Comparison of Reactivity and Enantioselectivity between Chiral Bimetallic Catalysts: Bismuth–Rhodium- and Dirhodium-Catalyzed Carbene Chemistry

Abstract

This paper describes the influence of replacement of one of the rhodium atoms by bismuth in a chiral dirhodium tetracarboxylate catalyst on asymmetric induction in the cyclopropanation and C–H functionalization chemistry of trichloroethyl aryldiazoacetates. The chiral ligand used in this study is S-tert-butylsulphonylprolinate (S-TBSP), which was used in the first highly enantioselective dirhodium tetracarboxylate catalyst. Even though the replacement of a Rh atom with a Bi atom has changed the electronic properties of the system, the RhBi complexes have several similarities to the corresponding Rh2 catalysts, with regard to their reactions with donor/acceptor carbenes. The asymmetric induction with RhBi(S-TBSP)4 is very similar to that achieved with Rh2(S-TBSP)4. The major differences between the two systems are the rates of reactions with the Rh2 complexes reacting much faster, and the scope of the C–H functionalization with Rh2 complexes capable of catalyzing reactions with a much wider range of substr...