Mononuclear ruthenium complexes and dinuclear Ru...Pd complexes having a series of 2,2'-bipyrimidine ligands, [(bpy)2Ru(Ln)]2+ [Ln = 2,2'-bipyrimidine (L1), 5,5'-dimethyl-2,2'-bipyrimidine (L2), 5,5'-dibromo-2,2'-bipyrimidine (L3), 4,4'-dimethyl-2,2'-bipyrimidine (L4), and 4,4',6,6'-tetramethyl- 2,2'-bipyrimidine (L5)] and [(bpy)2Ru(Ln)PdL]m+ [Ln = L1-L3; PdL = PdMeCl (m = 2) and PdMe(solvent) (m = 3)], are prepared, and the obtained complexes are characterized by means of spectroscopic and crystallographic methods. Introduction of the substituents on the bipyrimidine ligands led to the substantial differences in their electrochemical and photophysical properties. Density functional theory calculations have been performed to understand the substituent effect on the ground-state molecular orbital energy level. Reactivity studies on the catalytic dimerization of alpha-methylstyrene revealed that the Pd complex having a Br-substituted bipyrimidine ligand were much more active than those of the corresponding Pd complexes having methyl-substituted or nonsubstituted bipyrimidine ligands.

A novel dinuclear complex containing the photo-sensitizing Ru unit and a Pd center is effective toward selective catalytic dimerization of alpha-methylstyrene leading to 2,4-diphenyl-4-methyl-1-pentene under visible-light irradiated conditions.

Polyphenylalkane derivatives Q 0720Highly Selective Photo-Catalytic Dimerization of α-Methylstyrene by a Novel Palladium Complex with Photosensitizing Ruthenium(II) Polypyridyl Moiety. -A novel dinuclear complex containing the photo-sensitizing Ru unit and a Pd center is effective toward selective catalytic dimerization of title compound (I) under visible-light irradiated conditions. -(INAGAKI, A.; EDURE, S.; YATSUDA, S.; AKITA*, M.; Chem. Commun. (Cambridge) 2005, 43, 5468-5470; Chem. Resour. Lab., Tokyo Inst. Technol., Yokohama 226, Japan; Eng.) -M. Paetzel 12-100