Synthesis and characterization of a Zn(II) complex of a pyrazole-based ligand bearing a chiral l-alaninemethylester

Abstract

Reaction of ZnCl 2 with a new ligand N, N-bis(3,5-dimethylpyrazolylmethyl)- l-alaninemethylester (bdmpame) in methanol gives [ZnCl 2(bdmpame)]. The structure of [ZnCl 2(bdmpame)]·CH 2Cl 2 has been resolved by X-ray crystallographic analysis. The Zn atom has a distorted tetrahedral geometry involving a nitrogen atom from each pyrazole in bdmpame and two chloro ligands with bond lengths in the range 2.037(4)–2.237(2) Å. The nitrogen atom of the l-alaninemethylester group in the compound was not coordinated to the metal center, giving an eight-membered ring in which the nitrogen atoms of each pyrazole in bdmpame are coordinated to the metal center. The results of the catalytic enantioselective reduction of acetophenone promoted by ligand/Zn(OTf) 2=1:1 mole ratio in the presence of catecholborane for 48 h at 0°C gives ( S)-(−)-1-phenylethanol in 21% ee with 68% yield.