Comprehensive Experimental and Computational Study of η6‑Arene Ruthenium(II) and Osmium(II) Complexes Supported by Sulfur Analogues of the β‑Diketiminate Ligand

In comparison to β-diketiminates, a highly exploited class of N,N-chelating ligands, the corresponding β-thioketoiminates, monothio-substituted analogues, have received only minor attention. β-Thioketoiminates are straightforwardly prepared through treatment of an appropriate β-ketoiminate with Lawesson’s reagent. Employing standard synthetic techniques for η6-arene Ru­(II) and Os­(II) β-diketiminate complexes, an analogous series of chlorido-metal complexes supported by different sized N-aryl substituted β-thioketoiminate ligands is reported. However, metal ligation of a β-thioketoiminate bearing an electron-withdrawing CF3 group was not possible. The metal–chlorine bond in these complexes is readily activated by various sodium or silver salts of weakly coordinating anions, affording coordinately unsaturated cationic formally 16-electron species. All η6-C6H6 metal β-thioketoiminate complexes were characterized by NMR and in the solid state using single crystal X-ray diffraction techniques. Structural studies reveal that incorporation of a thio-group induces substantial bond angle distortion within the metallocycle. The reactivity of the cationic η6-C6H6 Ru­(II) β-thioketoiminate complexes toward alkynes and isonitriles is analogous to that of the β-diketiminate species. Specifically, the reaction with 1-hexyne results in a [4 + 2] cycloaddition involving the metal and β-C sites, while reaction with isonitrile completely displaces the η6-C6H6 ligand. A comprehensive DFT study employing charge decomposition analysis (CDA) reveals a strong covalent metal–sulfur bond which dominates the metal β-thioketoiminate interaction. The M–S bond (M = Ru or Os) is strengthened by charge transfer from metal to sulfur, in contrast to the β-diketiminate species where back electron donation from the metal to the nitrogen centers is negligible. The first reported β-selenoketoiminate was prepared by reacting a β-ketoiminate with the Woolins’ reagent. However, this seleno-analog demonstrated significant instability with respect to hydrolysis, and coordination to an η6-arene Ru­(II) or Os­(II) moiety proved unsuccessful.作为一类被广泛应用的N,N-螯合配体，β-二亚胺（β-diketiminates）与其对应的单硫代取代类似物β-硫代酮亚胺（β-thioketoiminates）相比，后者仅受到了有限的研究关注。β-硫代酮亚胺可通过将合适的β-酮亚胺与劳森试剂（Lawesson’s reagent）反应实现便捷制备。沿用η⁶-芳烃钌(II)与锇(II)β-二亚胺配合物的标准合成策略，本文报道了一系列由不同尺寸的N-芳基取代β-硫代酮亚胺配体支撑的氯化金属配合物类似物。然而，带有吸电子三氟甲基（CF₃）基团的β-硫代酮亚胺无法实现金属配位。此类配合物中的金属-氯键可被多种弱配位阴离子的钠盐或银盐轻易活化，得到配位不饱和的阳离子型形式16电子物种。所有η⁶-苯（η⁶-C₆H₆）金属β-硫代酮亚胺配合物均通过核磁共振（NMR）技术以及固态单晶X射线衍射技术完成了表征。结构研究表明，硫原子的引入会导致金属环内出现显著的键角畸变。阳离子型η⁶-苯钌(II)β-硫代酮亚胺配合物对炔烃与异腈的反应活性与β-二亚胺类配合物类似。具体而言，其与1-己炔的反应会涉及金属与β-碳位点的[4+2]环加成，而与异腈的反应则会完全取代η⁶-苯配体。采用电荷分解分析（charge decomposition analysis, CDA）的系统性密度泛函理论（DFT）研究表明，强共价金属-硫键主导了金属与β-硫代酮亚胺之间的相互作用。与β-二亚胺类配合物中金属向氮中心的反向电子捐赠可忽略不计的情况不同，M-S键（M=Ru或Os）的强度得益于金属向硫原子的电荷转移。首个被报道的β-硒代酮亚胺是通过β-酮亚胺与伍林试剂（Woolins’ reagent）反应制备得到的。然而，该硒代类似物对水解表现出显著的不稳定性，且无法与η⁶-芳烃钌(II)或锇(II)片段进行配位。