Alkyl–Aryl Coupling Catalyzed by Tandem Systems of Pincer-Ligated Iridium Complexes and Zeolites

Abstract

We report that pincer-ligated iridium catalysts for alkane dehydrogenation can operate in tandem with zeolite catalysts for arene–alkene coupling, to effect the overall intramolecular dehydrocoupling of alkyl–H and aryl–H bonds (i.e., the dehydrocyclization of alkyl benzene). Thus, zeolite and soluble iridium cocatalysts in refluxing pentylbenzene (205 °C) gave high yields of 1-methyl-1,2,3,4-tetrahydronaphthalene. Subsequent dehydrogenation and isomerization affords 1- and 2-methylnaphthalene and 2-methyl-1,2,3,4-tetrahydronaphthalene. Total yields of cyclized product as high as 5.4 M (94%) have been obtained, corresponding to 6800 turnovers per mol Ir. Turnover numbers for the tandem-catalyzed dehydrocyclization are much greater than those obtained for simple dehydrogenation by Ir catalysts (to give olefins) in the absence of zeolite.