Phenylcyanamidoruthenium Scorpionate Complexes

Nine [Ru­(Tp)­(dppe)­L] complexes, where Tp is hydrotris­(pyrazol-1-yl)­borate, dppe is ethylenebis­(diphenylphosphine), and L is (4-nitrophenyl)­cyanamide (NO2pcyd–), (2-chlorophenyl)­cyanamide (2-Clpcyd–), (3-chlorophenyl)­cyanamide (3-Clpcyd–), (2,4-dichlorophenyl)­cyanamide (2,4-Cl2pcyd–), (2,3-dichlorophenyl)­cyanamide (2,3-Cl2pcyd–), (2,5-dichlorophenyl)­cyanamide (2,5-Cl2pcyd–), (2,4,5-trichlorophenyl)­cyanamide (2,4,5-Cl3pcyd–), (2,3,5,6-tetrachlorophenyl)­cyanamide (2,3,5,6-Cl4pcyd–), and (pentachlorophenyl)­cyanamide (Cl5pcyd–), and the dinuclear complex [{Ru­(Tp)­(dppe)}2(μ-adpc)], where adpc2– is azo-4,4-diphenylcyanamide, have been prepared and characterized. The crystal structures of [Ru­(Tp)­(dppe)­(Cl5pcyd)] and [{Ru­(Tp)­(dppe)}2(μ-adpc)] reveal the RuII ion to occupy a pseudooctahedral coordination sphere in which the cyanamide ligand coordinates to RuII by its terminal nitrogen atom. For both complexes, the cyanamide ligands are planar, indicating significant π mixing between the cyanamide and phenyl moieties as well as the azo group in the case of adpc2–. The optical spectra of the nominally ruthenium­(III) species [Ru­(Tp)­(dppe)­L]+ were obtained through spectroelectrochemistry measurements and showed an intense near-IR absorption band. Time-dependent density functional theory calculations of these species revealed that oxidation of the ruthenium­(II) species led to species where partial oxidation of the cyanamide ligand had occurred, indicative of noninnocent character for these ligands. The spin densities reveal that while the 3-Clpycd species has substantial RuII(3-Clpycd0) character, the Cl5pycd species is a much more localized ruthenium­(III) complex of the Cl5pycd monoanion. Some bond order and charge distribution data are derived for these ruthenium­(III) species. The near-IR band is assigned as a quite complex mixture of d–d, 4dπ to L­(NCN) MLCT, and L­(NCN) to Ru 4d LMCT with even a scorpionate ligand component. Spectroelectrochemistry was also performed on [{Ru­(Tp)­(dppe)}2(μ-adpc)] to generate the mixed-valence state. The intense intervalence transition that is observed in the near-IR is very similar to that previously reported for [{Ru­(trpy)­(bpy)}2(μ-adpc)]2+, where trpy is 2,2′:6′,2″-terpyridine and bpy is 2,2′-bipyridine, and by analogy identifies [{Ru­(Tp)­(dppe)}2(μ-adpc)]+ as a delocalized mixed-valence complex.本研究合成并表征了九种[Ru(Tp)(dppe)L]型配合物，其中Tp为氢化三(吡唑-1-基)硼酸根（hydrotris(pyrazol-1-yl)borate），dppe为亚乙基双(二苯基膦)（ethylenebis(diphenylphosphine)），L分别为(4-硝基苯基)氰酰胺根(NO₂pcyd⁻)、(2-氯苯基)氰酰胺根(2-Clpcyd⁻)、(3-氯苯基)氰酰胺根(3-Clpcyd⁻)、(2,4-二氯苯基)氰酰胺根(2,4-Cl₂pcyd⁻)、(2,3-二氯苯基)氰酰胺根(2,3-Cl₂pcyd⁻)、(2,5-二氯苯基)氰酰胺根(2,5-Cl₂pcyd⁻)、(2,4,5-三氯苯基)氰酰胺根(2,4,5-Cl₃pcyd⁻)、(2,3,5,6-四氯苯基)氰酰胺根(2,3,5,6-Cl₄pcyd⁻)以及(五氯苯基)氰酰胺根(Cl₅pcyd⁻)；此外还制备并表征了双核配合物[{Ru(Tp)(dppe)}₂(μ-adpc)]，其中adpc²⁻为偶氮-4,4'-二苯基氰酰胺根（azo-4,4-diphenylcyanamide）。对[Ru(Tp)(dppe)(Cl₅pcyd)]与[{Ru(Tp)(dppe)}₂(μ-adpc)]的晶体结构解析结果表明，Ru(II)离子处于伪八面体配位环境中，氰酰胺配体通过末端氮原子与Ru(II)配位。两种配合物中的氰酰胺配体均呈平面构型，这表明氰酰胺与苯基片段之间存在显著的π轨道相互作用；对于adpc²⁻配体而言，其还与偶氮基团存在类似相互作用。通过光谱电化学测试获取了名义价态为Ru(III)的[Ru(Tp)(dppe)L]⁺物种的光谱，该类物种展现出强的近红外吸收带。对该类物种开展的含时密度泛函理论（time-dependent density functional theory, TDDFT）计算结果显示，Ru(II)前体的氧化过程会引发氰酰胺配体发生部分氧化，这证实此类配体具有非无辜配体（noninnocent ligand）的特性。自旋密度分析结果表明，3-Clpcyd物种主要表现为Ru(II)(3-Clpcyd⁰)的特征，而Cl₅pcyd物种则为局域性更强的、由Cl₅pcyd单阴离子与Ru(III)形成的配合物。本研究还推导得到了此类Ru(III)物种的部分键级与电荷分布数据。该近红外吸收带被归因为多种跃迁混合的复杂谱带，包括d-d跃迁、4dπ→L(NCN)金属到配体电荷转移（MLCT）、L(NCN)→Ru 4d配体到金属电荷转移（LMCT），甚至还包含蝎型配体（scorpionate ligand）的贡献。本研究还对[{Ru(Tp)(dppe)}₂(μ-adpc)]开展了光谱电化学测试以制备其混合价态物种。在近红外区观测到的强区间电荷转移（intervalence transition, IVCT）吸收带，与此前报道的[{Ru(trpy)(bpy)}₂(μ-adpc)]²⁺的吸收带极为相似；其中trpy为2,2':6',2''-三联吡啶（2,2':6',2''-terpyridine），bpy为2,2'-联吡啶（2,2'-bipyridine）。通过类比可将[{Ru(Tp)(dppe)}₂(μ-adpc)]⁺归属于离域型混合价配合物。