Synthesis and Chemistry of Fluorinated Phosphine Ligands

Abstract

The synthesis of novel fluoroalkyl phosphines through the reaction between the perfluoroalkyl iodides i-C3F7I, n-C6F13I, n-C4F9I and s-C4F9I with PhMePSiMe3, Ph2PSiMe3, (p-tolyl)2PSiMe3 or (m-tolyl)2PSiMe3 was investigated. This route gave high yields of the compounds PhMePCF(CF3)2, PhMeP(CF2)5CF3, PhMeP(CF2)3CF3, Ph2PCF(CF3)2, (p-tolyl)2PCF(CF3)2, (p-tolyl)2P(CF2)3CF3, (p-tolyl)2PCF2CF(CF3)2, (m-tolyl)2PCF(CF3)2, (m-tolyl)2P(CF2)3CF3, and (m-tolyl)2PCF2CF(CF3)2 which were characterised by multinuclear NMR spectroscopy. The oxidation chemistry of the fluoroalkyl-containing phosphines was also investigated. Compounds containing MePh groups exhibited instability upon aerial oxidation, resulting in the formation of the corresponding MePhP(O)Rf oxides. While those containing aromatic systems such as (p-tolyl group) were oxidised using hydrogen peroxide solution. Oxidation with selenium resulted in the corresponding phosphine selenides, whose coupling constants were measured. Based on the 1JPSe values, these ligands are determined to be electronicallypoorer than hydrocarbon-based or fluorovinyl phosphines. Crystal structures for the phosphine selenides PhMePSe(CF2)5CF3, (p-tolyl)2PSeCF(CF3)2 and (p-tolyl)2PSe(CF2)3CF3, are reported. Oxidation with XeF2 produced compounds of the type R2PF2Rf which could be hydrolysed by moisture to generate the corresponding phosphine oxide. The coordination chemistry of the fluoroalkyl-containing phosphines resulted in the formation of the complexes trans-[PtCl2{PhMePCF(CF3)2}2], trans-[PtCl2{PhMeP(CF2)5CF3}2], trans-[PtCl2{(p-tolyl)2PCF(CF3)2}2], trans-[PdCl2{PhMePCF(CF3)2}2], trans-[PdCl2{PhMeP(CF2)5CF3}2], trans-[PdCl2{(p-tolyl)2PCF(CF3)2}2], trans-[PdCl2{(m-tolyl)2PCF(CF3)2}2] [AuClPhMePCF(CF3)2], [AuCl(p-tolyl)2PCF(CF3)2], and [AuCl(m-tolyl)2PCF(CF3)2] which were confirmed and characterised through multinuclear NMR spectroscopy, microanalysis and single crystal studies. Palladium and gold complexes were used as catalysts in three different catalytic systems. For Bayer-Villiger oxidation, the highest yield was obtained using non-fluorinated phosphines. In the palladium-catalysed Suzuki-Miyaura coupling, both fluorinated and non-fluorinated complexes gave moderate yields. In the hydroalkoxylation reaction, [AuCl(p-tolyl)2PCF(CF3)2] produced the highest yield, better than using non-fluorinated complexes.