| Research Abstract |
1.The pentacyclic ladder polysilane, anti, anti, anti-hexadecaisopropylpentacyclo [6.4.0.0^<2,7>.0^<3,6>.0^<9,12>] -dodecasilane was prepared and the structure was determined by X-ray crystallography. Two linear hexasilane chains of the ladder polysiane screw on one way, and the molecule has the partially double helical structure ; the helical structure results from the systematic catenation that the folded cyclotetrasilane rings are connected up and down alternatively. The anion radical of the pentacycle, which was generated by the reduction with K,persisted over several months at room temperature ; the intensity loss in the ESR Signal after one month is 19%, and the half-life time is too long to be measured. This remarkable stability is unprecedented for polysilane anion radicals. 2.Reaction of decaisopropylbicyclo [2.2.0] hexasilane with the divalent palladium PdCl_2 (PhCN) _2led to the formation of 1,4-dichlorodecaisopropylbicyclohexasilane. 3.Treatment of decaisopropylbicyclo [2.2
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.0] hexasilane with MCPBA afforded decaisopropyl-7-oxabicyclo- [2.2.1] heptasilane and decaisopropy1-2-oxabicyclo [3.2.0] -heptasilane as monoxidation products. The 7-oxa compound showed unusual properties in the UV spectrum due to the interaction of the n orbital of the oxygen atom and the Si-Si sigma bonds. The compound also showed far stronger fluorescence than the bicyclohexasilane. 4.The ring-opening reaction of anti-dodcaisopropyltricyclo [4.2.0.0^<2,5>] octasilane with PdCl_2 (PhCN) _2 gave the new bicyclic systems, dodocaisoproybicyclo [3.3.0] octasilane and dodoca-isopropylbicyclo [4.2.0] octasilane. 5.The ring-opening halogenation of octathexyloctasilacubane resulted in skeletal rearrangement with concomitant formation of stereoisomeric 4,8-dihalooctathexyltetracyclo- [3.3.0.0^<2,7>.0^<3,6>] octasilanes. The reductive dehalogenation of the 4,8-dihalotracyclooctasilanes with sodium metal led to unusual skeletal rearrangement, forming the octasilacubane. 6.Photooxidation of the octasila-cubane with dimethylsulfoxide resulted in formation of the new polyhedral systems, the oxaoctasila-homocubane, octathexylpentacyclo [4.3.0.0^<2,5>.0^<3,8>.0^<4,7>] -9-oxanonasilane and the dioxaoctasilabishomo-cubane, octathexylpentacyclo [5.3.0.0^<2,6>.0^<3,9>.0^<4,8>] -5,10-dioxadecasilane. 7.The reaction of di-tert-butyl-dichlorosilane with lithium produced hepta-tert-butylcyclotetrasilane and trans-1,1,2,3,3,4-hexa-tert-butylcyclotetrasilane. Less
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