期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 137, 期 22, 页码 7178-7188出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.5b03074
关键词
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资金
- Swiss National Science Foundation (SNF)
- Kekule fellowship (Fonds der Chemischen Industrie)
- Studienstiftung des Deutschen Volkes
- Israel Science Foundation (ISF) [1485/11]
Three series of stable, neutral, pi-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] pi-electron perimeters, the two 8 pi-electron pentalene subunits strongly influence bonding and spectral properties. H-1 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] pi-electron perimeter of the skeletons.
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