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Fluorous Biphasic Systems

Features of Fluorous Biphasic Systems

  • Scalable Systems for Catalysis and Separation
  • Unique Application of FLLE

Fluorous Biphasic Systems

What we now call Fluorous Biphasic Catalysis (FBC) was first introduced in the thesis of Dr. M. Vogt in Aachen in 1991. A seminal paper by Horváth and Rábai in 1994 introduced new concepts and results along with today's terminology. Since that time, fluorous biphasic catalytic methods have advanced rapidly, and a large number of fluorous catalysts and ligands (especially phosphines) are known. The defining feature of FBC is the use of a fluorous reaction solvent, and the technique is best viewed as a liquid phase catalyst immobilization method.

Hydroformylation with a fluorous variant of Wilkinson's catalyst provides a typical example of fluorous biphasic catalysis. A toluene solution of an enone and a silane is heated with a perfluoromethylcyclohexane solution of the catalyst. After the reaction is complete, the mixture is cooled and the two phases are separated to provide the organic hydrosilylation products and the recovered catalyst immobilized in the fluorous phase. In an important variant of fluorous biphasic catalysis, an organic solvent is choosen such that on warming a homogeneous (one phase) solution results. After the reaction is complete, the mixture is cooled to induce the phases to separate once again. In the hydrosilylation example, the replacement of toluene by hexane allows for one phase reaction and two phase separation.

biphasic illustration

FBC and related methods are ideally suited for economical and green chemical processes. A single liquid-liquid separation provides both the product and the recovered catalyst. The safety of fluorous solvents is also an attractive feature. For the single separation to succeed, high partition coefficients are needed, so the catalysts generally have large numbers of fluorines. Fluorous catalysts have advantages over solid-supported catalysts since they can be soluble in the reaction medium. Water-based biphasic catalysis reactions are also used, but are obviously limited to water-tolerant processes. Fluorous catalysts do not share this limitation. In an important recent advance, the thermomorphic (temperature dependent solubility) properties of fluorous compounds have been used - reactions are heated to dissolve a catalyst and cooled to precipitate it. No fluorous solvent is needed. If needed, spe through fluorous silica can remove last traces of the dissolved catalyst from the product.