Conformational Studies on Chiral Rhodium Complexes by ECD and VCD Spectroscopy

This article reports vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopic studies in acetonitrile on the chiral Rh-2(O-Phe-Cbz)(1)(OAc)(3) and Rh-2(O-Phe-Ac)(1)(OAc)(3) complexes (abbreviated Rh(2)Z(1) and Rh2Ac1, respectively; Phe, L-phenylalanine; Cbz, benzyloxycarbonyl; Ac, acetyl) supported by theoretical calculations. The ECD spectra of the complexes depend on temperature that indicates the conformational mobility of the chiral ligands. Calculations of the VCD spectra were performed at ab initio (DFT) level of theory using Gaussian 03 [B3LYP functional combined with the LANL2DZ basis set for the dirhodium core and the 6-31G(d) basis set for other atoms]. The population-weighted sums of the computed VCD spectra of the conformers are in excellent agreement with the experimental VCD spectra. The combination of the VCD and ECD spectroscopic methods led us to the structural characterization of the complexes. Chirality 23:294-299, 2011. (C) 2010 Wiley-Liss, Inc.