Design, synthesis and applications of functionalized ionic liquids

Room temperature ionic liquids (RTILs), considered as "designers' solvents", are attracting a great attention because of their possibility to be tailored based on property requirements. The ionic liquids designed and synthesized for carrying out specified task are referred as functionalized ionic liquids, which show great application potential in various processes. The efforts to produce functionalized ionic liquids, characterize them, and evaluate their properties and applications are presented in this thesis. In chapter 1 the recent developments in ionic liquid functionalization are highlighted. Chapter 2 describes the synthesis and characterization of imidazolium salts in which a nitrile group is attached to the alkyl side chain (single-armed as well as double-armed). The nitrile group was chosen as it is a promising donor to transition metals such as palladium and platinum. The physicochemical properties of these new ionic liquids are described and it is shown how the length of the alkyl unit linking the imidazolium ring and the CN group influences the melting point of the ionic liquid. The third chapter describes palladium complexation reactions with the nitrile functionalized imidazolium ionic liquids (prepared as described in Chapter 2). Their application in C-C coupling and hydrogenation reactions are described. It will be shown that the palladium complexes serve as precursors to nanoparticle catalyst reservoirs and are very efficiently stabilized by the nitrile-functionalized ionic liquids. In chapter 4, the synthesis of a series of nitrile functionalized ionic liquids based on the N-butylnitrile pyridinium cation is reported and their suitability as solvents for palladium-catalyzed biphasic Suzuki and Stille coupling reactions is demonstrated. TEM images reveal that nanoparticles are formed in situ in Stille reactions and show that the nitrile-functionalized ionic liquid exert a superior nanoparticle-stabilizing effect compared to non-functionalized ionic liquids. This allows excellent catalyst lifetimes. In the fifth chapter the synthesis and characterization of a series of ionic liquids incorporating the allyl functionality and some nascent reactions that they undergo, indicating that they are useful precursors to a wide range of other functionalized ionic liquids, will be described. Chapter 6 reports on a concept of "dual-functionalized" ionic liquids. Specifically imidazolium cations with various functionalities are combined with the nitrile functionalized anion [CH3CH(BF3)CH2CN]-, aiming at reducing the melting point and visocity of ionic liquids. In the final chapter the ionic liquid, 1-methyl-3-(4-vinylbenzyl)-imidazolium chloride, is prepared and polymerized to form a macromolecule that is subsequently used as a transition metal nanoparticle stabilizer. A methodology that enables transition metal nanoparticle transfer between liquid phases, via surface modification of the nanoparticles by anion exchange, is described.

Synthesis and characterization of ionic liquids incorporating the nitrile functionality

Paul Joseph Dyson, Zhaofu Fei, Dongbin Zhao

A series of imidazolium salts with the nitrile functional group attached to the alkyl side chain, viz. [C(n)CNmim][X] (where C(n)CNmim is the 1-alkylnitrile-3-methylimidazolium cation and C-n = (CH2)(n), n = 1-4; X = Cl, PF6, and BF4) and [C(3)CNdmim][X] (where C(n)CNdmim is the 1-alkylnitrile-2,3-dimethylimidazolium cation and C-n = (CH2)(n), n = 3; X = Cl, PF6, and BF4), have been prepared and characterized using spectroscopic methods. The majority of the nitrile-functionalized imidazolium salts can be classed as ionic liquids since they melt below 100 degreesC. Four of the imidazolium salts have been characterized in the solid state using single-crystal X-ray diffraction analysis to reveal an extensive series of hydrogen bonds between H atoms on the cation and the anion. The relationship between the solid-state structure and the melting point is discussed. Key physical properties (density, viscosity, and solubility in common solvents) of the low melting ionic liquid have been determined and are compared with those of the related 1-alkyl-3-methylimidazolium and 1-alkyl-2,3-dimethylimidazolium ionic liquids. It was envisaged that these ionic liquids could act as both solvent and ligand for catalyzed reactions, and this application is demonstrated in hydrogenation reactions, which show that retention of the catalyst in the ionic liquid during product extraction is extremely high.

2004

Palladium nanoparticles stabilized by an ionic polymer and ionic liquid: A versatile system for C-C cross-coupling reactions

Wee Han Ang, Paul Joseph Dyson, Zhaofu Fei, Yuehui Li, Xuemei Yang, Dongbin Zhao

Highly stable palladium nanoparticles 5 nm diam., protected by an imidazolium-based ionic polymer in a nitrile-functionalized ionic liq., have been prepd. and characterized by TEM. These Pd nanoparticles are excellent precatalysts for Suzuki, Heck, and Stille coupling reactions and can be stored without undergoing degrdn. for at ³2 yr. The nanoparticle system may therefore be considered as an alternative to the traditional palladium on carbon precatalyst used in many C-C coupling reactions, and also allowing reactions to be conducted under solvent-free conditions.

2008

Propelling the hydrogen economy: from chemical storage and delivery to utilization in biomass conversion

Lu Chen

Since H2 is a non-polluting, inexhaustible, efficient, and sustainable energy carrier, it has been forecast to become one of the major carriers of energy in the future and is also essential in the production of feedstock chemicals derived from renewable carbon sources. Initially, a Ru(II) catalyst with meta-trisulfonated triphenylphosphine ligands was shown to be a versatile homogeneous catalyst for the reversible dehydrogenation/hydrogenation of N-heterocycles. N-heterocyclic liquid organic hydrogen carrier compounds are attractive H2 storage and delivery compounds. Hydrogen is also essential in reductive fragmentation of lignin, an abundant biomass source that can be cleaved under reductive conditions to produce value-added renewable aromatic platform chemicals. In native lignin most of the units are linked by C-O bonds. Therefore, selective catalytic cleavage of the C-O bonds plays a pivotal role in maximizing the efficiency of the process while maintaining desirable functionality. A pseudo-homogeneous catalytic system consisting of in situ generated platinum nanoparticles dispersed in ionic liquids was used for upgrading high oxygen content bio-oil through hydrodeoxygenation. To improve further the stability of the catalyst, well-defined rhodium nanoparticles dispersed in sub-micrometer size carbon hollow spheres were prepared, which were able to hydrogenate lignin derived products under mild conditions. Confinement of active rhodium nanoparticles within a carbon shell, prevents the intact lignin polymer from entering and interacting with the catalyst. Thus, this catalysts was used to demonstrate that solvolysis leads to fractionation and fragmentation of lignin, with the internal catalysts hydrogenating any reactive fragments generated. An atomically dispersed catalyst, comprising single Pt atoms on Ni nanoparticles supported on carbon, were used in depolymerization of lignin and showed enhanced activity on selective C-O bonds cleavage.

EPFL2021

Propelling the hydrogen economy: from chemical storage and delivery to utilization in biomass conversion

Lu Chen

EPFL2021