on both solids. The alkyl groups seem to follow a beta-H elimi nation mechanism leading to tin hydrides and 1-butene rather than a di sproportionation mechanism leading to equimolar amounts of 1-butene an d butane.