Interactions of tertiary phosphines with p-benzoquinones; X-ray structures of [HO(CH 2) 3] 3P +C 6H 2(O −)(OH)(MeO) and Ph 3P +C 6H 3(O −)(OH)

Abstract

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 R 3P [R = (CH 2) 3OH, Ph, Et, Me] and Ph 2MeP, 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(CH 2) 3] 3P +C 6H 2(O −)(OH)(MeO) and the known Ph 3P +C 6H 3(O −)(OH), were structurally characterized by X-ray analysis. The PEt 3 reaction also produces small amounts of the ‘dimeric’, μ-oxo co-product Et 3P +C 6H 2(O −)(OH)–O–C 6H 3(O −)P +Et 3 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(CH 2) 3] 3P under the conditions noted above. Heating D 2O solutions of the water-soluble zwitterions R 3P +C 6H 3(O −)(OH) [R = (CH 2) 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.