SYNTHESES, STRUCTURES, AND REACTIONS OF SULFUR AND SELENIUM INSERTIONPRODUCTS OF 1,1-DI-TERT-BUTYLSILIRANES

One-atom and two-atom sulfur and selenium ring expansion products of t rans-1,1-di-tert-butyl-2,3-dimethylsilirane (1), 6,6-di-tert-butyl-6-s ilabicyclo[3.1.0]hexane (4), and 7,7-di-tert-butyl-7-silabicyclo[4.1.0 ]heptane (7) are prepared by stirring the silirane and the chalcogen i n the presence of tetrabutylammonium halide salts and/or alkali-metal halide salts with crown ethers. Potassium fluoride, 18-crown-6, and se lenium in benzene react with 1 to give the novel ring system -2,2-di-t ert-butyl-3,4-dimethyl-1,2-selenasiletane (17) in 85% yield. When tetr abutylammonium chloride (TBAC) is stirred with selenium and 1 or 17 in benzene, butyl-4,5-dimethyl-1,2-diselena-3-silacyclopentane (18) is f ormed in 87% and 82% yields, respectively. Similar results are observe d for analogous reactions with sulfur. The mechanism responsible for t he differences in product distributions seems to involve chalcogen act ivation by salts and crown ethers. Control of chalcogen insertions is demonstrated by reaction of 17 and sulfur in the presence of TBAC, whi ch results in a new ring system, yl-4,5-dimethyl-1-thia-2-selena-3-sil acyclopentane (21) in 64% yield. trans-2,2-Di-tert-butyl-3,4-dimethyl- 1,2 (2) and 7-di-tert-butyl-6-thia-7-silabicyclo[3.2.0]heptane (5), pr epared from reactions of sulfur with 1 and 4, respectively, are thermo lyzed and photolyzed. Products consistent with the generation of a di- tert-butylsilathione fragment are observed, but bimolecular processes are not excluded. Three-dimensional structures of the bicyclic inserti on products 7-9, 15, and 27 are elucidated using 1D and 2D NMR techniq ues. Experimental data are correlated with geometries calculated by mo lecular mechanics methods. The stereochemistries of -tert-butyl-2,3-di thia-4-silabicyclo[4.3.0]-nonane (8) and of ert-butyl-2,3-diselena-4-s ilabicyclo[4.3.0]-nonane (15), prepared from reactions with 7 and sulf ur and selenium, respectively, are further confirmed by single-crystal X-ray crystallography.