1 Ionic liquids—media for unique phosphorus chemistry Christopher Hardacre Chem. Commun., 2006, 72–74

2 Ionic Liquids Seddon, K. R. et. al. Pure Appl. Chem. 2000, 72,

3 Coordinative Characteristics of Various Anions Angew. Chem. Int. Ed. 2000, 39,

4 Room temperature ionic liquids exhibit many properties which make them potentially attractive media for homogeneous catalysis: They have essentially no vapour pressure. They generally have reasonable thermal stability. They are able to dissolve a wide range of organic, inorganic and organometallic compounds. The solubility of gases. They are immiscible with some organic solvents. Ionic liquids have been referred to as ‘designer solvents’ by a suitable choice of cation/anion.

5 PCl 3 and POCl 3 Major precursors for flame-retardant materials, pesticides, nerve gases and plasticizers. Key reagents in numerous synthetic conversions such as chlorination reactions and Vilsmeier–Hack formylations of aromatics

6 PCl 3 and POCl Continued The use of PCl 3 has been extended to the manufacture of nucleosidic phosphoramidites and related building blocks. This is often difficult to achieve as PCl 3, POCl 3 and many chlorinated derivatives are highly moisture sensitive and hydrolyse rapidly under conventional storage or standard reaction conditions.

7 For comparison, the stability of PCl 3 and POCl 3 in THF stirred in air showed >25 % hydrolysis after 15 min and no PCl 3 or POCl 3 remaining after 1 h.

8 [C n mim] + [C 4 mpyrr] + [NTf 2 ] – [OTf] – [OMs] – [FAP] –

9 PCl 3 in Dry ILs In dry [C 2 mim][OTf] and [C 2 mim][OMs], PCl 3 reacted with the IL forming phosphite–sulfate and –sulfonate mixed anhydrides, both mono- and bis-chlorinated, via nucleophilic displacement of the halogen. Halogen exchange was also surprisingly rapid in dry [C 4 mim][BF 4 ]. After 75 min, a ratio between PCl 3 (δ220 ppm), PCl 2 F (δ218 ppm), PClF 2 (δ174 ppm) and PF 3 (δ103 ppm) of 1 : 0.03 : 0.02 : 0.4 was found. This mixture gradually changed and, after 2 h, only PCl 3 and PF 3 were found with no hydrolysis products detected.

10 PCl 3 in Wet ILs b Balance is unassigned hydrolysis products.

11 Reaction Between N-methylimidazole and PCl 3 in ILs Addition of NMI to a solution of PCl 3 in [C 2 mim][OTf] resulted in the formation of a yellow precipitate, probably of [P(NMI) 3 ]Cl 3, which rapidly hydrolysed when exposed to air. The triimidazolium phosphine was confirmed by reacting imidazole with PCl 3 in CDCl 3 and in [C 4 mim][NTf 2 ]. It must be noted that in NMI-contaminated [C 2 mim][OTf], this phosphine can only form via demethylation of the methyl imidazole in situ in the presence of PCl 3.

12 POCl 3 in Dry ILs POCl 3 was found to be stable in dry [OTf] – and [NTf 2 ] – -based ILs; however, in dry [C 2 mim][OMs] mixed anhydrides, again both mono- and bis-chlorinated, were formed. As found with PCl 3, POCl 3 also underwent rapid halogen exchange in [C 4 mim][BF 4 ] with a ratio between POCl 3 (δ6 ppm), PO(OH) 2 F (δ– 8 ppm) and PO(OH)F 2 (δ–19 ppm) of 1 : 0.3 : 0.3. Unlike for PCl 3, no POF 3 was detected and the composition, as well as the signal-to- noise ratio, remained unchanged over 2 h. δ

13 POCl 3 in Wet ILs

14 The possible sources of the fluoride which exchanges for chloride in PCl 3 and POCl 3 in [C 4 mim][BF 4 ] Due to the high concentration of PCl 3 /POCl 3 compared with the amount of fluoride generated from IL hydrolysis and the fact that quantitative exchange occurs, the equilibrium reaction must be the source. Such rapid exchange is not achievable in conventional solvents at room temperature. Similar exchange reactions have been observed using Na[BF 4 ] and Na[PF 6 ] dissolved in glyme, but only at 200 °C. The decrease in intensity found for PCl 3 is due to evaporation of PF 3.

15 The strong hydrogen bonding interaction with the anion breaks up the water–water interactions and the nucleophilicity of the water is decreased, reducing its hydrolysis activity. Although significant hydrolysis occurs in most ILs on stirring in air, no hydrolysis is found in wet [C 4 mim][NTf 2 ] for PCl 3 and in wet [C 5 mim][FAP] for POCl 3 over weeks open to air without stirring. The deactivation of the water is clearly illustrated by examining the mole ratio of solvent to water. Even in dry ILs which contain ~0.1 wt% water content. This is in contrast with dry THF (0.005 wt% water content. The ability of the ILs to stabilize PCl 3 and POCl 3 may be understood by considering the distribution of water in ILs