Facile Synthesis of Bistridentate Ru^II Complexes Based on 2,6-Di(quinolin-8-yl)pyridyl Ligands: Sensitizers with Microsecond ³MLCT Excited State Lifetimes

Synthetic routes to meridional bistridentate ruthenium(II) complexes based on 2,6-di(quinolin-8-yl)pyridyl (dqp) ligands have been investigated. Microwave-assisted synthesis at 200 °C allowed the high yield (49−87%) preparation of homoleptic meridional [Ru(dqp)2]2+-based complexes containing inert functional groups. Applying this protocol for the synthesis of mer-[Ru(dqp)2]2+ (mer-1) but lowering the temperature to 180 °C and shorter reaction times revealed the formation of the facial isomers cis,fac-1 and trans,fac-1 (56% and 12% yields, respectively). The facial isomers were characterized by NMR spectroscopy and X-ray diffraction analysis. In a stepwise protocol, the reaction of Ru(dqp)Cl3 or Ru(dqp)(L)Cl2 (L = MeCN or DMSO) and a second equivalent dqp gave mer-1 in 12−26% yields and N5Cl-coordinated [Ru(dqp)2Cl]+ (28−46%). [Ru(dqp2)Cl]+ was photochemically, or thermally in the presence of AgI, converted to mer-1. By using mer-[Ru(dqp)(MeCN)3] 2+, which was crystallographically characterized, a wide range of homo- and heteroleptic meridional [Ru(dqp)2]2+-based complexes was synthesized in up to 77% yield. The synthetic utility of meridional [Ru(dqp)2]2+-based complexes as building blocks was demonstrated by palladium-catalyzed homocoupling of mer-[Ru(dqp)(dqpPhBr)]2+ to form a dinuclear complex. The redox and photophysical properties of the meridional complexes are discussed.本研究系统探究了基于2,6-二(8-喹啉基)吡啶基（2,6-di(quinolin-8-yl)pyridyl, dqp）配体的经式双三齿钌(II)配合物的合成路线。在200 ℃下采用微波辅助合成工艺，可实现带有惰性官能团的均配型经式[Ru(dqp)₂]²⁺类配合物的高产率（49%~87%）制备。采用该合成方案制备经式[Ru(dqp)₂]²⁺（mer-1）时，若将反应温度降至180 ℃并缩短反应时长，则可得到面式异构体cis,fac-1与trans,fac-1，二者产率分别为56%和12%。上述面式异构体通过核磁共振波谱与X射线衍射分析完成了结构表征。在分步合成方案中，以Ru(dqp)Cl₃或Ru(dqp)(L)Cl₂（L=乙腈MeCN或二甲基亚砜DMSO）与第二当量的dqp配体进行反应，可得到产率为12%~26%的mer-1，以及N5Cl配位的[Ru(dqp)₂Cl]⁺（产率28%~46%）。[Ru(dqp)₂Cl]⁺可通过光化学方法，或在碘化银（AgI）存在的热条件下转化为mer-1。通过使用经晶体学表征的经式[Ru(dqp)(MeCN)₃]²⁺，可合成一系列产率最高达77%的均配型与杂配型经式[Ru(dqp)₂]²⁺类配合物。本研究验证了经式[Ru(dqp)₂]²⁺类配合物作为构建模块的合成实用性：通过钯催化的mer-[Ru(dqp)(dqpPhBr)]²⁺均偶联反应，成功得到了双核配合物。文中还对该类经式配合物的氧化还原与光物理性质进行了讨论。