Controlling Rotational Motion of Nonplanar Porphyrin Atropisomers by Metal Coordination

ABSTRACT Porphyrin atropisomerism is an outstanding tool for the accessibility of shape‐specific molecules, yet over 20 years after the unusual rotational barriers of nonplanar porphyrins were observed, a quantitative relationship remains at large. There is a growing need to control this phenomenon in nonplanar porphyrin systems due to the mounting interest in these systems as enzyme mimics and organocatalysts. Hence, in this work, the influence of steric bulk on the stability of nonplanar 5,10,15,20‐tetraaryl‐2,3,7,8,12,13,17,18‐octaethyl‐porphyrin atropisomers was explored. The library of atropisomeric porphyrins synthesized herein emphasizes the delicate balance that must be achieved between steric bulk without inducing an undesired amount of macrocycle flexibility to obtain an atropisomer with a predictable rotational barrier. To overcome this challenge, a stabilization strategy was devised by exploiting metal coordination to the peripheral porphyrin functionalities, leading to an atroposelective superstructure formation.