The influence of ring strain on the formation of Si-H-Si stabilised oligosilanylsilyl cations.

Hydride transfer between Si(SiMe2H)4 (2) and [Ph3C][B(C6F5)4] in 3-fluorotoluene yields the intermolecularly silane-stabilised silylium ion [((HMe2Si)3SiSiMe2)2H]+ ([5]+), independently of the amount of [Ph3C][B(C6F5)4] (0.5, 1.0 or 2.0 equiv.) used. The cyclic silane-stabilised silylium ion [4]+ is not detected by NMR spectroscopy. This result demonstrates the influence of ring strain effects on the formation of intra- ([4]+) or intermolecularly ([5]+) Si-H-Si bridged silyl cations.