5,5′‐Diamino‐2,2′‐bipyridine: A Versatile Building Block for the Synthesis of Bipyridine/Catechol Ligands That Form Homo‐ and Heteronuclear Helicates

Herein we present an improved synthesis of 5.5'-diamino-2,2'-bi-pyridine (1) starting from the pyrrole-protected aminopyridine 4. By standard reactions 1 can easily be transformed into the imine- or amide-bridged dicatechol-bipyridine ligands L 1 -H 4 and L 2 -H 4 . Whereas ligand L 1 readily forms homodinuclear helicates [(L 1 ) 3 Ti 2 ] 4 - , the attempted formation of mono-, tri-, or even oligonuclear coordination compounds from this ligand did not work. However, the amide-connected ligand L 2 affords mononuclear ([(L 2 -H 4 )PdCl 2 ], [(L 2 -H 4 ) 3 Zn] 2 + ), dinuclear ([(L 2 ) 3 Ti 2 ] 4 - ), and heterotrinuclear coordination compounds ([(L 2 ) 3 Ti 2 Zn] 2 - ).