Cyclometalated ruthenium(II) carbonyl complexes containing 2-(biphenylazo)phenolate ligands: Synthesis, structure, DFT study and catalytic activity towards oxidation and transfer hydrogenation

摘要

2-(Biphenylazo)phenol ligands with various functional groups at the para-position of the phenol moiety (R = CH3, H2L1; R = OCH3, H2L2; R = (CH3)(3)C, H2L3; R = Cl, H2L4) readily undergo, upon reaction with [RuHCl (CO)(EPh3)(3)] (E = P, As) in toluene, cyclometalation via a C-H bond activation at the ortho-position to afford complexes of general formula [Ru(L)(CO)(EPh3)(2)] (E = P, L= L-1, 1; E= P, L= L-2, 2; E= P, L= L-3, 3; E = P, L = L-4 , 4; E = As, L = L-1, 5; E = As, L = L-2, 6; E = As, L = L-3, 7; E = As, L = L-4, 8). The molecular structure of five complexes has been determined by single-crystal X-ray structure analysis. In each complexes, the 2-(biphenylazo)phenol ligand is coordinated to the metal center as a di-anionic tridentate CNO-ligand with two triphenylphosphine/triphenylarsine in the axial positions along with one carbonyl group in the plane of the CNO- ligand. These new cyclometalated 2-(biphenylazo)phenolate complexes show intense absorption in the visible and ultraviolet regions and the nature of these transitions has been analyzed by TD-DFT calculations. The redox behavior of the complexes was also studied by cyclic voltammetry, revealing an irreversible reduction of the metallic center. The cyclometalated ruthenium(II) complexes were used as catalysts for oxidation and transfer hydrogenation reactions and they were found to be active catalysts. (C) 2018 Elsevier B.V. All rights reserved.