- Synthesis of New Alkyn-1-ylsilanes. 1,1-Organoboration, 1,2-Hydroboration (2009)
- New alkyn-1-ylsilanes were prepared, characterized and their use in 1,2-hydroboration, 1,1-organoboration reactions or combination of these two was demonstrated. Although the silanes were in general obtained as mixtures, they could be purified by fractional distillation or crystallization. Many of these silanes were fully characterized for the first time by modern NMR spectroscopic techniques and in some cases by X-ray structural analysis. The monoalkyn-1-yl(chloro)silanes were treated with BEt3 at 373-393 K for prolonged periods of time (up to 30 d), and the reactivity of the products was explored. For the first time the 1,2-hydroborating behavior of BEt3 was discovered in a series of reactions. Silanes containing two or more than two (up to four) alkyn-1-yl groups were used for the synthesis of different heterocyclic systems e.g., 1-silacyclobutenes, 1-silacyclopent-2-enes, siloles, borolenes, etc. Intermediates of sufficient stability and final products were studied by multinuclear NMR spectroscopy (1H, 11B, 13C, 29Si and 119Sn NMR). Numerous molecular structures were determined by X-ray structural analysis. Alkenes bearing Si-Cl function(s) are useful precursors for further transformations. They were converted into 1-silacyclobutene derivatives. Various intermediates on the way to 1-silacyclobutenes were discovered aiding in the understanding of the reaction mechanism. The aforementioned heterocycles were also prepared by reacting dialkyn-1-ylsilanes with 9-BBN at 353-373 K. In a first step, alkenyl(alkyn-1-yl)silanes are formed as a result of intermolecular 1,2-hydroboration followed by intramolecular 1,1-vinylboration at the same temperature to afford 1-silacyclobutene derivatives. The first molecular structure of one example was determined by X-ray structural analysis. Corresponding tetraalkyn-1-ylsilanes afforded 4-silaspiro[3,3]hepta-1,5-diene derivatives. The hydroborating reagent 9-BBN, on reaction with alkyn-1-yl(vinyl)silanes, leads to the 1-silacyclopent-2-ene derivatives at ambient temperature. Dialkyn-1-yl(divinyl)silanes gave 5-silaspiro[4,4]nona-1,6-diene derivatives. X-ray structures for representative examples 1-silacyclopent-2-ene as well as for spirosilanes were determined for the first time. Many dialkynylsilanes react with BEt3 and 9-Et-9-BBN under harsh reaction conditions (at 373-393 K for several days) to afford siloles as the result of a slow intermolecular 1,1-alkylboration followed by a fast intramolecular 1,1-vinylboration. This method is very simple and useful and fairly pure siloles were isolated. Protodeborylation using acetic acid as protic reagent was successful for a large number of novel heterocycles. New protodeborylated compounds were prepared and studied. The boron was found as part of a boron-oxygen bicyclic compound which was for the first time isolated and characterized by single crystal X-ray structural analysis.