Post-Modification of Octahedral Chiral-at-Metal Cobalt(III) Complexes by Suzuki-Miyaura Cross-Coupling and Evaluation of Their Catalytic Activity

A family of well-defined lambda- and delta-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-cou-pling 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 (delta(R,R)-1 and lambda(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.