Examining the impact of steric and electronic variation in N2S scorpionate ligands on the properties of zinc(II) and cadmium(II) complexes

Abstract A series of LZn(II)Br ( 1 – 4 ) and LCd(II)Cl complexes ( 9 – 11 ) has been prepared by the reaction of metal halide precursors with the lithium salts of the N 2 S − ligands bis(3,5-diisopropylpyrazol-1-yl)dithioacetate (L 1 ), bis(3,5-di- tert -butylpyrazol-1-yl)dithioacetate (L 2 ), N -phenyl-2,2-bis(3,5-diisopropylpyrazol-1-yl)thioacetamide (L 3 ) and N -phenyl-2,2-bis(3,5-di- tert -butylpyrazol-1-yl)thioacetamide (L 4 ). Characterization by X-ray crystallography and DOSY NMR studies indicate that LZnBr complexes 1 – 4 are mononuclear both in the solid state and in solution. Steric differences between ligands L 1 –L 4 result in distortion from an ideal tetrahedral geometry for each complex, with the degree of distortion depending on the bulk of the ligand substituents. In contrast, the related complex L 3 CdCl was shown by X-ray crystallography to dimerize in the solid state to form the chloride-bridged five-coordinate complex [L 3 CdCl] 2 ( 10 ). Despite 10 having a dinuclear structure in the solid state, DOSY NMR studies indicate 9 – 11 exist as mononuclear LCdCl species in solution. In addition, Zn(II) cyanide complexes of the form LZnCN [L = L 1 ( 5 ), L 3 ( 7 ), L 4 ( 8 )] have been characterized and the X-ray structure of 8 determined. Moreover, density functional theory calculations have been conducted which yield important insight into the bonding in 1 – 4 and 5 – 8 and the electronic impact of ligands L 1 –L 4 on the zinc(II) ion and its ability to function as a Lewis acid catalyst.