Nitrile-functionalized pyridinium ionic liquids: Synthesis, characterization, and their application in carbon - Carbon coupling reactions

A series of relatively low-cost ionic liquids, based on the N-butyronitrile pyridinium cation C(3)CNpy, designed to improve catalyst retention, have been prepared and evaluated in Suzuki and Stille coupling reactions. Depending on the nature of the anion, these salts react with palladium chloride to form C(3)CNpy[PdCl4] when the anion is Cl- and complexes of the formula [PdCl2(C(3)CNpy)(2)]anion when the anion is PF6-, BF4-, or N(SO2CF3)(2)(-). The solid-state structures of [C(3)CNpy]Cl and C(3)CNpy[PdCl4] have been established by single-crystal X-ray diffraction. The catalytic activity of these palladium complexes following immobilization in both N-butylpyridinium and nitrile-functionalized ionic liquids has been evaluated in Suzuki and Stille coupling reactions. All of the palladium complexes show good catalytic activity, but recycling and reuse is considerably superior in the nitrile-functionalized ionic liquid. Inductive coupled plasma spectroscopy reveals that the presence of the coordinating nitrile moiety in the ionic liquid leads to a significant decrease in palladium leaching relative to simple N-alkylpyridinium ionic liquids. Palladium nanoparticles have been identified as the active catalyst in the Stille reaction and were characterized using transmission electron microscopy.

Development of nitrile-functionalized ionic liquids for C-C coupling reactions: implication of carbene and nanoparticle catalysts

Wee Han Ang, Cinzia Chiappe, Paul Joseph Dyson, Zhaofu Fei, Dongbin Zhao

A series of nitrile-functionalized imidazolium salts (many of which are liquid at room temperature) have been prepared. The reactivity of these salts with PdCl2 has been studied, resulting in salts containing a tetrachloropalladate dianion or compounds in which the nitrile substituent coordinates to the palladium center. Further derivation of the latter compounds affords carbenes. All the new compounds have been characterized by spectroscopic methods and nine of them by single-crystal X-ray diffraction. The catalytic activity of the different palladium salts in Suzuki, Stille, and Heck reactions has been evaluated in some of the nitrile-functionalized ionic liquids (ILs) and compared with that of nonfunctionalized ILs, providing insights into the nature of the actual catalyst. In some instances, palladium nanoparticles have been identified, but the nature of the catalyst strongly depends on the IL employed.

2007

Design, synthesis and applications of functionalized ionic liquids

Dongbin Zhao

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.

EPFL2007

Design, synthesis and applications of functionalized ionic liquids

Dongbin Zhao

EPFL2007