Unveiling the Activity and Mechanism Alterations by Pyrene Decoration on a Co(II) Macrocyclic Catalyst for CO 2 Reduction.

Mechanistic studies involving characterization of crucial intermediates are desirable for rational optimization of molecular catalysts toward CO 2 reduction, while fundamental challenges are associated with such studies. Herein we present the systematic mechanistic investigations on a pyrene-appended Co II macrocyclic catalyst in comparison with its pyrene-free prototype. The comparative results also verify the reasons of the higher catalytic activity of the pyrene-tethered catalyst in noble-metal-free CO 2 photoreduction with various photosensitizers, where a remarkable apparent quantum yield of 36±3 % at 425 nm can be obtained for selective CO production. Electrochemical and spectroelectrochemical studies in conjunction with DFT calculations between the two catalysts have characterized the key CO-bound intermediates and revealed their different CO-binding behavior, demonstrating that the pyrene group endows the corresponding Co II catalyst a lower catalytic potential, a higher stability, and a greater ease in CO release, all of which contribute to its better performance.