Matthias Schmeisser

Gutmann donor and acceptor numbers for ionic liquids.

We present for the first time Gutmann donor and acceptor numbers for a series of 36 different ionic liquids that include 26 distinct anions. The donor numbers were obtained by (23)Na NMR spectroscopy and show a strong dependence on the anionic component of the ionic liquid. The donor numbers measured vary from -12.3 kcal mol(-1) for the ionic liquid containing the weakest coordinative anion [emim][FAP] (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate), which is a weaker donor than 1,2-dichloroethane, to 76.7 kcal mol(-1) found for the ionic liquid [emim][Br], which exhibits a coordinative strength in the range of tertiary amines. The acceptor numbers were measured by using (31)P NMR spectroscopy and also vary as a function of the anionic and cationic component of the ionic liquid. The data are presented and correlated with other solvent parameters like the Kamlet-Taft set of parameters, and compared to the donor numbers reported by other groups.

Thermodynamic and kinetic studies on reactions of Fe(III)(meso-[tetra(3-sulfonatomesityl)porphin]) with NO in an ionic liquid. Trace impurities can change the mechanism!

To elucidate the applicability and effects of ionic liquids as reaction media for bioinorganic catalysis, detailed kinetic and mechanistic studies on the reversible binding of NO to the monohydroxo ligated iron(III) phorphyrin, (TMPS)Fe(III)(OH) were performed in the ionic liquid [emim][NTf(2)] as solvent. We report for the first time the determination of activation volumes via high pressure stopped flow methods in an ionic liquid. The studies clearly show that impurities of methylimidazole, present at the micromolar concentration level, can generate the 6-fold coordinated (TMPS)Fe(III)(OH)(MeIm) complex and lead to a complete changeover in mechanism from associatively activated for (TMPS)Fe(III)(OH) to dissociatively activated for (TMPS)Fe(III)(OH)(MeIm). NMR measurements on the chemical shift of the beta-pyrrole protons revealed a spin state change from high spin (S = 5/2 for (TMPS)Fe(III)(OH)) to an intermediate spin-state (S = 5/2 and 3/2) following the coordination of methylimidazole. Because of the effect of the cationic component of the ionic liquid, Fe(III)(TMPS) also reacts with nitrite unlike the case in aqueous solution. Kinetic and thermodynamic studies on the reaction of (TMPS)Fe(III)(OH) with tetrabutylammonium nitrite allowed the determination of the equilibrium constant and thermodynamic parameters for the coordination of nitrite in [emim][NTf(2)].

Coordination of terpyridine to Li+ in two different ionic liquids.

On the basis of (7)Li NMR experiments, the complex-formation reaction between Li(+) and the tridentate N-donor ligand terpyridine was studied in the ionic liquids [emim][NTf2] and [emim][ClO4] as solvents. For both ionic liquids, the NMR data implicate the formation of [Li(terpy)2](+). Density functional theory calculations show that partial coordination of terpyridine involving the coordination of a solvent anion can be excluded. In contrast to the studies in solution, X-ray diffraction measurements led to completely different results. In the case of [emim][NTf2], the polymeric lithium species [Li(terpy)(NTf2)]n was found to control the stacking of this complex, whereas crystals grown from [emim][ClO4] exhibit the discrete dimeric species [Li(terpy)(ClO4)]2. However, both structures indicate that each lithium ion is formally coordinated by one terpy molecule and one solvent anion in the solid state, suggesting that charge neutralization and π stacking mainly control the crystallization process.

Reply to the Comment on the Article “Gutmann Donor and Acceptor Numbers for Ionic Liquids” (Chem. Eur. J. 2012, 18, 10969–10982) by J.‐F. Gal and C. Laurence

The application of ionic liquids (ILs) in a wide range of chemical processes has stimulated the development of new ILs tuned for specific applications. A recent extended review article noted that “there have been well over 6000 papers published over the past 10 years with the phrase ”ionic liquids“ in the title”. [1] Today between 300 and 400 ILs are commercially available. [2] In our own work we focused on the study of inorganic/bioinorganic reaction mechanisms in ionic liquids [3–6] especially in terms of the role of the anionic component of the IL that can be a potential nucleophile and act as a coordinating ligand for transitionmetal complexes. Indeed, even the rather simple ligand substitution process on square-planar complexes showed a characteristic dependence on the nature of the anionic component of the IL in terms of its nucleophilicity/basicity. For that reason we set out to find suitable solvent parameters that would assist the quantitative description of the behavior of ILs in reactions of transition-metal complexes. In our earlier work we have employed conventional solvent parame

Ligand Exchange Processes on Solvated Lithium Cations. VI. Determination of Coordination Numbers by Ligand Substitution and 7Li NMR

Graphical Abstract Ligand Exchange Processes on Solvated Lithium Cations. VI. Determination of Coordination Numbers by Ligand Substitution and 7Li NMR On the basis of 7Li NMR studies the coordination mode of phenantroline (phen) and bipyridine (bipy) to Li+ ions was found to be [Li(phen)2]+ and [Li(bipy)2]+ in the weakly coordinating solvent nitromethane. A large chemical shift of the 7Li signal indicated a strong interaction between the ligand and the metal center. The related sp2-hybridized N-donor ligand 2,2´-bis[(4S)-4-benzyl-2- oxazoline] (biox) showed a negligible effect on the 7Li shift, suggesting that almost no interaction occurs between the Li+ center and biox as compared to Li+ and the solvent γ -butyrolactone. Corresponding DFT (RB3LYP/LANL2DZp) calculations have clearly indicated that the poor coordination of biox is not caused by steric effects but rather by the electronic nature of the heterocyclic biox system.