Basic Phosphonium Ionic Liquids as Wittig Reagents

Abstract

The possibility of designing a solvent/reagent for Wittig reactions from basic phosphonium salts is explored theoretically. In the suggested R 4 P + PhO – and Ph 3 PR + PhO – ionic liquids (ILs), the phenolate anion is prone to remove the α-proton from the alkyl chains, forming a phosphorous ylide. Significant hydrogen bonding between the oxygen atoms of the anions and α-hydrogen atoms of the cations were found by molecular dynamics simulations of these substances; therefore, proton transfer between the two ions is inherently supported by the structure of the liquid as well. The subsequent steps of the Wittig reaction from the phosphorous ylide were also found to be energetically possible. The mesoscopic structure of these materials exhibits a significant segregation into polar and nonpolar domains, which may also allow an easy dissolution of the substrates. The formation of a pentacoordinated phosphorous derivative through P–O bond formation was found to be also possible in the gas phase for both kind of compounds. Accordingly, having such basic anions in phosphonium-based ILs may produce such a neutral and therefore volatile species, which may hold further significant applications for these solvents in ion-exchange and separation techniques and in synthesis.

New Insights into the Reaction Capabilities of Ionic Organic Bases in Cu‐Catalyzed Amination

“…A similar exchange reaction has been reported by Chu et al in phosphonium ionic liquids . It has also been reported in the ionic liquid literature that under suitably basic conditions phosphonium cations can be deprotonated to generate phosphonium ylides, with H/D exchange at the α‐CH 2 of the phosphonium cation most likely proceeding via such a ylide . Since a basic malonate dianion is present in TBPM ( B7 ), we wanted to determine if it too will exhibit similar reactivity.…”

Phosphonium‐Based Ionic Liquids Used as Reagents or Catalysts

“…Wittig reaction was studied related to the formation of ylide by deprotonation of suitable quaternary phosphonium cation. The intermediate further reacts with a carbonyl compound in an ionic liquid based on quaternary phosphonium salt, designed as reagent and also as solvent for this Wittig reaction …”

“…The intermediate further reacts with a carbonyl compound in an ionic liquid based on quaternary phosphonium salt, designed as reagent and also as solvent for this Wittig reaction. [24] Based on experimental data, [25] and the report that if the strong bases are dissolved in phosphonium based ILs, the cation can be deprotonated to phosphorous ylides. [26] Tetraalkylphosphonium R 4 P + OPh À and alkyl-triphenylphosphonium Ph 3 PR + OPh À phenolate ionic liquids, where R is ethyl, butyl, hexyl, or octyl (8) can participate in a reaction with carbonyl derivatives by (9) forming an oxaphosphetane intermediate (10).…”

High‐Performance Porous Ionic Liquids for Low‐Pressure CO2 Capture**

“…The corresponding acid of the anion is formed as well as an ylide species that is subsequently trapped with CO 2 (Figure 2). The ylide generation from phosphonium-based ionic liquids has been used as Wittig reagents 22 or reaction catalysts. 23 Concerning the acetate anion, it is long known that it is basic enough to abstract the acid S3.…”