4.7 Article

[(η6-p-Cymene)[3-(pyrid-2-yl)-1,2,4,5-tetrazine]chlororuthenium(II)]+, Redox Noninnocence and Dienophile Addition to Coordinated Tetrazine

Journal

INORGANIC CHEMISTRY
Volume 60, Issue 9, Pages 6367-6374

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.1c00094

Keywords

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Funding

  1. state of Baden-Wurttemberg through bwHPC
  2. German Research Foundation [INST 40/467-1 FUGG]
  3. [SFB1333 C2]

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The bidentate ligand TzPy showed noninnocent behavior and could be modified by dienophiles. The kinetic analysis of the reaction between [1](+) and ViFc yielded Delta G double dagger(298 K) = 67 kJ mol(-1), while that of [1](+) and EthFc was Delta G double dagger(298 K) = 83 kJ mol(-1). The electrochemical reduction mechanism of [1Fc](+) was studied using cyclic voltammetry and UV-vis SEC experiments, supported by DFT calculations.
The bidentate ligand 3-(pyrid-2-yl)-1,2,4,5-tetrazine (TzPy) coordinated in the complex [CyRuCl(TzPy)]PF6 ([1](+); Cy = eta(6)-p-cymene) shows noninnocent behavior and can be modified through the addition of dienophiles, vinylferrocene (ViFc) or ethynylferrocene (EthFc). The kinetics and transition-state thermo-dynamic analysis of the reaction of [1](+) + ViFc found Delta G double dagger(298 K) = 67 kJ mol(-1), while that of [1](+) + EthFc was Delta G double dagger(298 K) = 83 kJ mol(-1). The room temperature second-order rate of [1](+) + EthFc, k(2) = 1.51(4) x 10(-2) M-1 s(-1), was 3 orders of magnitude faster than that of EthFc + TzPy, k(2) = 1.05(15) x 10(-4) M-1 s(-1). The [1H(2)Fc](+) complex was converted to [1Fc](+) by oxidation with oxygen and 3,5-di-tert-butyl-o-quinone, and the molecular structure of [1Fc](+) was determined by single-crystal X-ray diffraction. The title complex [1](+) showed a quasi-reversible reduction in the cyclic voltammogram, and the electrochemical reduction mechanism was determined by UV-vis spectroelectrochemistry (SEC) experiments, as well as supported by density functional theory (DFT) calculations. The dihydropyridazine [1H(2)Fc](+) and pyridazine [1Fc](+) states of the ligand showed ligand noninnocence similar to that of the parent tetrazine but at a cathodically shifted potential. The dihydropyridazine [1H(2)Fc](+) showed a mixture of several products; however, upon oxidation, only a single product, [1Fc](+), was formed from the endo addition of the dienophile to [1](+). The electrochemical mechanism of [1Fc](+) was also studied by cyclic voltammetry and UV-vis SEC experiments, as well as supported by DFT calculations.

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