Hydrogen bond donors (HBD) are a sustainable privileged class of catalysts which are broadly used for the activation of compounds in synthetic chemistry. Among them, the metal-templated HBD complexes present...

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.

Here we report the first synthesis of two diastereomeric cationic octahedral Co­(III) complexes based on commercially available (R,R)-1,2-diphenylethylenediamine and salicylaldehyde. Both diastereoisomers with opposite chiralities at the metal center (Λ and Δ configurations) were prepared. The new Co­(III) complexes possessed both acidic hydrogen-bond donating (HBD) NH moieties and nucleophilic counteranions and operate as bifunctional chiral catalysts for the challenging kinetic resolution of terminal and disubstituted epoxides by the reaction with CO2 under mild conditions. The highest selectivity factor (s) of 2.8 for the trans-chalcone epoxide was achieved at low catalyst loading (2 mol %) in chlorobenzene, which is the best achieved result currently for this type of substrate.

The metal-templated hydrogen bond donors (HBD) are prospective catalytic systems for the activation of organic molecules in chemical reactions. Here we report the application of the chiral cationic Co(III) complexes based on commercially available (S,S)-1,2-diaminocyclohexane and (R,R)-1,2-diphenylethylendiamine and salicylaldehydes with an iodide counter-anion as bifunctional one-component hydrogen bond donor/nucleophilic catalysts for the conversion of carbon dioxide with epoxides into valuable cyclic carbonates under solvent-and co-catalyst free conditions. We demonstrated that (R,R)-1,2-diphenylethylendiamine based complex Λ(R,R)-2 is superior to (S,S)-1,2-diaminocyclohexane based Δ(S,S)-1 a catalyzing the reaction at ambient conditions (RT and 1 bar CO 2 ). The TON and TOF values of 850 and 35 h À 1 , respectively, were achieved at low catalyst loading (0.1 mol %) at 10 bars of CO 2 and 100 °C. Furthermore, the Co(III) complexes catalyzed the reaction with diluted air/CO 2 mixture (15 vol % of CO 2 ) producing the desired styrene carbonate in up to 75% yield. A plausible catalytic cycle consistent with all experimental observations was proposed based on DFT calculations. The DFT calculations elucidated the difference in the ring opening step in cases of propylene oxide and styrene oxide. In addition, the kinetic resolution of terminal epoxides was observed with selectivity factor (s) of up to 1.6 in case of the complex Λ(R,R)-2.

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