Klaus Eichele Publication Abstracts 2024

Trivalent group 3 and 13 light metal pyrazolates were synthesised and their reactivity towards CO₂ was investigated. The homoleptic complex Al(pztBu₂)₃ reversibly inserts two molecules of CO₂ to afford Al(CO₂·pztBu₂)₂(pztBu₂), exhibiting CO₂ release only at elevated temperatures (>100 °C). In contrast, donor-stabilised Sc(pztBu₂)₃(thf) forms mono-inserted species [Sc(μ-CO₂·pztBu₂)(pztBu₂)₂]₂, which already releases CO₂ at ambient temperature and pressure and hence is isolable only at low temperature. For the yttrium complex Y(pztBu₂)₃(thf)₂, insertion of CO₂ is not observable at ambient temperature. The new homoleptic aluminium diisopropyl pyrazolate complex [Al(pziPr₂)₃]₂ shows exhaustive CO₂ insertion, while dimethyl pyrazolate could be isolated as the separated ion pair [Al(N,N',N''-Al{pzMe₂}₃Me)₂][Al(pzMe₂)₃Me]. The scandium complex Sc(pztBu₂)₃(thf) performed best in the catalytic cycloaddition reaction of CO₂ and epoxides, unveiling an inverse correlation of carboxophilicity ( =CO2 affinity) and catalytic activity. Carboxophilicity is assessed using CO₂-release temperature (via VT ¹H NMR spectroscopy and thermogravimetric analysis).

The tetracyanamidometallates Li₄[T(CN₂)₄] with T = Si, Ge were prepared by solid-state metathesis (SSM) reactions between TI₄ and Li₂(CN₂). The new compounds Li₄[T(CN₂)₄] are obtained as crystalline phases in high yields and represent the most basic examples of the family of tetracyanamidometallates. The formation of these compounds, via SiI₄ and Li₂(CN₂), is analyzed by means of differential scanning calorimetry (DSC). The [Si(CN₂)₄]^4- ion in the structure of Li₄[Si(CN₂)₄] can be considered an analogue to the [SiO₄]^4- ion in Li₄SiO₄. The crystal structures of Li₄[T(CN₂)₄] were solved and refined isotypically on the basis of single-crystal X-ray diffraction data in the space group C2/c, and further characterized by infrared and solid-state NMR techniques.