Beiträge zur Chemie des Phosphors, 621 Zur Frage des 31P-kernresonanzspektroskopischen Nachweises von monomerem und dimerem Phenylphosphor und der Ringgröße von Organyl-cyclophosphanen.

Abstract

The weak resonances at + 22 and + 49 ppm appearing in the ³¹P NMR spectrum of melts or solutions of (PPh)₅ that have been attributed previously in the literature to “dimeric” and “monomeric phenylphosphorus” are caused by (PPh)₆ and (PPh)4, respectively. This was proved by comparison with the ³¹P NMR parameters of related compounds and by ³¹P NMR spectroscopic investigation of authentic samples of (PPh)₆ and (PPh)₄, the latter of which was prepared in high yield from (Me₃Si)PhP–PPh–PPh(SiMe₃) and PhPCl₂. (PEt)4 and mixed-substituted phenyl-ethyl-cyclotetraphosphanes exhibit similar chemical shifts as (PPh)4, corresponding mixed-substituted cyclohexaphosphanes have similar chemical shifts as (PPh)₆. Generally, cyclophosphanes establish an equilibrium between (PR)_n-species of different ring-size. Probably, the ring-interconversion proceeds via a multi-center mechanism. No ³¹P NMR spectroscopic evidence for the existence of free PPh or P₂Ph₂ under the conditions described could be detected. On thermolysis of (PEt)4 the existence of (PEt)₃ was proved for the first time.