Synthesis of Ru- and Os-complexes of π-conjugated oligomers of 2,2′-bipyridine and 5,5′-bipyrimidine.: Optical properties and catalytic activity for photoevolution of H2 from aqueous media

Oligomers of 2,2'-bipyridine (Oligo-bpy) and 5,5'-bipyrimidine (Oligo-bpym) with a linear structure have been prepared by an organometallic C-C coupling reaction. The oligomeric chelating ligands have a molecular weight of about 1500 corresponding to about 10 chelating bpy or bpym units, and form soluble complexes with [M(bpy)(2)](2+) (M = Ru or Os). The W-vis absorption spectra of the metal complexes of Oligo-bpy exhibit a pi-pi* transition band at 355+/-6 nm and a peak at 453+/-18 nm assigned to a MLCT absorption. The UV-vis spectra of the metal complexes of Oligo-bpym also show an absorption peak attributed to the MLCT band. The water-soluble Ru complex of Oligo-bpy catalyzes visible-light-induced H-2 evolution from aqueous media in the presence of Pt cocatalyst and triethylamine.