Das Atanu Kumar, Sarkar Biprajit, Fiedler Jan, Zális Stanislav, Hartenbach Ingo, Strobel Sabine, Lahiri Goutam Kumar, Kaim Wolfgang
Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
J Am Chem Soc. 2009 Jul 1;131(25):8895-902. doi: 10.1021/ja901746x.
Combining the concepts of noninnocent behavior of metal/ligand entities and the coupling of redox-active moieties via an electronically mediating bridge led to the synthesis and the structural, electrochemical, and spectroscopic characterization of Cl(Q)Ru(mu-tppz)Ru(Q)Cl where Q(o) is 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone and tppz(o) is 2,3,5,6-tetrakis(2-pyridyl)pyrazine, the available oxidation states being Ru(II,III,IV), Q(o,-,2-), and tppz(o,-,2-). One-electron transfer steps between the n = (2-) and (4+) states were studied by cyclic voltammetry and by EPR, UV-vis-NIR spectroelectrochemistry for the structurally characterized anti isomer of Cl(Q)Ru(mu-tppz)Ru(Q)Cl(2), 2(PF(6))(2), the only configuration obtained. The combined investigations reveal that 2(2+) is best described as Cl(Q(-))Ru(III)(mu-tppz(o))Ru(III)(Q(-))Cl with antiferromagnetic coupling between the ruthenium(III) and the iminosemiquinone components at each end. A metal-based spin as evident from large g factor anisotropy (EPR) and an intense intervalence absorption band at 1850 nm in the near-infrared (NIR) suggest that oxidation occurs at both iminosemiquinones to yield two Ru(II,III)-bonded quinones, implying redox-induced electron transfer. Reduction takes place stepwise at the metal centers yielding iminosemiquinone complexes of Ru(III,II) as evident from radical complex EPR spectra with small (99,101)Ru hyperfine contributions. After complete metal reduction to ruthenium(II) the bridging ligand tppz is being reduced stepwise as apparent from typical NIR absorption bands around 1000 nm and from small g anisotropy of the monoanion Cl(Q(-))Ru(II)(mu-tppz(-))Ru(II)(Q(*-))Cl. A structure-based DFT calculation confirms the Ru-Cl character of the HOMO and the iminoquinone-dominated LUMO and illustrates the orbital interaction pattern of the five electron transfer active components in this new system.
将金属/配体实体的非无辜行为概念与通过电子介导桥连的氧化还原活性部分的偶联相结合，导致了Cl(Q)Ru(μ-tppz)Ru(Q)Cl的合成及其结构、电化学和光谱表征，其中Q(o)为4,6-二叔丁基-N-苯基-o-亚氨基苯醌，tppz(o)为2,3,5,6-四(2-吡啶基)吡嗪，可利用的氧化态为Ru(II,III,IV)、Q(o,-,2-)和tppz(o,-,2-)。通过循环伏安法以及EPR、紫外-可见-近红外光谱电化学，对结构表征的Cl(Q)Ru(μ-tppz)Ru(Q)Cl₂、2(PF₆)₂的反式异构体（唯一得到的构型）在n = (2-)和(4+)状态之间的单电子转移步骤进行了研究。综合研究表明，2(2+)最好描述为Cl(Q(-))Ru(III)(μ-tppz(o))Ru(III)(Q(-))Cl，在两端的钌(III)和亚氨基半醌组分之间存在反铁磁耦合。从大的g因子各向异性（EPR）以及近红外（NIR）中1850 nm处的强价间吸收带可以看出基于金属的自旋，这表明氧化发生在两个亚氨基半醌上，生成两个Ru(II,III)键合的醌，这意味着氧化还原诱导的电子转移。还原在金属中心逐步发生，产生Ru(III,II)的亚氨基半醌配合物，这从具有小的(⁹⁹,¹⁰¹)Ru超精细贡献的自由基配合物EPR光谱中可以明显看出。在金属完全还原为钌(II)后，桥连配体tppz逐步被还原，这从1000 nm左右的典型近红外吸收带以及单阴离子Cl(Q(-))Ru(II)(μ-tppz(-))Ru(II)(Q(*-))Cl的小g各向异性中可以明显看出。基于结构的密度泛函理论计算证实了HOMO的Ru-Cl特征以及亚氨基醌主导的LUMO，并说明了这个新体系中五个电子转移活性组分的轨道相互作用模式。
