A New Method for the Synthesis of Nonsymmetric Dinucleating Ligands by Aminomethylation of Phenols and Salicylaldehydes

Monoaminomethylated phenols 5-7 and symmetrically diaminomethylated phenols 8 and 9 were prepared in a one-step procedure from p-cresol, formaldehyde, and a variety of secondary amines by making use of the aromatic Mannich reaction. Nonsymmetric diaminomethylated phenols 10 and 11 were prepared by a sequential aromatic Mannich reaction using p-cresol, formaldehyde, and two different secondary amines. Alternatively, nonsymmetric diaminomethylated phenols 20-24 were prepared by aminomethylation of 5-methylsalicylaldehyde followed by (a) condensation with a primary amine and subsequent reduction or (b) reductive amination with a secondary amine. Monoaminomethylated and (non)symmetric diaminomethylated phenols are excellent ligands for the synthesis of mono- and dinuclear transition metal complexes as is illustrated by the isolation of mononuclear iron(III) complex 25 and nonsymmetric dinuclear copper(II) complex 26.