SURFACE ORGANOMETALLIC CHEMISTRY OF TIN - REACTION OF HYDRIDOTRIS(BUTYL)TIN WITH THE SURFACES OF PARTIALLY DEHYDROXYLATED ALUMINAS

Reaction of Bu(3)SnH with the surface of partially dehydroxylated alum inas was followed by analysis of the evolved gases and infrared, C-13 CP-MAS NMR, and Sn-119 MAS NMR spectroscopies. At room temperature, th e infrared and C-13 CP-MAS NMR data suggest an initial interaction of Bu(3)SnH with the hydroxyl groups of the eta-alumina((500)) surface vi a hydrogen-type bonding with the delta-CH3 groups of the butyl ligand. The formation of the grafted entity >AlOSnBu(3) was accompanied by th e release of 1 mol H-2 per mole of Sn. Data were obtained on alpha-, g amma-, and eta-aluminas dehydroxylated at either 200 or 500 degrees C. The various NMR data coupled with published data for molecular analog s indicate that the tin atoms can be tetra- or pentacoordinated on the alumina surface. Al-27 NMR is used to estimate the ratio of octahedra l to tetrahedral aluminum atoms in various aluminas. Detailed study of the Sn-119 NMR of the series of Sn/Al2O3 species revealed three basic types of tin coordination environments. Tin signals around 80 ppm pre sent in some of the complexes are attributed to >AlOSnBu(3) or tetraco ordinated tin. Peaks in the regions around -230 and -170 ppm are ascri bed to a pentacoordinated tris(alkyl)tin fragment. The fifth ligand co ordinated to tin may be either a hydroxyl group ora surface O2- ion: f ormation of (>AlO) (>AlOH)Sn(n-C4H9)(3) and of (>AlO)(>AlO2-)Sn(n-C4H9 )(3). The complexity of these resonances and the dependence thereof on the type of alumina used and the degree of dehydroxylation are attrib uted to the influence of the geometry of neighboring aluminum atoms on the tin chemical shift. These results apply the extreme sensitivity o f tin chemical shifts to molecular environment, producing a method whe reby surface organometallic complexes of tin can be used as molecular probes for determining surface structures of oxides. The Sn-119 NMR is shown to be much more sensitive than other previously used spectrosco pic techniques, such as IR, Raman, and Al-29 NMR.