Effect of “X” Ligands on the Photocatalytic Reduction of CO₂ to CO with Re(pyridylNHC‐CF₃)(CO)₃X Complexes

Abstract

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 [a] H.ing the effects of varying the monodentate "X" ligand on catalyst behavior. 1850 necessary to lower the Coupled Perturbed Hartree Fock convergence tolerance to 1 × 10 -7 maximum change in the U matrix.

Probing the Effects of Electron Deficient Aryl Substituents and a π‐System Extended NHC Ring on the Photocatalytic CO2 Reduction Reaction with Re‐pyNHC‐Aryl Complexes**

“…The highest performing catalyst ( 2 ), the lowest performing catalyst ( 3 ), and the second highest performing catalyst ( 6 ) were analyzed computationally via density functional theory (DFT) with the M06‐2X [10] and PBE0 [10b,11] functionals and implicit MeCN solvation (see experimental section for a description of the computational approach and how the rhenium atom was treated). The M06‐2X and PBE0 functionals have been successfully employed elsewhere to characterize the structures and ligand dissociation energies of transition metal complexes [8a,10b] . In addition, time dependant DFT (TDDFT) computations with both functionals have been shown to reliably reproduce experimental UV‐Vis spectral features in combination with an appropriate implicit solvent model, specifically PBE0 with the closely related Re(bpy)(CO) 3 (Cl) complex and M06‐2X with polycyclic organic dyes [10b,12] .…”

N‐Heterocyclic and Mesoionic Carbenes of Manganese and Rhenium in Catalysis

“…In a later work, the axial ligand in 31 a was replaced by NCS, NCMe and P(OEt) 3 . [65] The catalytic performance of complexes bearing Br or NCMe was comparable, whereas the use of NCS and P(OEt) 3 significantly decreased the TON value reached by their metal complexes. Computational studies, together with excited-state lifetime measurements, revealed higher axial bond dissociation energy for the catalysts with less catalytic performance.…”

“…Re complexes bearing inductively electron withdrawing substituents ( 31 a – 31 d ) exhibited higher TOF numbers compared to complex 35 bearing π‐electron withdrawing groups via resonance. In a later work, the axial ligand in 31 a was replaced by NCS, NCMe and P(OEt) 3 [65] . The catalytic performance of complexes bearing Br or NCMe was comparable, whereas the use of NCS and P(OEt) 3 significantly decreased the TON value reached by their metal complexes.…”

“…In fact, the authors stated that the axial bond dissociation energy explains the different reactivity between these complexes and the parent complex [Re(bpy)(CO) 3 Br]. [65] The use of a silicon nanowire photoelectrode for the CO 2 reduction, mediated by 36 and 37 a,b (Scheme 26, and entries 10 and 11, Table 3), was explored by Li, Wang and coworkers. [66] Photovoltages greater than 44 mV were observed with excellent selectivity towards CO over H 2 formation.…”

“…Computational studies, together with excited‐state lifetime measurements, revealed higher axial bond dissociation energy for the catalysts with less catalytic performance. In fact, the authors stated that the axial bond dissociation energy explains the different reactivity between these complexes and the parent complex [Re(bpy)(CO) 3 Br] [65] …”