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

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.