The Heck Reaction in Ionic Liquids: Progress and Challenges

As   the   interest   for   environmental   increases   and   environmental   laws   become   more   stringent,   the   need   to   replace   existing   processes   with   new   more   sustainable   technologies   becomes   a   primary   objective.   The   use   of   ionic   liquids   to   replace   organic   solvents  in  metal  catalyzed  reactions  has  recently  gained  much  attention  and  great  progress   has   been   accomplished   in   this   area   in   the   last   years.   This   paper   reviews   the   recent   developments   in   the   application   of   ionic   liquids   and   related   systems   (supported   ionic   liquids,  ionic  polymers,  and  so  on)  in  the  Heck  reaction.  Merits  and  achievements  of  ionic   liquids   were   analyzed   and   discussed   considering   the   possibility   of   increasing   the   effectiveness  of  industrial  processes

Structural Features and Properties of Metal Complexes in Ionic Liquids: Application in Alkylation Reactions

Metal-containing ionic liquids (ILs) represent a promising sub-class of “charged” liquids which increase the tunability of ILs combining the properties of common organic salts with magnetic, photophysical/optical or catalytic properties of the incorporated metal salts. In ILs lacking of coordinating groups on cation dissolution of metal salts is generally associated with the coordination of the metal cation with IL anion(s). Here we report on the anionic speciation of metals in ILs having either highly or poorly coordinating anions and we discuss some peculiar properties of these systems in the light of their structural features

Synthesis and study of the stability of amidinium/guanidinium carbamates of amines and α-amino acids

Thermally stable amidinium/guanidinium N,N-dialkylcarbamates, including vacuum stable compounds, have been prepared, and then isolated in the solid state, by reaction of tetramethylguanidine (TMG) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with secondary amines under atmospheric pressure of CO2. The same method has been successfully applied to a-amino acids, thus the corresponding carbamates of sarcosine, L-proline and L-phenylalanine have been obtained. All the products are highly moisture sensitive, and have been characterized by analytical and spectroscopic (IR, multinuclear NMR) techniques

Dissolution of metal salts in bis(trifluoromethylsulfonyl)imide-based ionic liquids: Studying the affinity of metal cations toward a "weakly coordinating" anion

Despite the weakly coordinating ability of the bis(trifluoromethylsulfonyl)imide anion ([Tf2N]-) the corresponding ionic liquids (ILs) are able to dissolve relevant amounts of metal salts having the same anion, M[Tf2N]x. To better understand the metal dissolution process we evaluated the interaction ability of a set of metal cations (Y(III), Al(III), Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Li(I), and Na(I)) toward the [Tf2N]- anion measuring the relative aptitude to give the corresponding anionic monocharged complex, [M(Tf2N)x+1]- using the ESI-MS technique. UV-vis and NMR measurements were carried out to verify the consistence between the liquid and the gas phase. Density functional theory calculations have been used to identify the metal-containing species and determine their relative stability. An interesting correlation between interaction ability and chemical properties (Lewis acidity) was found

Unexpected Intrinsic Lability of Thiol-Functionalized Carboxylate Imidazolium Ionic Liquids

New thiol-functionalized carboxylate ionic liquids (ILs), varying both for the cation and for the anion structures, have been prepared as new potential redox switching systems by reacting either 3-mercapto propionic acid (3-MPA) or N-acetyl-cysteine (NAC) with commercially available methyl carbonate ILs. Dierent ratios of thiol/disulfide ILs were obtained depending both on the acid employed in the neutralization reaction and on the reaction conditions used. Surprisingly, the imidazolium ILs displayed limited thermal stability which resulted in the formation of an imidazole 2-thione and a new sulfide ionic liquid. Conversely, the formation of the imidazole 2-thione was not observed when phosphonium disulfide ILs were heated, thus confirming the involvement of the imidazolium ring in an unexpected side reaction. An insight into the mechanism of the decomposition has been provided by means of DFT calculations

A general environmentally friendly access to long chain fatty acid ionic liquids (LCFA-ILs)

The development of bio-based ionic liquids (ILs) has attracted a great deal of interest in recent years. The so called long chain fatty acid ionic liquids (LCFA-ILs) represent a bio-based subfamily of hydrophobic ionic liquids. Here, a new preparation of the three major classes of LCFA-ILs (phosphonium, ammonium, imidazolium) is presented with the aim to overcome previous environmental synthetic issues. The undeniable interesting properties and potential applications of the LCFA-ILs often led to the underestimation of the drawbacks related to their synthetic pathways. Pure LCFA-ILs as well as cheaper mixture of LCFA-ILs have been obtained in a single step, in almost quantitative yields, and without production of waste water. The rheological and thermal stability properties of the prepared ILs have been analyzed

