Mononuclear and Binuclear Tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘‘,3‘‘‘-j]phenazine (tpphz) Ruthenium and Osmium Complexes

The monometallic complexes [(bpy)2Ru(tpphz)]2+ (4) and [(bpy)2Os(tpphz)]2+ (5), where tpphz is the poorly soluble fully aromatic tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine, have been obtained by reaction of 5,6-diamino-1,10-phenanthroline with [(bpy)2M(phendione)]2+ (M = RuII or OsII). Reaction of 4 and 5 with metallic precursors yielded the homo- and heterobimetallic complexes [(bpy)2Ru(tpphz)Ru(NH3)4]4+ (6), [(bpy)2Ru(tpphz)Ru(bpy)2]4+ (7), [(bpy)2Os(tpphz)Os(bpy)2]4+ (8), and [(bpy)2Ru(tpphz)Os(bpy)2]4+ (9). The mononuclear 4 and 5 aggregate in solution, probably by π−π stacking of the tpphz part as shown from proton NMR. The complexes show one reversible metal-centered oxidation and several reversible (except 6) reductions which add one electron on the tpphz ligand, one electron on one bpy of each metallic end, a second electron on one bpy of each metallic end, and then a second electron on the tpphz ligand. The complexes (except 8) are luminescent in acetonitrile. Quenching of the luminescence by water has been attributed to proton quenching at the phenazine nitrogen atoms.