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<p>A series of benzimidazolium salts and their corresponding η⁶-arene–η¹-carbene ruthenium(II) complexes were synthesized and fully characterized. The well-defined half-sandwich Ru(II) complexes incorporate a strongly σ-donating benzimidazole-derived N-heterocyclic carbene ligand coordinated in an η¹-fashion, together with an η⁶-bound arene ligand, generating a robust piano-stool architecture. All compounds were characterized by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy, IR spectroscopy, and elemental analysis. The molecular structure of a representative complex was unambiguously confirmed by single-crystal X-ray diffraction analysis, verifying the η⁶-arene–η¹-carbene coordination mode and providing detailed insight into the metal coordination environment. The catalytic performance of the synthesized complexes was evaluated in the base-promoted transfer hydrogenation of various ketones using isopropanol as hydrogen donor and KOBu<sup>t</sup> as base at 80&#xa0;°C. Comparative catalytic studies indicate that the electronic and steric properties of the benzimidazole derived NHC ligands significantly influence catalytic efficiency within the η⁶-arene–η¹-carbene framework. The rigid benzimidazole backbone contributes to catalyst stability under basic conditions, while modulation of ligand substituents affects hydride formation and substrate coordination. These findings highlight the importance of rational ligand design in tuning the reactivity of η⁶-arene–η¹-carbene ruthenium(II) complexes for transfer hydrogenation applications. Additionally, the molecules were optimized using density functional theory (DFT) calculations, and the energies as well as spatial distributions of the frontier molecular orbitals were analyzed to gain insight into potential interaction residues.</p>

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Synthesis, structural characterization and transfer hydrogenation activity of η⁶-Arene Ruthenium(II)–NHC complexes

  • 期刊论文

  • 发表日期：

    2026年7月31日

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  • Serpil Demir Düşünceli,
  • Elvan Üstün,
  • Onur Şahin

摘要

A series of benzimidazolium salts and their corresponding η⁶-arene–η¹-carbene ruthenium(II) complexes were synthesized and fully characterized. The well-defined half-sandwich Ru(II) complexes incorporate a strongly σ-donating benzimidazole-derived N-heterocyclic carbene ligand coordinated in an η¹-fashion, together with an η⁶-bound arene ligand, generating a robust piano-stool architecture. All compounds were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analysis. The molecular structure of a representative complex was unambiguously confirmed by single-crystal X-ray diffraction analysis, verifying the η⁶-arene–η¹-carbene coordination mode and providing detailed insight into the metal coordination environment. The catalytic performance of the synthesized complexes was evaluated in the base-promoted transfer hydrogenation of various ketones using isopropanol as hydrogen donor and KOBut as base at 80 °C. Comparative catalytic studies indicate that the electronic and steric properties of the benzimidazole derived NHC ligands significantly influence catalytic efficiency within the η⁶-arene–η¹-carbene framework. The rigid benzimidazole backbone contributes to catalyst stability under basic conditions, while modulation of ligand substituents affects hydride formation and substrate coordination. These findings highlight the importance of rational ligand design in tuning the reactivity of η⁶-arene–η¹-carbene ruthenium(II) complexes for transfer hydrogenation applications. Additionally, the molecules were optimized using density functional theory (DFT) calculations, and the energies as well as spatial distributions of the frontier molecular orbitals were analyzed to gain insight into potential interaction residues.