Triaminooxyphosphonium dipolar ions and triaminodioxy phosphoranes from the reaction of triaminophosphines with α-diketones: Demonstration of the co-existence of 4-coordinated and 5-coordinated phosphorus in solution. P 31 NMR spectra

Abstract

The phosphorus of trisdimethylaminophosphine added to the oxygen of the α-diketone, benzil, and gave a 1:1 adduct. This adduct could be isolated in two crystalline forms: one of them was a triaminooxyphosphonium dipolar ion, and the other was a cyclic triaminodioxyphosphorane. Solutions of these crystalline adducts contained the same molecular species in equilibrium with each other. Certain solvents favoured the cyclic form with 5-coordinated phosphorus, while others favoured the dipolar ion with 4-coordinated phosphorus. The value of the P 31 NMR shifts varied from +30·2 ppm vs H 3PO 4 in 0·8M hexane to +13·1 ppm in 1·2M methylene chloride solutions. In methylene chloride solutions, the value of the shift varied significantly with concentration. The 1:1 adducts made from the reactions of the 5-membered cyclic triaminophosphines 2-N-pyrrolidino-, 2-dimethylamino-, and 2-methoxy-1,3,2-diazaphospholanes with benzil existed exclusively as cyclic triaminodioxyphosphoranes in the crystalline state and in solutions. The reaction of acenaphthenequinone with the cyclic aminophosphines produced the corresponding aminophosphine oxides via unstable adducts with POC bonds, which were formed at −70°.