Synthesis of a novel series of 6,6′-disubstituted 4,4′-bipyrimidines by radical anion coupling:: New π-accepting ligands for coordination chemistry

A new family of 6,6'-disubstituted 4,4'-bipyrimidine ligands has been prepared and characterized. The reduction potentials of the new ligands, as determined by cyclic voltammetry, indicate that these new ligands are considerably better pi-acceptors than the ubiquitous 2,2'-bipyridine ligand, and are even superior to the parent unsubstituted 4,4'-bipyrimidine ligand. The substituents in 6,6' positions of the 4,4'-bipyrimidine also cause a red-shift in the pi ->pi* and n ->pi* absorptions throughout the UV region. The X-ray crystal structure of one member of the family of bipyrimidines demonstrates that the aryl substituents may lie coplanar with the pyrimidine rings in the solid state. The additional electron delocalization afforded by the aryl substituents on the pyrimidine rings contribute to the better pi-accepting ability of these compounds. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).