A family of well-defined Λ- and Δ-configured octahedral cationic chiral-at-cobalt catalysts were expanded through a straightforward postcomplexation of the bromine-functionalized Co(III) complexes based on (R,R)-1,2-cyclohexanediamine and (S,S)-1,2-diphenylethylenediamine by Suzuki–Miyaura cross-coupling reaction (CCR) with arylboronic acids. The corresponding modified Co(III) complexes were isolated by standard silica column chromatography with up to 65% yields. Indeed, it is the first example of the direct modification of the ligand sphere of chiral Co(III) catalysts through Suzuki–Miyaura CCR. It was observed for the first time that the chiral metal center is epimerized during the cross-coupling process at the transmetalation stage on palladium catalyst in the case of minor diastereomers of Co(III) complexes (Δ(R,R)-1 and Λ(S,S)-2). Next, the efficacies of obtained chiral metal-templated complexes 1–4 were evaluated in benchmark asymmetric reactions in order to compare their catalytic activity. Chiral Co(III) complexes 1–4 have been examined as hydrogen bond donor (HBD) catalysts in such important reactions as epoxidation of chalcone and the fixation of CO2 into valuable cyclic carbonates.

Chiral metal-templated complexes are attractive catalysts for organic synthetic transformations. Herein, we introduce a novel chiral cobalt(III)-templated complex based on chiral trans-3,4-diamino-1-benzylpyrrolidine and 3,5-di-tert-butyl-salicylaldehyde which features both hydrogen bond donor and Brønsted base functionalities. The obtained complexes were fully characterized by 1H, 13C NMR, IR-, UV-vis, CD-spectroscopy and by a single X-ray diffraction analysis. It was shown that chlorine anion is connected with amino groups of the complex via a hydrogen bonding. DFT calculations of charges and molecular electrostatic potential of the cobalt(III) complex showed that the basicity of the complex is certainly diminished as compared with the routine tertiary amines but the acidity of the conjugated acid of the complex should be increased. Thus, the catalytic potential of the complex may be much greater as a chiral acid than a chiral base. We believe that this work opens a new way in chiral bifunctional catalyst design.

A family of well-defined Λand Δ-diastereomeric octahedral cationic chiral-at-cobalt complexes were obtained by a simple two-step reaction of (R,R)-1,2-diaminocyclohexane, (R,R)-1,2-diphenylethylenediamine, or (S)-2-(aminomethyl)pyrrolidine and substituted salicylaldehydes with a cobalt(III) salt. It was observed for the first time that the use of an excess of cobalt(III) salt provides both the enantiopure Λ and Δ forms of the corresponding cobalt(III) complexes 1 and 2 in a ratio of diastereomers ranging from 1:1.6 to >20:1 (Λ/Δ) and in 31−95% combined yields. The obtained complexes were robust, air-and bench-stable, soluble in most of organic solvents, and insoluble in water. Through variation of the substituents in the phenyl ring of the salicylaldehyde moiety, it was shown that both steric and electronic effects of substituents have a significant impact on the formation of Λ and Δ isomers. Next, the efficacies of the enantiopure metal-templated complexes 1−3 were investigated in three benchmark asymmetric reactions in order to compare their catalytic activity. The chiral cobalt(III) complexes 1−3 were tested as enantioselective hydrogen-bond-donor catalysts in such important reactions as the Michael addition of the O'Donnell substrate to methyl acrylate, epoxidation of chalcone, and trimethylsilylcyanation of benzaldehyde. It was clearly demonstrated that the chirality at the cobalt center has an impact on the stereochemical outcome of the reactions. In particular, the Λ(R,R)-1 and Δ(R,R)-1 complexes acted as "pseudoenantiomeric" catalysts in the epoxidation and trimethylsilylcyanoation reactions, providing both enantiomers of the products with up to 57% enantiomeric excess.Article pubs.acs.org/IC