Synthesis of amino-bridged 6,6′-disubstituted-2,2′-bipyridine ligands for lanthanide coordination chemistry

Three cognate ligands containing bipyridine carboxylic frameworks were readily prepared under mild conditions from a pivotal 6-bromo-6'-bromomethyl-2,2'-bipyridine building block and a primary amine as starting materials. In one case, the amine was adequately functionalised with a nitro group. Transformation of the resulting bromo derivatives to the corresponding ethyl esters was made possible by the use of a carboethoxylation reaction promoted by palladium(0), while further hydrolysis afforded the targeted acids after protonation. Corresponding europium complexes show interesting luminescence properties in water at biological pH values.