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

Abstract

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.

From 2- to 3-Substituted Ferrocene Carboxamides or How to Apply Halogen “Dance” to the Ferrocene Series

“… Different aspects of the molecular structure of ferrocenes and their derived properties were studied by quantum chemical calculations . It is established that ferrocenes can exist as eclipsed and staggered conformations with a low internal rotation barrier .…”

Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

“…One class of metalloporphyrinoids, metallocenoporphyrins, stands out in the context of the metal complexes of PMPs (and thiaporphyrins) in that a metal complex constitutes the nonpyrrolic moiety. − Synthesized along [3 + 1] pathways (Scheme ), they provided the first insight into what extent the transmission of metallamacrocyclic π-electron conjugation can reach across the d-electrons of a metallocene (ferrocene or ruthenocene). Moreover, the hingelike flexibility of the metallocene sandwich complex allows for a number of compound topologies that affect the porphyrinoid π-system.…”

Flexible Porphyrinoids

“…69 In contrast, a recently reported 1,1′-ferrocene-incorporated expanded porphyrin demonstrated nonaromatic properties. 70 1,5-Naphthiporphyrins 18-6−18-8 provide other interesting examples of helical three-dimensional porphyrinoids (Scheme 18). 71 The molecules are constructed from a 1,5-naphthylene unit connected to a heterotripyrrin linker.…”

“…The formal conversion from synperiplanar to anticlinal conformations of the 1,1′-substituent ruthenocenyl moiety transforms the antiaromatic molecule into an aromatic one with an identical number of available electrons . In contrast, a recently reported 1,1′-ferrocene-incorporated expanded porphyrin demonstrated nonaromatic properties …”