Selective oxidation of benzyl alcohol catalyzed by ruthenium (III) complexes derived from tridentate mer-ligands having phenolato donor

In this work, four ruthenium complexes [Ru(L1-4)(PPh3)Cl-2](1-4) containing phenolate-imine ligands [L1-4H = condensed product of 2-(1-phenylhydrazinyl)-pyridine with different substituted salicylaldehyde, H = phenolic dissociable proton] were synthesized and characterized by different spectroscopic methods like IR and UV-Visible spectral studies. Solid-state structures of complexes 1 and 2 were determined by single-crystal X-ray diffraction and tridentate coordination of the ligand having NNO donors was observed in a meridional fashion. Structure optimization was performed by density functional theory (DFT) calculations. Time-dependent DFT (TD-DFT) method was utilized to explain and assign UV-Visible absorption bands found for complexes. These complexes were utilized for the oxidation of benzyl alcohol to benzaldehyde. The plausible mechanism for benzyl alcohol oxidation was proposed on the basis of literature. In situ generated Ru-IV=O intermediate obtained in solution in presence of various oxidants viz. H2O2, m-CPBA, TBHP was supposed to be key intermediate for such oxidation. (C) 2019 Elsevier B.V. All rights reserved.