From para-Benziporphyrin to Rhodium(III) 21-Carbaporphyrins: Imprinting Rh•••η2-CC, Rh•••η2-CO, and Rh•••η2-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 C-H 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 eta(2) fashion. This species demonstrates a remarkable axial affinity toward alkenes.