The hexafluoroacetone adducts of diphenyl phosphoramidites; a distinction between P–N bond rotation and pseudorotation

Abstract

The low-temperature ¹⁹F n.m.r. spectra of the 1,3,2-dioxaphospholans obtained from hexafluoroacetone and diphenyl phosphoramidites give barriers of 10–12 kcal mol^–1 for the pseudorotations which involve switching equatorial amino- and apical phenoxy-groups consistent with a large difference in apicophilicity between these groups. The changes in the spectra at lower temperatures are explained in terms of topomer formation from the most stable conformer either by P–N bond rotation or by pseudorotation, the former having the larger free energy of activation.