Direct organometallic synthesis: The metal-etching reactions of isobutyl iodide on Al(111)¹

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, β-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 ∼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 ∼490 K), diisobutylaluminum hydride (∼515 K), methylaluminum dihydride (∼725 K), and AlI_x, x = 1-3 (∼620 K). The kinetics of the processes yielding the various aluminum hydrides are coupled to that of the β-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 β-methyl elimination reaction of the surface alkyl groups.