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ABSTRACT: Diiron complexes containing pyridyl-phosphine ligands, that is, (mu-pdt)[Fe(2)(CO)(5)L] (pdt = S(CH(2))(3)S, L = Ph(2)PCH(2)Py, Ph(2)PPy, ) and (micro-pdt)[Fe(CO)(2)(PMe(3))][Fe(CO)(2)L] (L = Ph(2)PCH(2)Py, Ph(2)PPy, ) were prepared as model complexes of the [FeFe]-hydrogenase active site. Protonation of and by HOTf afforded the pyridyl-nitrogen protonated products [H(N)][OTf] and [H(N)][OTf], respectively. The molecular structures of, as well as [H(N)][OTf] and [H(N)][OTf] were confirmed by X-ray diffraction studies, which show that the Ph(2)PCH(2)Py ligand occupies the basal position both in and its protonated species [H(N)][OTf], while the Ph(2)PPy ligand prefers the apical position in and [H(N)][OTf]. The double protonation process of complex was monitored by in situ IR, (1)H and (31)P NMR spectroscopy at low temperature. The spectroscopic evidence indicates that the protonation of occurs first at the Fe-Fe bond and then at the pyridyl-nitrogen atom. Cyclic voltammograms reveal that protonation of and results in a considerable decrease in the overpotential for electrocatalytic proton reduction in the presence of HOTf, while the efficiency is not influenced by protonation. The electrocatalytic efficiency of for proton reduction in the presence of HOAc in CH(3)CN-H(2)O (50 : 1, v/v) is 5 times higher than that in pure CH(3)CN.
Dalton Transactions 04/2009; · 3.84 Impact Factor
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ABSTRACT: A diiron dithiolate complex holding a mu-hydride on the iron atoms and a proton on the basic site of a chelating diphosphine ligand was prepared and crystallographically characterized as a structural model of the [FeFe]-hydrogenase active site, and its molecular structure shows the H(mu)(-)...H(N)(+) distance is 3.934 A.
Chemical Communications 12/2008; · 6.17 Impact Factor
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ABSTRACT: Selective synthetic routes to isomeric diiron dithiolate complexes containing the (EtO) 2PN(Me)P(OEt) 2 (PNP) ligand in an unsymmetrical chelating role, for example, (mu-pdt)[Fe(CO) 3][Fe(CO)(kappa (2)-PNP)] ( 3) and as a symmetrically bridging ligand in (mu-pdt)(mu-PNP)[Fe(CO) 2] 2 ( 4), have been developed. 3 was converted to 4 in 75% yield after extensive reflux in toluene. The reactions of 3 with PMe 3 and P(OEt) 3 afforded bis-monodentate P-donor complexes (mu-pdt)[Fe(CO) 2PR 3][Fe(CO) 2(PNP)] (PR 3 = PMe 3, 5; P(OEt) 3, 7), respectively, which are formed via an associative PMe 3 coordination reaction followed by an intramolecular CO-migration process from the Fe(CO) 3 to the Fe(CO)(PNP) unit with concomitant opening of the Fe-PNP chelate ring. The PNP-monodentate complexes 5 and 7 were converted to a trisubstituted diiron complex (mu-pdt)(mu-PNP)[Fe(CO)PR 3][Fe(CO) 2] (PR 3 = PMe 3, 6; P(OEt) 3, 8) on release of 1 equiv CO when refluxing in toluene. Variable-temperature (31)P NMR spectra show that trisubstituted diiron complexes each exist as two configuration isomers in solution. All diiron dithiolate complexes obtained were characterized by MS, IR, NMR spectroscopy, elemental analysis, and X-ray diffraction studies.
Inorganic Chemistry 08/2008; 47(15):6948-55. · 4.60 Impact Factor
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ABSTRACT: Four diiron dithiolate complexes containing ortho-acylamino-functionalized arenethiolato ligands, [(micro-S-2-RCONHC6H4)2Fe2(CO)6] (R = CH3, 1; CF3, 2; C6H5, 3; 4-FC6H4, 4), were synthesized and well characterized as biomimetic models of the Fe-Fe hydrogenase active site. The molecular structures of and 4 were determined by X-ray crystallography. The intra-ligand NHS hydrogen bonds were studied by the X-ray analysis and by the (1)H NMR spectroscopy. The contribution of the NHS hydrogen bonds to the reduction potentials of complexes was investigated by electrochemistry. The first reduction potentials of complexes exhibit large positive shifts, that is, 220-320 mV in comparison to that of the analogous complex [(micro-SPh)2Fe2(CO)6] and 370-470 mV to that of [(micro-pdt)2Fe2(CO)6] (pdt = propane-1,3-dithiolato). Complex is capable of electrocatalysing proton reduction of acetic acid at relatively low overpotential (ca. 0.2 V) in acetonitrile.
