A Highly Stable Adamantyl-Substituted Pincer-Ligated Iridium Catalyst for Alkane Dehydrogenation

The adamantyl-substituted pincer-ligand precursor (Ad)PCP-H [((Ad)PCP = kappa(3)-C(6)H(3)-2,6-(CH(2)PAd(2))(2)); Ad = 1-adamantyl] has been synthesized by the reaction of 1,3-dibromoxylene with di-1-adamantylphosphine in the presence of triethylamine. Treatment of (Ad)PCP-H with [Ir(COD)Cl](2) (COD = 1,5-cyclo-octadiene) affords the pincer-ligated complex ((Ad)PCP)IrHCl, which was crystallographically characterized. Dehydrohalogenation of ((Ad)PCP)lrHCl either with LiBEt(3)H or with KO(t)Bu, under hydrogen atmosphere, yields the hydrides ((Ad)PCP)IrH(2) and ((Ad)PCP)lrH(4). ((Ad)PCP)lrH(2) catalyzes dehydrogenation of alkalies with a level of activity comparable to that of the previously reported ((tBu)PCP)IrH(2), while it is thermally much more robust than the (tBu)PCP analogue, as well as (iPr)PCP or (tBu)POCOP pincer complexes.