DIRECT ORGANOMETALLIC SYNTHESIS - THE METAL-ETCHING REACTIONS OF ISOBUTYL IODIDE ON AL(111)

We report a study of the thermal decomposition and reactions of isobut yl iodide on Al(111). Using temperature-programmed reaction and Auger electron spectroscopies, it was found that more than one product-formi ng pathway involving the alkyl moiety exists on this surface. A first- order, beta-hydride elimination reaction converts surface-bound isobut yl groups derived from the dissociation of the C-I bond to gas phase i sobutene and dihydrogen at temperatures above similar to 420 K. Compet ing with this unimolecular process is a collection of complex associat ive 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 pe ak maximum at similar to 490 K), diisobutylaluminum hydride (similar t o 515 K), methylaluminum dihydride (similar to 725 K), and AlIx, x = 1 -3 (similar to 620 K). The kinetics of the processes yielding the vari ous aluminum hydrides are coupled to that of the beta-hydride eliminat ion pathway (which serves as the hydrogen atom source) and are strongl y coverage dependent. The formation of MeAlH2 reveals the occurrence o f a kinetically competitive beta-methyl elimination reaction of the su rface alkyl groups.