Isolation and Structural Characterization of a Binuclear Intermediate Species Pertinent to Transmetalation of Zn(salphen) Complexes and the Formation of Polynuclear Salen Structures

Zinc(II) salphen complexes equipped with additional alkoxy donor groups at the 3-position of the salicylideneimine groups have been prepared to bind metal acetates in a second coordination sphere close to the central Zn(II) ion. The isolated binuclear monosalphen complexes have been studied in detail using NMR and MS techniques. Further synthesis has revealed that the formation of binuclear species from the parent salphen ligands is dependent on the nature of the bridging group between the two salicylideneimine groups and is prevented by replacement of one of the alkoxy substituents for a bulky t-Bu group. One of the binuclear Zn-2 complexes was crystallographically characterized and can be regarded as a structural model for the intermediate stage of the transmetalation of the central Zn(II) center within these dinuclear compounds by other metal acetate salts. Furthermore, the X-ray diffraction structure also relates well with some intermediate structural stages of the buildup of various polynuclear salen structures.