Interactions of tertiary phosphines with p-benzoquinones; X-ray structures of [HO(CH2)3]3P+C6H2(O−)(OH)(MeO) and Ph3P+C6H3(O−)(OH)

Phosphonium zwitterions of a known type were obtained in high yield via a 1:1 reaction of p-benzoquinone or methoxy-p-benzoquinone with the tertiary phosphines R3P [R = (CH2)3OH, Ph, Et, Me] and Ph2MeP, in acetone or benzene at room temperature. In all cases, attack of the P-atom occurs at a C-atom rather than at an O-atom. The products were characterized to various degrees by elemental analysis, 31P{1H}, 1H and 13C NMR spectroscopies, and mass spectrometry, and two of the zwitterions, the new [HO(CH2)3]3P+C6H2(O−)(OH)(MeO) and the known Ph3P+C6H3(O−)(OH), were structurally characterized by X-ray analysis. The PEt3 reaction also produces small amounts of the ‘dimeric’, μ-oxo co-product Et3P+C6H2(O−)(OH)–O–C6H3(O−)P+Et3 that is tentatively characterized by 1D- and 2D-NMR data. 2,5-Di-tert-butyl- and 2,3,5,6-tetramethyl-p-benzoquinone do not react with [HO(CH2)3]3P under the conditions noted above. Heating D2O solutions of the water-soluble zwitterions R3P+C6H3(O−)(OH) [R = (CH2)3OH, Et] at 90 °C for 72 h leads to complete H/D exchange of the H-atom in the position ortho to the phosphonium center.