Trinuclear copper and mononuclear nickel complexes of oxime containing Schiff bases: Single crystal X-ray structure, catecholase and phenoxazinone synthase activity, catalytic study for the homocoupling of benzyl amines

Abstract

Here we report the synthesis and characterisation of one trinuclear copper complex, [Cu3L3O]ClO4 (1), and one nickel complex, [Ni(L′H)2(dmso)2](ClO4)2) (2), with the Schiff base ligands (3Z)-3-((Z)-(1-(thiophen-2-yl)ethylidene)hydrazono)butan-2-one oxime (LH) and 1-(pyridin-2-yl)ethylidene)hydrazono)butan-2-one oxime (ĹH). Single crystal X-ray structures have been described for the ligand LH and the complexes 1 and 2. 1 shows high catecholase activity (kcat = 8.14 × 102 h−1 in MeOH) using 3,5-di-tert-butylcatechol as the substrate in methanol medium. 2 shows phenoxazinone synthase activity with a moderate value of kcat = 63.11 h−1 in dimethyl sulfoxide. This is the first report for phenox-azinone synthase activity by a nickel complex containing a ligand with oxime functionality. 1 has also been tested as a catalyst for the synthesis of benzylimine and substituted benzylimines from the corresponding amines. Substrates with electron withdrawing halo-substituted benzylamines undergo quantitative conversions to the corresponding benzylimines, whereas electron donating groups on the aromatic ring yielded lower conversions.