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ABSTRACT: The evolution of H(2) and the oxygenation of hydrocarbons from photocatalytic water splitting are reported by X. Zhao et al. in their Communication on page 1653 ff. A homogeneous system for simultaneous hydrogen production and hydrocarbon oxidation, in which water is the source of both oxygen and hydrogen, has been developed. Two photosensitizers allow the coupling of the hydrocarbon oxygenation reaction to the H(2) production process. (Photo courtesy of Rachel Wang.).
Angewandte Chemie International Edition 12/2011; 51(7):1729. · 13.45 Impact Factor
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ABSTRACT: On the sunny side: A homogeneous system for H(2) production and hydrocarbon oxidation was developed in the absence of any sacrificial reagent. This system consists of [Ru(TPA)(H(2) O)(2) ](2+) and [Fe(3) (CO)(12) ] as catalysts and [Ru(bpy)(3) ](2+) and [Ir(bpy)(ppy)(2) ](+) as photosensitizers (PS). Water is the oxygen source as well as the source for H(2) formation (see picture; Sub=organic substrate).
Angewandte Chemie International Edition 11/2011; 51(7):1653-6. · 13.45 Impact Factor
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ABSTRACT: The synthesis, characterization, and water oxidation activity of mononuclear ruthenium complexes with tris(2-pyridylmethyl)amine (TPA), tris(6-methyl-2-pyridylmethyl)amine (Me(3)TPA), and a new pentadentate ligand N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy) have been described. The electrochemical properties of these mononuclear Ru complexes have been investigated by both experimental and computational methods. Using Ce(IV) as oxidant, stoichiometric oxidation of water by [Ru(TPA)(H(2)O)(2)](2+) was observed, while Ru(Me(3)TPA)(H(2)O)(2)](2+) has much less activity for water oxidation. Compared to [Ru(TPA)(H(2)O)(2)](2+) and [Ru(Me(3)TPA)(H(2)O)(2)](2+), [Ru(DPA-Bpy)(H(2)O)](2+) exhibited 20 times higher activity for water oxidation. This study demonstrates a new type of ligand scaffold to support water oxidation by mononuclear Ru complexes.
Inorganic Chemistry 11/2011; 50(21):10564-71. · 4.60 Impact Factor
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ABSTRACT: The simple organometallic, (mu-S(2))Fe(2)(CO)(6), serves as a precursor to synthetic analogues of the chemically rudimentary iron-only hydrogenase enzyme active site. The fundamental properties of the (mu-SCH(2)CH(2)CH(2)S)[Fe(CO)(3)](2) compound, including structural mobility and regioselectivity in cyanidecarbon monoxide substitution reactions, relate to the enzyme active site in the form of transition-state structures along reaction paths rather than ground-state structures. Even in the absence of protein-based active-site organization, the ground-state structural model complexes are shown to serve as hydrogenase enzyme reaction models, H(2) uptake and H(2) production, with the input of photo- or electrochemical energy, respectively.
Proceedings of the National Academy of Sciences 05/2003; 100(7):3683-8. · 9.68 Impact Factor
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ABSTRACT: The established ability of the Fe(II) bridging hydride species (micro-H)(micro-pdt)[Fe(CO)2(PMe3)]2+, 1-H+, to take-up and heterolytically activate dihydrogen, resulting in H/D scrambling of H2/D2 and H2/D2O mixtures (Zhao et al. Inorg. Chem. 2002, 41, 3917) has prompted a study of simultaneous alkene/H2 activation by such [Fe]H2ase model complexes. That the required photolysis produced an open site was substantiated by substitution of CO in 1-H+ by CH3CN with formation of structurally characterized [(micro-H)(micro-pdt)[Fe(CO)2(PMe3)][Fe(CO)(CH3CN)(PMe3)]]+[PF6]-. Under similar photolytic conditions, H/D exchange reactions between D2 and terminal alkenes (ethylene, propene and 1-butene), but not bulkier alkenes such as 2-butene or cyclohexene, were catalyzed by 1-H+ and the edt (SCH2CH2S) analogue, 2-H+. Substantial regioselectivity for H/D exchange at the internal vinylic hydrogen was observed. The extent to which the olefins were deuterium enriched vs deuterated was catalyst dependent. The stabilizing effect of the binuclear chelating ligands, SCH2CH2CH2S, pdt, and SCH2CH2S, edt, is required for the activity of binuclear catalysts, as the mono-dentate micro-SEt analogue decomposed to inactive products under the photolytic conditions of the catalysis. Reactions of 1 and 2 with EtOSO2CF3 yielded the S-alkylated products, [(micro-SCH2CH2CH2SEt)[Fe(CO)2(PMe3)]2]+[SO3CF3]- (1-Et+), and 2-Et+, rather than micro-C2H5 analogues to the micro-H of 1-H+. The stability and lack of reactivity toward H2 of 1-Et+ and 2-Et+, indicates they are not on the reaction path of the olefin/D2 H/D exchange process. A mechanism with olefin binding to an open site created by CO loss and formation of an Fe-(CH2CHDR) intermediate is indicated. A likely role of a binuclear chelate effect is implicated for the unique S-XXX-S cofactor in the active site of [Fe]H2ase.
