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Models for conjugated metal acetylide polymers: Ruthenium oligothienylacetylide complexes

TitleModels for conjugated metal acetylide polymers: Ruthenium oligothienylacetylide complexes
Publication TypeJournal Article
Year of Publication1999
AuthorsZhu, YB, Millet, DB, Wolf, MO, Rettig, SJ
Date PublishedMAY 10

The series of ruthenium(II) mono(oligothienylacetylide) complexes trans-Ru(dppm)(2)(Cl)-(C drop CR) (dppm = Ph(2)PCH(2)PPh(2); R = 2-thienyl(1a), 5-(2,2'-bithienyl) (1b), and 5-(2,2':5',2{''}-terthienyl) (1c)) and bis(oligothienylacetylide) complexes trans-Ru(dppm)2(C drop CR)(2) (R = 2-thienyl (2a), 5-(2,2'-bithienyl) (2b), and 5-(2,2':5',2{''}-terthienyl) (2c)) were synthesized. Complex 2c was crystallographically characterized. The cyclic voltammograms of complexes 1a-c all contain two oxidation waves, a Ru(II/III) wave and a ligand-based oxidation wave. As the length of the conjugated oligothienyl ligand increases, the thiophene-based oxidation wave becomes more chemically reversible. Complexes 2a-c all have a Ru(II/III) wave in their cyclic voltammograms, as well as multiple ligand-based oxidation waves. Complexes 2b and 2c both form films on the electrode surfaces upon repeated cycling in the range 0-1.4 V vs SCE. The UV-vis spectra of complexes 1a-c and 2a-c all contain intense absorptions due to the pi-pi{*} transition in the oligothienyl ligand, and these appear at lower energy than the pi-pi{*} transitions in the corresponding oligothiophenes. The monocations 1c(+) and 2c(+) were synthesized in solution at -20 degrees C and were characterized by visible and near-IR spectroscopy. The pi-pi{*} transitions of the terthienyl ligand in 1c(+) and 2c(+) shift to higher energy compared with the analogous transitions in 1c and 2c, and a series of LMCT absorption bands of high intensity appear between 500 and 700 nm and between 900 and 1700 nm, respectively. These results support the conclusion that the pi system of the conjugated oligothienyl ligands interacts strongly with the Ru(III) center.