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'-bipyridine (1) starting from the pyrrole-protected aminopyridine 4. By standard reactions I 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 coor-dination compounds from this ligand did not work. However, the amide-connected ligand L 2 affords mononuclear ([(L-2 -H-4)PdCl2], [(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-)).