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

Abstract

Harnessing of solar energy to drive the reduction of carbon dioxide to fuels requires the development of efficient catalysts that absorb sunlight. In this work, we detail the synthesis, electrochemistry and photophysical properties of a set of homologous fac-ReI(CO)3 complexes containing either an ancillary phenyl (8) or BODIPY (12) substituent. These studies demonstrate that both the electronic properties of the rhenium center and BODIPY chromophore are maintained for these complexes. Photolysis studies demonstrate that both assemblies 8 and 12 are competent catalysts for the photochemical reduction of CO2 to CO in DMF using triethanolamine (TEOA) as a sacrificial reductant. Both compounds 8 and 12 display TOFs for photocatalytic CO production upon irradiation with light (λex ≥ 400 nm) of ~5 hr−1 with TON values of approximately 20. Although structural and photophysical measurements demonstrate that electronic coupling between the BODIPY and fac-ReI(CO)3 units is limited for complex 12, this work clearly shows that the photoactive BODIPY moiety is tolerated during catalysis and does not interfere with the observed photochemistry. When taken together, these results provide a clear roadmap for the development of advanced rhenium bipyridine complexes bearing ancillary BODIPY groups for the efficient photocatalytic reduction of CO2 using visible light.

Reduction of CO2 using a rhenium bipyridine complex containing ancillary BODIPY moieties

“…Since BODIPY 47 – 51 and other polypyrrole derivatives 52–55 can absorb light throughout the visible region we rationalized that [Re(BB2)(CO) 3 Cl] might support an improved photocatalysis with CO 2 using sunlight, as compared to fac -Re I (CO) 3 frameworks lacking indacene units. 56 …”

Electrocatalytic reduction of CO2 using the dinuclear rhenium(I) complex [ReCl(CO)3(μ-tptzH)Re(CO)3]

“…Generally, if the ligand reduction waves of the Re(I) complex occur at potentials more positive than À1.1 V, the complex displays very little electrocatalytic activity for the electroreduction CO 2 [19,27]. Thus, the tptzH À ligand in the complex acts as electron storage and improves the performance of the complex for its catalytic activity [16]. For an investigation of the stability and activity of the dinuclear Re(I) complex, the peak current of the CO 2 reduction was followed over 50 cycles of CVs recorded in a potential range from 700 to À1500 mV at a scan rate of 100 mV s À1 in an electrolyte solution saturated with CO 2 in the presence of the Re(I) complex.…”

“…In particular, rhenium and ruthenium complexes have been more attracted due to their efficacious catalytic properties. Since the Re(bpy) (CO) 3 Cl complex was originally reported by Lehn [13], many researchers have studied the electrocatalytic [14,15] and photocatalytic [16,17] properties of this complex and its analogs. Several Re complexes have high selectivity for the reduction of CO 2 in the presence of protons [18,19].…”

Selective and Efficient Photocatalytic CO2 Reduction to CO Using Visible Light and an Iron-Based Homogeneous Catalyst

“…38 Using Ru II −Re I binuclear complexes, Bian et al 40 reported TONs in CO of 50−100 after 9 h of irradiation (TOFs of 5.5−11.1 h −1 ). Andrade et al 13 However, at such a low concentration of catalyst, it is difficult to assess the nature of the active species (along this line, it should be noted that the concentration of CO produced slightly decreases when the catalyst concentration increases from 2 to 20 nM and then marginally increases (by a factor of 1.5) when the concentration is further increased by a factor of 10).…”