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. Temperaturedependence 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 Znbound 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.