Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities
We report here the synthesis, characterization and behavior of a series of Pt(II) cyclometalated rollover complexes with two substituted bipyridines, 6-ethyl-2,2′-bipyridine (bpy<sup>6Et</sup>) and 6-methoxy-2,2′-bipyridine (bpy<sup>6OMe</sup>), in comparison with previously...
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MDPI AG
2020-09-01
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| Series: | Applied Sciences |
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| Online Access: | https://www.mdpi.com/2076-3417/10/19/6665 |
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| author | Antonio Zucca Luca Maidich Maria I. Pilo Sara Pischedda Mondina Sedda Sergio Stoccoro |
| author_facet | Antonio Zucca Luca Maidich Maria I. Pilo Sara Pischedda Mondina Sedda Sergio Stoccoro |
| author_sort | Antonio Zucca |
| collection | DOAJ |
| description | We report here the synthesis, characterization and behavior of a series of Pt(II) cyclometalated rollover complexes with two substituted bipyridines, 6-ethyl-2,2′-bipyridine (bpy<sup>6Et</sup>) and 6-methoxy-2,2′-bipyridine (bpy<sup>6OMe</sup>), in comparison with previously studied 2,2′-bipyridine complexes. The two ligands have similar steric hindrance but different electronic properties. As a result, the reactivity of the two series of complexes follows very different routes. In particular, the new complexes behave differently towards protonation reactions, differences given by substituents and ancillary ligands, added to the presence of several nucleophilic centers. Reaction of complex [Pt(bpy<sup>6OMe</sup>-H)(PPh<sub>3</sub>)Me)] with [H<sub>3</sub>O⋅18-crown-6][BF<sub>4</sub>] results in a retro-rollover reaction whose final product is the cationic adduct [Pt(bpy<sup>6OMe</sup>)(PPh<sub>3</sub>)Me)]<sup>+</sup>. Surprisingly, only the isomer with the <i>cis</i>-PPh<sub>3</sub>-OMe geometry is formed; in spite of an expected instability due to steric hindrance, Density-Functional theory (DFT) calculations showed that this isomer is the most stable. This result shows that the cone angle is far from being a real “solid cone” and should lead to a different interpretation of well-known concepts concerning steric bulk of ligands, such as cone angle. Proton affinity values of ligands, neutral complexes and their protonated counterparts were analyzed by means of DFT calculations, allowing a comparison of their properties. |
| first_indexed | 2024-03-10T16:05:42Z |
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| institution | Directory Open Access Journal |
| issn | 2076-3417 |
| language | English |
| last_indexed | 2024-03-10T16:05:42Z |
| publishDate | 2020-09-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Applied Sciences |
| spelling | doaj.art-6ea03eab3c504c4d9c5945cb4c00fddb2023-11-20T14:52:15ZengMDPI AGApplied Sciences2076-34172020-09-011019666510.3390/app10196665Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple PersonalitiesAntonio Zucca0Luca Maidich1Maria I. Pilo2Sara Pischedda3Mondina Sedda4Sergio Stoccoro5Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, ItalyDipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, ItalyDipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, ItalyDipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, ItalyDipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, ItalyDipartimento di Chimica e Farmacia, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, ItalyWe report here the synthesis, characterization and behavior of a series of Pt(II) cyclometalated rollover complexes with two substituted bipyridines, 6-ethyl-2,2′-bipyridine (bpy<sup>6Et</sup>) and 6-methoxy-2,2′-bipyridine (bpy<sup>6OMe</sup>), in comparison with previously studied 2,2′-bipyridine complexes. The two ligands have similar steric hindrance but different electronic properties. As a result, the reactivity of the two series of complexes follows very different routes. In particular, the new complexes behave differently towards protonation reactions, differences given by substituents and ancillary ligands, added to the presence of several nucleophilic centers. Reaction of complex [Pt(bpy<sup>6OMe</sup>-H)(PPh<sub>3</sub>)Me)] with [H<sub>3</sub>O⋅18-crown-6][BF<sub>4</sub>] results in a retro-rollover reaction whose final product is the cationic adduct [Pt(bpy<sup>6OMe</sup>)(PPh<sub>3</sub>)Me)]<sup>+</sup>. Surprisingly, only the isomer with the <i>cis</i>-PPh<sub>3</sub>-OMe geometry is formed; in spite of an expected instability due to steric hindrance, Density-Functional theory (DFT) calculations showed that this isomer is the most stable. This result shows that the cone angle is far from being a real “solid cone” and should lead to a different interpretation of well-known concepts concerning steric bulk of ligands, such as cone angle. Proton affinity values of ligands, neutral complexes and their protonated counterparts were analyzed by means of DFT calculations, allowing a comparison of their properties.https://www.mdpi.com/2076-3417/10/19/6665cyclometalated compoundsrollover cyclometalationbipyridines |
| spellingShingle | Antonio Zucca Luca Maidich Maria I. Pilo Sara Pischedda Mondina Sedda Sergio Stoccoro Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities Applied Sciences cyclometalated compounds rollover cyclometalation bipyridines |
| title | Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities |
| title_full | Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities |
| title_fullStr | Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities |
| title_full_unstemmed | Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities |
| title_short | Pt(II) Derivatives with Rollover-Coordinated 6-substituted 2,2′-bipyridines: Ligands with Multiple Personalities |
| title_sort | pt ii derivatives with rollover coordinated 6 substituted 2 2 bipyridines ligands with multiple personalities |
| topic | cyclometalated compounds rollover cyclometalation bipyridines |
| url | https://www.mdpi.com/2076-3417/10/19/6665 |
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