Examining the Impact of Steric and Electronic Variation in N2S Scorpionate Ligands on the Properties of Zinc(II) and Cadmium(II) Complexes

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A series of LZn(II)Br (14) and LCd(II)Cl complexes (911) has been prepared by the reaction of metal halide precursors with the lithium salts of the N2S ligands bis(3,5-diisopropylpyrazol-1-yl)dithioacetate (L1), bis(3,5-di-tert-butylpyrazol-1-yl)dithioacetate (L2), N-phenyl-2,2-bis(3,5-diisopropylpyrazol-1-yl)thioacetamide (L3) and N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide (L4). Characterization by X-ray crystallography and DOSY NMR studies indicate that LZnBr complexes 14 are mononuclear both in the solid state and in solution. Steric differences between ligands L1–L4 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 L3CdCl was shown by X-ray crystallography to dimerize in the solid state to form the chloride-bridged five-coordinate complex [L3CdCl]2 (10). Despite 10 having a dinuclear structure in the solid state, DOSY NMR studies indicate 911 exist as mononuclear LCdCl species in solution. In addition, Zn(II) cyanide complexes of the form LZnCN [L = L1 (5), L3 (7), L4 (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 14 and 58 and the electronic impact of ligands L1–L4 on the zinc(II) ion and its ability to function as a Lewis acid catalyst.