Water‐Soluble Cobalt(II) and Copper(II) Complexes of 3‐(5‐Chloro‐2‐hydroxy‐3‐sulfophenylhydrazo)pentane‐2,4‐dione as Building Blocks for 3D Supramolecular Networks and Catalysts for TEMPO‐Mediated Aerobic Oxidation of Benzylic Alcohols

A new water‐soluble β‐diketone azo derivative ― 3‐(5‐chloro‐2‐hydroxy‐3‐sulfophenylhydrazo)pentane‐2,4‐dione(H3L, 1) ― was synthesized and found to be stable in DMSO solution and in the solid state in the hydrazo tautomeric form. Its water‐soluble complexes [Co(HL)(en)(H2O)]·4H2O (3) and the zwitterionic [Cu(L)(Hen)(H2O)] (4), with buffering properties, were prepared by reaction of cobalt(II) and copper(II) nitrates with the ethylenediammonium (H2en) salt of 1, (H2en)(HL) (2). In the formation of 3 and 4, 1 is a chelating ligand, and a crucial synthetic and structural role is played by en, allowing the organization of water‐soluble assemblies and influencing the overall 3D supramolecular arrangement. Compound 3 is the first cobalt complex with an azo derivative of a β‐diketone. Complex 4 acts as catalyst precursor for the aerobic TEMPO‐mediated selective oxidation of benzylic alcohols to the corresponding aldehydes in aqueous media.