Diversification of ligand families through ferroin-neocuproin metal-binding domain manipulation

Derivatization of 5,5-bis(3-hydroxyphenyl)-2,2-bipyridine to give two new ligands, 3 and 4, which possess terminal alkene functionalities is described. The syntheses and characterization of the palladium(II) complexes [Pd(3)2][BF4]2 and [Pd(4)2][BF4]2, and the related [Pd( 2)2][BF4]2 in which 2 is 5,5-bis(3-methoxyphenyl)-2,2-bipyridine are reported. The labile nature of the ligand leads to [Pd(2)2][BF4]2 co-crystallizing with the free ligand as [Pd(2)2][BF4]2 x 2; in the solid state, the ligands in the [Pd(2)2]2+ cation distort (a bow-incline distortion) to alleviate bpy H6...H6 repulsions. Compound 2 has been converted to 5,5-bis(3-methoxyphenyl)-6-methyl-2,2-bipyridine (5) and 5,5-bis(3-methoxyphenyl)-6,6-dimethyl-2,2-bipyridine (6) to produce ligands suited to forming air-stable, copper(I) complexes of type [CuL2]+. [Cu(5)2][PF6] and [Cu(6)2][PF6] have been prepared and characterized, and the single crystal structures of 6 and [Cu(5)2][PF6] x 0.1C2H4Cl2 x 0.15CH2Cl2 are described. By altering the conditions under which 2 is methylated, competitive formation of 5,5,5,5-tetrakis(3-methoxyphenyl)-2,2:3,3:2,2-quaterpyridine occurs.