Dalton Transactions 06/2008; · 3.84 Impact Factor
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ABSTRACT: Three diiron dithiolate complexes containing rigid and conjugated bridges, [mu-SC(6)H(4)-2-(CO)S-mu]Fe(2)(CO)(6) (1), [2-mu-SC(5)H(3)N-3-(CO)S-mu]Fe(2)(CO)(6) (2), and the PPh(3)-monosubstituted complex [mu-SC(6)H(4)-2-(CO)S-mu]Fe(2)(CO)(5)(PPh(3)) (1-P), were prepared as biomimetic models for the [FeFe]-hydrogenase active site. The structures of complexes 1 and 2 were determined by single crystal X-ray analysis, which shows that each complex features a rigid coplanar dithiolate bridge with a 2-3 degrees deviation from the bisect plane of the molecule. The influence of the rigid bridge on the reduction potentials of complexes 1, 2 and 1-P was investigated by electrochemistry. The cyclic voltammograms of complexes 1 and 2 display large positive shifts for the primary reduction potentials, that is, 380-480mV in comparison to that of the pdt-bridged (pdt=propane-1,3-dithiolato) complex (mu-pdt)Fe(2)(CO)(6) and 160-260mV to that of the bdt-bridged (bdt=benzene-1,2-dithiolato) analogue (mu-bdt)Fe(2)(CO)(6).
Journal of Inorganic Biochemistry 05/2008; 102(4):952-9. · 3.35 Impact Factor
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ABSTRACT: A bis(mu-alkoxo)-bridged dinuclear iron(III) complex [Fe(L)(NO3)]2(NO3)2 [1; HL = N,N-bis(2-pyridylmethyl)-N-(2-hydroxyethyl)amine] of the tripodal N3O ligand was prepared as a biomimetic model for the intradiol-cleaving dioxygenase enzymes. The reaction of 1 and catechol in the presence of excess triethylamine gave the catecholate (CAT) chelate bis(mu-alkoxo)-bridged dinuclear iron(III) complex [Fe(L)(CAT)]2 (2). The molecular structures of complexes 1 and 2 were determined by X-ray crystallography. Diiron complexes 1 and 2 contain the same bis(mu-alkoxo)diiron diamond core. All heteroatoms (N3O) of the ligand are coordinated to the iron center in complex 1 with two pyridine nitrogen atoms on the axial bonds, while one of the pyridyl arms of the ligand is left uncoordinated in complex 2. The interaction of the diiron complex 1 and 3,5-di-tert-butylcatechol (H2DBC) was investigated by electronic and mass spectroscopy. Complex 1 displays the intradiol-cleaving dioxygenase activity, and the coordinate ethoxyl arm of the ligand is capable of accepting the proton from catechol, which mimics the function of Tyr447 in the protocatechuate 3,4-dioxygenase as an internal base. The spectrophotometric titration experiment indicates the relatively low demand of the external base (0.8 equiv based on Fe(3+)) for attaining the highest dioxygenase activity of complex 1. The reaction rate of the reactive intermediate [Fe(HL)(DBC)]+ with dioxygen is 0.38 M(-1) s(-1) determined by kinetic studies.
Inorganic Chemistry 11/2007; 46(22):9364-71. · 4.60 Impact Factor
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ABSTRACT: Two asymmetrically disubstituted diiron complexes (micro-pdt)[Fe(CO)(3)][Fe(CO)(eta(2)-L)] (L = 1-methyl-3-(2-pyridyl)imidazol-2-ylidene (NHC(MePy)), 2; 1,3-bis(2-picolyl)imidazol-2-ylidene (NHC(diPic)), 4) and a mono-substituted diiron complex (mu-pdt)[Fe(CO)(3)][Fe(CO)(2)(NHC(diPic))] (3) were prepared as biomimetic models of the Fe-only hydrogenase active site. X-Ray studies show that the NHC(MePy) and NHC(diPic) ligands in 2 and 4 each coordinate to the single iron atom as NHC-Py chelating ligands in two basal positions and the NHC(diPic) ligand of complex 3 lies in an apical position as a monodentate ligand. The large ranges of the highest and the lowest nu(CO) frequencies of 2 and 4 reflect that the relatively uneven electron density on the two iron atoms of the 2Fe2S model complexes 2 and 4 is as that observed for mono-substituted diiron complexes of good donor ligands. The cyclic voltammograms and the electrochemical proton reduction by 2 and 3 were studied in the presence of HOAc to evaluate the effect of asymmetrical substitution of strong donor ligands on the redox properties of the iron atoms and on the electrocatalytic activity for proton reduction.
Dalton Transactions 05/2007; · 3.84 Impact Factor
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ABSTRACT: The title compound, [Fe(3)(C(8)H(8)N(2)O)S(2)(CO)(8)], was prepared by the direct reaction of Fe(3)(CO)(12) and 5-meth-oxy-1H-benzoimidazole-2-thiol in tetra-hydro-furan. Desulfurization took place readily to form a sulfide carbonyl cluster. The mol-ecule contains a triangle consisting of three Fe atoms capped by two S atoms above and below. There are two Fe-Fe bonds [2.6322 (5) and 2.5582 (5) Å] in the triangle; the length of the third edge [3.3987 (5) Å] is too long to represent an Fe-Fe bond.
Acta Crystallographica Section E Structure Reports Online 01/2007; 64(Pt 1):m217. · 0.35 Impact Factor
