Effect of “X” Ligands on the Photocatalytic Reduction of CO 2 to CO with Re(pyridylNHC‐CF 3 )(CO) 3 X Complexes

A series of five Re(pyNHC‐aryl)(CO) 3 X complexes varying the “X” ligand where pyNHC is a pyridyl N‐heterocyclic carbene have been synthesized and characterized through NMR, UV/Vis absorption spectroscopy, IR, mass spectrometry, time‐correlated single photon counting, computational analysis, and cyclic voltammetry. The photocatalytic reduction of CO 2 to CO in the presence of a sacrificial electron donor with these complexes is evaluated using a simulated solar spectrum (AM 1.5G). Comparison of Br and CH 3 CN as the “X” ligand shows the same photocatalytic activity (both 32 TON). The use of Cl, NCS and P(OEt) 3 “X” ligands all led to diminished reactivity with as little as 2 TON for the P(OEt) 3 complex. These results were rationalized through computational analysis of “X” dissociation and excited‐state lifetime measurements. These results highlight the importance of the “X” ligand selection on catalysis with Re‐pyNHC complexes.