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

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

doi:10.3390/molecules26092705

Abstract

The carbon-carbon cross-coupling of phenyl s-tetrazine (Tz) units at their ortho-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, PF6−, BF4−, SbF6−, ClO4−, NTf2−, and OTf−. These compounds were characterized in the solid state by single-crystal X-ray diffraction (XRD) and diffuse reflectance spectroscopy, and in solution by 1H-NMR, mass spectrometry, electroanalysis, and UV-visible absorption spectrophotometry. The X-ray crystal structure of complexes {[Ag(3)][PF6]}∞ (4) and {[Ag(3)][SbF6]}∞ (6), where 3 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. 1H-NMR titrations with AgNTf2 allowed the determination of the stoichiometry and apparent stability of two solution species, namely [Ag(3)]+ and [Ag(3)2]2+, that formed in CDCl3/CD3OD 2:1 v/v mixtures.

Highlights

The s-tetrazine (Tz) unit (Figure 1, 1) is an object of high interest in photophysics and for biomedical applications, owing to its electron-poor poly(hetero)aromatic nature that is amenable to click chemistry [1,2,3]
We recently reported a copper-catalyzed homocoupling protocol, which allowed the efficient synthesis of constrained bis(tetrazines) with a unique bridge clamp structure (Figure 1, 3) [3]
The resulting discrete coordination polymers were identified by the combination of physicochemical analyses in solution and X-ray diffraction (XRD) identification in the solid state

Summary

Introduction

The s-tetrazine (Tz) unit (Figure 1, 1) is an object of high interest in photophysics and for biomedical applications, owing to its electron-poor poly(hetero)aromatic nature that is amenable to click chemistry [1,2,3]. We recently reported a copper-catalyzed homocoupling protocol, which allowed the efficient synthesis of constrained bis(tetrazines) with a unique bridge clamp structure (Figure 1, 3) [3]. These compounds have been studied in the solid state by X-ray diffraction (XRD, Figure 1a) and analyzed by DFT. We have established that London dispersion forces between the Tz moieties clearly stabilize and favor the clamp geometry. In their absence, the tweezer-like interconversion barrier between the most stable rotamers corresponding

Methods

Results

Conclusion