Mixed cobalt(III) complexes with aromatic amino acids and diamine. Part IV. Influence of noncovalent intraand interligand interactions on rotamer population of the S-phenylalaninato and S-tyrosinato side groups in (1,2-diaminoethane)bis(S-aminocarboxylato

Abstract

Rotamer population of S-tyrosinato and S-phenylalaninato ligands side groups in diastereomers of (1,2-diaminoethane)bis(S-aminocarboxylato)cobalt(III) complexes is calculated by vicinal alpha and beta proton coupling constant analysis. The effect of noncovalent intra- and interligand interactions on the population of rotamers in D2O solution is discussed. It has been established that in all the complexes investigated the most abundant is rotamer t, in which aromatic voluminous moiety and carboxylic group are in an anti position. In almost all complexes the lowest content is of rotamer g, in which these two groups are in the nearest position. Relatively high population of rotamer b in complex 5 tyr, in spite of high steric hindrances, is due to intra- and interligand NH... pi interactions.