Insertion of a Hydroxido Bridge into a Diphenoxido Dinuclear Copper(II) Complex: Drastic Change of the Magnetic Property from Strong Antiferromagnetic to Ferromagnetic and Enhancement in the Catecholase Activity

Abstract

A diphenoxido-bridged dinuclear copper(II) complex, [Cu(2)L(2)(ClO(4))(2)] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu(2)L(2)(OH)]ClO(4) (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu···Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k(cat) = 233.4 h(-1)) than compound 1 (k(cat) = 93.6 h(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.

Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols

“…However, there are only few model systems which follow this pathway [138][139][140][141]. Most designed complexes that catalytically perform catechol oxidation are known to perform the oxidation through alternate pathway which involves production of quinone along with H 2 O 2 rather than water [24,[34][35][36]52,53,76,140,[142][143][144][145]. Presence or absence of hydrogen peroxide as end product in our cases were tested by using KI solution and Horse Radish Peroxidase [53,140] and also using potassium titanium(IV) oxalate [97,98].…”

“…15%, suggesting that peroxo intermediate is generated which may get consumed by the metal center. Though there are a few Cu II model complexes, which report the production of water during oxidation of DTBC but the predictions were made without any experimental evidences [103,138] [24,[34][35][36]52,53,140], in the protein active site it is known to generate water [21,103].…”

Synthesis, Characterisation and Magnetic Properties of Binuclear Copper (II) Complexes with Aliphatic Diamide Bridge

“…Earlier, it was discussed that spin exchange between two copper (II) centers depends on the energy of the interacting orbitals and on the variation in geometrical parameters such as metalligand bond length, M-L-M bridging angle, dihedral angle between the metal coordination plane and the degree of planarity of the bridging unit [13][14][15][16][17][18]. In order to examine this, systematic variations have been made in the non bridging ligand in the complexes.…”

A polynuclear and two dinuclear copper(II) Schiff base complexes: Synthesis, characterization, self-assembly, magnetic property and DFT study

“…bridged complexes of transition metals have attracted the attention of coordination chemists for their potential application in bioinorganic modelling chemistry [10], magnetic materials [11][12] and catalysis [13].…”