Chemical functionality of poly(methylenephosphine): phosphine–borane adducts and methylphosphonium ionomers

Abstract

The chemical functionality of poly(methylenephosphine) n-Bu[MesP–CPh₂]_nH (2) is examined in reactions with two isoelectronic species, namely BH₃ and CH₃⁺. The potential reactivity of polymer 2 is modelled by examining the reactivity of molecular phosphines bearing similar substituents as the polymer. In particular, the phosphine–borane adducts Mes(Me)P(BH₃)–CPh₂H (4a) and Mes(Me)P(BH₃)–CPh₂SiMe₂H (4b) are prepared from the reaction of BH₃·SMe₂ with Mes(Me)P–CPh₂H (3a) or Mes(Me)P–CPh₂SiMe₂H (3b), respectively. Treating 3a with MeOTf affords the methylated model compound, [Mes(Me)₂P–CPh₂H]OTf (5). X-Ray crystal structures are reported for each model compound. The reaction of n-Bu[MesP–CPh₂]_nH (M_n = 3.89 × 10⁴, PDI = 1.34) with BH₃·SMe₂ affords the phosphine–borane polymern-Bu[MesP(BH₃)–CPh₂]_nH (6) (M_n = 4.13 × 10⁴, PDI = 1.26). In contrast, methylation of phosphine polymer 2 gives n-Bu[MesP–CPh₂]_x–/–[MesP(Me)–CPh₂]_yH·(OTf)_y (7) where approximately 50% of the phosphine moieties are methylated (from ³¹P NMR).