Photocatalytic CO₂ Reduction and Surface Immobilization of a Tricarbonyl Re(I) Compound Modified with Amide Groups

Abstract

Amide bonds have been utilized as covalent linkages between photosensitizers and molecular catalysts in some supramolecular photocatalysts. It is unclear how the presence of amide groups affects properties of the molecular catalysts. This study examines the effect of amide derivatization on photocatalytic CO2 reduction using Re(bpy)(CO)3Cl, where bpy is 2,2′-bipyridine. Our results indicate that derivatization with electron-withdrawing amide (−CONH) groups lowered the catalytic activity by a factor of ∼6 when the Re(I) compound was directly excited in the absence of additional photosensitizers but facilitated electron transfer between Ru(bpy)3 •+ and the Re(I) catalyst when Ru(bpy)3 2+ was used as a photosensitizer for excited-state electron transfer. The electron-withdrawing amide bond was then utilized to graft the Re(I) complex onto the surface of silica nanoparticles. The surface Re(I) sites were found to be well separated in a diimine-tricarbonyl coordination environment. The surface-immobilized catalyst showed activity comparable to the homogeneous Re(I) compound in photocatalytic CO2 reduction. Photochemical properties of the surface Re(I) catalyst were further probed using in situ FTIR and EPR spectroscopies. In the presence of a sacrificial electron donor, bipyridine-based, one-electron reduction of the surface Re(I) catalyst occurred upon visible-light irradiation. The results are particularly relevant to the development of photoelectrochemical devices for sustainable fuel production via CO2 reduction.

Photocatalytic Conversion of CO2 to CO Using Rhenium Bipyridine Platforms Containing Ancillary Phenyl or BODIPY Moieties

“…As such, Huisgen/click chemistry may provide a straightforward and versatile method for immobilization of Re(bpy)(CO) 3 Cl catalysts onto heterogeneous supports. 53 More importantly, the work reported herein clearly shows that BODIPY chromophores are tolerated under the standard photocatalysis conditions we have employed. This finding suggests that this versatile organic chromophore can be used in conjunction with fac -Re I (CO) 3 complexes, and that properly designed assemblies in which coupling between the BODIPY and metal centers is optimized, may be promising platforms for the direct reduction of CO 2 using solar photons.…”

Covalent hybrids based on Re(i) tricarbonyl complexes and polypyridine-functionalized polyoxometalate: synthesis, characterization and electronic properties

“…The native POM 7 exhibits intense absorption in the UV region, which is attributed to the multiple ligand--to--metal charge transfer (O→W while a complex based on a bis--amide bipyridine as in 6 has been reported to emit around 650nm. 36 However, in the case of our covalently modified POM based Re complexes, no luminescence could be detected upon excitation of the 1 MLCT transition (see Fig. S27).…”

Highly Robust Hybrid Photocatalyst for Carbon Dioxide Reduction: Tuning and Optimization of Catalytic Activities of Dye/TiO2/Re(I) Organic–Inorganic Ternary Systems

“…In contrast to the hybrid-photocatalyzed reaction, the CO formation commonly shows levelling-off tendencies after 100 or 400 min irradiation to give lower TNCO ( Figure 2B). The levelling-off behavior is a general phenomenon observed in most reported investigations on homogeneous photocatalytic CO2 reductions by ReH and related Re(I) complexes 22,23,[40][41][42] with a few exceptions, 43-47 a consequence arising from chemical changes of the Re(I) catalysts. [48][49][50] As shown in Figure 4, on the other hand, IR spectra of the hybrid particles recovered after the photoreactions for 50 min, 100 min, and 20 h indicates no significant difference in the CO absorption bands of RePH, demonstrating that RePH does work as a persistent, stable catalyst in the reduction of CO2 to CO with little decomposition after its anchoring on TiO2.…”