Photochemical CO₂ Reduction Using Rhenium(I) Tricarbonyl Complexes with Bipyridyl‐Type Ligands with and without Second Coordination Sphere Effects

Abstract

The effect of phenyl, phenol, aniline, amino, and CF 3 substituents of the 2,2'-bipyridine ligand in fac-ReCl(L)(CO) 3 (L = 2,2'bipyridine derivative) catalysts on photochemical CO 2 reduction in dimethylacetamide is examined, in order to understand the structure-function relationships and to compare the catalytic activities with the previously published electrochemical results. All complexes including ReCl(bpy)(CO) 3 have similar excitedstate lifetimes and emission spectra, but complex 1 with the Ph-NH 2 moiety exhibits a significantly larger molar absorption coefficient for its metal-to-ligand charge transfer (MLCT) band. All complexes we tested produce CO with only a negligible amount of H 2 and formate in self-sensitized systems in the presence of triethanolamine (TEOA) and in some cases,The presence of the Ph-NH 2 moiety (complex 1) has a beneficial effect on both electrochemical and photochemical activity, allowing a turnover number (TON) of 32 and 120 for photochemical CO production (without and with BIH, respectively). In the case of the Ph-OH group in the second coordination sphere (complexes 4 and 6), these complexes are active for photochemical CO 2 reduction, despite the formation of a stable 6coordinate Re-OPh intermediate via reductive deprotonation as previously observed under electrochemical conditions. Overall, BIH accelerates the rate of formation of the one-electron reduced species (OERS) of the Re catalysts and allows higher turnover frequency (TOF) and TON for CO formation. The X-ray structures of complexes 1 and 4 were determined to have distorted octahedral Re centres, and show π-π stacking interactions with neighboring molecules as well as intramolecular hydrogen bonds to the internal chloride ligands. The unusually high absorptivity of the MLCT absorption of complex 1 has been explained by TD-DFT calculations.

Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH

“…With the addition of BIH, compared to TEA, TN was dramatically increased possibly due to the increase in reductive power and efficient formation of the one-electron reduced catalytic species. 20 When TEMPO was added in equimolar concentrations to BIH, the integration of formate increased, suggesting TEMPO acting as a hydride donor. These observations allude to a hydride mechanism.…”

Understanding the Role of Inter- and Intramolecular Promoters in Electro- and Photochemical CO2 Reduction Using Mn, Re, and Ru Catalysts

“…69 Recently, we collaborated with Nervi's group to better understand the electrochemical mechanism and to obtain stronger spectroscopic characterization of the NNO bpyphenolate chelate. 35 [ReCl(pmbpy)(CO) 3 ] (Chart 4) was designed with a single pendent acid to avoid complications caused by a second available site for reductive deprotonation. The CV features a reversible reduction at −1.7 V vs Fc +/0 (I) followed by two irreversible peaks at −2.06 (II) and −2.26 V (III) for a cumulative two-electron reduction (Figure 5).…”

“…We have also investigated photochemical CO 2 reduction using [ReCl(bpy)(CO) 3 ] and Re catalysts shown in Chart 4 containing 1.25 M TEOA with/without 0.1 M BIH. 35 Despite the Re−OPh bond derived from reductive deprotonation at the beginning stage of photoreduction, these complexes are still active for photochemical CO 2 reduction to form CO, but with lower TON and TOF compared to [ReCl(bpy)(CO) 3 ] when BIH is absent. [ReCl(fpmbpy)(CO) 3 ] and [ReCl(pdbpy)-(CO) 3 ] bearing an OH group in the peripheral position show higher TON and TOF due to more electron donation to the Re center compared to the pmbpy complex.…”

Photocatalytic Reduction of CO2 to CO in Aqueous Solution under Red-Light Irradiation by a Zn-Porphyrin-Sensitized Mn(I) Catalyst

“…Accordingly, significant efforts have been made to design efficient and selective CO 2 reduction catalysts. , Group 7 metal carbonyl complexes bearing diimine ligands have been studied extensively for this purpose, beginning with the demonstration of photo- and electrochemical catalytic reduction of CO 2 to CO using [ReCl­(NN)­(CO) 3 ] (NN = diimine ligand, for example, 2,2′-bipyridyl, bpy) . While many catalysts based on the [ReX­(NN)­(CO) 3 ] structure have been developed, − the scarcity of extractable Re in the earth’s crust prompted the development of catalysts with earth-abundant metals, such as Mn. The Mn­(I) diimine carbonyls of general formula [MnBr­(NN)­(CO) 3 ] have been shown to be effective electrochemical CO 2 reduction catalysts in the presence of a weak Brønsted acid, such as water. , Since 2011, many different Mn­(I) complexes have been reported based on this work, which incorporate functionalized polypyridyl ligands (Figure ).…”