Alexander Bergen

Heterogenized molecular catalysts commonly rely on covalent grafting to solid supports. Cleavage of these linkages under catalytic conditions, however, can compromise structural definition and control at the interface. Here, we introduce a ligand‐encoded anchoring strategy in which a platinum(II) bis(NHC) complex is immobilized on mesoporous silica (SBA‐15) exclusively through directional, non‐covalent F–Si interactions. The molecular pre‐catalyst trans ‐[Pt(L ^F ) ₂ Cl ₂ ] was structurally characterized by single‐crystal X‐ray diffraction and multinuclear solution‐state NMR spectroscopy. Advanced solid‐state MAS NMR experiments, including ¹⁹ F{ ²⁹ Si} REDOR, combined with molecular dynamics simulations, establish well‐defined F–Si contacts with internuclear distances on the Å‐scale and reveal the organization of the pre‐catalyst at the silica interface. A model hydrosilylation reaction demonstrates catalytic activity and retention of the molecular species on the support during turnover. This work establishes non‐covalent interface engineering as a viable strategy for structurally defined heterogenized catalysis.

We present the preparation and investigation of a fluorine‐free surface‐active bis‐N‐heterocyclic carbene (NHC) platinum(II) complex — trans‐[Pt(mPEG₃C₈Im)₂Cl₂] — for interface‐enhanced supported ionic liquid phase (SILP) catalysis within a group of (mPEG_n)‐substituted ionic liquids (ILs) ([(mPEG_n)₂Im][A] ILs). The complex was characterized by means of single‐crystal X‐ray diffraction (scXRD) analysis and multinuclear (¹H, ¹³C, ¹⁹⁵Pt) NMR spectroscopy, indicating the presence of two almost equimolar syn–anti‐rotamers of the square‐planar complex in solution. Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) revealed pronounced interface‐accumulation of trans‐[Pt(mPEG₃C₈Im)₂Cl₂] in IL solutions of [(mPEG₂)₂Im][A] (A⁻=I⁻ and PF₆⁻).

In this study, we systematically analyze the surface tension and Hansen solubility parameters (HSPs) of imidazolium-based ionic liquids (ILs) with different anions ([NTf₂]^-, [PF₆]^-, [I]^-, and [Br]^-). These anions are combined with the classical 1-alkyl-3-methyl-substituted imidazolium cations ([C_nC₁Im]⁺) and a group of oligoether-functionalized imidazolium cations ([(mPEG_n)₂Im]⁺) based on methylated polyethylene glycol (mPEG_n). In detail, the influences of the length of the alkyl- and the mPEG_n-chain, the anion size, and the water content are investigated experimentally. For [C_nC₁Im]⁺-based ILs, the surface tension decreases with increasing alkyl chain length in all cases, but the magnitude of this decrease depends on the size of the anion ([NTf₂]^- < [PF₆]^- < [Br]^- ≤ [I]^-). Molecular dynamics (MD) simulations on [C_nC₁Im]⁺-based ILs indicate that these differences are caused by the interplay of charged and uncharged domains, in particular in the different anions, which affects the ability of the alkyl chains of the cation to orient toward the liquid-gas interface. An increase in the mPEG_n-chain length of the [(mPEG_n)₂Im][A] ILs does not significantly influence the surface tension. These changes upon variation of the cation/anion combination do not correlate with the evolution of the HSPs for the two sets of ILs. Finally, our data suggest that significant water contents up to water mole fractions of x(H₂O) = 0.25 do not significantly affect the surface tension of the studied binary IL-water mixtures.

Separation and reuse of the catalytically active metal complexes are persistent issues in homogeneous catalysis. Supported Ionic Liquid Phase (SILP) catalysts, where the catalytic center is dissolved in a thin film of a stable ionic liquid, deposited on a solid support, present a promising alternative. However, the dissolution of the metal center in the film leaves little control over its position and its activity. We present here four novel, task‐specific ionic liquids [FPh_nIm^HR]I (n=1, 2; R=PEG₂, C₁₂H₂₅), designed to self‐assemble on a silica surface without any covalent bonding and offering a metal binding site in a controlled distance to the support. Advanced multinuclear solid‐state NMR spectroscopic techniques under Magic Angle Spinning, complemented by molecular dynamics (MD) simulations, allow us to determine their molecular conformation when deposited inside SBA‐15 as a model silica support. We provide here conceptual proof for a rational design of ionic liquids self‐assembling into thin films, opening an avenue for a second, improved generation of SILP catalysts.

The present study provides a strategy for the determination of the viscosity and surface tension of high-viscosity fluids in the form of ionic liquids (ILs) at equilibrium conditions by combining surface light scattering (SLS) and the pendant-drop (PD) method within one experimental setup. Through the study of the same sample under identical conditions by both methods inside a closed system, the surface tension determined via the PD method can be directly used to evaluate the dynamics of surface fluctuations of ILs with an overdamped behavior probed by SLS for accessing their viscosity. In connection with the SLS experiments, variations in the applied detection geometries in reflection and transmission direction and in the probed wave vectors down to relatively small values were also addressed. The reliability and self-consistency of SLS and the PD method applied within the same sample cell has been proven by investigating the reference fluids tris(2-ethylhexyl) trimellitate (TOTM) and n-dodecane featuring relatively high and low viscosities. For the two studied model ILs of opaque to non-transparent color, i.e., the hydrophobic 1-methyl-3-octylimidazolium hexafluorophosphate ([OMIM][PF₆]) and the hydrophilic 1,3-bis(2-(2-methoxyethoxy)ethyl)imidazolium iodide ([(mPEG₂)₂Im]I), the combination of PD measurements and SLS experiments in reflection direction performed at ambient pressure between (303 and 373) K allowed access to the viscosity and surface tension with typical relative expanded uncertainties of (4 and 2) %. These results agree well with own viscosity data from capillary viscometry and experimental data in the literature, demonstrating the performance of the novel approach for the contactless in-situ measurement of viscosity and surface tension of fluids with relatively high-viscosity such as ILs.