Synthesis, structure and catecholase activity study of dinuclear copper(II) complexes†

Abstract

A series of dinuclear copper(II) complexes as models for the type 3 copper protein catechol oxidase were synthesised. They were characterised by spectroscopic, electrochemical, and in some cases, by single-crystal X-ray diffraction studies: [Cu₂(L¹)(OH)(EtOH)(H₂O)][ClO₄]₂·H₂O 1, [Cu₂(L²)(OH)][NO₃]₂2, [Cu₂(L³)(OMe)(MeOH)(ClO₄)]ClO₄3, [Cu₂(L⁴)(OH)(MeOH)₂][BF₄]₂4, [Cu₂(L⁵)(OMe)][ClO₄]₂·2MeOH 5, [Cu₂(L⁶)(OMe)(MeOH)(ClO₄)]ClO₄6 and [Cu₂(L⁷)(OMe)(MeOH)(ClO₄)]ClO₄7 (HL¹ = 4-bromo-2,6-bis(4-methylpiperazin-1-ylmethyl)phenol, HL² = 4-bromo-2,6-bis[(2-pyridylmethyl)aminomethyl]phenol, HL³ = 4-bromo-2,6-bis{[2-(2-pyridyl)ethyl]aminomethyl}phenol, HL⁴ = 4-bromo-2,6-bis{[2-(1-methyl-2-imidazolyl)ethyl]aminomethyl}phenol, HL⁵ = 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[(2-pyridylmethyl)aminomethyl]phenol, HL⁶ = 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-{[2-(2-pyridyl)ethyl]aminomethyl}phenol and HL⁷ = 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-{[2-(1-methyl-2-imidazolyl)ethyl]aminomethyl}phenol). The copper centres are µ-phenoxo bridged by the pentadentate dinucleating ligand and exogenously µ-hydroxo or µ-methanolato bridged. Complex 1 crystallises in P2₁/c with a = 16.913(3), b = 11.046(2), c = 16.617(3) Å, β = 94.06(3)°, U = 3097 ų and Z = 4. Complex 3 crystallises in P2₁/n with a = 10.592(2), b = 12.123(2), c = 24.482(5) Å, β = 92.97(3)°, U = 3139 ų and Z = 4. Complex 4 crystallises in Pbcn with a = 16.043(3), b = 12.689(3), c = 15.810(3) Å, U = 3218 ų and Z = 4. Complex 6 crystallises in P2₁/c with a = 17.889(4), b = 10.401(2), c = 16.269(4) Å, β = 92.94(2)°, U = 3023 ų and Z = 4. Complex 7 crystallises in P2₁/c with a = 17.349(3), b = 8.828(2), c = 19.797(4) Å, β = 94.04(3)°, U = 3025 ų and Z = 4. A catecholase activity study revealed that only complexes 1, 5, 6 and 7 have significant catalytic activity with respect to the aerial oxidation of 3,5-di-tert-butylcatechol. A kinetic treatment on the basis of the Michaelis–Menten model was applied.