Hydrogen Atom Transfer-Mediated N-Heterocycles Dehydrogenation Coupled with the CO₂ Photoreduction to Syngas

Homogeneous photocatalytic organic oxidation coupled with CO2 reduction remains challenging due to the susceptibility to a back electron transfer scenario. Herein, a pyridinethiol iron-catalyzed system is developed to achieve N-heterocycles dehydrogenation coupled with CO2 photoreduction to syngas. The system is comprised of 2,4,5,6-tetrakis(diphenylamino)isophthalonitrile (4DPAIPN) photoredox catalysts, earth-abundant iron catalysts, and pyridinethiol organocatalysts, and the employment of pyridinethiol both as a hydrogen atom transfer (HAT) catalyst to promote N-heterocycles dehydrogenation and as an effective ligand for CO2 reduction is the key to realizing the coupled redox reaction. Experimental and theoretical calculation results demonstrate the positive correlation between the reactivity and the S-H bond dissociation enthalpy (BDE) as well as the radical polarity (ω) parameter, gaining deep insights into understanding and designing the coupled reaction.