Role of Mediator and Effects of Temperature on ortho-C–N Bond Fusion Reactions of Aniline Using Ruthenium Templates: Isolation and Characterization of New Ruthenium Complexes of the in-Situ-Generated Ligands

In this work, ortho-C–N bond fusion reactions of aniline are followed by the use of two different ruthenium mediators. Reaction of aniline with [RuIII(terpy)­Cl3] (terpy = 2,2′:6′,2″-terpyridine) resulted in a trans bis-aniline ruthenium­(II) complex [1]+ which upon oxidation with H2O2 produced compound [2]+ of a bidentate ligand, N-phenyl-1,2-benzoquinonediimine, due to an oxidative ortho-C–N bond fusion reaction. Complex [1]+ and aniline (neat) at 185 °C produced a bis-chelated ruthenium complex (3). A previously reported complex [RuII(N-phenyl-1,2-benzoquinonediimine)­(aniline)2(Cl)2] (5) undergoes similar oxidation by air at 185 °C to produce complex [3]. A separate chemical reaction between aniline and strongly oxidizing tetra-n-propylammonium perruthenate [(n-pr)4N]+[RuO4]− in air produced a ruthenium complex [4] of a N4-tetraamidophenylmacrocycle ligand via multiple ortho-C–N bond fusion reaction. Notably, the yield of this product is low (5%) at 100 °C but increases to 25% in refluxing aniline. All these complexes are characterized fully by their physicochemical characterizations and X-ray structure determination. From their structural parameters and other spectroscopic studies, complex [2]+ is assigned as [RuII(terpy)­(N-phenyl-1,2-benzoquinonediimine)­(Cl)]+ whereas complex [4] is described as a ruthenium­(VI) complex comprised of a reduced deprotonated N-phenyl-1,2-diamidobenzene and N4-tetraamidophenylmacrocyclic ligand. Complex [2]+ exhibits one reversible oxidation at 1.32 V and one reversible reduction at −0.75 V vs Ag/AgCl reference electrode. EPR of the electrogenerated complexes has revealed that the oxidized complex is a ruthenium­(III) complex with an axial EPR spectrum at gav= 2.06. The reduced complex [2], on the other hand, shows a single-line EPR signal at gav= 1.998. In contrast, complex [4] shows two successive one-electron oxidation waves at 0.5 and 0.8 V and an irreversible reduction wave at −0.9 V. EPR studies of the oxidized complexes [4]+ and [4]2+ reveal that oxidations are ligand centered. DFT calculations were employed to elucidate the electronic structures as well as the redox processes associated with the above complexes. Aerial ortho-C–N bond fusion reactions of aniline using two different mediators, viz. [RuIII(terpy)­Cl3] and [(n-pr)4N]+[RuO4]−, have been followed. It is found that in the case of oxidizable Ru­(III) mediator complex, C–N bond fusion is limited only to dimerization reaction whereas the high-valent Ru­(VII) salt mediates multiple C–N bond fusion reactions leading to the formation of a novel tetradentate N4-tetraamidophenylmacrocyclic ligand. Valence ambiguity in the complexes of the resultant redox-active ligands is scrutinized.本工作针对苯胺的邻位C-N键融合反应，采用两种不同的钌介导剂开展研究。苯胺与[RuIII(terpy)Cl3]（terpy = 2,2′:6′,2″-三联吡啶，2,2′:6′,2″-terpyridine）反应，生成反式双苯胺合钌(II)配合物[1]+；该配合物经过氧化氢氧化后，因发生氧化型邻位C-N键融合反应，得到双齿配体N-苯基-1,2-苯醌二亚胺配位的配合物[2]+。配合物[1]+与纯苯胺在185 ℃下反应，生成双螯合钌配合物(3)。此前已有报道的配合物[RuII(N-苯基-1,2-苯醌二亚胺)(苯胺)2(Cl)2] (5)，在185 ℃下经空气氧化后，同样得到配合物[3]。苯胺与强氧化性高钌酸四正丙基铵[(n-pr)4N]+[RuO4]−在空气氛围中发生独立化学反应，通过多步邻位C-N键融合反应，生成配位有N4-四酰胺苯基大环配体的钌配合物[4]。值得注意的是，该产物在100 ℃下产率仅为5%，但在回流苯胺条件下可提升至25%。所有上述配合物均通过完整的物理化学表征与X射线晶体结构测定完成了结构确认。基于结构参数与其他光谱学研究，配合物[2]+被指认为[RuII(terpy)(N-苯基-1,2-苯醌二亚胺)(Cl)]+，而配合物[4]则被描述为包含还原去质子化的N-苯基-1,2-二酰胺苯与N4-四酰胺苯基大环配体的钌(VI)配合物。配合物[2]+在相对于Ag/AgCl参比电极的条件下，于1.32 V处呈现一处可逆氧化峰，在-0.75 V处呈现一处可逆还原峰。对电化学生成的配合物进行电子顺磁共振（EPR）研究表明，氧化态配合物为钌(III)配合物，其轴向EPR谱的g因子平均值gav= 2.06；而还原态配合物[2]则在gav= 1.998处显示单峰EPR信号。与之相对，配合物[4]在0.5 V与0.8 V处呈现两处连续的单电子氧化波，在-0.9 V处呈现一处不可逆还原峰。对氧化态配合物[4]+与[4]2+的EPR研究显示，其氧化过程均发生在配体中心。本研究采用密度泛函理论（DFT）计算，阐明了上述配合物的电子结构以及与之相关的氧化还原过程。本工作针对两种不同介导剂——[RuIII(terpy)Cl3]与[(n-pr)4N]+[RuO4]−——催化的苯胺空气氧化邻位C-N键融合反应进行了追踪研究。结果发现，对于可被氧化的Ru(III)介导剂配合物，C-N键融合反应仅局限于二聚过程；而高价Ru(VII)盐则可介导多步C-N键融合反应，最终生成新型四齿N4-四酰胺苯基大环配体。本研究还对氧化还原活性配体配合物中存在的价态歧义问题进行了细致探讨。