Chiral Polysilanes

START project Y 120 Chiral Polysilanes Christoph MARSCHNER 18.06.1999 Although the chemistry of chiral silanes has been the subject of study for some 40 years, essentially nothing is known about chiral polysilanes. In the proposed project the synthesis of chiral.silanes is planned via the use of chiral polysilylanions. Although the latter also have not been known so far, preliminary studies have shown that they can be made and are configuratively stable. The reaction of chiral potassium alkoxides with suitable isotetra- or neopentasilanes shall provide synthetic access to this class of compounds. Once this is established, reactions with various electrophiles (silanes, main-group element and transition metal compounds) are planned in order to study whether the chirality can be transferred. The products obtained in these reactions may be used in studies of the stereochernical course of reactions with chiral silanes. The chiral metal silyl compounds are of special interest since the may serve as model compounds for mechanistic studies, silyl transfer reagents and maybe also as a source of "chiral at metal" compounds. Especially for early metal compounds there is not much known about metal centered chirality and it is planned to investigate the synthesis and use of these compounds in some detail. Chiral polysilyl group 4 metallocenes will be used to investigate the stereochernical course of the dehydrocoupling reaction of hydrosilanes. Besides the chiral silylanion approach it is also planned to investigate the use of late metal catalysts (Pd, Pt and Rh compounds) for the formation of Si-Si bonds. Based on a recently found reaction we hope that late metal catalysts in contrast to group 4 metallocenes may permit the use of functionalized silanes for polymerization reactions. In addition we are interested to utilize transition metal compounds not only for polymerization reactions but also for the formation of selective Si-Si bonds, thus, widening the repertoire for the synthesis of defined polysilanes. Influence of the proposed work on the development of the field With the advent of molecular electronics the use of polysilanes in electronic and optoelectronic devices becomes more and more interesting. However, the chemistry of polysilanes, especially with respect to selective transformations is not very well developed. The research described in the proposal attempts to explore the selective formation of stereochernically defined polysilanes. Once these compounds are available the influence of stereochemistry on the electronic and chemical properties can be investigated. The synthesis of chiral silyl metal compounds will help to investigate mechanistic details of silyl metal chemistry. If it will be possible to utilize the chiral polysilylanions for the synthesis of "chiral at metal" compounds, mechanistic investigations, stoichiometric and catalytic asymmetric syntheses of those can be studied. The investigations concerning the use of late metal catalysts for the polymerization of silanes again are of interest for the synthesis of functionalized polysilanes which have shown great potential as materials for optoelectronic devices.