Molecular silicon polycations of the types R 2 Si 2+ and RSi 3+ (R = H, organic groups) are elusive Lewis superacids and currently unknown in the condensed phase. Here, we report the synthesis of a series of isolable terpyridine-stabilized R 2 Si 2+ and RSi 3+ complexes, [R 2 Si(terpy)] 2+ (R = Ph 1 2+ ; R 2 = C 12 H 8 2 2+ , (CH 2) 3 3 2+) and [RSi(terpy)] 3+ (R = Ph 4 3+ , cyclohexyl 5 3+ , m-xylyl 6 3+), in form of their triflate salts. The stabilization of the latter is achieved through higher coordination and to the expense of reduced fluoride-ion affinities, but a significant level of Lewis superacidity is nonetheless retained as verified by theory and experiment. The complexes activate C(sp 3) À F bonds, as showcased by stoichiometric fluoride abstraction from 1-fluoroadamantane (AdF) and the catalytic hydrodefluorination of AdF. The formation of the crystalline adducts [2(F)] + and [5(H)] 2+ documents in particular the high reactivity towards fluoride and hydride donors.

A facile synthesis and isolation of pristine silicon tetrakis(trifluoromethanesulfonate), Si(OTf) 4 , is reported, acting as the first neutral silicon-based Lewis superacid suitable towards soft and hard Lewis bases. Its OTf groups have a dual function: they are excellent leaving groups and modulate the degree of reactivity towards soft and hard Lewis bases. Exposed to soft Lewis donors, Si(OTf) 4 leads to [L 2 Si(OTf) 4 ] complexes (L = isocyanide, thioether and carbonyl compounds) with retention of all SiÀOTf bonds. In contrast, it can cleave CÀX bonds (X = F, Cl) of hard organic Lewis bases with a high tendency to form SiX 4 (X = F, Cl) after halide/triflate exchange. Most notable, Si(OTf) 4 allows a gentle oxydefluorination of mono-and bis(trifluoromethyl)benzenes, resulting in the formation of the corresponding benzoylium species, which are stabilized by the weakly coordinating [Si(OTf) 6 ] dianion.

Tetraazaperopyrenes (TAPPs) have been functionalized with thiophene and terthiophene units of different architecture resulting in a variety of organic donor-acceptor (D-A) compounds. The influence of the connection of the thiophenes to the TAPP core on their structural, photophysical and electrochemical properties has been studied in detail by a combination of X-ray crystallography, UV-vis and fluorescence spectroscopy as well as cyclic voltammetry, which allowed the establishment of structure-property relationships. The HOMO-LUMO gap is significantly decreased upon substitution of the TAPP core with electron-donating thiophene units, the extent of which is strongly influenced by the orientation of the thiophene units. The latter also crucially directs the molecular packing in the solid. Linkage at the α-position allows both inter- and intramolecular N···S interaction, whereas linkage in the β-position prevents intramolecular N···S interaction, resulting in a less pronounced conjugation of the TAPP core and the thiophene units. The new TAPP derivatives were processed as semiconductors in organic thin-film transistors (TFTs) that show ambipolar behavior. The insight into band gap and structure engineering may open up new possibilities to tailor the electronic properties of TAPP-based materials for certain desired applications.

The synthesis of a (bis)NHC-silyldiium cation is reported and its reactivity towards sodium phosphaethynolate is shown to enable access to seven-membered heterocycles with P–X moieties (X = Si, P).

Cationic phosphines of the form [(L)PPh] are prepared by reaction of PhPCl with carbenes (L) including a chiral bis(oxazoline)-based carbene, a cyclic(alkyl)(amino) carbene (cAAC), and a 1,2,3-triazolium-derived carbene, affording the products, [(IBox-iPr)PPh][OSOCF] 1, [(cAAC)PPh][OSOCF] 2 and [((TripCHN(NMe)CPh)PPh)(AgCl)][Cl]3. Using PhPCl, the related dication [CH(NCHNDipp)PPh]4 was also prepared. Crystallographically-determined metric parameters and computational data indicate that these species are best described as cationic phosphines rather than phosphenium cations. The oxidation of these cations with XeF afforded [(IBox-iPr)PFPh][OSOCF] 5, [(cAAC)PFPh][OSOCF] 6 and [(TripCHN(NMe)CPh)PFPh][Cl] 7; 4 was not oxidized. These observations are understood by a computational assessment of the average local ionisation potentials at valence shell charge concentrations identified via topological analysis of the electron density.