Fluorous Wilkinson Catalyst

Hydroboration of a variety of alkenes and terminal alkynes with catecholborane in the fluorous solvent perfluoromethylcyclohexane was performed using fluorous analogs of the Wilkinson catalyst.135 136 Recycling of a rhodium-based alkene hydrosilylation catalyst was also successful.137 Activated aromatics and naphthalene showed satisfactory reactivity in Friedel-Crafts acylation with acid anhydrides in the presence of Yb tris(perfluoroalkanesulfonyl)methide catalysts.138... 

Fluorous-phase soluble h < acryloxysuccinimide-containinj hence Wilkinson catalyst analog Miscellaneous reactions. solvents while employing a fl diaryl diselenide used to assist t A multicomponent coupling and rapid Stifle couplings are with microwave irradiation. 

Fluorous-phase soluble hydrogenation catalysts are obtained by conversion of N-acryloxysuccinimide-containing fluoroacrylate polymers into phosphine ligands and hence Wilkinson catalyst analogues." ... 

The strategy of using two phases, one of which is an aqueous phase, has now been extended to fluorous . systems where perfluorinated solvents are used which are immiscible with many organic reactants nonaqueous ionic liquids have also been considered. Thus, toluene and fluorosolvents form two phases at room temperature but are soluble at 64 °C, and therefore,. solvent separation becomes easy (Klement et ai, 1997). For hydrogenation and oxo reactions, however, these systems are unlikely to compete with two-phase systems involving an aqueous pha.se. Recent work of Richier et al. (2000) refers to high rates of hydrogenation of alkenes with fluoro versions of Wilkinson s catalyst. De Wolf et al. (1999) have discussed the application and potential of fluorous phase separation techniques for soluble catalysts. 

Keurentjes et al. performed a continuous hydrogenation of 1-butene in supercritical carbon dioxide.[9,10] A fluorous derivative of Wilkinson s catalyst was prepared in situ by mixing the ligand with [(COD)RhCl]2 under hydrogen / carbon dioxide pressure (Figure 4.37). 

The hydrogenation of a number of 1-alkenes using fluorous derivatives of Wilkinson s catalyst has been investigated. Initial experiments established the effect of the fluorous ligands on catalytic activity [15], The ligands evaluated in this study are illustrated in Figure 8.7. 

The turnover frequency was found to be greatest for the two fluorous ligands and the control ligand with the trimethylsilyl function was found to be less effective than triphenylphosphine. These fluorous derivatives of Wilkinson s catalyst were used to hydrogenate 1-octene in perfluoromethylcyclohexane (PP2). The reaction was carried out a number of times in order to evaluate the efficiency of the system in terms of recycling and reuse [16], It was found that as the number... 

Figure 8.7 Fluorous and control ligands screened to gauge the effect of the fluorous ponytails on catalysis using Wilkinson s catalyst analogues...

Figure 8.8 The increase in turnover frequency for the hydrogenation of 1-octene using a fluorous derivative of Wilkinson s catalyst as the catalyst (or catalyst precursor)...

Our fluorous silica technology was also tested (1) on the catalytic hydrogenation of styrene. The fluorous silica phase contained a fluorinated version of Wilkinson s catalyst (Figure 3) deposited onto the surface of the fluorous silica. The organic phase consisted of styrene dissolved in cyclohexane. No fluorous solvent was used. 

In spite of the potential advantages of the use of a catalytic membrane reactor to perform chemical reactions in SC CO2, very few references are available on this topic. The concept was however demonstrated for the hydrogenation of 1-butene using a fluorous derivative of Wilkinson s catalyst [32]. The reaction was successfully performed in a free catalyst membrane reactor equipped with a silica membrane. 

A set of fluorous ponytails, perfluoropolyalkylethers, were incorporated into the Wilkinson-type Rh(I) complex (Scheme 7.22) [34]. The fluorous Rh(I) complexes were preferentially soluble in fluorous solvents and used as recyclable biphase hydrogenation catalysts with less than 0.35% Rh leaching. It was found that the fluorous Rh(I) complexes had lower partition coefficient values than their... 

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