N‐(Aryl)picolinamide Complexes of Ruthenium: Usual Coordination and Strategic Cyclometalation

Abstract

AbstractReaction of five N‐(4‐R‐phenyl)picolinamides (R = OCH3, CH3, H, Cl, and NO2) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2‐methoxyethanol in the presence of a base (NEt3) affords two geometrical isomers of a group of complexes (1‐R and 2‐R), each of which contains an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphanes, a carbonyl, and a hydride. Similar reaction of N‐(naphthyl)picolinamide with [Ru(PPh3)2(CO)2Cl2] affords an organometallic complex, 3, in which the amide ligand is coordinated to the metal center, by C–H activation of the naphthyl ring at the 8‐position, as a dianionic tridentate N,N,C donor along with two triphenylphosphanes and one carbonyl. Structures of the 1‐OCH3, 2‐CH3, and 3 complexes have been determined by X‐ray crystallography. In all the complexes the two triphenylphosphanes are trans. In the 1‐R complexes the hydride is trans to the pyridine nitrogen and in the 2‐R complexes it is trans to the amide‐nitrogen. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a RuII–RuIII oxidation within 0.71–0.93 V versus SCE. An oxidation and a reduction of the coordinated amide ligand are also observed within 1.29–1.69 V versus SCE and –1.02 to –1.21 V versus SCE respectively.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)