Direct organometallic synthesis: The metal-etching reactions of isobutyl iodide on Al(111)

We report a study of the thermal decomposition and reactions of isobutyl iodide on Al(111). Using temperature-programmed reaction and Auger electron spectroscopies, it was found that more than one product-forming pathway involving the alkyl moiety exists on this surface. A first-order, beta-hydride elimination reaction converts surface-bound isobutyl groups derived from the dissociation of the C-I bond to gas phase isobutene and dihydrogen at temperatures above similar to 420 K. Competing with this unimolecular process is a collection of complex associative reactions which effect the etching of the aluminum surface via the formation of volatile organometallic species. This includes formation and subsequent desorption of diisobutylaluminum iodide (desorption peak maximum at similar to 490 K), diisobutylaluminum hydride (similar to 515 K), methylaluminum dihydride (similar to 725 K), and AlIx, x = 1-3 (similar to 620 K). The kinetics of the processes yielding the various aluminum hydrides are coupled to that of the beta-hydride elimination pathway (which serves as the hydrogen atom source) and are strongly coverage dependent. The formation of MeAlH2 reveals the occurrence of a kinetically competitive beta-methyl elimination reaction of the surface alkyl groups.