A robust pyridyl-NHC-ligated rhenium photocatalyst for CO reduction in the presence of water and oxygen

Re(pyNHC-PhCF)(CO)Br is a highly active photocatalyst for CO reduction. The PhCF derivative was previously empirically shown to be a robust catalyst. Here, the role of the PhCF group is probed computationally and the robust nature of this catalyst is analyzed with regard to the presence of water and oxygen introduced in controlled amounts during the photocatalytic reduction of CO to CO with visible light. This complex was found to work well from 0-1% water concentration reproducibly; however, trace amounts of water were required for benchmark Re(bpy)(CO)Cl to give reproducible reactivity. When ambient air is added to the reaction mixture, the NHC complex was found to retain substantial performance (~50% of optimized reactivity) at up to 40% ambient atmosphere and 60% CO while the Re(bpy)(CO)Cl complex was found to give a dramatically reduced CO reduction reactivity upon introduction of ambient atmosphere. Through the use of time-correlated single photon counting studies and prior electrochemical results, we reasoned that this enhanced catalyst resilience is due to a mechanistic difference between the NHC- and bpy-based catalysts. These results highlight an important feature of this NHC-ligated catalyst: substantially enhanced stability toward common reaction contaminates.