Facile Isolation of Bisimines Based on 3,3‘-Diaminobenzidine: Direct Access to Unsymmetrical Bimetallic Salphen Building Blocks

Diimines obtained from 3,3‘-diaminobenzidine and tert-butyl-substituted salicylaldehydes in MeOH can be readily isolated in 60−90% yield and were obtained as a mixture of geometrical isomers. Two distinct diimine intermediates (4 and 5) with a higher molecular symmetry as related to the other isomeric diimine products were both isolated by crystallization of which 5 was subsequently used to demonstrate that nonsymmetrical bis-salphen complexes with different functional groups and metal centers can be assembled via a three-component one-pot procedure.