Mixed azido/phenoxido bridged trinuclear Cu() complexes of Mannich bases: Synthesis, structures, magnetic properties and catalytic oxidase activities

• Published in: Dalton transactions : an international journal of inorganic chemistry 2018-07, Vol.47 (28), p.9385-9399
• Main Authors: Das, Avijit, Bhattacharya, Kisholoy, Das, Lakshmi Kanta, Giri, Sanjib, Ghosh, Ashutosh
• Format: Article
• Language: English
• Subjects: Aminophenol; Antiferromagnetism; Catalysis; Chemical synthesis; Hydrogen peroxide; Ligands; Magnetic permeability; Magnetic properties; Oxidation; Single crystals; Sodium azides; X-ray diffraction
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt01400k

Three similar Mannich base ligands viz . N , N -bis(3,5-dimethyl-2-hydroxybenzyl)- N ′, N ′-dimethyl-1,3-diaminopropane (H 2 L 1 ), N , N -bis(3,5-dimethyl-2-hydroxybenzyl)- N ′, N ′-dimethyl-1,2-diaminoethane (H 2 L 2 ) and N , N -bis(3,5-dimethyl-2-hydroxybenzyl)- N ′, N ′-diethyl-1,2-diaminoethane (H 2 L 3 ) upon reaction with Cu(CH 3 COO) 2 ·H 2 O produced dinuclear complexes [Cu 2 L 2 1-3 ]. The reaction of each of these isolated dimeric species with Cu(ClO 4 ) 2 ·6H 2 O and NaN 3 resulted in three new trinuclear complexes, [(CuL 1 ) 2 (μ 1,1 -N 3 ) 2 Cu(H 2 O)]·CH 3 OH ( 1 ), [(CuL 2 ) 2 (μ 1,1 -N 3 ) 2 Cu(H 2 O)]·CH 3 OH ( 2 ) and [(CuL 3 ) 2 (μ 1,1 -N 3 ) 2 Cu(H 2 O)]·2CH 3 OH ( 3 ), respectively. The complexes ( 1-3 ) have been characterized by elemental analysis and single crystal X-ray diffraction. In all three complexes, the central Cu( ii ) ion is coordinated by two terminal [CuL] units through a phenoxido and an azido bridge. These are the first trinuclear Cu( ii ) complexes of this type of Mannich base ligands. Magnetic susceptibility measurements showed intramolecular antiferromagnetic interactions with J = −64.42, −9.60 and −4.54 cm −1 for 1 , 2 and 3 , respectively. All three complexes exhibited catecholase-like and phenoxazinone synthase-like activities towards the aerobic oxidation of 3,5-di- tert -butylcatechol and o -aminophenol, respectively. The turnover numbers ( k cat ) for the aerobic oxidation of 3,5-di- tert -butylcatechol are 568.8, 542.1 and 500.4 h −1 and those of o -aminophenol are 125.83, 118.9 and 114.7 h −1 for complexes 1-3 , respectively. The X-band EPR spectroscopy and estimation of the produced hydrogen peroxide indicated that the aerobic oxidation of 3,5-di- tert -butylcatechol proceeded through the formation of a semiquinonate radical. The mechanism of phenoxazinone synthase-like activities is also proposed for trinuclear Cu( ii ) catalysts with the help of mass spectral analysis. Three mixed azido/phenoxido bridged trinuclear Cu( ii ) complexes of tetradentate Mannich base ligands, synthesised by a metalloligand approach show antiferromagnetic coupling and significant catecholase and phenoxazinone synthase like activities.