Ionic liquids (ILs), salts with melting points below 100 °C, represent a fascinating class of liquid materials typically characterized by an extremely low vapor pressure. Besides their application as new solvents or as electrolytes for electrochemical purposes, there are two important concepts of using ILs in catalysis: Liquid–liquid biphasic catalysis and IL thin film catalysis. Liquid–liquid biphasic catalysis enables either a very efficient manner to apply catalytic ILs, e.g. in Friedel–Crafts reactions, or to apply ionic transition metal catalyst solutions. In both cases, phase separation after reaction allows an easy separation of reaction products and catalyst re-use. One problem of liquid–liquid biphasic catalysis is mass transfer limitation. If the chemical reaction is much faster than the liquid–liquid mass transfer the latter limits the overall reaction rate. This problem is overcome in IL thin film catalysis where diffusion pathways and thus the characteristic time of diffusion are short. Here, Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL) are the two most important concepts. In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. In each concept, interface phenomena play a very important role: These may concern the interface of an IL phase with an organic phase in the case of liquid–liquid biphasic catalysis. For IL thin film catalysis, the interfaces of the IL with the gas phase and with catalytic nanoparticles and/or support materials are of critical importance. It has recently been demonstrated that these interfaces and also the bulk of ILs can be investigated in great detail using surface science studies, which greatly contributed to the fundamental understanding of the catalytic properties of ILs and supported IL materials. Exemplary results concerning the IL/vacuum or IL/gas interface, the solubility and surface enrichment of dissolved metal complexes, the IL/support interface and the in situ monitoring of chemical reactions in ILs are presented. Important concepts in catalysis with ionic liquids are reviewed, including Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL), along with the detailed analysis of the relevant interfaces using surface science methods.

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Ionic Liquids in Catalysis

We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multiconfiguration and multireference (MR) electronic structure calculations. Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a coordination complex). This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wave function (such as from a Hartree–Fock or Kohn–Sham calculations) based on projectors to targeted atomic valence orbitals. We discuss the premises, theory, and implementation of the idea, and several of its variations are tested. To investigate the performance and accuracy, we calculate the excitation energies for various transition-metal complexes in typical application scenarios. Additionally, we follow the homoly...

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Automated Construction of Molecular Active Spaces from Atomic Valence Orbitals

Vinyl cyclopropanes are amongst the most useful building blocks in organic synthesis. Their easy opening and capacity to generate dipoles have been exploited for the synthesis of cyclopentanes with good yields and sometimes excellent stereoselectivities. In this review we give an overview of their applications, focusing on the present century.

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Synthetic applications of vinyl cyclopropane opening.

The nucleophilic iron complex Bu4N[Fe(CO)3(NO)] (TBA[Fe]) catalyzes the direct intramolecular C-H amination of α-azidobiaryls and (azidoaryl)alkenes into the corresponding carbazoles and indoles, respectively, under mild conditions and with low catalyst loadings. These features and the broad functional-group tolerance render this method a particularly attractive alternative to established noble-metal-based procedures.

Iron‐Catalyzed Intramolecular C(sp2)−H Amination

The nucleophilic iron complex Bu4 N[Fe(CO)3 (NO)] (TBA[Fe]) catalyzes the direct intramolecular amination of unactivated C(sp3 )-H bonds in alkylaryl azides, which results in the formation of substituted indoline and tetrahydroquinoline derivatives.

Iron-Catalyzed Intramolecular Aminations of C(sp3)−H Bonds in Alkylaryl Azides

The base metal complex Bu4N[Fe(CO)3(NO)] (TBA[Fe]) catalyzes the rearrangement of vinyl and arylcyclopropanes both under thermal or photochemical conditions to give the corresponding vinyl or aryldihydrofurans in good to excellent yields. Under photochemical conditions the reaction is performed at room temperature. Spectroscopic investigations show that the metal carbonyl catalyst is not decarbonylated. The best performance was observed at a wavelength of 415 nm. icMRCI+Q analysis of the excited singlet and triplet states of the [Fe(CO)3(NO)] anion was performed and used to calculate the vertical excitation energies which are in good agreement with the experimental data. CASSCF analysis indicates that the Fe center in all excited states of the ferrate becomes more electrophilic while adopting a distorted tetrahedral configuration. Both aspects have a positive synergistic effect on the formation of the initial π-complex with the incoming organic substrate.

