Further studies of the kinetic template effect in the metal ion-catalysed reactions of ortho-donor-substituted aryl halides with tertiary phosphines. Structural requirements of the template

Abstract

The reactions of a series of Schiff's bases, derived from ortho-chloro-, bromo- or iodo-benzaldehydes and p-anisidine, with tertiary phosphines in the presence of nickel(II) bromide in refluxing ethanol proceed with displacement of the ortho-halogen to form the related ortho-substituted aryl-phosphonium salts. These reactions appear to be examples of a kinetic template effect in which the Schiff's base moiety aids the catalytic role of the metal ion in promoting the substitution reaction. Introduction of a second donor atom into the substituent group present at the nitrogen of related Schiff's bases inhibits the reactions due to diversion of the metal ion in other modes of co-ordination. The reactions are also inhibited by steric crowding at the imino-nitrogen. A range of other aryl halides bearing ortho-substituents having the potential to act as co-ordination templates has been prepared and their reactions with phosphines in the presence of metal ions studied enabling the rather critical nature of effective template groups to be defined. Detailed ¹³C n.m.r. data are also reported for the Schiff's bases and related arylphosphonium salts.