Stereochemically inert and positively charged chiral complexes of Co III prepared from Schiff bases derived from chiral diamines and salicylaldehydes were shown to be efficient catalysts of the asymmetric phase transfer benchmark reaction of alkylation of O'Donnell's substrate with alkyl halides. The enantiomeric purities of the reaction products were up to 92%.

Stereochemically inert cationic cobalt(III) complexes were shown to be one-component catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa carbon dioxide pressure. The optimal catalyst possessed an iodide counter anion and could be recycled. A catalytic cycle is proposed in which the ligand of the cobalt complexes acts as a hydrogen-bond donor, activating the epoxide towards ring opening by the halide anion and activating the carbon dioxide for subsequent reaction with the halo-alkoxide. No kinetic resolution was observed when terminal epoxides were used as substrates, but chalcone oxide underwent kinetic resolution.

Stereochemically inert and positively charged chiral complexes of cobalt(III) prepared from Schiff bases derived from chiral diamines and salicylaldehydes were shown to be efficient catalysts of the benchmark asymmetric phase‐transfer Michael addition of nine activated olefins to O’Donnell’s substrate. The reaction products had enantiomeric purities of up to 96%. DFT calculations were invoked to rationalize the stereochemistry of the addition.magnified image

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Stereochemically inert and positively charged chiral complexes of Co(III) were shown to catalyze the asymmetric epoxidation of chalcones with H 2 O 2 under phase transfer conditions. The reaction products had enantiomeric purities of up to 55%. It was also shown that complex 1a Icatalyzed the coupling reaction of a resulting epoxide with CO 2 (conversion 72%).Enantiomerically enriched α,β-epoxy ketones are versatile chiral building blocks for access to natural compounds and drugs in medicinal chemistry. 1,2 They can be converted into many types of useful chiral compounds, such as αhydroxy, β-hydroxy, α,β-dihydroxy carbonyl compounds, as well as epoxy alcohols. 3 The basic method of producing the enantiomerically enriched epoxy ketones is the asymmetric oxidation of activated olefins. 4 By far the most attractive method for the preparation of epoxy ketones is asymmetric epoxidation of chalcones. 5 A green and most cost effective approach is to use hydrogen peroxide as the oxidizing agent, 4e because the only by-products of the reaction is are water and molecular oxygen. The catalytic protocols usually employ either chiral metal complexes of iron 6 and manganese 7 or chiral organocatalysts, in particular, those operating under phase transfer conditions. 8 Recently we successfully elaborated chiral, positively charged, stereochemically inert complexes of Co(III) as chiral phase transfer catalysts for efficient asymmetric alkylation of a glycine Schiff base ester (O'Donnell substrate) with alkyl halides. 9a In addition, the family of the complexes could be successfully applied for the asymmetric 1,4-addition of O'Donnell's substrate to activated olefins. 9b The convincing evidence was put forward proving the complexes functioned in the reactions as "organic catalysts in disguise". 10 We believed further attempts at employing the catalysts in classical asymmetric reactions of C-C formation could be of interest.Herein we describe the use of octahedral stereochemically inert and positively charged "chiral-at-metal" Co(III) complexes 9 (depicted on Fig. 1) of both Λ− and Δ-configurations. The complexes were used as catalysts for the asymmetric epoxidation of chalcones under phase-transfer conditions and some preliminary results on the CO 2 coupling with the forming epoxides, promoted by the same complexes.

An overview about the principles, applications and perspectives on the catalytic use of chiral metal-templated complexes that operate as “chiral organocatalysts in disguise” is presented.

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The covalent immobilization of a chiral-at-metal biscyclometalated iridium(III) catalyst on a solid support is reported, and its catalytic activity has been investigated. As a catalyst immobilization strategy, a catalyst precursor was tethered to polystyrene macrobeads through an ester or amide linkage and subsequently converted to the immobilized active chiral Lewis acid by treatment with a Brønsted acid. The amide-linked catalyst displays high robustness and can be recycled multiple times without deterioration of enantioselectivity and only a gradual loss of catalytic activity. Chiral Lewis acid activity was demonstrated as an example for the enantioselective Friedel−Crafts alkylation of indole with an α,β-unsaturated 2-acyl imidazole and for the enantioselective Diels−Alder reactions of an α,β-unsaturated 2-acyl imidazole with 2,3-dihydrofuran or isoprene.