Ionic liquid solute

A similar catalytic dimerization system has been investigated [40] in a continuous flow loop reactor in order to study the stability of the ionic liquid solution. The catalyst used is the organometallic nickel(II) complex (Hcod)Ni(hfacac) (Hcod = cyclooct-4-ene-l-yl and hfacac = l,l,l,5,5,5-hexafluoro-2,4-pentanedionato-0,0 ), and the ionic liquid is an acidic chloroaluminate based on the acidic mixture of 1-butyl-4-methylpyridinium chloride and aluminium chloride. No alkylaluminium is added, but an organic Lewis base is added to buffer the acidity of the medium. The ionic catalyst solution is introduced into the reactor loop at the beginning of the reaction and the loop is filled with the reactants (total volume 160 mL). The feed enters continuously into the loop and the products are continuously separated in a settler. The overall activity is 18,000 (TON). The selectivity to dimers is in the 98 % range and the selectivity to linear octenes is 52 %. 

A related study used the air- and moisture-stable ionic liquids [RMIM][PFg] (R = butyl-decyl) as solvents for the oligomerization of ethylene to higher a-olefins [49]. The reaction used the cationic nickel complex 2 (Figure 7.4-1) under biphasic conditions to give oligomers of up to nine repeat units, with better selectivity and reactivity than obtained in conventional solvents. Recycling of the catalyst/ionic liquid solution was possible with little change in selectivity, and only a small drop in activity was observed. 

Additional amount of chiral ligand was added to the recovered ionic liquid solution g [47]... 

The term Supported Ionic Liquid Phase (SILP) catalysis has recently been introduced into the literature to describe the heterogenisation of a homogeneous catalyst system by confining an ionic liquid solution of catalytically active complexes on a solid support [68], In comparison to the conventional liquid-liquid biphasic catalysis in organic-ionic liquid mixtures, the concept of SILP-catalysis offers very efficient use of the ionic liquid. Figure 7.10 exemplifies the concept for the Rh-catalysed hydroformylation. 

Lachwa, J. et al.. Evidence for lower critical solution behavior in ionic liquid solutions, /. Am. Chem. Soc., 127,6542,2005. 

Moulthrop, J. S., Swatloski, R. R, Moyna, G. et al.. High-resolution NMR studies of cellulose and cellulose oligomers in ionic liquid solutions, Chem. Commun., 1557,2005. 

The reactions of a range of aryl, benzylic, and heterocyclic zinc reagents with iodo- and bromoarenes were reported at ambient temperature under biphasic conditions with [C4mmim][PF6] and toluene. The biaryl products were readily isolated by decanting the toluene phase, with yields of 70-92% achieved after several minutes. However, attempts to recycle the catalytic ionic liquid solution resulted in significantly decreased activities. 

Another interesting carbonylation that has been carried out in ionic liquids is that of 3-alkyn-l-ols and l-alkyn-4-ols by [Pd(OAc)2]/ PyPPh2(PyPPh2=2-(diphenylphosphino)pyridine) to give evo-a-methylene y- and 8-lactones, respectively.60 The products were isolated in almost quantitative yields by distillation under reduced pressure or by solvent extraction from the ionic liquid with diethyl ether. However, when recycling of the ionic liquid solution was attempted for the carbonylation of 3-butyn-l-ol the yield fell from 99 to 37% after only two runs. 

Also, metals have significantly different reduction potentials in ionic liquid solutions compared to water. For example the difference in reduction potential between Cr and Pt in ionic liquids may be as little as 100 mV whereas in aqueous solutions it is in excess of 2 V. One consequence of this characteristic is that alloy coatings may be prepared more readily and that it should be possible to develop many novel alloy coatings. 

The separation of non-volatile products from ionic liquid solutions using nanofiltration was suggested by Krockel and Kragl [136]. It was shown for both bromophe-nol blue and lactose, each in ionic liquid, that the product was rejected while the ionic liquid permeated. It should be noted that in such cases the products are not isolated. Instead, concentrated ionic liquid solutions are produced. However, depending on the solubility, phase separation might occur. 

