Isolation and Characterization of a Monoprotonated Hydroporphyrin.

Arkhypchuk, Anna I.; Orthaber, Andreas; Kovacs, Daniel; Borbas, K. Eszter

A simple protocol for the controlled preparation of mono‐ and diprotonated hydroporphyrins (chlorins) is presented. The chlorins carried 10‐aryl groups with electron‐neutral (phenyl), electron‐donating (p‐OMe‐C6H4) or electron‐withdrawing (pentafluorophenyl) substituents. The protonation reactions were readily followed by UV/Vis absorption spectroscopy, enabling the determination of the first (4.8–5.3) and second pKa's (1.7–0.5). Both mono‐ and diprotonated species were fully characterized by 1H NMR spectroscopy, which, in combination with theoretical studies, showed that these macrocycles were significantly distorted in solution. A 10‐phenyl‐substituted monoprotonated chlorin was characterized by X‐ray crystallography. This is the first structurally characterized hydroporphyrin monocation, and the first crystal structure of a sterically unencumbered singly protonated tetrapyrrole. The photostabilities of the mono‐ and diprotonated 10‐phenylchlorins were measured upon irradiation into their Soret bands; protonation yielded increased photostabilities. The controlled stepwise mono‐ and diprotonation of synthetic hydroporphyrins carrying is reported. Protonations were readily followed by UV/Vis absorption spectroscopy, enabling the determination of the first and second pKa's. Both mono‐ and diprotonated species were significantly distorted in solution. A monoprotonated chlorin was characterized by X‐ray crystallography.

MACROCYCLIC compounds; PORPHYRINS; ABSORPTION; X-ray crystallography; SOLUTION (Chemistry)

European Journal of Organic Chemistry, 2018, Vol 2018, Issue 48, p7051

1434-193X

Academic Journal

10.1002/ejoc.201801472