Formation of spiro and ansa derivatives in the reaction of 2,2,3,3,4,4-hexafluoropentane-1,5-diol with cyclotriphosphazene: Comparison with 2,2,3,3-tetrafluorobutane-1,4-diol

Abstract

Reaction of cyclophosphazene, N 3P 3Cl 6 ( 1), with the sodium derivative of the fluorinated diol, 2,2,3,3,4,4-hexafluoropentane-1,5-diol ( 2), in THF solution at room temperature afforded five isolated products, whose structures have been characterised by X-ray crystallography and 1H, 19F and 31P NMR spectroscopy: the mono-spiro compound, N 3P 3Cl 4(OCH 2CF 2CF 2CF 2CH 2O) ( 3), its ansa isomer ( 4), a di-spiro derivative N 3P 3Cl 2(OCH 2CF 2CF 2CF 2CH 2O) 2 ( 5), its spiro-ansa ( 6) isomer and the tri-spiro compound N 3P 3(OCH 2CF 2CF 2CF 2CH 2O) 3 ( 7). Quantitative 31P NMR measurements of the soluble portion of the reaction mixture show that in the reaction of ( 1) with the sodium derivative of the fluorinated pentanediol ( 2) there is a small preference for spiro compounds compared to ansa compounds (ratio ca. 1.3:1), similar to the analogous reaction of ( 1) with the sodium derivative of the fluorinated butanediol where there is a slightly greater proportion of spiro compared to ansa compounds (ratio ca. 1.5:1). The relative proportions of spiro and ansa compounds is likely to depend on the fine balance in stabilities of the different medium-sized rings in the fluorinated pentanediol (spiro, 8- and ansa, 10-membered rings) compared to the fluorinated butanediol (spiro, 7- and ansa, nine-membered rings) derivatives of cyclophosphazene.