Infrared study of the surface species formed by sequential chemical vapor deposition of dimethyl zinc and ethanethiol on hydroxylated alumina surfaces

The surface species formed by the reaction of gas-phase dimethylzinc with self-supported alumina pellets are examined by Fourier transform infrared spectroscopy. Dimethylzinc reacts with the surface -OH groups of alumina at room temperature evolving methane and yielding mainly surface Al-O-Zn-CH3 species. A small amount of CH3 species appears to bind to the Lewis acid sites of alumina as well, forming Al-CH3 groups. Temperature-dependence studies reveal that these species are stable at room temperature and gradually decompose upon heating in vacuo. During the annealing process, some of the Zn-bound methyl groups also appear to migrate to free Lewis acid sites of the alumina surface. The dimethylzinc-treated alumina surface is then exposed to ethanethiol, which reacts with the surface methylzinc species at room temperature, eliminating methane and producing Zn-bound ethanethiolate surface species. These are stable in air and aqueous environments, and up to about 523 K in vacuo and may provide a possible synthetic strategy for formation of protective layers. The major gas-phase products from their thermal decomposition are found to be diethyl sulfide and ethylene. In addition, a small amount of methylzinc-thiol coordination intermediate is found on the dimethylzinc-treated alumina surface following the room-temperature reaction with ethanethiol. This intermediate decomposes with methane evolution upon annealing up to 398 K.