Complexation of selenomethionine and its derivatives with some dimeric rhodium(II) tetracarboxylates: 1H and 13C nuclear magnetic resonance spectroscopy

Abstract

Complexation of three dimeric rhodium(II) tetracarboxylates: tetraacetylate, tetrakistrifluoroacetylate and optically pure rhodium(II) Mosher's acid derivative, with selenomethionine, the methyl ester of selenomethionine and its N-phthaloyl and N-formyl derivatives, have been investigated by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Studies were performed using the NMR titration procedure, in D2O or CDCl3 solution depending on the solubility of substrates and ligands. In the presence of rhodium substrate, ligands formed subsequently 1:1 and 1:2 complexes, consisting of one dirhodium moiety and one or two ligand molecules, respectively. The parameter complexation shift Δδ, defined as a difference between the chemical shift of a nucleus in a complex and corresponding chemical shift in the free ligand, varied from −0.3 to +0.6 ppm (1H) and from −3.3 to +5.4 ppm (13C). Complexation shift pattern indicated the complexation via the selenium atom. For chiral substrate and racemic ligands, diastereomeric dispersions Δν(1H) reached the value up to 140 Hz.