Fig. 2: Synthesis and NMR spectroscopic characterization of halogen-substituted silylium ions.

a, Attempts to generate a chlorine-substituted silylium ion by classical hydride abstraction (top) and successful synthesis by our protolysis approach (bottom). b, Synthesis of the full series of halogen-substituted silylium carborates. For the preparation of the individual silanes as silylium ion precursors, see Supplementary Figs. 1–4 in Supplementary Information Section 3. c, Plots of the experimental (left) and calculated (right) ²⁹Si NMR chemical shifts of the halosilylium carborates. The computed ²⁹Si chemical shifts (in ppm relative to tetramethylsilane) were obtained at the X2C-PBE0/x2c-TZVPall-2c level of theory, comparing one-component (1c) calculations with only scalar-relativistic effects (values on the dashed lines) and two-component (2c) calculations including also spin–orbit effects (values on the solid lines). ^aAll reactions were performed at ca. 0.02 mmol scale in C₆D₆ (0.2 ml, 0.1 M) in a glovebox under an argon atmosphere. ^bIsolated yields. ^cExperimental ²⁹Si NMR chemical shifts determined by ¹H,²⁹Si HMQC NMR spectroscopy (500/99 MHz, 298 K, optimized for J = 7 Hz) in 1,2-Cl₂C₆D₄. ¹J(Si,F) coupling constant in Hz in parentheses. ^dComputed ²⁹Si NMR chemical shifts at the ‘exact two-component’ (X2C) spin–orbit PBE0/x2c-TZVPall-2c level.