Asymmetric Catalysis with Heterobimetallic Compounds

Abstract

This review focuses on a new concept in catalytic asymmetric reactions that was first realized for the use of heterobimetallic complexes. As these heterobimetallic complexes function as both a Brernsted base and as a Lewis acid, just like an enzyme, they make possible a variety of efficient catalytic asymmetric reactions. This heterobimetallic concept should prove to be applicable to a variety of new asymmetric catalyses. The first part of this review describes the development of rare earth-alkali metal complexes such as LnM,tris(binaphthoxide) complexes (LnMB, Ln = rareearth metal, M = alkali metal), which are readily prepared from the corresponding rare-earth trichlorides or rareearth isopropoxides, and their application to catalytic asymmetric synthesis. By using a catalytic amount of LnMB complexes several asymmetric reactions proceed efficiently to give the corresponding desired products in up to 98 % ee: LnLB-catalyzed asymmetric nitroaldol reactions (L = Li), LnSBcatalyzed asymmetric Michael reactions (S = Na), and LnPB-catalyzed asymmetric hydrophosphonylations of either imines or aldehydes (P = K). Applications of these heterobimetallic catalysts to the syntheses of several biologically and medicinally important compounds are also described. Spectral analyses and computational simulations of the asymmetric reactions catalyzed by the heterobimetallic complexes reveal that the two different metals play different roles to enhance the reactivity of both reaction partners and to position them. From mechanistic considerations, a useful activation of the heterobimetallic catalyses was realized by addition of alkali metal reagents. The second part describes the development of another type of heterobimetallic catalysts featuring Group 13 elements such as A1 and Ga as the central metal. Among them, the AILibis(binaphthoxide) complex (ALB) is an effective catalyst for asymmetric Michael reactions, tandem Michael -aldol reactions, and hydrophosphonylation of aldehydes.

Synthesis, Characterization, Antioxidant Activities, and DNA-Binding Studies of (<i>E</i>)-<i>N</i>&prime;-[1-(Pyridin-2-yl)ethylidene]isonicotinohydrazide and Its Pr(III) and Nd(III) Complexes

“…[4][5][6] However, there have been only a few DNA-binding investigations of such complexes have been relatively few. Because the interaction between metal complexes and DNA is closely related to their potential biological and pharmaceutical activities, studies on the DNAbinding of metal complexes are very important in the development of new therapeutic reagents and DNA molecular probes.…”

Development of Chiral Thiourea Catalysts and Its Application to Asymmetric Catalytic Reactions

“…However, their application to enantioselective reactions was somewhat limited in the early stage, because thioureas are weaker acids than metallic Lewis acids. In 2003, we first introduced a chiral bifunctional thiourea bearing a tertiary amino group, 74,75) by which a wide range of asymmetric reactions were dramatically promoted with high enantioselectivity on the basis of the dual-activation protocol [76][77][78][79][80] of electrophile and nucleophile. In this review, we provide a comprehensive overview of our recent studies on bifunctional thiourea-mediated asymmetric nucleophilic reactions.…”

Kinematic molecular manufacturing machines

“…The binding interactions employed are typically dynamic in character, such as hydrophobic-hydrophilic interactions. Reviews of such catalysts are available [50][51][52][53].…”