Disupersilyldisilane R*X2SiSiX2R*: Darstellung, Charakterisierung und Strukturen; sterische Effekte der Substituenten

Disupersilyldisilanes R*X2SiSiX2R* (R*=supersilyl=Sit-Bu3; two diastereomers in case of R*XX′SiSiX′XR*) are prepared in organic solvent (i) by dehalogenations of supersilylhalosilanes with Na, NaC10H8 or NaR*; (ii) by reactions of disupersilylhalodisilanes with H− (Hal/H exchange); (iii) by reactions of disupersilyldisilanes with Hal2 (H/Hal exchange); (iv) by reactions of disupersilylhalodisilanes first with NaR* (Hal/Na exchange) then with agents for protonation, alkylation, silylation (Na/H, Na/Me, Na/SiMe3 exchange); or (v) by reactions of disupersilyldisilenes (here R*PhSiSiPhR*) with HHal or Hal2 (formation of addition products). As discussed, (29Si) of the SiX2 groups of R*X2SiSiX2R* depends strongly on the nature of X. The disupersilyldisilanes are in part moisture sensitive (compounds with SiX2=SiHHal), in part sensitive against oxygen (compounds with SiX2=SiHal2, SiHHal; Hal=Br, I). X-ray structure analyses of the disupersilyldisilanes R*X2SiSiX2R* (X2=H2, Cl2, Br2, BrH, IH, MeBr, PhH, PhCl) as well as R*PhClSiSiHPhR* and R*PhBrSiSiClPhR* show a staggered conformation. Due to steric repulsions of groups R*/X/X, the SiSi bond lengths are longer than 2.34 Å (normal SiSi single bond; exception: R*H2SiSiH2R*). From the extent of SiSi bond elongation it is concluded that the bulkiness of X increases in direction H