Dehydrogenation and related reactions of alkanes catalyzed by pincerâ-iridium complexes

Pincer-ligated iridium complexes catalyze the dehydrogenation of alkanes to give the corresponding alkenes. In some cases high selectivity for the terminal position of n-alkanes, to yield alpha-olefins, is observed; this selectivity is highly dependent on the nature of the pincer ligand. We have found that dehydrogenation can be usefully coupled with secondary reactions (tandem catalysis), particularly olefin metathesis, to afford an overall cycle for the metathesis of n-alkanes. More extensive dehydrogenation can result in the unprecedented homogeneously catalyzed dehydroaromatization of n-alkanes. For example, n-octane is converted to ethylbenzene and predominantly o-xylene while n-decane gives primarily o-propyltoluene as well as o-diethylbenzene and n-butylbenzene. Studies of the factors determining selectivity and the mechanism and scope of these reactions and will be discussed.