Interaction of N-(aryl) picolinamides with iridium.: N-H and C-H bond activations

Reaction of N-(4-R-phenyl) picolinamide (R = OCH3, CH3, H, Cl and NO2) with [Ir(PPh3)(3)Cl] in refluxing ethanol in the presence of a base (NEt3) affords two yellow complexes (1-R and 2-R). The 1-R complexes contain an amide ligand coordinated to the metal center as a monoanionic bidentate N, N donor along with two triphenylphosphines, a chloride and a hydride. The 2-R complexes contain an amide ligand coordinated to the metal center as a monoanionic bidentate N, N donor along with two triphenylphosphines and two hydrides. Similar reaction of N-(naphthyl) picolinamide with [Ir(PPh3)(3)Cl] affords two organometallic complexes, 3 and 4. In complex 3 the amide ligand is coordinated to the metal center, via C-H activation of the naphthyl ring at the 8-position, as a dianionic tridentate N, N, C donor, along with two triphenylphosphines and one chloride. Complex 4 is similar to complex 3, except a hydride is bonded to iridium instead of the chloride. Structures of the 1-OCH3, 2-Cl and 4 complexes have been determined by X-ray crystallography. All the complexes are diamagnetic, and show characteristic H-1 NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ir-III-Ir-IV oxidation within 0.50-1.16 V vs. SCE and a reduction of the coordinated amide ligand within-1.02 to -1.25 V vs. SCE. (C) 2008 Elsevier B. V. All rights reserved.