Synthesis of an Organometallic Alkyl-Co(III) Complex with Amidoquinoline Directing Groups via C(sp3)-H Activation and Its UV-vis/NMR Spectroscopic, Crystallographic, DFT, and Electrochemical Studies

The use of earth-abundant and inexpensive Co catalysts for carbon-hydrogen (C-H) bond activation has received increasing attention because of the advantages including air stability. Although directing groups have been effectively introduced in substrates to promote C(sp(3))-H activation through chelation assistance, there is a lack of basic information about the isolated alkyl-Co complexes containing directing groups as polydentate ligands. In this study, we report the synthesis and characterization of an alkyl-Co(III) complex 2Co, prepared from a N,N'-bis(8-quinolyl)malonamide derivative, the malonyl fragment of which was disubstituted by two ethyl groups. 2Co was straightforwardly obtained from a Co(II) salt without any use of chemical oxidants but in the presence of air, through selective beta-C(sp(3))-H activation. The combined NMR spectroscopic and X-ray crystal structural analyses revealed that the malonamide substrate was converted into a pentadentate ligand with an N4C set, acquiring a helical configuration around the Co(III) center. The non-innocent ligand properties of 2Co were unambiguously confirmed by UV-vis spectroscopic, electrochemical, and DFT studies. Thermolysis of 2Co enabled C(sp(3))-N reductive elimination in the absence of chemical oxidants. The present study provides important insights into the reactivity of alkylCo(III) complexes with a defined coordination geometry around the Co center toward designing elaborate C(sp(3))-H functionalization systems.

Automated summary

This study reports the synthesis and characterization of a novel alkyl-Co(III) complex that enables C-H functionalization through C(sp(3))-H bond activation. The complex shows a unique coordination geometry and exhibits good reactivity and stability.