322 Complexation Chemistry of Tetradentate Polypyridyl Ligands

Thursday, November 5, 2009: 2:15 PM
Rio Grande (Camino Real Hotel)
Randolph P. Thummel , Department of Chemistry, University of Houston, Houston, TX
Ruifa Zong , Department of Chemistry, University of Houston, Houston, TX
Gang Zhang , Department of Chemistry, University of Houston, Houston, TX
Tseng Huan-Wei , Department of Chemistry, University of Houston, Houston, TX
A series of 1,10-phenanthrolines were prepared having additional ligating substituents at the 2,9-positions. These substituents were either a 4-substituted pyrid-2-yl, quinolin-2-yl, 1,8-naphthyrid-2-yl, N-methyl imidazo-2-yl, or N-methyl benzimidazo-2-yl group. Additionally, 3,6-di-(pyrid-2'-yl)-dipyrido[3,2-a:2',3'-c]phenazine was prepared. All but two of these ligands coordinated Ru(II) in a tetradentate equatorial fashion with two 4-methylpyridines bound in the axial sites. An X-ray structure analysis of the di-imidazoyl system indicates considerable distortion from square planar geometry in the equatorial plane. Previously reported variations in the axial ligand for such complexes appear to have a stronger effect on the electronic absorption and redox properties of the system than similar changes in the equatorial ligand. In the presence of excess Ce(IV) as a sacrificial oxidant at pH = 1, all the systems examined catalyze the decomposition of water to generate oxygen. Turnover numbers are modest, ranging from 186-416 and a mechanistic explanation for this process is proposed.