Mixed-ligand 1,3-diaryltriazenide complexes of ruthenium: Synthesis, structure and catalytic properties

Abstract

Reaction of 1,3-diaryltriazenes (abbreviated in general as HL-R, where H represents the dissociable N–H proton and R is the para substituent (R = OCH3, CH3, H, Cl, NO2) on the aryl fragment) with [Ru(PPh3)2(CO)2Cl2] in 2-methoxyethanol in the presence of a base (NEt3) affords a family of yellow complexes of the type [Ru(PPh3)2(L-R)(CO)(H)], where the 1,3-diaryltriazenes are coordinated as monoanionic bidentate NN-donors. Two triphenylphosphines, a hydride and a carbonyl are also coordinated to ruthenium. The triphenylphosphines are mutually trans, and the hydride and carbonyl are mutually cis. Structure of the [Ru(PPh3)2(L-H)(CO)(H)] complex has been determined by X-ray crystallography. All the complexes show intense absorptions in the visible region, which are assigned, based on DFT calculations, to transitions within orbitals of the triazenide ligand. The complexes exhibit an irreversible oxidation on the positive side of SCE and an irreversible reduction on the negative side. All the complexes are found to efficiently catalyze transfer hydrogenation reactions.