Organometallic compounds ionic liquids

Due to the good solubility of organometallic compounds, ionic liquids have been used as reaction media, replacing traditional molecular solvents, or as the catalyst-supporting phase in a biphasic system. Influences of the ionic liquid on the reaction rate and selectivity can mostly be explained by the reactivity of the anion, which can be noncoordinating or coordinating as well as Lewis-acidic, Lewis-basic or neutral. The cation, in contrast, is considered to be essentially noncoordinating and innocent. 

Although a great deal of excitement has surrounded the use of ionic liquids as solvents for organic synthesis, the rational synthesis of inorganic and organometallic compounds in ionic liquids has remained largely unexplored. 

One of the important new directions in the study of addition reactions of organozinc compounds to aldehydes is the use of ionic liquids. Usually, application of these compounds in reactions with common organometallic reagents has a serious problem ionic solvents are usually reactive toward them, particularly Grignard and organolithium derivatives. It has been recently reported that carbonyl compounds react with allylzinc bromide formed in situ from allyl bromide and zinc in the ionic liquid 3-butyl-l-methylimidazolium tetrafluoroborate, [bmim][BF4].285 Another important finding is that the more reactive ZnEt2 alkylates aldehydes in a number of ionic liquids at room temperature.286 The best yields (up to 96%) were obtained in A-butylpyridinium tetrafluoroborate, [bpy][BF4] (Scheme 107). 

Room-temperature ionic liquids exhibit many properties that make them potentially attractive as solvents for catalysis [11]. They dissolve a wide range of organic, inorganic and organometallic compounds as well as gases, e.g., CO2, HCl, NH3, and to a much lower extent also H2 and CO. Many ionic liquids show temperature operating ranges of more than 300 °C compared... 

Many organometallic catalysts are soluble in ionic liquids, especially including ionic compounds. Neutral species, such as Wilkinson s catalyst, are also soluble to some extent in ionic liquids (169). There are numerous examples illustrating the dispersion and isolation of organometallic catalysts in ionic liquids a list of examples is given in a recent review (/). 

Iodo dimethyl amido complexes, with Ti(IV), 4, 331-332 Iodonium salts, cross-coupling with lead reagents, 9, 413 Ionic addition reactions, mechanisms, 1, 101 Ionic bis(isonitrile) complexes, liquid crystals, 12, 280 Ionic character, organometallic compound dn configuration,... 

Since late 2007, the Energy Biosciences Institute in Berkeley has been the center for cooperation between scientists from the University of California and the Agricultural Department of the University of Illinois for the production of fuels from so-called energy crops like switch grass. In this second-generation biofuel project that is financed over a 10-year period with 500 million by oil company BP, biomass is converted with the help of synthetic catalysts, for example, organometallic compounds, in a special solvent medium, better known as ionic liquids, into hydrocarbons with properties close to automotive fuels. 

The organometallic compounds most likely to undergo hydrolysis are those with ionic bonds, those with relatively polar covalent bonds, and those with vacant atomic orbitals (see Chapter 1) on the metal atom, which can accept more electrons. These provide sites of attack for the water molecules. For example, liquid trimethylaluminum reacts almost explosively with water or water and air ... 

We have described four significant catalytic systems consisting of stabilized metal nanoparticles in the hydrogenation of monocyclic aromatic compounds. Four noble metals are efficient in this reaction Rh, Ru, Ir, and Pt. Several stabilization methods have been described which represent typical nanoparticle stabihzers polymers, surfactants, polyoxoanions and ionic liquids. Two approaches are developed for the preparation of nanocatalysts which provide interesting results in catalytic apphcations the reduction starting with an organometalhc precursor or a metal salt. The organometallic... 

An interesting aspect is the application of these arene functionalised imidazolium salts as organometallic ionic liquids [139,142,143] whereby the imidazolium salt functions as the ionic liquid itself [139,143] or as the ionic liquid compatible part of the compound using the transition metal arene complex as a catalyst in biphasic applications [142],... 

In some cases, it is possible to couple an alcohol with an organometallic compound. Allylic alcohols are coupled with alkylmagnesium bromides in the presence of Ti(OiPr)4, for example. Allylic alcohols can be coupled with arylboronic acids in ionic liquid solvent and a rhodium catalyst. The palladium-catalyzed... 

Other organometallic compounds, including aUylic stannanes, allylic samarium, allylic germanium, and allylic indium compounds add to aldi-mines in the same manner. Aryltrialkylstannanes also add the aryl group to Al-tosyl imines using a rhodium catalyst and sonication. Catalytic enantioselective addition reactions are well known, including reactions in an ionic liquid.Allylic... 

The formation of unsymmetric biaryls via catalytic cross-coupling of aryl halides and organometallic compounds has been shown to proceed in ionic liquids with enhanced activity. The Suzuki-Miyaura cross coupling (cf. Section 2.11)... 

Ionic liquids have good solubility for organometallic compounds. 

On the other hand, coordination complexes or organometallic compounds can be solubilized in ionic liquids, especially hydrophobic or anionic complexes [71, 78], It has been pointed out earlier that there are tricks to circumvent dissolution problems such as dissolving a metal salt and the IL in an organic solvent followed by solvent evaporation. Furthermore, the viscosity, which is much higher in ILs than in conventional solvents, will dramatically reduce mass transfer, which in turn will lead to a much slower metal salt dissolution [71]. 

Neutral organometallic compounds are mostly sparingly soluble only (or after extensive period of sonication) in ionic liquids. 

Last but not least, the success of aqueous-phase catalysis has drawn the interest of the homogeneous-catalysis community to other biphasic possibilities such as or-ganic/organic separations, fluorous phases, nonaqueous ionic liquids, supercritical solvents, amphiphilic compounds, or water-soluble, polymer-bound catalysts. As in the field of aqueous-phase catalysis, the first textbooks on these developments have been published, not to mention Job s book on Aqueous Organometallic Catalysis which followed three years after our own publication and which put the spotlight on Job s special merits as one of the pioneers in aqueous biphasic catalysis. Up to now, most of the alternatives mentioned are only in a state of intensive development (except for one industrial realization that of Swan/Chematur for hydrogenations in scC02 [2]) but other pilot plant adaptations and even technical operations may be expected in the near future. 

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