From para ‐Benziporphyrin to Rhodium(III) 21‐Carbaporphyrins: Imprinting Rh⋅⋅⋅η 2 ‐CC, Rh⋅⋅⋅η 2 ‐CO, and Rh⋅⋅⋅η 2 ‐CH Coordination Motifs

Rhodium(III) para‐ benziporphyrin alters the fundamental reactivity of the built‐in para ‐phenylene moiety. Due to additional macrocyclic stabilization, a sequence of intramolecular rearrangements are triggered to afford rhodium(III) 21‐carbaporphyrin, which incorporates the rhodacyclopropane motif. The peculiar reversible transformations of the bridging methylene unit provide an example of selective and reversible aliphatic CH bond elimination. Rhodium(III) 21‐carbaporphyrin can be oxygenated to rhodium(III) 21‐oxy‐21‐carbaporphyrin, whereas the metal ion interacts with the C(21)O(25) fragment in an η 2  fashion. This species demonstrates a remarkable axial affinity toward alkenes.