期刊
ACS CATALYSIS
卷 6, 期 8, 页码 5473-5481出版社
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.6b01208
关键词
CO; reduction; photocatalysis; homogeneous catalysis; isotope effects; isotopic discrimination
资金
- University of Connecticut
- U.S. Department of Energy, Office of Science, Division of Chemical Sciences, Geosciences, & Biosciences, Office of Basic Energy Sciences [DE-SC00112704]
The rhenium complex Re(bpy)(CO)(3)Cl (1, bpy = 2,2'-bipyridine) catalyzes CO2 reduction to CO in mixtures containing triethanolamine (TEOA) as a sacrificial reductant. The mechanism of this reaction under photocatalytic conditions remains to be fully characterized. Here, we report the competitive carbon kinetic isotope effects (C-13 KIEs) on photocatalytic CO2 reduction by 1 and analyze the results of experimental measurements by comparing with computed KIEs via density functional theory (DFT) calculations as a means of formulating a chemical mechanism and illustrating the utility of this approach. The C-13 KIEs, k(C-12)/k(C-13), in acetonitrile (ACN) and dimethylformamide (DMF) were determined to be 1.0718 +/- 0.0036 and 1.0685 +/- 0.0075, respectively. When [Ru(bpy)(3)]Cl-2 is added to the reaction mixture in acetonitrile as a photosensitizer, the reduction of CO2 exhibited a C-13 KIE = 1.0703 +/- 0.0043. These values are consistent with the calculated isotope effect of CO2 binding to the one-electron reduced [Re-I(bpy(center dot-))(CO)(3)] species. The findings reported here provide strong evidence that the reactions in the two different solvents have the same first irreversible step and proceed with similar reactive intermediates upon reduction. Theoretically, we found that the major contribution for the large C-13 isotope effects comes from a dominant zero-point energy (ZPE) term. These results lay the groundwork for combined experimental and theoretical approaches for analysis of competitive isotope effects toward understanding CO2 reduction catalyzed by other complexes.
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