Inorganic Chemistry, Vol.38, No.10, 2267-2278, 1999
Preparation of coordinatively asymmetrical ruthenium(II) polypyridine complexes
A series of salts of the type cis- [Ru-II(bpy')(bpy ") (CO)(2)](PF6)(2) (bpy' and bpy " represent different bipyridine derivatives) have been prepared by using literature procedures and utilized as precursors for the preparation of highly functionalized complexes of Ru-II incorporating neutral and anionic, mono- and bidentate, nitrogen-, phosphorus- sulfur-, and oxygen-donor ligands. The new synthetic approach builds upon previous work with the I trimethylamine N-oxide-assisted removal of the carbonyl ligand. Difficulties with the use of this potent oxidant in the presence of reducing ligands such as dppe and nitrite have been overcome by the use of acetonitrile complexes of the type cis-[Ru(bpy')(bpy ")(CH3CN)(2)](2+) and pyridine complexes of the type cis-[Ru(bpy')(bpy ")(py)(2)](2+) as highly versatile intermediates. Strategies for the selective removal of a single carbonyl ligand from the precursors have been developed and used to synthesize the highly asymmetrical complexes cis- [Ru-II(bpy')(bpy ")(py)(CO)](2+) and cis-[Ru-II(bpy') (bpy ") (py)(NO)](3+). The synthetic chemistry has been extended by using either of these complexes and the complex-as-ligand strategy to prepare the pyrazine-bridged complex cis,cis- [(Ru-II(bpy')(bpy ") (py))(2)(pz)]-(PF6)(4) (pz is pyrazine). Finally, a methodology for the preparation of isothiocyanate complexes such as cis-Ru(bpy')(bpy ")(NCS)(2) has been developed. For the pyridyl/carbonyl, pyridyl/nitrosyl, and ligand-bridged complexes, geometrical isomers were formed in statistical yields. For the isothiocyanate complex cis-Ru(dmb)(4,4'-(COOEt)(2)bpy)(NCS)(2), the majority (N,N-bound) isomer was isolated from the other three linkage isomers. For all the syntheses reported, yields were high, 44-96%, and each procedure appears to be both general and redundant in that multiple schemes are, possible for the preparation of most targets.
Keywords:PHOTOINDUCED ELECTRON-TRANSFER;INTRAMOLECULAR ENERGY-TRANSFER;CHROMOPHORE-QUENCHER COMPLEX;CHARGE-TRANSFER SENSITIZERS;TRISCHELATE COMPLEXES;LIGAND-BASED REDUCTION;PHOTOPHYSICALPROPERTIES;NITRO COMPLEXES;ARTIFICIAL PHOTOSYNTHESIS;2;2'-BIPYRIDINE COMPLEXES