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Non-decarbonylative photochemical versus thermal activation of Bu4N[Fe(CO)3(NO)] – the Fe-catalyzed Cloke–Wilson rearrangement of vinyl and arylcyclopropanes

The synthesis of the novel ionic Ru–alkylidenes [Ru[(4-CO2)(1-CH3)Py+)]2(IMesH2)(CH-2-(2-PrO)-C6H4)][OTf−]2 (1, IMesH2=1,3-dimesitylimidazolin-2-ylidene, Py=pyridine, OTf−=triflate) and [RuCl[(4-CO2)(1-CH3)Py+)](IMesH2)(CH-2-(2-PrO)-C6H4)][OTf−] (2) is reported. Catalysts 1 and 2 were successfully used in various metathesis reactions under biphasic liquid–liquid conditions using 1-butyl-2,3-dimethylimidazolium tetrafluoroborate and heptane as liquid phases. Ruthenium leaching into the heptane phase was very low (<0.4 %), translating into Ru contamination of the products between 0.3 and 2.5 ppm. Both 1 and 2 exhibited comparable reactivity in organic solvents and under biphasic conditions. Catalyst 1 and 2 were also successfully used in the continuous metathesis of methyl oleate and 1,7-octadiene under supported liquid–liquid conditions. Finally, the disproportionation of the monocarboxylato monochloro substituted Ru–alkylidene 2 was traced by 1H NMR analysis at 40 °C, thereby demonstrating the formation of complex 1 and the neutral complex [RuCl2(IMesH2)(CH-2-(2-PrO)-C6H4)].

Ionically Tagged Ru–Alkylidenes for Metathesis Reactions under Biphasic Liquid–Liquid Conditions

Pyrrols are substructures in various biological active molecules. A straightforward iron-catalyzed synthesis of pyrrols via insertion of an imine into a vinylcyclopropane is presented. The corresponding pyrrols are obtained in moderate to good yields. Scope and limitations will be discussed.

Insertion of Imines into Vinylcyclopropanes Catalyzed by Nucleophilic Iron Complexes: A Formal [3+2]-Cycloaddition Strategy for the Synthesis of Substituted Pyrrolidine Derivatives

Insertion of Imines into Vinylcyclopropanes Catalyzed by Nucleophilic Iron Complexes: A Formal [3 + 2]‐Cycloaddition Strategy for the Synthesis of Substituted Pyrrolidine Derivatives.

The Fe-catalyzed Cloke—Wilson rearrangement of vinylcyclopropanes (I), (IV), and (VI) under photochemical conditions proceeds in a shorter time and with similar or higher yields compared to the reaction under thermal conditions.

Non-decarbonylative Photochemical versus Thermal Activation of Bu4N[Fe(CO)3(NO)] — The Fe-Catalyzed Cloke—Wilson Rearrangement of Vinyl and Arylcyclopropanes.

Dominik Pursley

Papers

Non-decarbonylative photochemical versus thermal activation of Bu4N[Fe(CO)3(NO)] – the Fe-catalyzed Cloke–Wilson rearrangement of vinyl and arylcyclopropanes

Ionically Tagged Ru–Alkylidenes for Metathesis Reactions under Biphasic Liquid–Liquid Conditions

Insertion of Imines into Vinylcyclopropanes Catalyzed by Nucleophilic Iron Complexes: A Formal [3+2]-Cycloaddition Strategy for the Synthesis of Substituted Pyrrolidine Derivatives

Insertion of Imines into Vinylcyclopropanes Catalyzed by Nucleophilic Iron Complexes: A Formal [3 + 2]‐Cycloaddition Strategy for the Synthesis of Substituted Pyrrolidine Derivatives.

Non-decarbonylative Photochemical versus Thermal Activation of Bu4N[Fe(CO)3(NO)] — The Fe-Catalyzed Cloke—Wilson Rearrangement of Vinyl and Arylcyclopropanes.