Two Rhodium(III) Ions Confined in a [18]Porphyrin Frame: 5,10,15,20‐Tetraaryl‐21,23‐Dirhodaporphyrin

• Published in: Chemistry : a European journal Vol. 28; no. 46; pp. e202201513 - n/a
• Main Authors: Vetter, Grzegorz, Białońska, Agata, Krzyszowska, Paulina, Koniarz, Sebastian, Pacholska‐Dudziak, Ewa
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 16.08.2022
• Subjects: Bimetals; Chemistry; Exchanging; fluxionality; Ions; metallacycles; NMR; Nuclear magnetic resonance; Oxygen exchange; porphyrinoids; Porphyrins; Rhodium; Tellurium; tellurium; fluxionality; porphyrinoids; metallacycles; rhodium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202201513

Tetraaryl‐21,23‐dirhodaporphyrin and a series of related monorhodaporphyrins have been obtained by tellurium‐to‐rhodium exchange in a reaction of tetraaryl‐21,23‐ditelluraporphyrin with [RhCl(CO)2]2. These organometallic metallaporphyrins contain rhodium(III) centers embedded in rhodacyclopentadiene rings, incorporated within the porphyrin frames. The skeletons of 21,23‐dirhodaporphyrin and 21‐rhoda‐23‐telluraporphyrin are strongly deformed in‐plane from the rectangular shape typical for porphyrins, due to rhodium(III) coordination preferences, the large size of the two core atoms, and the porphyrin skeleton constrains. These two metallaporphyrins exhibit fluxional behavior, as studied by 1H NMR and DFT, involving the in‐plane motion and the switch of the rhodium center(s) between two nitrogen donors. A side product detected in the reaction mixture, 21‐oxa‐23‐rhodaporphyrin, results from tellurium‐to‐oxygen exchange, occurring in parallel to the tellurium‐to‐rhodium exchange. The reaction paths and mechanisms have been analyzed. The title 21,23‐dirhodaporphyrin contains a bridged bimetallic unit, Rh2Cl2, in the center of the macrocycle, with two rhodium(III) ions lying approximately in the plane of the porphyrinoid skeleton. The geometry of the implanted Rh2Cl2 unit is affected by macrocyclic constrains. Pack more into the box: How to fit two metal ions in one porphyrin. Porphyrins’ default coordination mode allows the binding of a single metal cation in the central NNNN cavity. In order to allow the accommodation of two metal ions inside a standard porphyrin perimeter, they are introduced in place of two inner NH groups, yielding a 21,23‐dimetallaporphyrin. The 18‐π‐electron aromatic circuit is maintained, playing a crucial role in macrocycle stabilization, and enforcing the metal centers’ proximity.