An investigation into the unusual Linkage isomerisation and nitrite reduction activity of a novel Tris(2-pyridyl) copper complex

The copper-containing nitrite reductases are a class of enzymes that mediate the reduction of nitrite to nitric oxide in biological systems. Metal-ligand complexes that reproduce the salient features of the active site of copper-containing nitrite reductases are therefore of fundamental interest, both for elucidating the possible mode of action of the enzymes and for developing biomimetic catalysts for nitrite reduction. Herein, we describe the synthesis and characterisation of a new tris(2-pyridyl) copper complex ([Cu1(NO2)2]) that binds two molecules of nitrite, and displays all three of the common binding modes for NO2−, with one nitrite bound in a κ2-ONO manner and the other bound in a monodentate fashion with linkage isomerism between the κ1-ONO and κ1-NO2 binding modes. We use density functional theory to help rationalise the presence of all three of these linkage isomers in one compound, before assessing the redox activity of [Cu1(NO2)2]. These latter studies show that the complex is not a competent nitrite reduction electrocatalyst in non-aqueous solvent, even in the presence of additional proton donors, a finding which may have implications for the design of biomimetic catalysts for nitrite reduction.