Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization
Searching for new and efficient transfer hydrogenation catalysts, a series of new organometallic ruthenium(II)-arene complexes of the formulae [Ru(η<sup>6</sup>-<i>p</i>-cymene)(L)Cl][PF<sub>6</sub>] (<b>1</b>–<b>8</b>) and [Ru(η<sup>...
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| author | Nikolaos Zacharopoulos Gregor Schnakenburg Eleni I. Panagopoulou Nikolaos S. Thomaidis Athanassios I. Philippopoulos |
| author_facet | Nikolaos Zacharopoulos Gregor Schnakenburg Eleni I. Panagopoulou Nikolaos S. Thomaidis Athanassios I. Philippopoulos |
| author_sort | Nikolaos Zacharopoulos |
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| description | Searching for new and efficient transfer hydrogenation catalysts, a series of new organometallic ruthenium(II)-arene complexes of the formulae [Ru(η<sup>6</sup>-<i>p</i>-cymene)(L)Cl][PF<sub>6</sub>] (<b>1</b>–<b>8</b>) and [Ru(η<sup>6</sup>-<i>p</i>-cymene)(L)Cl][Ru(η<sup>6</sup>-<i>p</i>-cymene)Cl<sub>3</sub>] (<b>9</b>–<b>11</b>) were synthesized and fully characterized. These were prepared from the reaction of pyridine–quinoline and biquinoline-based ligands (L) with [Ru(η<sup>6</sup>-<i>p</i>-cymene)(μ-Cl)Cl]<sub>2</sub>, in 1:2 and 1:1, metal (M) to ligand (L) molar ratios. Characterization includes a combination of spectroscopic methods (FT-IR, UV-Vis, multi nuclear NMR), elemental analysis and single-crystal X-ray crystallography. The pyridine–quinoline organic entities encountered, were prepared in high yield either via the thermal decarboxylation of the carboxylic acid congeners, namely 2,2′-pyridyl-quinoline-4-carboxylic acid (<b>pqca</b>), 8-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (<b>8-Mepqca</b>), 6′-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (<b>6′-Mepqca</b>) and 8,6′-dimethyl-2,2′-pyridyl-quinoline-4-carboxylic acid (<b>8,6′-Me<sub>2</sub>pqca</b>), affording the desired ligands <b>pq</b>, <b>8-Mepq, 6′-Mepq</b> and <b>8,6′-Me<sub>2</sub>pq</b>, or by the classical Friedländer condensation, to yield 4,6′-dimethyl-2,2′-pyridyl-quinoline (<b>4,6′-Me<sub>2</sub>pq</b>) and 4-methyl-2,2′-pyridyl-quinoline (<b>4-Mepq</b>), respectively. The solid-state structures of complexes <b>1</b>–<b>4</b>, <b>6, 8</b> and <b>9</b> were determined showing a distorted octahedral coordination geometry. The unit cell of <b>3</b> contains two independent molecules (Ru-<b>3</b>), (Ru′-<b>3</b>) in a 1:1 ratio, due to a slight rotation of the arene ring. All complexes catalyze the transfer hydrogenation of acetophenone, using 2-propanol as a hydrogen donor in the presence of KO<i>i</i>Pr. Among them, complexes <b>1</b> and <b>5</b> bearing methyl groups at the 8 and 4 position of the quinoline moiety, convert acetophenone to 1-phenylethanol quantitatively, within approximately 10 min with final TOFs of 1600 h<sup>−1</sup>. The catalytic performance of complexes <b>1</b>–<b>11</b>, towards the transfer hydrogenation of <i>p</i>-substituted acetophenone derivatives and benzophenone, ranges from moderate to excellent. An inner-sphere mechanism has been suggested based on the detection of ruthenium(II) hydride species. |
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| institution | Kabale University |
| issn | 1420-3049 |
| language | English |
| publishDate | 2025-07-01 |
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| spelling | doaj-art-516456d689c544f4a1735eecccb81de22025-08-20T03:56:49ZengMDPI AGMolecules1420-30492025-07-013014294510.3390/molecules30142945Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural CharacterizationNikolaos Zacharopoulos0Gregor Schnakenburg1Eleni I. Panagopoulou2Nikolaos S. Thomaidis3Athanassios I. Philippopoulos4Laboratory of Inorganic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, 15771 Athens, GreeceInstitut für Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Straße 1, D-53121 Bonn, GermanyLaboratory of Analytical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, 15771 Athens, GreeceLaboratory