SYNTHESIS WITH CHELATED IMINO CARBOXYLATES - THE INFLUENCE OF CHELATECOLIGANDS ON REACTION PATHWAYS

Synthesis and X-ray crystallography have been used to explore the chem istry 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+. T he latter complex was obtained by an especially facile dehydration of the corresponding beta-phenylserine complex. Significant differences i n both stereo- and regio-selectivity were detected in reactions of the two complexes, and, for the reaction of butenone with [Co(en)2(HNC(CH 3)CO2)]2+, a pathway indetectable in previously studied reactions of t he tetraammine analogue, and leading to a chelate of 4-methyl-5,6-dihy dropyridine-2-carboxylate, was observed to be dominant. Kinetically de termined stereospecificity was evident in the addition of ethyl cyanoa cetate to [Co(en)2(HNC(CH3)CO2)]2+, whereas equilibrium control appear s to exist in the stereoselective addition of nitromethane to both com plexes. Crystal structure determinations on five new complexes have be en used to establish these points and other important aspects of the c hemical syntheses. A considerable number of new imino and amino acids can be derived through the reactions described, and the synthetic util ity of both the tetraammine and bis(ethanediamine) complex ion systems in providing the 'free' organic products has been subjected to prelim inary evaluation through the isolation of t-leucine, N-methyl-2-phenyl glycine, 2-aminomethylalanine, and some vinylglycine derivatives.