Molecular structure of a free-base β-Octaiodo -meso-tetraarylporphyrin. A rational route to cis porphyrin tautomers?

Thomassen, Ivar K., McCormick, Laura J. and Ghosh, Abhik (2018) Molecular structure of a free-base β-Octaiodo -meso-tetraarylporphyrin. A rational route to cis porphyrin tautomers? Crystal Growth and Design, 18 (8), 4257-4259. (doi:10.1021/acs.cgd.8b00629).

Record type: Article

Abstract

Although a cis tautomer has long been invoked as an intermediate in porphyrin tautomerism, the first such species was only recently isolated and structurally characterized in the form of a β-heptakis(trifluoromethyl)-meso-tetraarylporphyrin. Reported herein is the molecular structure of a β-octaiodo-meso-tetraarylporphyrin solvate, which also exhibits a cis tautomeric structure. Both structures implicate two factors as critical to the stabilization of the cis tautomeric form - a free-base porphyrin that is naturally strongly saddled on steric grounds and a hydroxylic or amphiprotic solvent that can provide hydrogen-bonded N-H···X-H···N (X = O in both the above examples) straps connecting the central NH groups with the antipodal unprotonated nitrogens. The results raise the prospect that a rational strategy affording cis porphyrin tautomers in a predictable manner may be within reach.

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