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

Abstract

Cyclometalation on the substituted imidazo­[1,2-<i>a</i>]­[1,8]­naphthyridine platform involves either the C₃-aryl or C₄′-aryl <i>ortho</i> 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*Ir^III (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