N‐Fused Pentaphyrins and Their Rhodium Complexes: Oxidation‐Induced Rhodium Rearrangement

meso ‐Aryl‐substituted pentaphyrins were isolated in the modified Rothemund–Lindsey porphyrin synthesis as a 22‐π‐electron N‐fused pentaphyrin ([22]NFP 5 ) and a 24‐π‐electron N‐fused pentaphyrin ([24]NFP 5 ), which were reversibly interconvertible by means of two‐electron reduction with NaBH 4 or two‐electron oxidation with dichlorodicyanobenzoquinone (DDQ). Judging from 1 H NMR data, [22]NFP 5 is aromatic and possesses a diatropic ring current, while [24]NFP 5 exhibits partial anti‐aromatic character. Metalation of [22]NFP 5 1 with a rhodium( I ) salt led to isolation of rhodium complexes 9 and 10 , whose structures were unambiguously characterized by X‐ray diffraction analyses and were assigned as conjugated 24‐π and 22‐π electronic systems, respectively. In the rhodium( I ) metalation of 1 , the complex 9 was a major product at 20 °C, but the complex 10 became preferential at 55 °C. Upon treatment with DDQ, compound 9 was converted to 10 with an unprecedented rearrangement of the rhodium atom.