An end-on superoxido complex with formula {[Co III (OH 2 )(trpy)][Co III (OO·)(trpy)](µ-bpp)} 4+ , 3 4+ , (bpp -is bis-2-pyridyl-3,5-pyrazolate; trpy is 2,2';6':2"-terpyridine) has been characterized by resonance Raman, electron paramagnetic resonance and x-ray absorption spectroscopies. These results together with on-line mass spectrometry experiments using 17 . Density Functional Theory calculations agree and complement the experimental data, and offer a complete description of the transition states and intermediates involved in the catalytic cycle.Oxygen activation by first-row transition metal complexes in low oxidation states has been a very active field of research for the last two decades.1 A plethora of transition metal peroxido and superoxido complexes in different coordination modes have been prepared and characterized with spectroscopic techniques and even via single-crystal X-ray diffraction in selected instances.2 The reverse reaction, the oxidation of water to molecular oxygen assisted by first rowtransition metal complexes is a field that has emerged recently and the proper characterization of the potential peroxido and/or superoxido reaction intermediates is practically nonexistent. 3 The characterization of such intermediates is hampered by the lability of the metal-ligand bonds that can undergo substitution by water solvent molecules and by the relatively low temperature range at which the reaction can be operated. In sharp contrast, the inverse reaction i.e. the oxygen activation can be carried out in organic solvents and at very low temperatures. Additionally, for the water oxidation reaction, in a number of cases, a competing and/or preferential ligand oxidation occurs 4 which prevents extraction of reliable and meaningful information. In previous work, we have reported the synthesis and X-ray structure of the dinu-3+ hereafter, (trpy is 2,2';6':2"-terpyridine; bpp -is the bis-2-pyridyl-3,5-pyrazolate) that behaves as powerful catalyst for the 4e -reduction of dioxygen to water. 5 The key structures are depicted in Scheme 1. Further, we have electrochemically characterized the properties of 1 3+ and have shown by voltammetric and potentiometric techniques its capacity to act as a catalyst for the 4e -oxidation of water to dioxygen. ).
Four heterotrinuclear complexes containing the ligands 3,5-bis(2-pyridyl)pyrazolate (bpp–) and 2,2′:6′,2′′-terpyridine (trpy) of the general formula {[RuII(trpy)]2(μ-[M(X)2(bpp)2])}(PF6)2 have been prepared for the first time.
Anchoring terminal octenyl tails on molecular polyoxotungstates yield polymerizable organic-inorganic monomers with formula [{CH(2)=CH(CH(2))(6)Si}(x)O(y)SiW(w)O(z)](4-) [x = 2, w = 11, y = 1, z = 39 (1); x = 2, w = 10, y = 1, z = 36 (2); and x = 4, w = 9, y = 3, z = 34 (3)]. These molecular hybrids can use aqueous hydrogen peroxide to catalyze the selective oxidation of organic sulfides in CH(3)CN. Copolymerization of 1-3 with methyl methacrylate and ethylene glycol dimethacrylate leads to porous materials with a homogeneous distribution of the functional monomers, as indicated by converging evidence from FTIR spectroscopy and electronic microscopy. The catalytic polymers activate hydrogen peroxide for oxygen transfer, as demonstrated by the quantitative and selective oxidation of methyl p-tolyl sulfide, which was screened as model substrate. The hybrid material containing monomer 2 was also tested in n-octane to evaluate its potential for the oxidation and removal of dibenzothiophene, a well-known gasoline contaminant.
The synthetic intermediate cis(out),cis-[Ru(Cl) 2 (HL)-(DMSO) 2 ], 1 (DMSO = dimethyl sulfoxide), and four new mononuclear ruthenium complexes with general formula out/in-[Ru(HL)(trpy)(X)] m+ (trpy = 4-tert-butylpyridine; X = Cl − , m = 1, 2a + and 2b + ; X = H 2 O, m = 2, 3a 2+ and 3b 2+ ) based on the ligand 1H-pyrazole-3-carboxylic acid, 5-(2-pyridinil)-, ethyl ester (HL), are synthesized and characterized by analytical, spectroscopic, and electrochemical methods. A linkage isomerism is observed for a DMSO moiety of 1, and relevant thermodynamics and kinetics values are obtained through electrochemical experiments and compared to literature. Different synthetic routes are developed to obtain isomeric 2a + and 2b + , with different relative yields. Water oxidation activity of 3a 2+ and 3b 2+ is analyzed by means of electrochemical methods, through foot of the wave analysis, yielding k obs values of 1.00 and 2.23 s −1 , respectively. Chemically driven water oxidation activity is tested using [(NH 4 ) 2 Ce(NO 3 ) 6 ] as sacrificial electron acceptor, and turnover number (TON) and turnover frequency (TOF) values of TON = 10.8 and TOF i = 58.2 × 10 −3 s −1 for 3a 2+ and TON = 4.2 and TOF i = 15.4 × 10 −3 s −1 for 3b 2+ are obtained.
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