Journal of the American Chemical Society 02/2003; 125(2):518-24. · 9.91 Impact Factor
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ABSTRACT: Protonation of the [Fe]-hydrogenase model complex (mu-pdt)[Fe(CO)(2)(PMe(3))](2) (pdt = SCH(2)CH(2)CH(2)S) produces a species with a high field (1)H NMR resonance, isolated as the stable [(mu-H)(mu-pdt)[Fe(CO)(2)(PMe(3))](2)](+)[PF(6)](-) salt. Structural characterization found little difference in the 2Fe2S butterfly cores, with Fe.Fe distances of 2.555(2) and 2.578(1) A for the Fe-Fe bonded neutral species and the bridging hydride species, respectively (Zhao, X.; Georgakaki, I. P.; Miller, M. L.; Yarbrough, J. C.; Darensbourg, M. Y. J. Am. Chem. Soc. 2001, 123, 9710). Both are similar to the average Fe.Fe distance found in structures of three Fe-only hydrogenase active site 2Fe2S clusters: 2.6 A. A series of similar complexes (mu-edt)-, (mu-o-xyldt)-, and (mu-SEt)(2)[Fe(CO)(2)(PMe(3))](2) (edt = SCH(2)CH(2)S; o-xyldt = SCH(2)C(6)H(4)CH(2)S), (mu-pdt)[Fe(CO)(2)(PMe(2)Ph)](2), and their protonated derivatives likewise show uniformity in the Fe-Fe bond lengths of the neutral complexes and Fe.Fe distances in the cationic bridging hydrides. The positions of the PMe(3) and PMe(2)Ph ligands are dictated by the orientation of the S-C bonds in the (mu-SRS) or (mu-SR)(2) bridges and the subsequent steric hindrance of R. The Fe(II)(mu-H)Fe(II) complexes were compared for their ability to facilitate H/D exchange reactions, as have been used as assays of H(2)ase activity. In a reaction that is promoted by light but inhibited by CO, the [(mu-H)(mu-pdt)[Fe(CO)(2)(PMe(3))](2)](+) complex shows H/D exchange activity with D(2), producing [(mu-D)(mu-pdt)[Fe(CO)(2)(PMe(3))](2)](+) in CH(2)Cl(2) and in acetone, but not in CH(3)CN. In the presence of light, H/D scrambling between D(2)O and H(2) is also promoted by the Fe(II)(mu-H)Fe(II) catalyst. The requirement of an open site suggests that the key step in the reactions involves D(2) or H(2) binding to Fe(II) followed by deprotonation by the internal hydride base, or by external water. As indicated by similar catalytic efficiencies of members of the series, the nature of the bridging thiolates has little influence on the reactions. Comparison to [Fe]H(2)ase enzyme active site redox levels suggests that at least one Fe(II) must be available for H(2) uptake while a reduced or an electron-rich Fe(I)Fe(I) metal-metal bonded redox level is required for proton uptake.
