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

Abstract

The syntheses and properties of three new ruthenium(I1) complexes based on the ligand 2,2':4,4":4',4'"-quaterpyridyl (qpy) are reported. Each new complex is of the type [R~(bpy),L]~, where L is the parent qpy ligand or is qpy derivatized by the methylation of one or both of the non-a-diimine nitrogen atoms and n = 2,3, or 4. The photophysical and electrochemical properties of the new complex ions are reported. The parent ion [R~(bpy)~qpy]~+ 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),(qpyme,)14+ is less than 100 ns. This dimethylated complex has some novel properties. The excited state produced by M-L excitation to the qpyme? ligand can be considered in terms of a Ru(II1) core and a positively charged ligand. Typically, the excited states of other ruthenium(I1) 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(I1) 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 qpyme?+ ligand.

Tuning the Excited State of Photoactive Building Blocks for Metal‐Templated Self‐Assembly

“…All chemicals were purchased from commercial sources and used as supplied unless otherwise stated. The ligands qtpy,33 dipyrido [3,2‐a:2′,3′‐c] phenazine (dppz)34 RuL 2 Cl 2 .2 H 2 O (L=bpy, phen or dppz)35 5 , 8 , 9 h, and 10 were synthesized through adaptations of literature methods 16–18. All reactions were carried out under a nitrogen‐free atmosphere.…”

“…Previous studies by Baker and co-workers, [18] explored the luminescence lifetimes of 5 and 8, and as we used slightly different conditions and instrumentation, we repeated their experiments for completeness. Previous studies by Baker and co-workers, [18] explored the luminescence lifetimes of 5 and 8, and as we used slightly different conditions and instrumentation, we repeated their experiments for completeness.…”

“…All the new complexes were characterized by 1 H NMR, FAB or ES-mass spectroscopy, and elemental analysis; the 1 H NMR spectra of the new complexes in [D 3 ]acetonitrile are quite complicated owing to the low symmetry of the complexes, however, by using the previously reported NMR spectrum of 5 as a guide, [17,18] complete structural assignments could be accomplished. The spectrums for 6 and 7 show a similar pattern for the qtpy signals as that for 5.…”

“…All the hexafluorophosphate salts of the Ru II and Re I complexes show unstructured emissions in acetonitrile at room temperature. Previous studies by Baker and co-workers, [18] explored the luminescence lifetimes of 5 and 8, and as we used slightly different conditions and instrumentation, we repeated their experiments for completeness. As complexes 7 and 12 incorporate dppz, a ligand known to induce solvent sensitivity in photo-excited states, [4,20] we also investigated the luminescence of the Ru II systems in water.…”

“…The ligands qtpy, [33] dipyrido [3,2-a:2',3'-c] phenazine (dppz) [34] RuL 2 Cl 2 .2 H 2 O (L= bpy, phen or dppz) [35] 5, 8, 9, and 10 were synthesized through adaptations of literature methods. [16][17][18] All reactions were carried out under a nitrogen-free atmosphere. Alumina column chromatography was carried out on Brockmann grade I alumina.…”