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

Reaction of five N ‐(4‐ R ‐phenyl)picolinamides (R = OCH 3 , CH 3 , H, Cl, and NO 2 ) with [Ru(PPh 3 ) 2 (CO) 2 Cl 2 ] in refluxing 2‐methoxyethanol in the presence of a base (NEt 3 ) 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(PPh 3 ) 2 (CO) 2 Cl 2 ] 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‐OCH 3 , 2‐CH 3 , 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 1 H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru II –Ru III 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)