Fluorous phosphine ligand

The first fluorous phosphine ligands for application in fluorous phase catalysis were fluorous trialkylphosphines 1 [7-9]. 

A new separation procedure for homogeneous catalysts that combines a membrane reactor and SCCO2 was recently developed (Scheme 89 and Figure 4.6). Amixture of a rhodium complex with a fluorous phosphine ligand 49,1 -butene, hydrogen and SCCO2 is introduced into a membrane reactor with a pore size of 0.6 nm. Since... 

Fluorous ligands introduce an ease of purification in that the tagged phosphine ligand, the palladium catalyst complexed ligand, and the oxidized ligand can be completely removed by direct fluorous solid-phase separation (F-SPE) prior to product isolation. Similarly, an example of a fluorous palladium-catalyzed microwave-induced synthesis of aryl sulfides has been reported, whereby the product purification was aided by fluorous solid-phase extraction [91]. 

The concept makes use of the complimentary strengths and weaknesses of the two unconventional media. While ionic liquids are known to be excellent solvents for many transition metal catalysts, the solubility of most transition metal complexes in scC02 is poor (if not modified with e. g. phosphine ligands with fluorous "ponytails" [64]). However, product isolation from scC02 is always very simple, while from an ionic catalyst solution it may become more and more complicated depending on the solubility of the product in the ionic liquid and on the product s boiling point. 

To solve the issue of ligand leaching that was encountered in some of the examples above, fluorous polymeric phosphine ligands 15a-c [28] were developed. The rhodium complexes prepared from 15a-c using a 3 1 ratio of P Rh [28b, 29] displayed good turnover frequencies (TOFs) in the case of 15 a, but reaction rates for 15b,c were lower. The catalyst derived from 15 a was recycled seven times without loss of activity, although leaching was not studied quantitatively. 

Primary fluorous phosphines PH2(CH2)raRf8 (n = 2-4) (24) (Scheme 2) were prepared from fluor-ous primary alkyl iodides and Li PI I2-dmc (dme = dimethoxyethane), generated from PH3 and nBuLi, in THF at —45 °C.34 The primary phosphines were isolated either as clear liquids or as a low-melting white solid.34 Subsequent free-radical addition reactions of olefinic fluorous precursors with these primary phosphines afforded unsymmetrical ligands. 

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