AbstractDue to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi‐hydrogenation/reduction strategy utilizing CsPbBr3 quantum dots (CPB‐QDs) and Hantzsch ester (HEH2) as a synergistic catalytic system was introduced to reduce the BDE of Cβ−O−Ar, achieving effective cleavage of the Cβ−O−Ar bond. This strategy offers a wide substrate scope encompassing various β‐O‐4 model lignin dimers, preoxidized β‐O‐4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir‐catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH2 can be activated by CPB‐QDs via single electron transfer (SET), generating HEH2⋅+ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH2⋅+ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton‐coupled electron transfer (PCET) from HEH2⋅+ to the carbonyl group of the substrate generates a Cα⋅ intermediate.
摘要由于苛刻的解聚条件和有限的催化效率,提高木质素的价值仍具有挑战性。因此,降低键解离能(BDE)已成为实现温和而高效的键裂解的可行策略。本研究采用了一种光催化半氢化/还原策略,利用 CsPbBr3 量子点(CPB-QDs)和汉茨酯(HEH2)作为协同催化系统,降低 Cβ-O-Ar 的 BDE,从而实现 Cβ-O-Ar 键的有效裂解。这种策略提供了广泛的底物范围,包括各种 β-O-4 模型木质素二聚体、预氧化的 β-O-4 聚合物和原生氧化木质素,从而产生相应的酮和酚。值得注意的是,在木质素模型二聚体的光催化解聚过程中,这种方法达到的周转频率(TOF)是已报道的铱催化系统的 17 倍。通过细致的实验观察发现,CPB-QDs 可通过单电子转移(SET)激活 HEH2,生成 HEH2⋅+ 作为氢供体,同时还可作为空穴淬灭剂。此外,HEH2⋅+ 很容易通过氢键与底物形成活性过渡态。随后,质子耦合电子转移(PCET)从 HEH2⋅+ 到底物的羰基,生成 Cα⋅ 中间体。