Carboxylate Ligand-Induced Intramolecular C−H Bond Activation of Iridium Complexes with N-Phenylperimidine-Based Carbene Ligands

We report the synthesis and structure of iridium(I) complexes with N,N′-disubstituted perimidine carbene ligands and halides or carboxylate ligands. Iodo-, chloro-, and acetate-Ir(carbene)(cod) complexes were selectively prepared by changing the bases and silver salts. Intramolecular C−H bond activation to prepare a cyclometalated Ir(III) complex, (C∧C:)2Ir(OAc) (6), where C∧C: is a cyclometalated perimidine carbene ligand, was achieved using a carboxylate-ligated iridium complex; otherwise, C−H activation did not proceed. Acetate-Ir(carbene)(cod) (3c) reacted with benzoic anhydride at room temperature to afford benzoate-Ir(carbene)(cod) (3d). A perimidine-carbene- and phenylpyridine-ligated Ir(III) complex, (C∧C:)(C∧N)Ir(OCOR) (8), where C∧N is a cyclometalated phenylpyridine ligand, was isolated in good yield by mixing 3c or 3d and phenylpyridine under reflux in toluene. On the basis of the formation of 1,3-cyclooctadiene from the reaction mixture, we propose the following reaction mechanism for the int...