Coordination Chemistry of a Bis(Tetrazine) Tweezer: A Case of Host-Guest Behavior with Silver Salts

oleh: Clève D. Mboyi, Ons Amamou, Paul Fleurat-Lessard, Julien Roger, Hélène Cattey, Charles H. Devillers, Michel Meyer, Taoufik Boubaker, Jean-Cyrille Hierso

Format: Article
Diterbitkan: MDPI AG 2021-05-01

Deskripsi

The carbon-carbon cross-coupling of phenyl <i>s</i>-tetrazine (Tz) units at their <i>ortho</i>-phenyl positions allows the formation of constrained bis(tetrazines) with original tweezer structures. In these compounds, the face-to-face positioning of the central tetrazine cores is reinforced by π-stacking of the electron-poor nitrogen-containing heteroaromatic moieties. The resulting tetra-aromatic structure can be used as a weak coordinating ligand with cationic silver. This coordination generates a set of bis(tetrazine)-silver(I) coordination complexes tolerating a large variety of counter anions of various geometries, namely, PF<sub>6</sub><sup>−</sup>, BF<sub>4</sub><sup>−</sup>, SbF<sub>6</sub><sup>−</sup>, ClO<sub>4</sub><sup>−</sup>, NTf<sub>2</sub><sup>−</sup>, and OTf<sup>−</sup>. These compounds were characterized in the solid state by single-crystal X-ray diffraction (XRD) and diffuse reflectance spectroscopy, and in solution by <sup>1</sup>H-NMR, mass spectrometry, electroanalysis, and UV-visible absorption spectrophotometry. The X-ray crystal structure of complexes {[Ag(<b>3</b>)][PF<sub>6</sub>]}<sub>∞</sub> (<b>4</b>) and {[Ag(<b>3</b>)][SbF<sub>6</sub>]}<sub>∞</sub> (<b>6</b>), where <b>3</b> is 3,3′-[(1,1′-biphenyl)-2,2′-diyl]-6,6′-bis(phenyl)-1,2,4,5-tetrazine, revealed the formation of 1D polymeric chains, characterized by an evolution to a large opening of the original tweezer and a coordination of silver(I) via two chelating nitrogen atom and some C=C π-interactions. Electrochemical and UV spectroscopic properties of the original tweezer and of the corresponding silver complexes are reported and compared. <sup>1</sup>H-NMR titrations with AgNTf<sub>2</sub> allowed the determination of the stoichiometry and apparent stability of two solution species, namely [Ag(<b>3</b>)]<sup>+</sup> and [Ag(<b>3</b>)<sub>2</sub>]<sup>2+</sup>, that formed in CDCl<sub>3</sub>/CD<sub>3</sub>OD 2:1 <i>v</i>/<i>v</i> mixtures.