Convenient synthetic route to tetraarylphosphonium polyelectrolytes via palladium‐catalyzed P–C coupling of aryl triflates and diphenylphosphine

Abstract

A series of eight tetraarylphosphonium polyelectrolytes (TPELs) has been successfully synthesized by polymerization of diphenylphosphine and bis(aryl triflate)s. The bis(aryl triflate)s are readily prepared from bisphenols, some of which are commodity feedstocks such as bisphenol A. The polymerization via palladium catalyzed P-C bond formation produces degrees of polymerization up to 65. All polymeric triflates have reasonable thermal stability in the range of 350-450 8C. The stability of the TPELs to alkaline solution is strongly depending on the spacer between adjacent phosphonium sites. Polymers with electron-releasing and bulky substituent para-to the phosphonium site have improved stability while those with electron-withdrawing substituent para-to phosphonium site have decreased alkaline stability due to decomposition via a nucleophilic aromatic substitution pathway. These findings have important ramifications for the design of ionomers for alkaline exchange membrane fuel cells and related electrochemical energy conversion devices.

Tetraarylphosphonium perfluorocyclobutyl polyelectrolyte with low critical surface energy, high thermal stability, and high alkaline resistance

“…NMR end‐group analysis comparing main chain phosphonium to end‐group phosphine oxide units was employed to determine a M n of 31.8 kDa, corresponding to a degree of polymerization of 52. This degree of polymerization is similar to the reported values for TPELs prepared by Pd‐catalysis . Although 31 P NMR integrations are not accurate in a typically acquired spectrum, a 10 s delay between scans was employed and triphenylphosphine was added as an external standard after acquiring spectra of the polymer alone to further validate the calculation following the reported procedure …”

“…TPELs require installation of four aryl groups onto the phosphorus center, and synthetic routes for accomplishing this are limited. The preferred method for preparing TPELs is copolymerization of a bifunctional aryl halide or aryl triflate with diphenylphosphine via a Pd‐catalyzed PC bond‐forming reaction (Scheme ) . In selecting potential backbone components for the current study, a perfluorinated moiety having high thermal stability and which could be readily incorporated into the requisite bifunctional aryl comonomer was targeted.…”

“…INTRODUCTION Tetraarylphosphonium salts are among the most stable ionic liquids known, [1][2][3][4][5] and their incorporation into polymer backbones has been targeted as a strategy to likewise access polymers with high thermal stability. [6][7][8][9][10] The resistance of tetraarylphosphonium moieties to alkali degradation has also garnered interest in utilizing tetraarylphosphonium polyelectrolytes (TPELs, Scheme 1) as membrane components of alkaline fuel cells and related electrochemical energy technologies. Previously reported TPELs have had relatively high critical surface energies and at least partial attendant solubility in polar solvents such as water and methanol.…”

Correlating structure with ionic conductivity in bis(phosphonium)‐containing [NTf2] thiol–ene networks

“…A metal‐catalyzed phosphorus–carbon coupling strategy involving aryl halides or aryl triflates with diphenylphosphine was recently utilized by Smith and co‐workers to prepare tetraarylphosphonium polyelectrolytes. The resulting PILs exhibited thermal stability up to 460 °C and reasonable alkaline stability …”

“…The resulting PILs exhibited thermal stability up to 460 ∘ C and reasonable alkaline stability. 25,26 Phosphonium PILs have also been explored in other important applications. Noble and co-workers reported a series of neat PIL films based upon the polymerization of trialkyl-4-vinylbenzyl phosphonium bis(trifluoromethylsulfonimide) monomers for light gas separation.…”