3 years ago

Dioxidomolybdenum(VI) complexes bearing sterically constrained aroylazine ligands: Synthesis, structural investigation and catalytic evaluation

Dioxidomolybdenum(VI) complexes bearing sterically constrained aroylazine ligands: Synthesis, structural investigation and catalytic evaluation
Seven new dioxidomolybdenum(VI) complexes [MoO2L1(X)].X (1) and [MoO2L2–7(X)] (27) [Where X=EtOH in case of 1 and 5 and X=DMSO in case of 24 and 6, 7] of aroylazines containing a bulky 3-hydroxy-2-naphthoic substituent, were isolated and structurally characterized. The aroylazine ligands H2L1–7 were derived from the condensation of 3-hydroxy-2-naphthoic acid hydrazide with several substituted aromatic aldehydes/ketones. All the synthesized ligands and metal complexes were successfully characterized by elemental analysis, IR, UV–Vis and NMR spectroscopy. X-ray structures of 16 revealed that the ligands coordinate to the metal center as a dibasic tridentate ligand. Cyclic voltammetry of the complexes shows two irreversible reductive responses within the potential window −0.50 to −1.36V, due to MoVI/MoV and MoV/MoIV processes. The synthesized complexes 17 were used as catalysts for the oxidation of benzoin, and for the oxidative bromination of salicylaldehyde, as a functional mimic of haloperoxidase. It was found that the percentage of conversion increased significantly in the presence of catalysts 17 which contained bulky substituents, and showed high percentage of conversion (>90%) with high turnover frequency (>1100h−1) than previously reported catalysts. Benzil, benzoic acid and benzaldehyde-dimethylacetal were formed selectively for the oxidation of benzoin. Formation of 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde took place during the oxidative bromination of salicylaldehyde in presence of H2O2 asan oxidant and therefore 17 act as functional models of vanadium dependent haloperoxidases.

Publisher URL: www.sciencedirect.com/science

DOI: S0020169317310472

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