Troponate/Aminotroponate Ruthenium–Arene Complexes: Synthesis, Structure, and Ligand-Tuned Mechanistic Pathway for Direct C–H Bond Arylation with Aryl Chlorides in Water

A series of water-soluble troponate/aminotroponate ruthenium­(II)–arene complexes were synthesized, where O,O and N,O chelating troponate/aminotroponate ligands stabilized the piano-stool mononuclear ruthenium–arene complexes. Structural identities for two of the representating complexes were also established by single-crystal X-ray diffraction studies. These newly synthesized troponate/aminotroponate ruthenium–arene complexes enable efficient C–H bond arylation of arylpyridine in water. The unique structure–activity relationship in these complexes is the key to achieve efficient direct C–H bond arylation of arylpyridine. Moreover, the steric bulkiness of the carboxylate additives systematically directs the selectivity toward mono- versus diarylation of arylpyridines. Detailed mechanistic studies were performed using mass-spectral studies including identification of several key cyclometalated intermediates. These studies provided strong support for an initial cycloruthenation driven by carbonate-assisted deprotonation of 2-phenylpyridine, where the relative strength of η6-arene and the troponate/aminotroponate ligand drives the formation of cyclometalated 2-phenylpyridine Ru–arene species, [(η6-arene)­Ru­(κ2-C,N-phenylpyridine) (OH2)]+ by elimination of troponate/aminotroponate ligands and retaining η6-arene, while cyclometalated 2-phenylpyridine Ru–troponate/aminotroponate species [(κ 2-troponate/aminotroponate)­Ru­(κ2-C,N-phenylpyridine)­(OH2)2] was generated by decoordination of η6-arene ring during initial C–H bond activation of 2-phenylpyridine. Along with the experimental mass-spectral evidence, density functional theory calculation also supports the formation of such species for these complexes. Subsequently, these cycloruthenated products activate aryl chloride by facile oxidative addition to generate C–H arylated products.本研究合成了一系列水溶性草酚酮（troponate）/氨基草酚酮（aminotroponate）合钌(II)-芳烃配合物，其中O,O与N,O双齿螯合的草酚酮/氨基草酚酮配体稳定了该类“钢琴凳”型单核钌-芳烃配合物。研究通过单晶X射线衍射分析确定了两款代表性配合物的晶体结构。这些新合成的草酚酮/氨基草酚酮合钌(II)-芳烃配合物可在水相中高效实现芳基吡啶的C-H键芳基化反应。该类配合物独特的构效关系是实现芳基吡啶直接C-H键高效芳基化的核心关键。此外，羧酸添加剂的空间位阻效应可系统调控芳基吡啶单芳基化与双芳基化的反应选择性。本研究通过质谱表征开展了详细的机理研究，成功鉴定出多个关键环金属化中间体。上述研究为以下反应路径提供了有力支撑：2-苯基吡啶在碳酸根辅助下发生去质子化，进而引发初始环钌化过程；其中η⁶-芳烃（η⁶-arene）与草酚酮/氨基草酚酮配体的相对配位强度决定了两类环金属化钌-芳烃物种的生成路径：其一为脱除草酚酮/氨基草酚酮配体并保留η⁶-芳烃，生成[(η⁶-芳烃)Ru(κ²-C,N-苯基吡啶)(OH₂)]⁺；其二为在2-苯基吡啶初始C-H键活化阶段发生η⁶-芳烃环脱配位，生成[(κ²-草酚酮/氨基草酚酮)Ru(κ²-C,N-苯基吡啶)(OH₂)₂]。除实验质谱证据外，密度泛函理论（density functional theory, DFT）计算也佐证了该类物种在上述配合物中的形成过程。后续，这些环钌化产物可通过易于进行的氧化加成步骤活化芳基氯代物，最终生成C-H键芳基化产物。