Abstract
Re(pyNHC-PhCF3)(CO)3Br is a highly active photocatalyst for CO2 reduction. The PhCF3 derivative was previously empirically shown to be a robust catalyst. Here, the role of the PhCF3 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 CO2 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)3Cl 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% CO2 while the Re(bpy)(CO)3Cl complex was found to give a dramatically reduced CO2 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.
Highlights
The photocatalytic transformation of CO2 into a useful fuel is one of humanity’s paramount challenges [1,2,3,4]
Substituent was previously to give the mostthe reactive compared with phenyl, p-hexyloxyphenyl, or methyl substituents found to give most catalyst reactivewhen catalyst when compared with phenyl, p-hexyloxyphenyl, or methyl on the NHC ring
We reasoned that this group betterallows delocalization of the added substituents on the
Summary
The photocatalytic transformation of CO2 into a useful fuel is one of humanity’s paramount challenges [1,2,3,4]. Despite more than 30 years of exploration, very few catalysts meet these criteria with a single metal center, and most of them are based on one of five frameworks: Fe-p-TMA, Ir(tpy)(ppy)X, Ir(tpy)(bpy)X, Re(bpy)(CO) X, or Re(pyNHC-R)(CO) X (Figure 1) [7,8,9,10,11,12] Among these catalysts, the Re(pyNHC-R)(CO) X catalyst is unique in allowing the reduction of CO2 to occur at the first reduction potential of the neutral catalyst (Figure 2) [10,13]. Reactions beneficial in designing catalysts with lower overpotentials (the excess energy beyond what is needed to reduce CO22)) which which will will be be important important in in complete complete photoelectrochemical photoelectrochemical systems In these these systems, systems, are readily readily measured measured and can be rationally the energetics of the active catalyst which attacks CO22 are tuned [18]
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