Cyclometalations on the Imidazo[1,2‑<i>a</i>][1,8]naphthyridine Framework

Cyclometalation on the substituted imidazo­[1,2-a]­[1,8]­naphthyridine platform involves either the C3-aryl or C4′-aryl ortho carbon and the imidazo nitrogen N3′. The higher donor strength of the imidazo nitrogen in comparison to that of the naphthyridine nitrogen aids regioselective orthometalation at the C3/C4′-aryl ring with Cp*IrIII (Cp* = η5-pentamethylcyclopentadienyl). A longer reaction time led to double cyclometalations at C3-aryl and imidazo C5′-H, creating six- and five-membered metallacycles on a single skeleton. Mixed-metal Ir/Sn compounds are accessed by insertion of SnCl2 into the Ir–Cl bond. Pd­(OAc)2 afforded an acetate-bridged dinuclear ortho-metalated product involving the C3-aryl unit. Metalation at the imidazo carbon (C5′) was achieved via an oxidative route in the reaction of the bromo derivative with the Pd(0) precursor Pd2(dba)3 (dba = dibenzylideneacetone). Regioselective C–H/Br activation on a rigid and planar imidazonaphthyridine platform is described in this work.