Synthesis, structure, and dynamic behavior of cyclopentadienyl-lithium, -sodium, and -potassium annelated with bicyclo[2.2.2]octene units: a systematic study on site exchange of alkali metals on a cyclopentadienyl ring in tetrahydrofuran

Coordination Polymers of Polyphenyl-Substituted Potassium Cyclopentadienides

A series of potassium salts of di- and tri-arylsubstituted cyclopentadienes has been obtained by the metalation of the corresponding cyclopentadienes with benzylpotassium in THF media. Crystals of all compounds, afforded by recrystallization from THF/hexane, diglyme-THF/hexane and toluene/hexane mixtures, have been studied by X-ray diffraction. All studied potassium cyclopentadienides exhibit the luminescence at room temperature and overall quantum yield of photoluminescence for potassium salt of diarylsubstituted cyclopentadiene is 18%.

Bulking up CpBIG: A Penta-Terphenyl Cyclopentadienyl Ligand

The modification of cyclopentadienyl ligands with carefully selected substituents is a widely used strategy for tuning their steric and electronic properties. We describe the synthesis of an extremely bulky penta-terphenyl cyclopentadienyl ligand (Cp^T5) by arylation of cyclopentadiene. Deprotonation reactions with various group 1 metals and bases afforded a complete series of alkali metal salts MCp^T5 (M = Li–Cs). The compounds were isolated as solvate-free salts, which were characterized by multinuclear nuclear magnetic resonance spectroscopy, ultraviolet–visible spectroscopy, and elemental analysis. Single-crystal X-ray diffraction studies of LiCp^T5, NaCp^T5 (crystallized as a solvate with one tetrahydrofuran molecule per formula unit), and KCp^T5 revealed the formation of metallocene-like sandwich structures in the solid state.

ILs through the looking glass: electrostatics and structure probed using charge-inverted ionic liquid pairs

Ionic liquids combining potassium cations with 1-alkyl-3-methylcyclopentadienyl anions, K[C_nC₁Cp] (n = 4, 6) have been synthesized. Differential scanning calorimetry measurements have shown that K[C₄C₁Cp] and K[C₆C₁Cp] melt without decomposition at around 90 °C. These two ionic liquids are the charge-inverted counterparts of [C₄C₁Im]Cl and [C₆C₁Im]Cl, two common ionic liquids. The concept of charge-inverted ionic pairs is used to explore the nature of the interactions and structure in different ionic compounds, from simple alkali halide salts to ionic liquids based on complex molecular ions. Different sets of experimental data, empirical correlations and molecular dynamics simulations are used to that effect.

Accurate molecular weight determination of small molecules via DOSY-NMR by using external calibration curves with normalized diffusion coefficients

Determination of the aggregation and solvation numbers of organometallic complexes in solution is an important task to increase insight in reaction mechanisms. Thus knowing which aggregates are formed during a reaction is of high interest to develop better selectivity and higher yields. Diffusion-ordered spectroscopy (DOSY), which separates NMR signals according to the diffusion coefficient, finds increasing use to identify species in solution. However, there still is no simple relationship between diffusion coefficient and molecular weight (MW). Some methods have been developed to estimate the MW but still with a significant error of ±30%. Here we describe a novel development of MW-determination by using an external calibration curve (ECC) approach with normalized diffusion coefficients. Taking the shape of the molecules into account enables accurate MW-predictions with a maximum error of smaller than ±9%. Moreover we show that the addition of multiple internal references is dispensable. One internal reference (that also can be the solvent) is sufficient. If the solvent signal is not accessible, 16 other internal standards (aliphatics and aromatics) are available to avoid signal overlapping problems and provide flexible choice of analytes. This method is independent of NMR-device properties and diversities in temperature or viscosity and offers an easy and robust method to determine accurate MWs in solution.