Fluorous olefin oxidation

Complex 33 was found to also catalyze the epoxidation of various disubstituted olefins with 02 as the primary oxidant and isobutyraldehyde as the sacrificial co-oxidant (Mukayama conditions Klement et al., 1997). Yields of 70-85% were obtained after heating the olefins and 33 under oxygen atmosphere in a mixture of toluene and 1-bromoperfluorooctane to 50 °C for 5-12 h, as exemplified in eq. 5.10 for the synthesis of cyclo-octeneoxide 34. The ruthenium was held back almost quantitatively in the fluorous phase and could be separated after cooling to 0°C and reused several times. 

For typical fluorous biphase catalysis the most important aspect is the simple recycling and re-use of the catalyst. Fluorous solvents have one special advantage over hydrocarbon solvents, however. Their very high oxygen dissolving capacity, combined with their extreme resistance to oxidative decomposition makes perfluorocarbons in combination with fluorous catalysts the optimum choice for oxidation reactions. Thus, the biomimetic oxidation of olefins with molecular oxygen and 2-methylpropanal as a co-reductand has been achieved with a fluorous cobalt porphyrin catalyst (22) [23], and also even without catalyst [24] (Scheme 3.7). 

Similar, fluorous palladium /i-dikctonatc complexes (27) have been employed for Wacker oxidation of olefins to the corresponding ketones in a biphasic system [27] (Scheme 3.10). 

The use of fluorous chiral manganese salene (Jacobsen-Katsuki) catalysts (29, 30) [30] in combination with different oxidants enables enantioselective epoxidation of olefins [31] in high yields and with moderate to high enantiomeric excess (Scheme 3.12). 

A similar oxidative protocol has been used for the oxidation of (fluoroalkyl)alkanols, Rf(CH2) CH20H, to the respective aldehydes [146], in the one-pot selective oxidation/olefination of primary alcohols using the PhI(OAc)2-TEMPO system and stabilized phosphorus ylides [147] and in the chemo-enzymatic oxidation-hydrocyanation of 7,8-unsaturated alcohols [148]. Other [bis(acyloxy)iodo]arenes can be used instead of PhI(OAc)2 in the TEMPO-catalyzed oxidations, in particular the recyclable monomeric and the polymer-supported hypervalent iodine reagents (Chapter 5). Further modifications of this method include the use of polymer-supported TEMPO [151], fluorous-tagged TEMPO [152,153], ion-supported TEMPO [154] and TEMPO immobilized on silica [148],... 

These unusual properties were the basis of the fluorous biphasic catalysis process (FBC) first published in 1994 by Horvdth and Rdbai and demonstrated using hydroformylation chemistry as a pertinent example (7, 2) in a 1991 Ph.D. thesis, that was unfortunately not readily available to the homogeneous catalysis community nor published in the open literature, M. Vogt, under the guidance of his Ph.D. advisor, W. Keim, of the Rheinisch-WestflUischen Technischen Hochschule in Aachen, Germany, presented the first conceptual aspects of the FBC approach with an emphasis on oligomerization of alkenes, oxidation of alkenes, hydroformylation of olefins, and telomerization of dienes (5, 4). 

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