Azothioformamides (ATFs) are redox active ligands with the unique ability to coordinate and dissolve various transition metals through a 1,3-azothiocarbonyl heterodiene moiety. ATF ligands have potential for the recycling of waste metals into useful catalysts. UV-Vis titration experiments along with computational studies using copper(I) salts revealed that by modifying the electronics of the system, the redox-activity and binding association of the ligand is affected. Relative association strength is higher for electron donating species and lower for electron withdrawing para-substituted compounds. ATF ligands rapidly coordinate with zerovalent copper and copper(I)salts yielding many unique complexes. ATF-Cu(I) complexes were found to act catalytically to effectively transform terminal alkynes to propiolic acids in the presence of base and 1 atm CO2 at 40 °C. Sixteen different ATF-Cu(I) complexes were evaluated as well as various bases, solvents, and temperatures. The N,N-diethyl-para-methoxyphenyl-azothioformamide Cu(I)I complex with cesium carbonate and dimethyl sulfoxide was found to be most efficient system to produce propiolic acid in good to excellent yields with high functional group tolerance. Supercritical carbon dioxide as a building block and carbon dioxide insertion reactions in sp2 C-H alkenes and sp3 C-X alkyl halides are now being explored using this system.

Coordination and catalysis of redox-active copper(I)-azothioformamide systems

ACS Spring 2022

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