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Syntheses of Trisila Analogues of Allyl Chlorides and Their Transformations to Chlorocyclotrisilanes, Cyclotrisilanides, and a Trisilaindane

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posted on 2008-03-26, 00:00 authored by Kai Abersfelder, David Scheschkewitz
The rearrangements of (chlorosilyl)disilenes R2(Cl)Si−(Tip)SiSiTip2 (5a,b:  Tip = 2,4,6-iPr3C6H2, a:  R = Me, b:  R = Ph) quantitatively yield the isomeric chlorocyclotrisilanes (6a,b). The disilene precursors 5a,b are, in turn, accessible from the reactions of the disilenide Tip2SiSi(Tip)Li (1), that is, a disila analogue to vinyl anions, with dichlorosilanes R2SiCl2. This novel approach to cyclotrisilanes potentially allows for the facile variation of the substitution pattern and grants access to the first anionic derivatives; while the rearrangement of 5a,b to 6a,b is slow at room temperature and additionally requires the presence of THF or other n-donors, reduction of 5b with lithium instantly yields the corresponding cyclotrisilanide (7b) without detection of any open-chained isomer. Heating of a neat sample of 5b to 150 °C provides a completely characterized 1,2,3-trisilaindane derivative (13), strongly supporting the intermediacy of a disilanyl silylene species that inserts into an ortho-CH bond of the phenyl substituents. The X-ray diffraction studies on single crystals of 6a,b and 7b reveal that the Si−Si bond distance in cyclotrisilanes depends significantly on the electronegativity of the opposing silicon atom's substituents, which is rationalized by density functional theory (DFT) calculations on model systems.