Binuclear rhenium(i) complexes for the photocatalytic reduction of CO2

Abstract

Binuclear rhenium(I) complexes with 1,2-bis(4,4'-methyl-[2,2']bipyridyl)-ethane and 1,2-bis(4,4'-methyl-[2,2']bipyridyl)-dodecane as bridging ligands and their mononuclear analogues have been synthesized and characterized by their spectroscopic and electrochemical properties. First reduction potentials and luminescence properties as well as the reductive quenching of the emissive state with TEOA were not affected by the alkyl linker. By means of a detailed comparison of the photocatalytic CO(2) reductions of the monometallic and the bimetallic complexes a great beneficial effect on the activity depending on the proximity of the centres was found. In high dilution the overall kinetics in the CO(2) photoreduction of mononuclear complexes are clearly monometallic. If the proximity of the centres is adjusted according to the lifetime of the OER (one electron reduced species) the photocatalytic activity is greatly improved showing a clear bimetallic mechanism. In the binuclear rhenium complexes, both the facile generation of a free coordination site and binuclear interactions for effective two electron transfer can be realized.

Experimental and theoretical studies of the ancillary ligand (E)-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol in the rhenium(i) core

“…S9, ESI †), and showed an irreversible process with only oxidative peak potential, according to analogous complexes. [43][44][45][46] Computational optimizations of the oxidized and reduced states of the studied compounds, deeb, C1 and C2, were performed. In this sense, this process occurs at higher potentials relative to C1, which means that L has an electron-withdrawing effect over the positive charge on the rhenium atom.…”

Comparison of CO2 Photoreduction Systems: A Review

“…However, Bruckmeier et al (2012) reported that in fact Re-Br photocatalysts showed better photocatalytic activity if the centers are brought in closer proximity through covalent linkage, which would be expected considering the ease with which the bromo-ligand leaves thus providing a new coordination site. Ettedgui et al (2011) , for the photoreduction of CO 2 in visible light.…”

“…For this review, we will focus mostly on type two systems in which the sensitizer and catalyst of the system are the same large molecule and type one systems in which the catalyst is not a metal semiconductor, but rather another molecular complex covalently bonded to the sensitizer. Bruckmeier et al (2012) reported the photocatalytic activities of type 2 rhenium(I) based catalysts, which stated that the transfer of the second electron for CO 2 reduction to CO originates from the long lived one-electron reduced species (OER), dominates if the proximity of the coordination centers is adjusted according to the lifetime of the OER. In the case of Re-NCS type complexes with a naturally long lived OER, the bimetallic mechanism will occur by simply increasing the concentration of the catalyst, which changes the proximity of the coordination centers, thus it has often been the case in the literature that Re-NCS photocatalysts are reported as the best rhenium(I) based photocatalysts.…”

Push or Pull? Proton Responsive Ligand Effects in Rhenium Tricarbonyl CO2 Reduction Catalysts

“…The fac-[Re(α-diimine)(CO) 3 X] n+ (X = halide; n = 0 or X = neutral ligand, n = 1) family of complexes selectively catalyzes the reduction of CO 2 to CO. [7][8][9][10][11][12][13][14][15][16][17][18][19] Electrocatalysis is effective in solution and using surface-bound catalysts while photochemical systems have been identified with or without separate sensitizers. Mechanistic studies have revealed one-electron or two-electron pathways for catalysis.…”