Infoscience

Thesis

Salts of electrophilic cations and Lewis acid-base adducts with weakly coordinating anions: synthesis, characterization and quantum chemical calculations

During the last decades, weakly coordinating anions (WCAs) have become a field of great interest both in basic and applied chemistry, as – if compared to "normal" classical anions like Cl- or SO42- – they have a lot of unique and unusual properties, such as high solubility in low dielectric media (like CH2Cl2 or toluene), "pseudo gas phase conditions" in condensed phases and the stabilization of strong electrophilic cations as well as of weakly bound and low charged complexes. Within the present thesis, several contributions to the chemistry of WCAs were made: Based on quantum chemical calculations, the stability of the most widely used WCAs have been investigated, using parameters such as the fluoride ion affinity (FIA), partial charges or frontier orbital energies. One class of the WCAs, the poly- and perfluorinated alkoxyaluminates of the type [Al(ORF)4]- and [(RFO)3Al-F-Al(ORF)3]-, has been used to investigate weakly bound Ag(P4S3) Lewis acid-base adducts and electrophilic cations: When the silver salts of fluorinated alkoxyaluminates are reacted with P4S3, different structure types are found for the adducts, depending on the anion used. The dynamics of these complexes has been explored by different spectroscopic methods (IR, Raman, MAS-NMR, NMR in solution) and X-ray diffraction. The first structurally characterized trihalocarbenium ions CI3+ as salts of different aluminates have been prepared and fully characterized using various spectroscopic techniques, e.g. NMR and vibrational spectroscopy, as well as single-crystal diffraction. The Lewis acidities of the halocarbenium ions have been investigated both on experimental and theoretical grounds and they have been compared to those of the isoelectronic haloboranes. The NO2+ salt of the [Al(OC(CF3)3)4]- anion has been synthesized by a metathesis reaction. It has been reacted with P4 in order to obtain naked phosphorus cations Px+. Another project was the synthesis and characterization of the tetraalkylammonium salts of the [Al(ORF)4]- anions, a promising class of substances for the use in electrochemical applications in non-polar solvents. All subjects treated experimentally within this thesis have been accompanied by quantum chemical calculations.

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