Diastereoselective synthesis of the first enantiomerically pure (triazolinylidene)ruthenium(II) and -rhodium(III) chelate complexes

The chloro bridges of the dinuclear complexes [(eta(6)-cymene)RuCl2](2) and [(eta(5)-C5Me5)RhCl2](2) can be cleaved by reaction with an N-phenyltriazolium perchlorate ii) and a base, resulting in the formation of (carbene)metal complexes. In this manner, abstraction of one ortho-proton of the phenyl group and elimination of HCl leads to pseudo-tetrahedral ruthenium (2) and rhodium (3) complexes, thereby creating a stereogenic center at the transition metal. By using enantiomerically pure triazolium perchlorates, the diastereoselective synthesis of these complexes with diastereomeric excesses of up to 95% can be achieved, with the possibility of separating the two diastereomers by column chromatography The relative, and therefore also the absolute configuration of the ruthenium complex (R-Rn)-2b could be determined by X-ray structure analysis. A stereospecific substitution of chlorine by iodine or acetonitrile to form the diastereomerically pure complexes 4, 5 and 6 (the latter as cationic ruthenium complexes) allows a further variation of the ligands.