of Analytical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, 15771 Athens, GreeceLaboratory of Inorganic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, 15771 Athens, GreeceSearching for new and efficient transfer hydrogenation catalysts, a series of new organometallic ruthenium(II)-arene complexes of the formulae [Ru(η<sup>6</sup>-<i>p</i>-cymene)(L)Cl][PF<sub>6</sub>] (<b>1</b>–<b>8</b>) and [Ru(η<sup>6</sup>-<i>p</i>-cymene)(L)Cl][Ru(η<sup>6</sup>-<i>p</i>-cymene)Cl<sub>3</sub>] (<b>9</b>–<b>11</b>) were synthesized and fully characterized. These were prepared from the reaction of pyridine–quinoline and biquinoline-based ligands (L) with [Ru(η<sup>6</sup>-<i>p</i>-cymene)(μ-Cl)Cl]<sub>2</sub>, in 1:2 and 1:1, metal (M) to ligand (L) molar ratios. Characterization includes a combination of spectroscopic methods (FT-IR, UV-Vis, multi nuclear NMR), elemental analysis and single-crystal X-ray crystallography. The pyridine–quinoline organic entities encountered, were prepared in high yield either via the thermal decarboxylation of the carboxylic acid congeners, namely 2,2′-pyridyl-quinoline-4-carboxylic acid (<b>pqca</b>), 8-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (<b>8-Mepqca</b>), 6′-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (<b>6′-Mepqca</b>) and 8,6′-dimethyl-2,2′-pyridyl-quinoline-4-carboxylic acid (<b>8,6′-Me<sub>2</sub>pqca</b>), affording the desired ligands <b>pq</b>, <b>8-Mepq, 6′-Mepq</b> and <b>8,6′-Me<sub>2</sub>pq</b>, or by the classical Friedländer condensation, to yield 4,6′-dimethyl-2,2′-pyridyl-quinoline (<b>4,6′-Me<sub>2</sub>pq</b>) and 4-methyl-2,2′-pyridyl-quinoline (<b>4-Mepq</b>), respectively. The solid-state structures of complexes <b>1</b>–<b>4</b>, <b>6, 8</b> and <b>9</b> were determined showing a distorted octahedral coordination geometry. The unit cell of <b>3</b> contains two independent molecules (Ru-<b>3</b>), (Ru′-<b>3</b>) in a 1:1 ratio, due to a slight rotation of the arene ring. All complexes catalyze the transfer hydrogenation of acetophenone, using 2-propanol as a hydrogen donor in the presence of KO<i>i</i>Pr. Among them, complexes <b>1</b> and <b>5</b> bearing methyl groups at the 8 and 4 position of the quinoline moiety, convert acetophenone to 1-phenylethanol quantitatively, within approximately 10 min with final TOFs of 1600 h<sup>−1</sup>. The catalytic performance of complexes <b>1</b>–<b>11</b>, towards the transfer hydrogenation of <i>p</i>-substituted acetophenone derivatives and benzophenone, ranges from moderate to excellent. An inner-sphere mechanism has been suggested based on the detection of ruthenium(II) hydride species.https://www.mdpi.com/1420-3049/30/14/2945pyridine–quinoline ligands<i>p</i>-cymeneruthenium complexesketonestransfer hydrogenationhydrogenation |
| spellingShingle | Nikolaos Zacharopoulos Gregor Schnakenburg Eleni I. Panagopoulou Nikolaos S. Thomaidis Athanassios I. Philippopoulos Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization Molecules pyridine–quinoline ligands <i>p</i>-cymene ruthenium complexes ketones transfer hydrogenation hydrogenation |
| title | Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization |
| title_full | Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization |
| title_fullStr | Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization |
| title_full_unstemmed | Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization |
| title_short | Pyridine–Quinoline and Biquinoline-Based Ruthenium <i>p</i>-Cymene Complexes as Efficient Catalysts for Transfer Hydrogenation Studies: Synthesis and Structural Characterization |
| title_sort | pyridine quinoline and biquinoline based ruthenium i p i cymene complexes as efficient catalysts for transfer hydrogenation studies synthesis and structural characterization |
| topic | pyridine–quinoline ligands <i>p</i>-cymene ruthenium complexes ketones transfer hydrogenation hydrogenation |
| url | https://www.mdpi.com/1420-3049/30/14/2945 |
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