An aqua-Ru-quinone complex, [Ru(trpy)(Q)(OH
2)]
2+ (trpy=2,2’: 6’,2”-terpyridine, Q=3,5-di-
tert-butyl-1,2-benzoquinone, or 3,6-di-
tert-butyl-1,2-benzoquinone) dissociates two protons in a stepwise fashion. The p
Kavalues of [Ru(trpy)(Q)(OH
2)]
+ and [Ru(trpy)(Q)(OH)]
+ are 5.5 and 10.5, respectively. Proton dissociation of the latter is coupled with electron transfer from the resultant O
2− to Q to produce an unusual O-radical complex, [Ru(trpy)(Sq)(O
−·)]
0 (Sq=3,5-di-
tert-butyl-1,2-benzosemiquinone). Dissociation of an amino proton of analogous [Ru(trpy)(Q)(NH
3)]
2+ (p
Ka6.2) results in similar intramolecular electron transfer from NH
2− to Q with generating an N-radical complex, [Ru(trpy)(Sq)(NH
2·)]
+. One-electron oxidation of [Ru(trpy)(Sq)(NH
2·)]
2+ produces [Ru(trpy)(Q)(NH
2·)]
2+, which reacts with alcohols to give the correspondent aldehyde or ketone with regeneration of [Ru(trpy)(Sq)(NH
3)]
+. On the other hand, two electron oxidation of [Ru(trpy)(Sq)(O
−·)]
0 generates a catalytic ability to oxidize alcohols. The catalytic activity of the O-radical complex is less than that of N-radical one. Dinuclear Ru complexes bridged with an anthracene framework, [Ru
2(btpyan)(Q)
2(OH)
2]
2+ and [Ru
2(btpyan)(bpy)
2(OH)
2]
2+ (btpyan=1,8-bis(2,2’: 6’,2”-terpyrid-4’-yl)anthracene) catalyze four-electron oxidation of water. The catalytic activity for O
2 production by [Ru
2(btpyan)(Q)
2(OH)
2]
2+ is much higher than [Ru
2(btpyan)(bpy)
2(OH)
2]
2+. Proton dissociation of [Ru
2(btpyan)(Q)
2(OH)
2]
2+ spontaneously produces [Ru
2(btpyan)(Sq)
2(O
−·)
2]
0, and the subsequent oxidation of the two Ru(Sq)(O
−·) groups induces O-O bond formation through the coupling reaction of two O-radicals. On the other hand, deprotonation of [Ru
2(btpyan)(bpy)
2(OH)
2]
2+ is caused by oxidation of [Ru
2(btpyan)(bpy)
2(OH)
2]
2+, and four electron oxidation affords [Ru
IV2(btpyan)(bpy)
2(=O)
2]
4+ without passing through an O-radical complex. High catalytic activity of [Ru
2(btpyan)(Q)
2(OH)
2]
2+ compared with [Ru
2(btpyan)(bpy)
2(OH)
2]
2+ as to the O
2 evolution is associated with the easiness of the O-O bond formation by the coupling reaction of two Ru-O
· radicals compared with that of two Ru
IV=O groups. A new pbn (pbn=2-pyridylbenzo[
b]-1,5-naphthyridine) ligand was designed to simulate the NAD
+/NADH redox reaction as a possible renewable hydride donor. A series of [Ru(bpy)
3−n(pbn)
n]
2+ (n=1, 2, 3) complexes undergoes photo-induced two-(n=1), four-(n=2), and six-electron reductions (n=3) under irradiation of visible light in the presence of N(CH
2CH
2OH)
3.
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