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Molecular Engineering of Free‐Base Porphyrins as Ligands—The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles
Author(s) -
Kielmann Marc,
Senge Mathias O.
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201806281
Subject(s) - porphyrin , chemistry , hydrogen bond , molecule , tetrapyrrole , intermolecular force , stereochemistry , free base , protonation , acceptor , crystallography , combinatorial chemistry , photochemistry , organic chemistry , ion , salt (chemistry) , physics , enzyme , condensed matter physics
The core N−H units of planar porphyrins are often inaccessible to forming hydrogen‐bonding complexes with acceptor molecules. This is due to the fact that the amine moieties are “shielded” by the macrocyclic system, impeding the formation of intermolecular H‐bonds. However, methods exist to modulate the tetrapyrrole conformations and to reshape the vector of N−H orientation outwards, thus increasing their availability and reactivity. Strategies include the use of porpho(di)methenes and phlorins (calixphyrins), as well as saddle‐distorted porphyrins. The former form cavities due to interruption of the aromatic system. The latter are highly basic systems and capable of binding anions and neutral molecules via N−H⋅⋅⋅X‐type H‐bonds. This Review discusses the role of porphyrin(oid) ligands in various coordination‐type complexes, means to access the core for hydrogen bonding, the concept of conformational control, and emerging applications, such as organocatalysis and sensors.