Ligands perfluoroalkylated phosphine

Various attempts have been made at quantifying the overall a-donorand 7r-acceptor effects of the many different types of phosphine.1,2 Chemists have access to Ti-acceptors such as tris-V-pyrrolyl phosphine, perfluoroalkyl phosphines and phosphites, right through to the potent o-donor, tris(2,4, 6-trimethoxyphenyl)phosphine, 6 (Scheme 2). It is important to note that the donor/acceptor properties of a ligand are dependent on the metal, its oxidation state, and the ancillary ligands on the metal. 

Fig. 4. A general concept for solubilizing catalyticaUy relevant ligands for the use m SCCO2, exemplified for a bidentate aryl phosphine ligand. Perfluoroalkyl chains or other solubitoers waved line) are fixed at the periphery of the ligand. The position of the substitution and the use of appropriate spacers bold line) are used to tune the stereo-electronic properties of the ligand...

Figure 1.6 Like dissolves like perfluoroalkyl ponytails make phosphines more soluble in a fluorous solvent. These phosphines are suitable ligands for metal catalysts, and will therefore aid the solubility of these catalysts in fluorous solvents...

The value of perfluoroalkyl-derivatised ligands in FBS catalysis depends on the preferential solubility of the catalyst in a fluorous solvent. Initially, this was established, qualitatively, by 31P NMR spectroscopic studies [37,49], but very recently [52] the fluorous partition coefficients of metal complexes of the trialkyl phosphine (la) have been measured analytically, from which both a fluorine content of > 60% and the number of perfluoroalkyl groups, which shield the hydrocarbon domain of the complex, are crucial for a high fluorous partition. 

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