Speciation of metal ions and complex ions in ionic liquid solution prior to electrodeposition is also clearly an important issue in understanding and developing electrowinning processes. Little is known about the stoichiometry and structure of... 

Functionalised ionic liquids based on cations other than imidazolium have also been developed. For example, pyridinium cations functionalised with pentafluorosulfanyl[89] or alkyl-nitrile groups1901 have been prepared as cheaper alternatives to their imidazolium-based counterparts (see Figure 2.8). The latter have been evaluated in palladium catalysed C-C cross coupling reactions and improved catalyst retention and stability were observed in the nitrile-functionalised ionic liquid compared to the simple alkyl-analogue. Consequently, the nitrile-functionalised ionic liquid solution can be reused repeatedly without significant decrease in activity (see Chapter 6 for further information). 

By the end of 2004 ring-opening polymerisation in ionic liquids has been reported in only one paper, using complexes 35a, 35b or 36 as catalysts.[33] A biphasic system comprised of [C4CiCiim][PF6] and toluene in a 1 4 ratio was used to minimise catalyst loss during product isolation and the polymer could be obtained almost quantitatively by simple decantation. The activity of ionic liquid solutions of 35a drop markedly after the first cycle and become inactive in the third cycle, whereas 35b and 36 could be used for three and five cycles, respectively, with very good conversions, as shown in Scheme 7.5. 

The common route to bis(indoyl)methanes is via condensation of indoles with aldehydes or ketones in the presence of either protic or Lewis acids. The reaction has been evaluated in tetrafluoroborate and hexafluorophosphate ionic liquids and of the metal salts tested best results were obtained with In(OTf)3 and FeCl3-6H20. Although In(OTf)3 is somewhat more active, its higher price makes the use of iron(III)chloride more attractive. Furthermore, whereas the activity of In(OTf)3 decreases quickly upon recycling, ionic liquid solutions of FeCl3 remain reasonably active for at least four runs.[62] It was found that in hydrophilic ionic liquids the reaction did not proceed at all, whereas fast conversion was observed with the [PF6] -anion, see Scheme 9.17. As water is produced in the course of the reaction it is possible that elimination of the water from the reaction medium helps to protect the catalyst, however, it cannot be excluded that at least some of the catalytic activity is due to the formation of HF. While the... 

Asymmetric hydroamination using a chiral PIGIPHOS-Ni(II) complex has also been achieved in ionic liquids, as shown in Scheme 9.38.11431 A number of different imidazolium and picolinium ionic liquids were tested and relative to THF, much higher turnover numbers (300 vs. 20) were observed in the reaction between methacrylonitrile and morpholine at comparable selectivity (64% ee vs. 69%). Moreover, the catalyst in the ionic liquid solution is less sensitive to air and moisture so that non-distilled reagents can be used. 

Summary The use of an ionic liquid in hydrosilylation reactions enables standard hydrosilylation catalysts to be easily recovered and subsequently reused after separation from the product at the end of the reaction. Remarkably, the recovered catalyst/ionic liquid solution does not need to be purified or treated before its reuse. Employing this method, a variety of organomodified polydiraethylsiloxanes were synthesized. 

Typically, the reaction is performed in a liquid-liquid biphasic system where the substrates and products (upper phase) are not miscible with the catalyst/ionic liquid solution (lower phase). The SiH-functional polydimethylsiloxane and the olefin are placed in the reaction vessel and heated up to 90 °C. Then the precious metal catalyst (20 ppm) and the ionic liquid (1 %) are added. After complete SiH conversion, the reaction mixture is cooled to room temperature and the products are removed from the reaction mixture by either simple decantation or filtration (in case of non-room-temperature ionic liquids). The recovered catalyst/ionic liquid solution can be reused several times without any significant change in catalytic activity. A treatment or workup of the ionic liquid-catalyst solution after each reaction cycle is not necessary. The metal content of the products was analyzed by ICP-OES (Inductively coupled plasma optical emission spectroscopy) and the chemical identity of the organomodified polydimethylsiloxane was verified by NMR spectroscopy. 

---