Comparative Coordination Chemistry of PNP and SNS Pincer Ruthenium Complexes

Ruthenium carbonyl complexes supported by PNP pincer ligands are prominent catalysts for a range of hydrogenation and dehydrogenation reactions. Recently, Ru complexes with cheaper, more air stable SNS pincer ligands have emerged as attractive alternatives for the development of improved catalysts. However, there is currently a paucity of information on how the replacement of the phosphine donors in PNP ligands with the sulfur donors in SNS ligands influences the synthesis, structure, and electronic properties of the resulting metal complexes. Herein, the coordination chemistry of a series of Ru carbonyl complexes with SNS pincer ligands has been systematically compared with related PNP-ligated species. Three different SNS pincer ligands were explored including a pyridyl based NC5H3{CH2(StBu)}2 ligand and two aliphatic ligands, HN­{CH2CH2(StBu)}2 and NCH3{CH2CH2(StBu)}2, along with different combinations of monodentate ancillary ligands. The geometric structures of the SNS and PNP Ru complexes were studied using NMR spectroscopy and X-ray crystallography. Additionally, the redox properties and electronic structures of these complexes were probed through a combination of cyclic voltammetry and DFT calculations. Overall, differences between SNS and PNP complexes extend well beyond simply modulating inductive donation to the metal and include changes in synthetic outcomes, as well as variations in geometry that impact redox behavior. Our study reveals fundamental information about the coordination chemistry of the SNS ligand, which may aid in interpreting catalytic results.由PNP钳形配体（PNP pincer ligands）配位稳定的钌羰基配合物，是一类可催化多种氢化与脱氢反应的高效催化剂。近年来，采用更廉价、空气稳定性更优的SNS钳形配体（SNS pincer ligands）的钌配合物，逐渐成为开发改良型催化剂的极具吸引力的备选方案。然而目前仍缺乏相关研究，阐明将PNP配体中的膦供体替换为SNS配体中的硫供体后，会对所得金属配合物的合成、结构及电子性质产生何种影响。本文中，我们将一系列基于SNS钳形配体的钌羰基配合物的配位化学行为，与相关的PNP配体配位的同类型配合物进行了系统对比。本次研究共考察了三种不同的SNS钳形配体：包括基于吡啶基的NC5H3{CH2(StBu)}2配体，以及两种脂肪族配体HN{CH2CH2(StBu)}2与NCH3{CH2CH2(StBu)}2，并搭配了不同组合的单齿辅助配体。我们借助核磁共振波谱（NMR spectroscopy）与X射线晶体学（X-ray crystallography），对SNS型与PNP型钌配合物的几何结构进行了表征分析。此外，我们通过循环伏安法与密度泛函理论（DFT）计算的组合手段，探究了上述配合物的氧化还原性质与电子结构。总体而言，SNS型与PNP型配合物之间的差异远不止对金属中心的诱导配位作用发生改变，还涵盖合成结果的变化，以及影响氧化还原行为的几何结构差异。本研究揭示了SNS配体配位化学的基础信息，可为催化反应结果的解析提供有力支撑。