Dynamic NMR Studies of Chiral 1,1'-binaphthyl Ligands

Abstract

Chiral monomeric and polymeric binaphthyl ligands have been shown to be highly enantioselective for the asymmetric addition of dialkylzinc and diarylzinc compounds to aldehydes. Previous studies by Pu and coworkers show that differences in efficiencies between monomeric and polymeric ligands hinge on differences in the conformation of the aryl substituents. In order to better understand these chiral binaphthyl ligands, dynamic NMR studies have been undertaken to derive the activation energy and thermodynamic parameters for conformational exchange. Preliminary results give an activation barrier of 6.4 kcal/mol, [delta]H++ value of 6.0 kcal/mol, [delta]S++ value of -21 cal/mol, and [delta]G++ value of 11. 7 kcal/mol at 23 7 K.