2,2'-4,4''-4',4'''-QUATERPYRIDYL - A BUILDING BLOCK FOR THE PREPARATION OF NOVEL REDOX REAGENTS .2. BIS(2,2'-BIPYRIDINE)RUTHENIUM(II) COMPLEXES

The syntheses and properties of three new ruthenium(II) complexes based on the ligand 2,2':4,4":4',4'''-quaterpyridyl (qpy) are reported. Each new complex is of the type [Ru(bpy)2L]n+, where L is the parent qpy ligand or is qpy derivatized by the methylation of one or both of the non-alpha-diimine nitrogen atoms and n = 2,3, or 4. The photophysical and electrochemical properties of the new complex ions are reported. The parent ion [Ru(bpy)2qpy]2+ is strongly luminescent and has a relatively long lifetime, e.g. in excess of 1400 ns in acetonitrile solution. In contrast, the lifetime of the dimethyl derivative [Ru(bpy)2(qpyme2)]4+ is less than 100 ns. This dimethylated complex has some novel properties. The excited state produced by M-L excitation to the qpyme2(2+) ligand can be considered in terms of a Ru(III) core and a positively charged ligand. Typically, the excited states of other ruthenium(II) diimine complexes have had neutral or negatively charged ligands. Further, in structural terms, the complex can be considered as an intramolecular assembly of a ruthenium(II) diimine site and a viologen site. Cyclic voltammetry indicates that the first two electrons added to the complex enter the viologen-like acceptor site constituted by the qpyme2(2+) ligand.