A modular approach towards nonsymmetrical bis(metallosalen) building blocks

New bis(metallosalen) building blocks are described that can be accessed through di- or tetraimine precursors derived from the 3,3'-diaminobenzidine backbone. A selective procedure for the introduction of two imine groups in 3,3'-diaminobenzidine was developed to furnish starting materials for nonsymmetrical metallosalen complexes. The procedure proved to be widely applicable and several diimine derivatives were isolated and fully characterized. The diimine compounds were used to prepare the first nonsymmetrical bis(salen) complexes (M = Zn, Nil with different peripheral groups upon treatment with various salicylaldehydes in a one-pot procedure. The identity of the bis(metallosalen)s was verified by a range of analytical techniques, and for two of these derivatives the X-ray molecular structures are described. The crystallographic data revealed that the biphenylene linker between the two N(2)O(2) donor sets can adopt conformations with different dihedral angles. The supramolecular potential of the bis[Zn(salen)] derivatives was investigated by combining two of these complexes with a ditopic ligand to yield supramolecular assemblies with nanoscale dimensions. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).