Synthesis and characterization of ruthenium complexes with substituted pyrazino[2,3-f][1,10]-phenanthroline (= Rppl; R =Me, COOH, COOMe)

A series of substituted pyrazino[2,3-f][1,10]-phenanthroline (Rppl) ligands (with R=Me, COOH, COOMe) were synthetized (see 1-4 in Scheme 1). The ligands can be visualized as formed by a bipyridine and a quinoxaline fragment (see A and B). Homoleptic [Ru(R(1)ppl)(3)](PF6)(2) and heteropleptic [Ru(R(1)ppl){(R-2)(2)bpy}(2)](PF6)(2) (R-1=H, Me, COOMe and R-2=H, Me) metal complexes 5-7 and 8-13, respectively, based on these ligands were also synthesized and characterized by conventional techniques (Schemes 2 and 3, resp.). In the heteroleptic complexes, the RI-pp] ligand reduces at a less-negative potential than the bpy ligand, reflecting the acceptor property conferred by the quinoxaline moiety. The potentiality of some of these complexes as solar-cell dyes is discussed.