Copper(I) nitro complex with an anionic [HB(3,5-Me2Pz) 3]- ligand: A synthetic model for the copper nitrite reductase active site

Article abstract of DOI:10.1021/ic300932a

The new copper(I) nitro complex [(Ph₃P)₂N][Cu(HB(3,5- Me₂Pz)₃)(NO₂)] (2), containing the anionic hydrotris(3,5-dimethylpyrazolyl)borate ligand, was synthesized, and its structural features were probed using X-ray crystallography. Complex 2 was found to cocrystallize with a water molecule, and X-ray crystallographic analysis showed that the resulting molecule had the structure [(Ph₃P) ₂N][Cu(HB(3,5-Me₂Pz)₃)(NO₂)] ·H₂O (3), containing a water hydrogen bonded to an oxygen of the nitrite moiety. This complex represents the first example in the solid state of an analogue of the nitrous acid intermediate (CuNO₂H). A comparison of the nitrite reduction reactivity of the electron-rich ligand containing the CuNO₂ complex 2 with that of the known neutral ligand containing the CuNO₂ complex [Cu(HC(3,5-Me₂Pz) ₃)(NO₂)] (1) shows that reactivity is significantly influenced by the electron density around the copper and nitrite centers. The detailed mechanisms of nitrite reduction reactions of 1 and 2 with acetic acid were explored by using density functional theory calculations. Overall, the results of this effort show that synthetic models, based on neutral HC(3,5-Me₂Pz)₃ and anionic [HB(3,5-Me₂Pz) ₃]^- ligands, mimic the electronic influence of (His) ₃ ligands in the environment of the type II copper center of copper nitrite reductases (Cu-NIRs).