Inorganic Chemistry 08/2002; 41(15):3917-28. · 4.60 Impact Factor
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ABSTRACT: Protonation of the [Fe]-hydrogenase model complex (μ-pdt)[Fe(CO)2(PMe3)]2 (pdt = SCH2CH2CH2S) produces a species with a high field 1H NMR resonance, isolated as the stable {(μ-H)(μ-pdt)[Fe(CO)2(PMe3)]2}+[PF6]- salt. Structural characterization found little difference in the 2Fe2S butterfly cores, with Fe···Fe distances of 2.555(2) and 2.578(1) Å for the Fe−Fe bonded neutral species and the bridging hydride species, respectively (Zhao, X.; Georgakaki, I. P.; Miller, M. L.; Yarbrough, J. C.; Darensbourg, M. Y. J. Am. Chem. Soc. 2001, 123, 9710). Both are similar to the average Fe···Fe distance found in structures of three Fe-only hydrogenase active site 2Fe2S clusters: 2.6 Å. A series of similar complexes (μ-edt)-, (μ-o-xyldt)-, and (μ-SEt)2[Fe(CO)2(PMe3)]2 (edt = SCH2CH2S; o-xyldt = SCH2C6H4CH2S), (μ-pdt)[Fe(CO)2(PMe2Ph)]2, and their protonated derivatives likewise show uniformity in the Fe−Fe bond lengths of the neutral complexes and Fe···Fe distances in the cationic bridging hydrides. The positions of the PMe3 and PMe2Ph ligands are dictated by the orientation of the S−C bonds in the (μ-SRS) or (μ-SR)2 bridges and the subsequent steric hindrance of R. The FeII(μ-H)FeII complexes were compared for their ability to facilitate H/D exchange reactions, as have been used as assays of H2ase activity. In a reaction that is promoted by light but inhibited by CO, the {(μ-H)(μ-pdt)[Fe(CO)2(PMe3)]2}+ complex shows H/D exchange activity with D2, producing {(μ-D)(μ-pdt)[Fe(CO)2(PMe3)]2}+ in CH2Cl2 and in acetone, but not in CH3CN. In the presence of light, H/D scrambling between D2O and H2 is also promoted by the FeII(μ-H)FeII catalyst. The requirement of an open site suggests that the key step in the reactions involves D2 or H2 binding to FeII followed by deprotonation by the internal hydride base, or by external water. As indicated by similar catalytic efficiencies of members of the series, the nature of the bridging thiolates has little influence on the reactions. Comparison to [Fe]H2ase enzyme active site redox levels suggests that at least one FeII must be available for H2 uptake while a reduced or an electron-rich FeIFeI metal−metal bonded redox level is required for proton uptake.
07/2002;
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ABSTRACT: The mononuclear complex Fe(CO)(4)(PPh(2)CH(2)CH(2)SH), 1, is isolated as an intermediate in the overall reaction of PPh(2)CH(2)CH(2)SH with [Fe(0)(CO)(4)] sources to produce binuclear bridging thiolate complexes. Photolysis is required for loss of CO and subsequent S-H activation to generate the metal-metal bonded Fe(I)-Fe(I) complex, (mu-SCH(2)CH(2)PPh(2))(2)Fe(2)(CO)(4), 2. Isomeric forms of 2 derive from the apical or basal position of the P-donor ligand in the pseudo square pyramidal S(2)Fe(CO)(2)P coordination spheres. This position in turn is dictated by the stereochemistry of the mu-S-CH(2) bond, designated as syn or anti with respect to the Fe(2)S(2) butterfly core. Addition of strong acids engages the Fe(I)-Fe(I) bond density as a bridging hydride, [(mu-H)-anti-2](+)[SO(3)CF(3)](-) or [(mu-H)-syn-2](+)[SO(3)CF(3)](-), with formal oxidation to Fe(II)-H-Fe(II). Molecular structures of anti-2, syn-2, and [(mu-H)-anti-2](+)[SO(3)CF(3)](-) were determined by X-ray crystallography and show insignificant differences in distance and angle metric parameters, including the Fe-Fe bond distances which average 2.6 A. The lack of coordination sphere rearrangements is consistent with the ease with which deprotonation occurs, even with the weak base, chloride. The Fe(I)-Fe(I) bond, supported by bridging thiolates, therefore presents a site where a proton might be taken up and stored as a hydride without impacting the overall structure of the binuclear complex.
Inorganic Chemistry 03/2002; 41(4):699-708. · 4.60 Impact Factor
