Liu Chengyu, de Haas Titus, Buda Francesco, Bonnet Sylvestre
Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, P.O. Box 9502, 2333CC Leiden, The Netherlands.
ACS Catal. 2025 Mar 5;15(6):4681-4697. doi: 10.1021/acscatal.5c00788. eCollection 2025 Mar 21.
Molecular catalysts offer an ideal platform for conducting mechanistic studies of the hydrogen evolution reaction (HER) due to their electronic tunability. This study explores a series of anionic M=Co(III)- and M=Zn(II)-porphyrin complexes with electron-donating ([M(OMeP)] , [M(MeP)] ) and electron-withdrawing ([M(F8P)] , [M(F16P)] ) substituents. The activity of these complexes for the HER was analyzed in homogeneous photocatalytic conditions using [Ru(bpy)] as a photosensitizer under blue light (450 nm) irradiation. The substituent-induced electronic effects were found to tightly control the activity and mechanism of the photocatalytic HER. As expected, the electron-rich [Co(OMeP)] catalyst showed higher activity in acidic media (pH 4.1) with a maximum TOF of 7.2 ± 0.4 h and TON of 175 ± 5 after 39.5 h. DFT calculations were performed to investigate the HER mechanism. H formation was found to initiate following proton-coupled reduction of a Co-H hydride intermediate in such conditions. More surprisingly, however, the electron-poor [Co(F16P)] catalyst was more active at neutral pH (7.0), achieving a maximum TOF of 6.7 ± 0.3 h and TON of 70 ± 3 after 39.5 h. Instead of forming the Co-H hydride, an additional ligand-based reduction led to a ligand-protonated intermediate. This work demonstrates that electron-poor HER catalysts can outperform electron-rich catalysts near neutral pH conditions.
由于其电子可调性，分子催化剂为进行析氢反应（HER）的机理研究提供了一个理想的平台。本研究探索了一系列带有供电子基团（[M(OMeP)]、[M(MeP)]）和吸电子基团（[M(F8P)]、[M(F16P)]）的阴离子M=Co(III)和M=Zn(II)卟啉配合物。在蓝光（450 nm）照射下，以[Ru(bpy)]作为光敏剂，在均相光催化条件下分析了这些配合物对HER的活性。发现取代基诱导的电子效应紧密控制着光催化HER的活性和机理。正如预期的那样，富电子的[Co(OMeP)]催化剂在酸性介质（pH 4.1）中表现出更高的活性，在39.5小时后最大周转频率（TOF）为7.2±0.4 h，周转数（TON）为175±5。进行了密度泛函理论（DFT）计算以研究HER机理。发现在这种条件下，H的形成是通过钴氢化物中间体的质子耦合还原开始的。然而，更令人惊讶的是，贫电子的[Co(F16P)]催化剂在中性pH（7.0）下更具活性，在39.5小时后最大TOF为6.7±0.3 h，TON为70±3。不是形成钴氢化物，额外的基于配体的还原导致了配体质子化中间体。这项工作表明，在接近中性pH条件下，贫电子的HER催化剂可以优于富电子催化剂。
