Photocatalytic Reduction of CO$_2$ by Highly Efficient Homogeneous Fe$^{II}$ Catalyst based on 2,6‐Bis(1’,2’,3’‐triazolyl‐methyl)pyridine - Comparison with Analogues

Fully earth-abundant and highly efficient systems for producing syngas CO/H$_2$ through photocatalytic reduction from CO$_2$ are essential to approach a sustainable way of closing the carbon cycle. Herein, the synthesis and characterization of a new iron complex, Fe$^{II}$L(NCS)$_2$py, coordinated to an N,N,N-pincer ligand 2,6-bis(4’-phenyl-1’,2’,3’-triazol-1’-yl-methyl)pyridine (L), two isothiocyanate groups (NCS) and one pyridine is reported. Its catalytic activity in the photo-driven reduction of carbon dioxide has been investigated and compared with its Co$^{II}$ analogue (CoL(NCS)$_2$py) and their homoleptic complexes ML$_2$. In this work, the catalysts are used in combination with the heteroleptic complex [Cu$^I$(dmp)(DPEphos)], where dmp is 2,9-dimethyl-1,10-phenanthroline and DPEPhos is bis[(2-diphenylphosphino)phenyl] ether, to reach entirely earth-abundant systems. The new iron heteroleptic complex Fe$^{II}$L(NCS)$_2$py showed considerable activity with a TON$_{CO}$ of 576 obtained after 4 h (TOF=144 h$^{−1}$) through visible light (λ=420 nm) and a quantum yield of 7.1 %.