HL₂[P(1,2-O₂C₆H₄)₃] (L = DMSO or DMF): A Convenient Proton Source with a Weakly Basic Phosphorus(V) Anion

Abstract

Treating phosphorus pentachloride with catechol (3 equiv) followed by the addition of dimethylsulfoxide (DMSO) or dimethylformamide (DMF) affords isolable Brønsted acids of the tris(o-phenylenedioxy)phosphate anion, [P(1,2-O2C6H4)3]−. Specifically, H(DMSO)2[P(1,2-O2C6H4)3] and H(DMF)2[P(1,2-O2C6H4)3] have been isolated as crystalline solids. The downfield shifts of the acidic proton in their 1H NMR spectra are consistent with its expected high acidity. The molecular structures of H(DMSO)2[P(1,2-O2C6H4)3] and H(DMF)2[P(1,2-O2C6H4)3] reveal that the protons in each are O-bound by either DMSO (×2) or DMF (×2). The N−H stretching frequency for the Oct3NH[P(1,2-O2C6H4)3] (ν̅N−H = 3129 cm−1) is identical to that observed for trioctylammonium tetrafluoroborate (ν̅N−H = 3129 cm−1), suggesting that the basicity of these two weakly coordinating anions is similar. A preliminary investigation of the effectiveness of H(DMF)2[P(1,2-O2C6H4)3] in the protonolysis of metal−alkyl bonds was undertaken. Treating (dppe)PdMe2 [dppe = 1,2-bis(diphenylphosphino)ethane] with H(DMF)2[P(1,2-O2C6H4)3] affords either [(dppe)Pd(NCMe)Me][P(1,2-O2C6H4)3] (1:1 ratio) or [(dppe)Pd(NCMe)2][P(1,2-O2C6H4)3]2 (1:2 ratio), both of which are structurally characterized.