title: Highly nonplanar, electron deficient, N-substituted tetra-oxocyclohexadienylidene porphyrinogens: structural, computational, and electrochemical investigations.
abstract: The structures and electrochemistry of N-benzylated meso-tetrakis (3,5-di-tert-butyl-4-oxo-cyclohexa-2,5-dienylidene) porphyrinogens have been investigated. Structural determinations reveal the isomeric identity of the products obtained from the N-alkylation of the parent meso-tetra (oxo-cyclohexadienylidene) porphyrinogen. The compounds are subject to increased macrocyclic deformations upon increasing N-substitution culminating in the tetra-N-benzyl derivative, which has a buckling superimposed on the already highly puckered macrocycle. The electrochemical analyses emphasize the electron deficiency of the N-benzylated meso-tetra(oxo-cyclohexadienylidene) porphyrinogens and indicate that they can be considered as quinones conjugated via the unsaturated tetrapyrrolic macrocycle. The N-benzylated compounds studied form stable and well-defined pi-cation radical and pi-anion radical species because of their highly conjugated nature. Ab initio molecular orbital calculations at the B3LYP/3-21G() level confirmed the high degree of conjugation between tetrapyrrole and meso substituents and also gave good agreement between calculated and experimentally determined HOMO-LUMO band gap energies.
authors.affiliation: Institut für Anorganische Chemie, Universität Karlsruhe, Engesserstrasse 15, 76128 Karlsruhe, Germany. hill@nanospace.miraikan.jst.go.jp
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Hill
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Hewitt
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Anson
authors.forename: Annie K
authors.initials: AK
authors.lastname: Powell
authors.forename: Amy Lea
authors.initials: AL
authors.lastname: McCarty
authors.forename: Paul A
authors.initials: PA
authors.lastname: Karr
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Zandler
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza