Water-induced Selectivity Switching and Steric Control of Activity in Photochemical CO2 Reduction Catalyzed by RhCp*(bpy) Derivatives

20 May 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Photocatalytic reduction of CO2 to formic acid (HCOOH) was investigated in either organic or aqueous/organic media by employing three newly synthesized water-soluble Rh(Cp*)(n,n’-dihydroxy-2,2’-bipyridine) (n = 4, 5, or 6) in the presence of [Ru(bpy)3]2+, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) and triethanolamine (TEOA). Through studying the electron-donating effects of two hydroxyl groups introduced to the bipyridyl ligand, we found that the hydroxyl group positions of the catalyst greatly affect both the catalytic efficiency and selectivity in CO2 reduction. More importantly, the HCOOH selectivity shows a dramatic increase from 14% to 83% upon switching the solvent media from pure organic to aqueous/organic mixture, where the H2 selectivity shows a reverse phenomenon. The enhanced HCOOH selectivity and the drastic decrease in the apparent H2 yield are well rationalized by the fact that the catalytic CO2 hydrogenation by the evolved H2 simultaneously proceeds as a dark catalytic reaction, which was also separately investigated under the dark conditions. Our DFT studies unveil that the exceptionally large structural strain given by the steric contacts between the 6,6’-dihydroxyl groups and the Cp* moiety plays a significant role in bringing about an outstanding catalytic performance of the 6,6’-subsituted derivative. The intrinsic reaction coordinate calculations on the hydride transfer steps leading to generate formate together the heterolytic H2 cleavage steps leading to afford the key hydridorhodium intermediates afford the results useful to interpret the observed phenomena. This study represents the first report on the water-induced high selectivity in CO2-to-HCOOH conversion, shedding a new light on the strategy to control the efficiency and selectivity in CO2 reduction.


Photocatalytic CO2 Reduction
Rhodium Cyclopentadienyl Catalysts
Solar Energy Conversion
Dihydrogen Production
Formate Selectivity
DFT Calculations

Supplementary materials

Supporting Information
Experimental and computational results


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.