AMINO ACID DERIVED TRANSITION METAL COMPLEXES: STRUCTURAL AND CATALYTIC STUDIES.

Abstract

A group of ligands were designed based on a minimalist reduction of the structure of metalloproteins. It was thought that a modular design with facile synthesis could lead to a new family of privileged ligands. Towards this goal a series of tri-, tetra, and penta-dentate ligands were synthesized. The ligands had a common chiral core based on inexpensive amino acid starting materials. A modular diamine backbone was adjusted to control the size, bite angle and electronic nature of the binding pocket. The ligands were capped with Schiff base imines to provide an initial binding point for the metal and to create steric bulk at one face of the complex.The tetra-dentate ligands were shown to efficiently bind zinc(II), copper((II), nickel(II), and palladium(II). In the case of the penta-dentate ligands the series was extended to cobalt(II), manganese(II) and iron(II). The tri-dentate ligands did not form isolated metal complexes. The structures of these complexes were confirmed by NMR, ESR and X-ray crystallography. The chiral copper complexes were applied to a model asymmetric acylation reaction. The results were disappointing as the reactions showed no stereoselectivity.