Chemistry Department Seminar
"Synthetic molecular catalysts for water oxidation toward artificial photosynthesis"
Presented by Masayuki Yagi, Niigata University, Department of Materials Science and Technology, Japan
Monday, February 10, 2014, 11 am
Room 300, Chemistry Bldg. 555
Hosted by: Etsuko Fujita
Polypyridyl ruthenium(II) complexes are well known to undergo the photoluminescence, photoredox, photosubstitution, and photoisomerization reactions typically involving a photoexcited triplet metal-to-ligand charge transfer (3MLCT). We recently reported the irreversible and stoichiometric photoisomerization of distal-[Ru(tpy)(pynp)OH2]2+ (tpy = 2,2',6',2"-terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) to proximal-[Ru(tpy)(pynp)OH2]2+,1) which has not been reported with respect to polypyridyl ruthenium(II) aquo complexes so far. Recently, much attention has been given to poly(pyridyl)ruthenium aquo complexes as water oxidation catalyst. Most of these complexes undergo proton coupled electron transfer reactions to give RuV=O species which have been pointed out as a key intermediate in the catalytic cycle of water oxidation. One could expect that dinuclear ruthenium complexes capable of being intramolecular coupling of RuV=O moieties work as a highly water oxidation catalyst. We design a new dinuclear ruthenium complex (denoted as Ru2, see Fig.1) shown in the below scheme. However, the thermochemical reaction of Ru(tpy)Cl3 with the bridging ligand (L) having an anthridine moiety selectively produces trans-[Ru(tpy)(L)Cl]+ (trans-RuLCl). The subsequent reaction of trans-RuLCl with additional Ru(tpy)Cl3 can not give Ru2 due to the steric hindrance between tpy ligands on trans-RuLCl and Ru(tpy)Cl3 To overcome the problem on the thermochemical synthesis, we focus on the utilization of photoisomerization reactions of poly(pyridyl)ruthenium(II) aquo complexes which was recently reported in our earlier paper.1) The thermochemical reaction of L and Ru(tpy)Cl3 in water gave a green solid of trans-RuLCl, which is identified from single X-ray crystallography and NMR data. trans-[Ru(tpy)(L)OH2]2+ (trans-RuLH2O) was obtaine