Effective catalysis of imine metathesis by means of fast transiminations between aromatic-aromatic or aromatic-aliphatic amines

This paper reports on a quantitative investigation of rates of amine-imine exchange reactions of primary amines with their benzylidene derivatives in organic solvents at room temperature. Exchange reactions involving aromatic-aromatic or aromatic-aliphatic amines were in all cases fast enough to allow their use in the effective catalysis of imine metathesis in the absence of acid and metal catalysis. Transiminations based on exchange between aromatic and aliphatic amines were retarded both by electron-donating and electron-withdrawing substituents in the para-position of the benzylidene moiety. This result was interpreted as arising from a change in the rate-determining step of the two-step transimination reaction.