Inagaki Akiko, Hada Masahiko, Abe Minori
Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-0364, Japan.
Department of Chemistry, Islamic University of Indonesia, Jl. Kaliurang km 14.5, Sleman,Yogyakarta, 55584, Indonesia.
J Phys Chem A. 2023 Mar 30;127(12):2810-2818. doi: 10.1021/acs.jpca.3c01299. Epub 2023 Mar 21.
A density functional study was performed to investigate the mechanism of the photocatalytic reactivity of styrene polymerization using dinuclear Ru-Pd and Ir-Pd catalytic complexes. In previous experiments with these catalysts, the reactivity increased, and more polymer products were yielded compared to dimers under visible light irradiation. The best catalytic reactivity was obtained using an Ir-Pd complex containing naphthyl substituents at the phenyl ligands coordinated to Ir (-). In contrast, -, an isomer of -, containing naphthyl substituents at the pyridine ligands, did not show good reactivity, which may be related to the stability of the excited state of the catalytic complexes. In this study, we calculated the radiative lifetimes of these catalytic complexes and had the longest lifetime; this result was consistent with the experimental results. The longest lifetime of the - was attributed to the destabilization of the highest occupied molecular orbital (HOMO) energy by π*-π* interactions between the naphthyl and phenyl ligands. Further, this destabilization of the HOMO energy afforded a small energy gap between the HOMO and lowest unoccupied molecular orbital, enhancing the metal-to-ligand charge transfer to the bridging ligand between Ir and Pd. Additionally, we focused on the reaction of the second insertion of styrene, which was identified as the rate-determining step of the polymerization cycle in a previous study. The singlet-triplet crossing points of the intermediates were estimated, and the barrier heights of the intersystem crossing were much lower than those in the thermal paths, which explained the efficiency of the photocatalytic reactivity in the experiment.
进行了一项密度泛函研究，以探究使用双核Ru-Pd和Ir-Pd催化配合物进行苯乙烯聚合光催化反应的机理。在之前使用这些催化剂的实验中，与二聚体相比，在可见光照射下反应活性增加，且生成了更多的聚合物产物。使用在与Ir配位的苯基配体上含有萘基取代基的Ir-Pd配合物时，获得了最佳的催化反应活性。相比之下，在与Ir配位的吡啶配体上含有萘基取代基的-的异构体，其-的异构体，没有表现出良好的反应活性，这可能与催化配合物激发态的稳定性有关。在本研究中，我们计算了这些催化配合物的辐射寿命，并且具有最长的寿命；这一结果与实验结果一致。-的最长寿命归因于萘基和苯基配体之间通过π*-π*相互作用使最高占据分子轨道（HOMO）能量不稳定。此外，HOMO能量的这种不稳定在HOMO和最低未占据分子轨道之间提供了一个小的能隙，增强了从金属到Ir和Pd之间桥连配体的配体电荷转移。此外，我们关注了苯乙烯的第二次插入反应，在之前的研究中该反应被确定为聚合循环的速率决定步骤。估计了中间体的单重态-三重态交叉点，并且系间窜越的势垒高度远低于热路径中的势垒高度，这解释了实验中光催化反应的效率。