Chiral ionic liquid assisted synthesis of some metal oxides

A chiral ionic liquid with a natural alcohol based chain was used as a tailoring agent for the synthesis of simple and cost effective materials such as ZnO, CuO, CuO-ZnO with peculiar morphology. The morphology and chemical composition of the microstructures were investigated by bright-field and scanning transmission microscopy (BF-TEM and STEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and UV-VIS spectroscopy. Furthermore, the photocatalytic activity of ZnO, CuO and ZnO-CuO nanostructures was quantified for methylene blue (MB) dye. CuO needles had the lowest photocatalytic activity (23.8% in 40 min). Due to their peculiar forms, ZnO (flower like shape) and ZnO/CuO (leaf like shape where ZnO nanoparticles were deposited) had the highest photocatalytic activity in 40 min (93.6% for ZnO nanoparticles and 95% for ZnO-CuO nanostructures)

Ionic liquid-promoted green synthesis of biologically relevant diaryl thioethers

This study reports an ionic liquid (IL) promoted green method to obtain diaryl thioethers useful as key intermediates for the synthesis of matrix metalloproteinase (MMP) inhibitors. The synthetic pathway includes a sequential Ullmann reaction and Suzuki cross-coupling. The Ullmann conditions were optimized as regards the catalyst, the ionic liquid, reaction time, and temperature. Under optimal conditions (1-butyl-3-methylimidazolium bromide ([BMIM]Br) as solvent; catalyst, Cu; base, K2CO3; reaction time, 22 h; reaction temperature, 150°C) the aryl iodide conversion was 95%. The Suzuki cross-coupling was conducted in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) at 110°C, using Pd(PPh3)4 as catalyst and Na2CO3 as base. For both reactions, a combination of ILs with microwave (MW) irradiation determined a substantial improvement of reaction time and yields compared to conventional heating. This multi-step process reduces reaction times and removes organic solvents providing a more eco-friendly alternative for the synthesis of important pharmaceutical building blocks

Chiral ionic liquids supported on natural sporopollenin microcapsules

Supported chiral ionic liquids (SILs) were prepared choosing the starting material for the ionic liquid part from the enantiopure stock of the chiral pool (monoterpenoids and an amino acid) and the sporopollenin as an environmentally friendly support. Sporopollenins are microcapsules with naturally well-defined sizes and shapes that can be obtained from pollen grains after removal of the internal cytoplasm and the second shell layer. As thermally stable organic biocompatible structures, sporopollenins have attracted increasing interest in recent years for several applications. Herein, bio-based ILs were anchored onto the surface of sporopollenins obtained from the pollen of Populus deltoides, selected as a model pollen grain. These new structures, which present an external positively charged shell, were characterized by physico-chemical techniques (ATR-FTIR, TGA, SEM, EDX, and solid-state 13C NMR). A metathesis reaction was also performed on selected bio-based IL modified sporopollenins, demonstrating the possibility to switch the surface properties by exploiting well-known IL chemistry

Alkylation of methyl linoleate with propene in ionic liquids in the presence of metal salts

Vegetable oils and fatty acid esters are suitable precursor molecules for the production of a variety of bio-based products and materials, such as paints and coatings, plastics, soaps, lubricants, cosmetics, pharmaceuticals, printing inks, surfactants, and biofuels. Here, we report the possibility of using Lewis acidic ionic liquids (ILs) to obtain polyunsaturated ester dimerization-oligomerization and/or, in the presence of another terminal alkene (propene), co-polymerization. In particular, we have tested the Lewis acidic mixtures arising from the addition of a proper amount of GaCl3 (X > 0.5) to two chloride-based (1-butyl-3-methylimidazolium chloride, [bmim]Cl, and 1-butylisoquinolium chloride, [BuIsoq]Cl) or by dissolution of a smaller amount of Al(Tf2N)3 (X = 0.1) in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf2N]. On the basis of product distribution studies, [bmim][Tf2N]/Al(Tf2N)3 appears the most suitable medium in which methyl linoleate alkylation with propene can compete with methyl linoleate or propene oligomerization