Bis(benzimidazolyl)amine copper complexes with a synthetic ‘histidine brace’ structural motif relevant to polysaccharide monooxygenases

Abstract

Reaction of Cu2+ salts with the benzimidazole-N-methylated bis[(1-methyl-2-benzimidazolyl)ethyl]amine ligand 2BB results in either bi- or monometallic complexes. Spectroscopic and solid state characterization reveals either square pyramidal or trigonal bipyramidal coordination geometries around the cupric ions. In [{2BBCu(μ-F)}2](BF4)2, the dicopper structure is determined by the bridging nature of the fluoro ligands, which complement the T-shape arrangement of N3 donors provided by 2BB to define a square pyramidal (or capped distorted tetrahedral) coordination geometry. The monocopper complexes 2BBCuCl2 and [2BBCu(H2O)2](OTf)2 are characterized by a trigonal bipyramidal geometry both in solution and in the solid state. In all complexes, the T-shape N3 donor set of 2BB is analogous to the coordination environment of the copper ions provided by a ‘histidine brace’ and an additional histidine imidazole in the active site of polysaccharide monooxygenases.