Spectral and redox models for blue copper proteins: copper(II) complexes of β-diketonimines from a Knoevenagel condensate

Abstract

Low molecular weight and low symmetric solid copper complexes have been synthesised, in an attempt to simulate the spectral and redox properties of blue copper proteins, in a template manner via an unisolable ligand system. The Knoevenagel condensate, 3-salicylideneacetylacetone (salac: C 12H 12O 3), reacts with the primary amines, aniline, p-Cl-aniline, and methyl amine and copper salts in an in situ manner, producing neutral copper complexes. The complexes thus synthesised are: ( A) Cusalac(aniline) 2Br 2, ( B) Cusalac(aniline) 2Cl 2, ( C) Cusalac(p-Cl-aniline) 2Br 2, ( D) Cusalac(MeNH 2) 2Cl 2, ( E) Cusalac(aniline) 2(OAc) 2, and ( F) Cusalac(MeNH 2) 2(OAc) 2. The ethanolic solution of A exhibits high extinction value (3000 M −1, cm −1 (Type I) and the acetonitrile solution of D has normal extinction value of 100 M −1, cm −1 (Type II). The copper hyperfine data (cm −1) and reduction potential (vs Ag/AgCl) of A ( A ‖=0.0115 and E 1/2=+605 mV) and B ( A ‖=0.0117 and E 1/2=+595 mV) correspond well with typical blue copper protein models. But the complex E ( A ‖=0.0177 and E 1/2=−555 mV) and F ( A ‖=0.016 and E 1/2=−910 mV) widely deviate from the model systems.