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

Abstract

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]₂·2; 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]·0.1C₂H₄Cl₂·0.15CH₂Cl₂ 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.