The synthesis of two series of silylated chalconium borates, 9 and 10, which are based on the peri-naphthyl and peri-acenaphthyl framework, is reported (chalcogen (Ch): O, S, Se, Te). NMR investigations of the selenium- and tellurium-containing precursor silanes 3 d-f and 8 d, f revealed a significant through-space J-coupling between the chalcogen nuclei and the Me SiH group. Experimental and computational results typify the synthesized cations 9 and 10 as chalconium ions. The imposed ring strain weakens the Si-Ch linkage compared to acyclic chalconium ions. This attenuation of the Si-Ch bond strength is more pronounced in the acenaphthene series. Surprisingly, the Si-O bonds in oxonium ions 9 a and 10 a are the weakest Si-Ch linkage in both series. The synthesized silyl chalconium borates are active in hydrodefluorination reactions of alkyl fluorides with silanes. A cooperative activation of the silane by the Lewis acidic (silicon) and by the Lewis basic side (chalcogen) is suggested.

The synthesis of the digermyl and germylsilyl hydronium borates 7[B(C 6 F 5 ) 4 ] and 8[B(C 6 F 5 ) 4 ] is reported. Spectroscopic (IR, NMR) and structural data supported by the results of density functional calculations indicate in both cases a symmetric or almost symmetric E−H−E′ three-center−two-electron linkage (7, E = E′ = Ge; 8, E = Si, E′ = Ge). The [B(C 6 F 5 ) 4 ] − and the [HCB 11 H 5 Br 6 ] − salts of both cations are active in catalytic hydrodefluorination reactions of alkyl and benzyl fluorides. No significant effect of the element atom E on the determined turnover numbers was found.

The stabilizing neighboring effect of halo substituents on silyl cations was tested for a series of peri‐halo substituted acenaphthyl‐based silyl cations 3. The chloro‐ (3 b), bromo‐ (3 c), and iodo‐ (3 d) stabilized cations were synthesized by the Corey protocol. Structural and NMR spectroscopic investigations for cations 3 b–d supported by the results of density functional calculations, which indicate their halonium ion nature. According to the fluorobenzonitrile (FBN) method, the silyl Lewis acidity decreases along the series of halonium ions 3, the fluoronium ion 3 a being a very strong and the iodonium ion 3 d a moderate Lewis acid. Halonium ions 3 b and 3 c react with starting silanes in a substituent redistribution reaction and form siliconium ions 4 b and 4 c. The structure of siliconium borate 4 c2[B12Br12] reveals the trigonal bipyramidal coordination environment of the silicon atom with the two bromo substituents in the apical positions.

Who made the cover design and how?The illustration was done with ink and watercolors on watercolor paper 30 x3 0c mbyN atalie Kordts.

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