A Highly Sterically Congested Bis‐Zinc‐Porphyrin Containing a Single Buta‐1,3‐diyne Linkage: From a Serendipitous Finding to Supramolecular Encapsulation

Abstract

A unique example of a bis‐zinc‐porphyrin chemical system in which both macrocycles are covalently connected with a single, short buta‐1,3‐diyne 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 106 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.