title: Metal-free polymerization of phenylsilane: tris(pentafluorophenyl)borane-catalyzed synthesis of branched polysilanes at elevated temperatures.
abstract: The strong organoborane Lewis acid B(C6F5)3 catalyzes the polymerization of phenylsilane at elevated temperatures forming benzene and SiH4 as side-products. The resulting polymer is a branched polysilane with an irregular substitution pattern, as revealed by 2D NMR spectroscopy. Having explored the mechanism of this novel metal-free polymerization by computational chemistry methods at the DFT level, we have suggested that unusual cationic active species, namely monomer-stabilized silyl cations, propagate the polymerization. Hydride abstraction of SiH3 moiety by the catalyst in the initiation step was found to be kinetically preferred by around 9 kcal mol(-1) over activation by coordination of the monomer at the aromatic ring. The formation of linear Si-Si bonds during propagation was calculated to be less favorable than branching and ligand scrambling, which accounts for the branched and highly substituted form of the polymer that was obtained. This novel type of polymerization bears the potential for further optimization with respect to degree of polymerization and structure control for both primary as well as secondary silanes, which can be polymerized by sterically less hindered boranes.
authors.affiliation: Wacker-Lehrstuhl für Makromolekulare Chemie, Institut für Siliciumchemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching (Germany), Fax: (+49) 89-289-13562.
authors.forename: Andreas
authors.initials: A
authors.lastname: Feigl
authors.forename: Ion
authors.initials: I
authors.lastname: Chiorescu
authors.forename: Katrin
authors.initials: K
authors.lastname: Deller
authors.forename: Sven U H
authors.initials: SU
authors.lastname: Heidsieck
authors.forename: Magnus R
authors.initials: MR
authors.lastname: Buchner
authors.forename: Virve
authors.initials: V
authors.lastname: Karttunen
authors.forename: Andreas
authors.initials: A
authors.lastname: Bockholt
authors.forename: Alexander
authors.initials: A
authors.lastname: Genest
authors.forename: Notker
authors.initials: N
authors.lastname: Rösch
authors.forename: Bernhard
authors.initials: B
authors.lastname: Rieger
keywords: Lewis acids; boranes; density functional calculations; polymerization; silanes