Synthesis and Quantum Mechanical Studies of a Highly Stable Ferrocene-Incorporated Expanded Porphyrin

We present the first evidence for an unusual stable metallocene-containing expanded porphyrinoid macrocycle that was synthesized by condensing one equivalent of 1,1'-bis[phenyl(2-pyrroyl)methyl]ferrocene with one equivalent of 5,10-di(p-tolyl)-16-oxa-15,17-dihydrotripyrrane under acid-catalyzed conditions. The formation of ferrocene-incorporated expanded porphyrin macrocycle was confirmed by HR-MS and 1D/2D NMR spectroscopy. The macrocycle was nonaromatic and displayed absorption bands in the region of 420-550 nm. The molecular and electronic structure of the ferrocene-incorporated expanded porphyrin was investigated by DFT methods. The DFT calculations indicated a partially twisted structure of the molecule, and the extent of torsional distortion was larger than previously observed for ruthenocenoporphyrinoids and ferrocenothiaporphyrin. The HOMO and LUMO states that were obtained from the DFT calculations indicated partial charge density on all four pyrrole nitrogen atoms and the furanyl oxygen atom in the HOMO state and partial charge density on the α and β carbon atoms in the LUMO state. In addition, the ferrocene moiety displayed the presence of partial charge density on the Fe atom and the cp rings in both the HOMO and LUMO states. Moreover, DFT studies of the diprotonated form of macrocycle indicated that the diprotonated form also retained a synclinal conformation and that its torsional strain was slightly higher than its free base form.