Computational Investigation into Heteroleptic Photoredox Catalysts Based on Nickel(II) Tris-Pyridinethiolate for Water Splitting Reactions

This work demonstrates a strategy to fine-tune the efficiency
of
a photoredox water splitting Ni(II) tris-pyridinethiolate catalyst
through heteroleptic ligand design using computational investigation
of the catalytic mechanism. Density functional theory (DFT) calculations,
supported by topology analyses using quantum theory of atoms in molecules
(QTAIM), show that the introduction of electron donating (ED) −CH3 and electron withdrawing (EW) −CF3 groups
on the thiopyridyl (PyS–) ligands of the same complex
can tune the pKa and E0, simultaneously. Computational modeling of two heteroleptic
nickel(II) tris-pyridinethiolate complexes with 2:1 and 1:2 ED and
EW −CH3 and −CF3 group containing
PyS– ligands, respectively, suggests that the ideal
combination of EW to ED groups is 2:1. This work also outlines the
possibility of formation of a large number of isomers after the protonation
of one of the pyridyl N atoms and suggests that to acquire unambiguous
computational results it is necessary to carefully account for all
possible geometric isomers.

本研究提出一种策略，通过催化机理的计算研究结合异配体设计，精准调控光驱动水分解用三吡啶硫醇合镍(II)催化剂的催化效率。
密度泛函理论（Density functional theory, DFT）计算结合量子原子分子理论（Quantum Theory of Atoms in Molecules, QTAIM）的拓扑分析结果显示，在同一配合物的吡啶硫基（PyS–）配体上引入给电子（electron donating, ED）-CH₃与吸电子（electron withdrawing, EW）-CF₃基团，可同时调控其酸度系数（pKa）与标准电极电势（E₀）。
本研究对两种异配型三吡啶硫醇合镍(II)配合物开展计算建模：二者分别带有含2:1与1:2比例给电子/吸电子取代基的吡啶硫基配体，结果显示吸电子基团与给电子基团的最优配比为2:1。
本研究同时指出，当其中一个吡啶氮原子发生质子化后，可能生成大量异构体；为获得准确无歧义的计算结果，需全面考量所有可能的几何异构体。