MOLECULAR MECHANICS STUDIES ON THE LIGAND CONFORMATION OF CHIRAL RUTHENIUM TRIS(2,2'-BIPYRIDINE)-TYPE COMPLEXES

Molecular mechanics (MM) calculations were performed for two chiral ligands, 4,4'-bis[R(or S)-phenylethylamino carbonyl]-2,2'-bipyridine (R(or S)-PhEtbpy) and 4,4'-bis(menthoxycarbonyl)-2,2'-bipyridine (Menbpy) by the MM2PRIME program with several new parameters. These ruthenium complexes have been already found to be efficient catalysts for photochemical and enantioselective electron transfer reactions. The bonded terms in the new parameters were determined by Hopfinger's method with molecular orbital (MO) calculations. The MO calculations were mainly performed with AM1 program, however some torsional parameters were also determined by ab initio MO methods to compare with the results derived by semi-empirical methods. The electrostatic parameters were determined with the AM1 program by using the electrostatic potential (ESP) method. To find the most stable conformation, the contour maps of the strain energy of the chiral ligands were drawn as a function of rotation of the chiral groups, and the favorable conformation obtained was supported by H-1 NMR measurement. The structures of these ruthenium complexes were also discussed on the CD spectra of the complexes and the enantioselectivity of the reaction.