- FROM SILABENZENE TO CYCLOPROPENYLIDENE.
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Isolation and identification of a number of highly reactive species are described. The main route for their preparation involves the combination of flash pyrolysis and matrix isolation in argon at 10 K. This article covers hetero- pi -systems like silabenzene, silaethene, 1,4-disilabenzene, derivatives of borabenzene and boraethene as well as pure carbocyclic compounds with peculiar electronic characteristics. In this context some new aspects of cyclobutadiene-, tetrahedrane- and cyclopentadienone-chemistry are discussed. The main emphasis within this part is directed towards the C//4H//4 potential surface. The article ends with a short comment on cyclopropenylidene.
- Maier
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- Synthesis and Structure Investigation of Pyridine-Borabenzene and Pyridine-2-Boranaphthalene
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The synthesis of pyridine-borabenzene (8) succeeds when methoxytrimethylsilane is eliminated from 1-methoxy-6-(trimethylsilyl)-1-bora-2,4-cyclohexadiene (7) in the presence of pyridine at 60 deg C.The yellow compound shows a charge transfer band at 472 nm.The X-ray structure analysis as well as the proton NMR signals of 8 prove the aromatic character of the borabenzene.Pyridine and borabenzene ring are twisted by 43.3 deg.Pyridine-2-boranaphthalene (14a), whose synthesis occurs by elimination of chlorotrimethylsilane from 2-chloro-1,2-dihydro-1-(trimethylsilyl)-2-bor anaphthalene (13) in the presence of pyridine, forms deep red crystals.Its charge transfer band at 486 nm results like that in 8 by a transition from the HOMO of the boraarene part of the molecule into the LUMO of the pyridine part.The small twist of the two ring systems in 14a of 8.1 deg facilitates the electron transfer.The conjugation of both parts of the molecule in 14a leads to a shortening of the B-N-bond compared with 8 from 155.8 to 151.5 pm.In contrast to the red 14a, triethylamine-2-boranaphthalene (14b) is colourless.
- Boese, Roland,Finke, Norbert,Henkelmann, Jochem,Maier, Guenther,Paetzold, Peter,et al.
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p. 1644 - 1654
(2007/10/02)
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