The selective dehydrogenation of alkanes to give olefins is a reaction of great interest. Alkane dehydrogenation has been studied extensively with iridium complexes of pincer ligands of which the central coordinating group coordinates through carbon (most commonly an aryl group) and the terminal groups coordinate through phosphorus, i.e. PCP-type. Ir complexes of pincer ligands with terminal N-coordinating groups (NCN) are comparatively less studied, one notable exception being the Phebox type ligand. Herein we report the preparation and characterization of an (NCN)Ir complex that is active for both transfer- and acceptorless alkane dehydrogenation; NCN = (k<sup>3</sup>-2,6-bis(xylylimino)phenyl)iridium. The precursor for catalytic alkane dehydrogenation is the corresponding iridium dihydride acetonitrile complex. The catalyst gives high turnover numbers for acceptorless dehydrogenation of n-dodecane even with a concentration as low as 0.05 mM. Transfer dehydrogenation is also explored. DFT calculations indicate that the catalytic cycle likely proceeds through an Ir(I)/(III) pathway, analogously to (PCP)Ir. In contrast with (PCP)Ir, however, oxidative addition of the alkane C-H bond is calculated to be the rate-determining step.

Studies on alkane dehydrogenation by an (aryldiimine)iridium complex

ACS Spring 2022

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