PFEIFFER EFFECT, OUTER-SPHERE COMPLEXATION, AND THE ABSOLUTE-CONFIGURATION OF DISSYMMETRIC COORDINATION-COMPOUNDS

The Pfeiffer Effect is the change in optical rotation of a solution of one enantiomer an optically stable compound (called the “environment” substance) upon the addition of a racemic mixture of an optically labile complex compound. The nature of the Effect is described, along with evidence supporting the “equilibrium displacement” mechanism proposed for the Effect in tris bidentate complexes with carboxylic acid environment compounds. Further, the effect of Pfeiffer activity on the racemization and resolution of dissymmetric complexes is described, along with the application of the Pfeiffer Effect to the determination of absolute configuration of coordination compounds which are both optically active and optically labile. Still further, a proposal to describe the basic nature of the Effect at the molecular level is presented, which utilizes the concept of hydrogen bonding of the environment substance to pi-electron cloud systems of the ligands of the complex. With regard to dissymmetric, optically stable complexes, it has been shown that an interaction occurs between such complexes and environment substances when the latter are present in much higher concentrations than the former. A technique will be described which utilizes this phenomenon to predict the absolute configurations of dissymmetric, optically stable complexes, which is based upon a proposal of “outer-sphere” complexation through hydrogen bonding between the optically active environment substances and the ligands of the complexes. © IUPAC