2,5-Dihydroxy-1,4-quinones appended with two phosphinyl groups: syntheses, structures, and redox properties

Abstract

Low temperature reactions of 1,4-dichloro-2,5-dimethoxybenzene with two equivalents of lithium diisopropylamide (LDA) followed by quenches with chlorophosphines ClPR2 (R = Ph or iPr) yielded 1,4-bis(diphenylphosphino)-2,5-dichloro-3,6-dimethoxy-benzene (1a) and 1,4-bis(diisopropylphosphino)-2,5-dichloro-3,6-dimethoxy-benzene (1b). Reactions of 1a-b with 30% hydrogen peroxide yielded 1,4-bis(diphenylphosphinyl)-2,5-dichloro-3,6-dimethoxybenzene (2a) and 1,4-bis(diisopropylphosphinyl)-2,5-dichloro-3,6-dimethoxybenzene (2b). Subjecting compounds 2a-b to BBr3/CH3OH resulted in 2,5-bis(diphenylphosphinyl)-3,6-dichlorohydroquinone 3a and 2,5-bis(diisopropylphosphinyl)-3,6-dichlorohydroquinone 3b. Reactions of 3a-b with K2S2O8 under basic conditions followed by acidification allowed for isolation of 2,5-bis(diphenylphosphinyl)-3,6-dihydroxy-quinone (4a) and 2,5-bis(diisopropylphosphinyl)-3,6-dihydroxy-quinone (4b). Compounds 1a-b – 4a-b were fully characterized by spectroscopic methods (nuclear magnetic resonance [FT-NMR] spectroscopy, infrared [FT-IR] spectroscopy, and high resolution mass spectrometry [HRMS]); 3a-b and 4a-b were also investigated by cyclic voltammetry. Compounds 1a-b , 2a , and 4a-b were also characterized by single-crystal X-ray diffraction methods.