A Highly Sterically Congested Bis‐Zinc‐Porphyrin Containing a Single Buta‐1,3‐diyne Linkage: From a Serendipitous Finding to Supramolecular Encapsulation
Résumé
A unique example of a bis-zinc-porphyrin chemical system in which both macrocycles are covalently connected with a single, short 1,3-butadiyne linkage placed at the ortho sites of the meso phenyl rings is presented. This dimeric compound resulted from an homo-coupling side-reaction taking place during a copper-catalyzed click reaction between an alkyne porphyrin and 2-azidopyridine derivatives. Its unexpected formation was rationalized by control experiments and an improved synthesis was achieved under copper-catalyzed Glaser-Hay coupling reaction conditions. This highly sterically congested bis-zinc-porphyrin derivative behaved as a supramolecular host for encapsulating ditopic molecular guests such as 1,4-diazabicyclo[2.2.2]octane (DABCO) with association constant K1.1 in the order of 10 6 M-1. This value is comparable to current systems that typically feature several connecting linkages between the two zinc-porphyrin sites resulting in (supra)molecular cages ensuring a high pre-organization. As such, the requirements to take benefit from supramolecular encapsulation can be reduced to a highly rigid, minimal covalent linkage of four atoms between zinc-porphyrins as herein described.
Domaines
Chimie
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