Benzene- and pyridine-incorporated octaphyrins with different coordination modes toward two PdII centers

Expanded porphyrins have received considerable attention due to their unique optical, electrochemical and coordination properties. Here, we report benzene- and pyridine-incorporated octaphyrins(1.1.0.0.1.1.0.0), which are synthesized through Suzuki-Miyaura coupling of α,α′-diboryltripyrrane with m-dibromobenzene and 2,6-dibromopyridine, respectively, and subsequent oxidation with 2,3-dicyano-5,6-dichlorobenzoquinone. Both octaphyrins are nonaromatic and take on dumbbell structures. Upon treatment with Pd(OOCCH3)2, the benzene-incorporated one gives a Ci symmetric NNNC coordinated bis-PdII complex but the pyridine incorporated one gives Ci and Cs symmetric NNNC coordinated bis-PdII complexes along with an NNNN coordinated bis-PdII complex bearing a transannular C–C bond between the pyrrole α-positions. In addition, these two pyridine-containing NNNC PdII complexes undergo trifluoroacetic acid-induced clean interconversion.