Ruthenium complexes ionic liquids

The (5 )-selective DKR of alcohols with subtilisin was also possible in ionic liquid at room temperature (Table 14). " In this case, the cymene-ruthenium complex 3 was used as the racemization catalyst. In general, the optical purities of (5 )-esters were lower than those of (R)-esters described in Table 5. 

In this case, the ruthenium complex was synthesized with an ionic tag moiety that is fully compatible with the [BMIM]PF6. A minimum amount of this ionic liquid was used for the reaction in a mixture containing 90 vol% CH2CI2. The catalyst (5mol%) was selectively retained in the ionic liquid after 10 repeated uses, without significant loss of activity in tests at 50°C that lasted 3h each (Table VI). 

A ruthenium complex containing a novel imidazolium salt moiety catalyses the asymmetric transfer hydrogenation of acetophenone derivatives, with a formic acid- triethylamine azeotropic mixture in an ionic liquid, [bmim][PF6]. The yields and ee are excellent.308... 

It is mostly complexes of ruthenium and rhodium that have been used to conduct hydrogenation reactions in ionic liquids and little attention has so far been paid to modifying the employed catalysts to improve their performance in the ionic environment. The majority of the catalysts used are identical to those employed in conventional homogeneous catalysis conducted in molecular solvents like, for example, RhCl(PPh3)3 and RuCl2(PPh3)3. 

In an extension of this work, either zinc(II), palladium(II), rhodium(I) or copper(I) salts were immobilised in an ionic liquid film (SILP, vide supra) onto diatomic earth and the catalysts tested for activity in the reaction between phenylacetylene and 4-isopropyl-phenylaminc.1 391401 The supported rhodium, ruthenium and zinc complexes afford higher rates and selectivities relative to their use under homogenous reaction conditions. Lower rates are, however, observed with the copper salt, which is rationalised by strong complexation of the ionic liquid to the Cu(I) centre. 

Steines, S. Wasserscheid, P. Driessen-Holscher, B. An Ionic Liquid as Catalyst Medium for Stereoselective Hydrogenations of Sorbic Acid with Ruthenium Complexes, J. Prakt. Chem. 2000, 342, 348-354. 

To overcome the problem of catalyst decomposition, Audic and coworkers [53] designed a novel alkyl imidazolium salt-snpported ruthenium carbene complex (Scheme 17.7). The resulting ionic catalyst is completely soluble in ionic liquid and allows the RCM reaction to be carried out under standard homogeneous conditions. This new catalyst system provided high conversion and yields (92-98%). Moreover, the recycled catalyst solution was used for the metathesis, and similar results were obtained up to the tenth cycle. The catalyst has shown high activity with a remarkable recyclability and can be stored in [bmijPFg for several months without loss of activity. 

Further modification in snpport of the ruthenium carbene complex with ionic liquid media was described by Wakamatsu et al. [54]. The RCM of diethyl diallyl-malonate using a new catalyst was carried out under an argon atmosphere in the presence of 5 mol% catalyst in CHjClj/[bmim]BF (9 1) at room temperature. The starting material was consumed after 0.5 h to provide a product with 94% yield (Scheme 17.8). Continuous fast conversion was observed, and reliable reusability was realized by the fifth cycle. 

Audic N, Clavier H, Mauduit M, Giiillemin JC (2003) An ionic liquid-supported ruthenium carbene complex a robust and recyclable catalyst for ring-closing olefin metathesis in ionic liquids. J Am Chem Soc 125 9248-49... 

Wakamatsu H, Saito Y, Masubuchi M, Fujita R (2008) Synthesis of imidazoUum-tagged ruthenium carbene complex remarkable activity and reusability in regard to olefin metathesis in ionic liquids. Synlett 1805-1808... 

The same acidic chloroaluminate ionic liquids have been used as solvent for tungsten aryl oxide complexes for the metathesis of alkenes [24]. Slightly acidic chloroaluminates also dissolve the [Cl2W=NPh(PMe3)3] complex which catalyze ethene oligomerization without the addition of co-catalysts [25]. In a similar way, Ni-catalyzed 1-butene dimerization into linear octenes was carried out in acidic chloroaluminates buffered with small amount of weak bases [26]. Neutral chloroaluminates (l-ethyl-3-methylimidazolium chloride/AlCl3 = 1) were employed to immobilize ruthenium carbene complexes for biphasic ADMET (acyclic diene metathesis) polymerization of an acyclic diene ester [27]. 

Highly soluble cationic ruthenium-dusters complexes have also been used for hydrogenation of aromatic substrates [31]. Compared with water these ionic liquids dissolve higher concentration of hydrogen gas which leads to increased reaction rate in biphasic conditions. 

The Mukaiyama aldol reaction involves the addition reaction of a TMS-enol ether to an aldehyde. Loh et al. have investigated the reaction of l-methoxy-2-methyl-l-trimethylsiloxypropene with aliphatic and aromatic aldehydes in chloride, [BF4] and [PFg] ionic liquids. The yields varied considerably and it was found that the chloride ionic liquids gave the best yields (50-74%) [230]. Ruthenium complexes have been used in the addition of aUyl alcohols to aldehydes and imines in [BMIM][Pp6] [231] (and later in a very similar paper [232]). The addition of a cootalyst such as indium(iii) acetate was found to dramatically improve the yields in some cases and it was foimd that the ionic Uquid/catalyst combination could be recycled. Examples of these reactions are shown in Scheme 5.2-100. 

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