A kinetic template effect in the metal ion-catalysed reactions of o-bromodiarylazo compounds with tertiary phosphines. 13C n.m.r. and X-ray structural studies of o-phosphoniodiarylazo derivatives.

Abstract

o-Bromodiarylazo compounds react with tertiary phosphines in the presence of either nickel(II) bromide or copper(II) acetate in refluxing ethanol to give the related o-phosphoniodiarylazo compounds in good yield. The phosphonium derivatives are also formed in the reactions of the o-bromodiarylazo compounds with either [Ni(Ph₃P)₃]Br or [Cu(Ph₃P)_nOAc](n= 2 or 3). The possible involvement of co-ordination-template assisted electron-transfer processes in the reactions is discussed. ¹³C N.m.r. data for the o-phosphoniodiarylazo products are also presented, as is also a single crystal X-ray study of one member of the series. Crystals of tri-n-butyl [6-(2-acetylamino-4-diethylaminophenylazo)-3-bromo-5-methylphenyl]phosphonium bromide are monoclinic, space group C2/c, a= 25.695(16), b= 10.910(11), c= 25.363(15)Å, β= 90.63(5)°, U= 7 109.2 ų. The structure was solved using heavy-atom methods in conjunction with least-squares refinement of diffractometer data, giving a final R value of 0.069 for 710 observed reflections [I/σ(I) 1.5].