title: Efficient access to substituted silafluorenes by nickel-catalyzed reactions of biphenylenes with Et₂SiH₂.
abstract: The reaction of biphenylene (1) with Et2SiH2 in the presence of [Ni(PPhMe2)4] results in the formation of a mixture of 2-diethylhydrosilylbiphenyl [2(Et2HSi)] and 9,9,-diethyl-9-silafluorene (3). Silafluorene 3 was isolated in 37.5% and 2(Et2HSi) in 36.9% yield. The underlying reaction mechanism was elucidated by DFT calculations. 4-Methyl-9,9-diethyl-9-silafluorene (7) was obtained selectively from the [Ni(PPhMe2)4]-catalyzed reaction of Et2SiH2 and 1-methylbiphenylene. By contrast, no selectivity could be found in the Ni-catalyzed reaction between Et2SiH2 and the biphenylene derivative that bears tBu substituents in the 2- and 7-positions. Therefore, two pairs of isomers of tBu-substituted silafluorenes and of the related diethylhydrosilylbiphenyls were formed in this reaction. However, a subsequent dehydrogenation of the diethylhydrosilylbiphenyls with Wilkinson's catalyst yielded a mixture of 2,7-di-tert-butyl-9,9-diethyl-9-silafluorene (8) and 3,6-di-tert-butyl-9,9-diethyl-9-silafluorene (9). Silafluorenes 8 and 9 were separated by column chromatography.
authors.affiliation: Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt (Germany), Fax: (+49) 69-79829260.
authors.forename: Jens Michael
authors.initials: JM
authors.lastname: Breunig
authors.forename: Puneet
authors.initials: P
authors.lastname: Gupta
authors.forename: Animesh
authors.initials: A
authors.lastname: Das
authors.forename: Samat
authors.initials: S
authors.lastname: Tussupbayev
authors.forename: Martin
authors.initials: M
authors.lastname: Diefenbach
authors.forename: Michael
authors.initials: M
authors.lastname: Bolte
authors.forename: Matthias
authors.initials: M
authors.lastname: Wagner
authors.forename: Max C
authors.initials: MC
authors.lastname: Holthausen
authors.forename: Hans-Wolfram
authors.initials: HW
authors.lastname: Lerner
keywords: CC activation; SiH activation; density functional calculations; nickel; silanes