Hydrogenation catalysts tetrafluoroborate

The first successful hydrogenation reactions in ionic liquids were studied by the groups of de Souza [45] and Chauvin [46] in 1995. De Souza et al. investigated the Rh-catalyzed hydrogenation of cyclohexene in l-n-butyl-3-methylimidazolium ([BMIM]) tetrafluoroborate. Chauvin et al. dissolved the cationic Osborn complex [Rh(nbd)(PPh3)2][PFg] (nbd = norbornadiene) in ionic liquids with weakly coordinating anions (e.g., [PFg] , [BFJ , and [SbF ] ) and used the obtained ionic catalyst solutions for the biphasic hydrogenation of 1-pentene as seen in Scheme 5.2-7. 

In the ideal biphasic hydrogenation process, the substrate will be more soluble or partially soluble in the immobilization solvent and the hydrogenation product will be insoluble as this facilitates both reaction and product separation. Mixing problems are sometimes encountered with biphasic processes and much work has been conducted to elucidate exactly where catalysis takes place (see Chapter 2). Clearly, if the substrates are soluble in the catalyst support phase, then mixing is not an issue. The hydrogenation of benzene to cyclohexane in tetrafluoroborate ionic liquids exploits the differing solubilities of the substrate and product. The solubility of benzene and cyclohexane has been measured in... 

Potassium tetrafluoroborate is used as catalyst with fluorosulfonic acid in the addition of hydrogen fluoride to acetylene (4) in the liquid phase.67... 

Attempts have also been made to develop biphasic methodologies for the hydrogenation of aromatics. The hydrogenation of benzene derivatives was studied using various Ru complexes.468,469 A trinuclear cluster cationic species was isolated as the tetrafluoroborate salt and showed increased activity in hydrogenation.470 The air/ moisture-stable [bmim][BF4] ionic liquid and water with [Rh r -CgHg).,] [BF4] as the catalyst precursor is an effective system under usual conditions (90°C, 60 atm)471 A system composed of stabilized Rh(0) nanoparticles proved to be an efficient catalyst in the hydrogenation of alkylbenzenes 472... 

Diastereoselectivehydrogenation.3 The 8-hydroxy-a,p-unsaturated ester (3) undergoes hydrogenation in the presence of rhodium [(+ )-BINAP]-norbornadiene tetrafluoroborate (1) (10, 36) almost exclusively to give 4. This catalyst (1) is more effective than rhodium(DIPHOS)norbornadiene tetrafluoroborate (2) (12, 426). 

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