Unprecedented copper(ii)-assisted acetal formation of a formyl-substituted bispyrazole. The X-ray structures of copper[1,2-bis(3′-dimethoxymethylpyrazol-1′-yl)ethane] dichloride and dibromide

Abstract

The formation of two new acetal-containing ligands 1,2-bis(3′-dimethoxymethylpyrazol-1′-yl)ethane (bdmpe) and 1,2-bis(3′-diethoxymethylpyrazol-1′-yl)ethane (bdepe) in a Cu(II)-assisted alcoholysis of the initial ligand 1,2-bis(3′-formylpyrazol-1′-yl)ethane is described. The new ligands form polymeric complexes with Cu(II) salts of the general formula [Cu(L)X₂]_x, where L = bdmpe or bdepe, and X = Cl or Br. The single-crystal X-ray structures of [Cu(bdmpe)Cl₂]_x and [Cu(bdmpe)Br₂]_x show that two of the four oxygen atoms of the acetal fragments are axially semi-coordinated to the copper(II) ions, adjusting the coordination sphere around the metal ion to a very distorted octahedron. The coordination of the oxygen atoms of the acetal groups to the metal ion may well be the driving force for the transformation of the initial aldehyde groups into the acetal fragments. The equatorial plane in [Cu(bdmpe)Cl₂]_x is a trans-CuN₂Cl₂ chromophore, while in [Cu(bdmpe)Br₂]_x it is a cis-CuN₂Br₂ species with a large in-plane distortion.