Proton ionizable 1H-1,2,4-triazole pi-electron deficient cyclophanes as hosts and in [2]catenanes

Abstract

The incorporation of proton ionizable moieties, such as 1H-1,2,4-triazole rings, within cyclophanes and pi-donor/pi-acceptor [2]catenanes is explored as a tool of inducing chemical switchability through either the inherent prototropic tautomerism or chemical deprotonation. Bearing this in mind, in this paper we describe the template-directed synthesis of two tetracationic cyclophanes incorporating two bipyridinium units linked by either one 3,5-bis(methylene)-1H-1,2,4-triazole unit and a p-xylyl unit or two 3,5-bis(methylene)-1H-1,2,4-triazole units, as well as the template-directed synthesis of two [2]catenanes wherein these pi-acceptor cyclophanes are interlocked with (bis-p-phenylene-34-crown-10), as the pi-electron rich polyether macrocycle. We also report on the full characterization of the cyclophanes and the [2]catenanes by electrospray mass spectrometry (ESMS) and fast atom bombardment mass spectrometry (FABMS), X-ray crystallography of the [2]catenanes and dynamic H-1 NMR spectroscopy. We reveal that the [2]catenane incorporating one triazole ring in the tetracationic cyclophane exists, in the solid-state, as hydrogen bond cross-linked enantiomeric pair stacks, whereas the [2]catenane incorporating two triazole rings in the tetracationic cyclophane does not form polar stacks, unlike most of the [2]catenanes of this class. Finally, we studied the chemical stability of these pi-donor/pi-acceptor motifs to explore their chemical switchability, to show the triazolate-bipyridinium pair is a challenging one in this sense.