Synthesis, X‐ray Structure and Reactivity of a Sterically Protected Azobisphenol Ligand: On the Quest for New Multifunctional Active Ligands

Different synthetic routes have been explored for the synthesis of the sterically protected 2,2′‐dihydroxy‐4,3,4,3′‐tetra‐ tert ‐butylazobenzene ligand ( 2 ), which is an excellent candidate for the development of valence tautomeric complexes. As expected, such a ligand exhibits good reactivity with transition‐metal ions, as shown by the synthesis and characterization of the new cobalt complex [Co( 2 2– )(H 2 O) 3 ]Cl · 2.5EtOH · H 2 O ( 8 ). This fact together with the reversible deprotonation/protonation of the phenol groups has been used to create a chromophoric array of three states with significantly different colours, which can interconvert reversibly between them. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)