title: The Impact of Antiaromatic Subunits in [4n+2] π-Systems: Bispentalenes with [4n+2] π-Electron Perimeters and Antiaromatic Character.
abstract: Three series of stable, neutral, π-extended bispentalene derivatives, with two pentalenes fused to a central benzene or naphthalene moiety, have been prepared through a modified double carbopalladation cascade reaction. While these chromophores feature skeletons with [4n+2] π-electron perimeters, the two 8 π-electron pentalene subunits strongly influence bonding and spectral properties. (1)H NMR spectra showed large upfield shifts of the protons in the pentalene moieties, comparable to antiaromatic monobenzopentalenes. Further investigations on magnetic ring currents through NICS-XY-scans suggest a global paratropic current and a local diatropic current at the central benzene ring in two of the series, while the third series, with a central naphthalene ring, showed more localized ring currents, with stronger paratropic ring currents on the pentalene moieties. X-ray diffraction analyses revealed planar bispentalene cores with large double- and single-bond alternation in the pentalene units, characteristic for antiaromaticity, and small alternation in the central aromatic rings. In agreement with TD-DFT calculations, both optical and electrochemical data showed much smaller HOMO-LUMO energy gaps compared to other neutral, acene-like hydrocarbons with the same number of fused rings. Both experimental and computational results suggest that the molecular properties of the presented bispentalenes are dominated by the antiaromatic pentalene-subunits despite the [4n+2] π-electron perimeter of the skeletons.
authors.affiliation: †Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
authors.forename: Jing
authors.initials: J
authors.lastname: Cao
authors.affiliation: †Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
authors.forename: Gábor
authors.initials: G
authors.lastname: London
authors.affiliation: †Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
authors.forename: Oliver
authors.initials: O
authors.lastname: Dumele
authors.affiliation: †Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
authors.forename: Margarete
authors.initials: M
authors.lastname: von Wantoch Rekowski
authors.affiliation: †Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
authors.forename: Nils
authors.initials: N
authors.lastname: Trapp
authors.affiliation: ‡Laboratoire d'Electrochimie et de Chimie Physique du Corps Solide, Institut de Chimie-UMR 7177, C.N.R.S., Université de Strasbourg, 4 rue Blaise Pascal, 67081 Strasbourg Cedex, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Ruhlmann
authors.affiliation: ‡Laboratoire d'Electrochimie et de Chimie Physique du Corps Solide, Institut de Chimie-UMR 7177, C.N.R.S., Université de Strasbourg, 4 rue Blaise Pascal, 67081 Strasbourg Cedex, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Boudon
authors.affiliation: §Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 3200008, Israel.
authors.forename: Amnon
authors.initials: A
authors.lastname: Stanger
authors.affiliation: †Laboratory of Organic Chemistry, ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland.
authors.forename: François
authors.initials: F
authors.lastname: Diederich