cis‐Dioxomolybdenum(VI) complexes with unsymmetric linear tetradentate ligands: syntheses,structures and bromoperoxidase activities

Reactions of MoO₂(acetylacetonate)₂], 2‐((2‐(2‐hydroxyethylamino)ethylamino)methyl)‐4‐R‐phenols (H₂Lⁿ, n = 1–5 for R = H, Me, OMe, Cl and Br, respectively) and KOH in 1:1:2 mole ratio in methanol afford a series of complexes having the general formula cis‐MoO₂(Lⁿ)] ( 1 , 2 , 3 , 4 , 5 ) in 81–86% yields. The complexes have been characterized using elemental analysis, spectroscopy (infrared, UV–visible, and ¹H NMR, ¹³C NMR and ¹³C‐DEPT NMR) and electrochemical measurements. The molecular structures of 1 , 2 , 3 , 4 have been determined using single‐crystal X‐ray crystallography. In each of 1 , 2 , 3 , 4 , the ONNO‐donor 6,5,5‐membered fused chelate rings forming (Lⁿ)²⁻ and the two mutually cis oxo groups assemble a distorted octahedral N₂O₄ coordination sphere around the metal centre. In the crystal lattice, each of 1 , 2 , 3 , 4 forms a one‐dimensional infinite chain structure via intermolecular N  H⋅⋅⋅O hydrogen bonding interactions. In cyclic voltammograms, the diamagnetic complexes display an irreversible metal‐centred reduction in the potential range −0.73 to −0.88 V (vs Ag/AgCl). The physicochemical data are consistent with a very similar gross molecular structure for all of 1 , 2 , 3 , 4 , 5 . All the complexes exhibit decent bromoperoxidase activities and are also able to effectively catalyse benzoin and methyl(phenyl)sulfide oxidation reactions. Copyright © 2015 John Wiley & Sons, Ltd.