From 1,3-Diphosphacyclobutadiene to 1,3,5-Triphosphabenzene

Abstract

Alkyl- and aryldiaminodifluorophosphoranes 1 can easily be obtained by fluorination of alkyl- and aryldiaminophosphanes with sulfur tetrafluoride, SF₄ ¹. Peralkylated alkyldiaminodifluorophosphoranes react with one mole of n-butyllithium to form P-fluoro-ylides, a class of compounds which had not been described previously ² . Methylbis(dimethylamino)difluorophosphorane 2, e.g., reacts with butyllithium to give methylenebis(dimethylamino)fluorophosphorane 3, a colorless liquid, b.p. 42 °C (10 Torr)²:

For P-chloro-ylides such as (t-C₄H₉)₂PCI=CHSi(CH₃)₃, the chloro ligand is substituted by the alkyl group upon reaction with methyl-or n-butyllithium ^3,4; however, P-fluoro-ylides behave in a different way. If 2 is reacted with two moles of butyllithium, the main product is the crystalline, colorless 1,1,3,3-tetrakis(dimethylamino)-1Δ⁵, 3Δ⁵−diphosphete or 1,1,3,3-tetrakis(dimethylamino)-1Δ⁵, 3Δ⁵−diphosphacyclobutadiene 4 (chemical shift δ (P) = 48.9 ppm)⁵.