Synthesis With Chelated Imino Carboxylates: The Influence of Chelate Coligands on Reaction Pathways

Abstract

Synthesis and X-ray crystallography have been used to explore the chemistry of chelates derived from the imines of pyruvic and phenylpyruvic acids held in a chiral environment on cobalt(III) as [Co(en)₂(HNC(CH₃)CO₂)]²⁺ (en = ethane-1,2-diamine) and [Co(en)₂(HNC(CH₂C₆H₅)CO₂)]²⁺. The latter complex was obtained by an especially facile dehydration of the corresponding β-phenylserine complex. Significant differences in both stereo- and regio-selectivity were detected in reactions of the two complexes, and, for the reaction of butenone with [Co(en)₂(HNC(CH₃)CO₂)]²⁺, a pathway indetectable in previously studied reactions of the tetraammine analogue, and leading to a chelate of 4-methyl-5,6-dihydropyridine-2-carboxylate, was observed to be dominant. Kinetically determined stereospecificity was evident in the addition of ethyl cyanoacetate to [Co(en)₂(HNC(CH₃)CO₂)]²⁺, whereas equilibrium control appears to exist in the stereoselective addition of nitromethane to both complexes. Crystal structure determinations on five new complexes have been used to establish these points and other important aspects of the chemical syntheses. A considerable number of new imino and amino acids can be derived through the reactions described, and the synthetic utility of both the tetraammine and bis ( ethanediamine ) complex ion systems in providing the 'free' organic products has been subjected to preliminary evaluation through the isolation of t- leucine , N-methyl-2-phenylglycine, 2-aminomethylalanine, and some vinylglycine derivatives.