Benzene- and pyridine-incorporated octaphyrins with different coordination modes toward two Pd(II) 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(OOCCH(3))(2), the benzene-incorporated one gives a C(i) symmetric NNNC coordinated bis-Pd(II) complex but the pyridine incorporated one gives C(i) and C(s) symmetric NNNC coordinated bis-Pd(II) complexes along with an NNNN coordinated bis-Pd(II) complex bearing a transannular C–C bond between the pyrrole α-positions. In addition, these two pyridine-containing NNNC Pd(II) complexes undergo trifluoroacetic acid-induced clean interconversion.