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1.
Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron(II) complex [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(THF)(2)], where (-)O(2)CAr(R) is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-MeSpy)] (4) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-MeS(O)py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply bridged diiron(II) complex, [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(3)-(O(2)CAr(4)(-)(FPh))(2-Ph(2)Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph(2)Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe(O(2)CAr(Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-PhSpy)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-Ph(2)Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O(2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH(2)Cl(2) yields [Fe(2)(mu-OH)(2)(mu-O(2)CAr(4)(-)(FPh))(O(2)CAr(4)(-FPh))(3)(OH(2))(2-Ph(2)P(O)py)] (8), which contains the biologically relevant {Fe(2)(mu-OH)(2)(mu-O(2)CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation. 相似文献
2.
Lee D Pierce B Krebs C Hendrich MP Huynh BH Lippard SJ 《Journal of the American Chemical Society》2002,124(15):3993-4007
Two tetracarboxylate diiron(II) complexes, [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(C(5)H(5)N)(2)] (1a) and [Fe(2)(mu-O(2)CAr(Tol))(4)(4-(t)BuC(5)H(4)N)(2)] (2a), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate, react with O(2) in CH(2)Cl(2) at -78 degrees C to afford dark green intermediates 1b (lambda(max) congruent with 660 nm; epsilon = 1600 M(-1) cm(-1)) and 2b (lambda(max) congruent with 670 nm; epsilon = 1700 M(-1) cm(-1)), respectively. Upon warming to room temperature, the solutions turn yellow, ultimately converting to isolable diiron(III) compounds [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (1c), 4-(t)BuC(5)H(4)N (2c)). EPR and M?ssbauer spectroscopic studies revealed the presence of equimolar amounts of valence-delocalized Fe(II)Fe(III) and valence-trapped Fe(III)Fe(IV) species as major components of solution 2b. The spectroscopic and reactivity properties of the Fe(III)Fe(IV) species are similar to those of the intermediate X in the RNR-R2 catalytic cycle. EPR kinetic studies revealed that the processes leading to the formation of these two distinctive paramagnetic components are coupled to one another. A mechanism for this reaction is proposed and compared with those of other synthetic and biological systems, in which electron transfer occurs from a low-valent starting material to putative high-valent dioxygen adduct(s). 相似文献
3.
We describe the synthesis and dioxygen reactivity of diiron(II) tetracarboxylate complexes [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(N,N-Me(2)en)(2)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(N,N-Bn(2)en)(2)] (6), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate. These complexes were prepared as models for the diiron(II) center in the hydroxylase component of soluble methane monooxygenase (MMOH). Compound 6 reacts with dioxygen to afford PhCHO in approximately 60(5)% yield, following oxidative N-dealkylation of the pendant benzyl group on the diamine ligand. The diiron(III) complex [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(O(2)CAr(Tol))(3)(N-Bnen)(N,N-Bn(2)en)] (8) was isolated from the reaction mixture. The 4.2 K M?ssbauer spectrum of 8 displays a single quadrupole doublet with parameters delta = 0.48(2) mm s(-1) and Delta E(Q) = 0.61(2) mm s(-1). The [Fe(2)(mu-OH)(2)(mu-O(2)CR)](3+) core structure in 8 matches that of the fully oxidized form of MMOH. The conversion of 6 to 8 closely parallels the chemistry of MMOH in which an O(2)-derived oxygen atom is inserted into the C-H bond of methane. Several reaction pathways are considered to account for this novel chemical transformation, and these are compared with mechanistic frameworks previously developed for related cytochrome P450 and copper(I) dioxygen chemistry. 相似文献
4.
General synthetic routes are described for a series of diiron(II) complexes supported by sterically demanding carboxylate ligands 2,6-di(p-tolyl)benzoate (Ar(Tol)CO(2)(-)) and 2,6-di(4-fluorophenyl)benzoate (Ar(4-FPh)CO(2)(-)). The interlocking nature of the m-terphenyl units in self-assembled [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (4); 1-MeIm (5)) promotes the formation of coordination geometries analogous to those of the non-heme diiron cores in the enzymes RNR-R2 and Delta 9D. Magnetic susceptibility and M?ssbauer studies of 4 and 5 revealed properties consistent with weak antiferromagnetic coupling between the high-spin iron(II) centers. Structural studies of several derivatives obtained by ligand substitution reactions demonstrated that the [Fe(2)(O(2)CAr')(4)L(2)] (Ar' = Ar(Tol); Ar(4-FPh)) module is geometrically flexible. Details of ligand migration within the tetracarboxylate diiron core, facilitated by carboxylate shifts, were probed by solution variable-temperature (19)F NMR spectroscopic studies of [Fe(2)(mu-O(2)CAr(4-FPh))(2)-(O(2)CAr(4-FPh))(2)(THF)(2)] (8) and [Fe(2)(mu-O(2)CAr(4-FPh))(4)(4-(t)BuC(5)H(4)N)(2)] (12). Dynamic motion in the primary coordination sphere controls the positioning of open sites and regulates the access of exogenous ligands, processes that also occur in non-heme diiron enzymes during catalysis. 相似文献
5.
In this study benzyl and ethyl groups were appended to pyridine and aniline ancillary ligands in diiron(II) complexes of the type [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(L)(2)], where (-)O(2)CAr(R) is a sterically hindered terphenyl carboxylate, 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh, respectively). These crystallographically characterized compounds were prepared as analogues of the diiron(II) center in the hydroxylase component of soluble methane monooxygenase (MMOH). The use of 2-benzylpyridine (2-Bnpy) yielded doubly bridged [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Bnpy)(2)] (1) and [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(2)(O(2)CAr(4)(-)(FPh))(2)(2-Bnpy)(2)] (4), whereas tetra-bridged [Fe(2)(mu-O(2)CAr(Tol))(4)(4-Bnpy)(2)] (3) resulted when 4-benzylpyridine (4-Bnpy) was employed. Similarly, 2-(4-chlorobenzyl)pyridine (2-(4-ClBn)py) and 2-benzylaniline (2-Bnan) were employed as N-donor ligands to prepare [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-(4-ClBn)py)(2)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Bnan)(2)] (5). The placement of the substituent on the pyridine ring had no effect on the geometry of the diiron(II) compounds isolated when 2-, 3-, or 4-ethylpyridine (2-, 3-, or 4-Etpy) was introduced as the ancillary nitrogen ligand. The isolated [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-Etpy)] (6), [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(3-Etpy)] (7), [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-Etpy)] (8), and [Fe(2)(mu-O(2)CAr(4)(-FPh))(2)(O(2)CAr(4)(-)(FPh))(2)(2-Etpy)(2)] (9) complexes all contain doubly bridged metal centers. The oxygenation of compounds 1-9 was studied by GC-MS and NMR analysis of the organic fragments following decomposition of the product complexes. Hydrocarbon fragment oxidation occurred for compounds in which the substrate moiety was in close proximity to the diiron center. The extent of oxidation depended upon the exact makeup of the ligand set. 相似文献
6.
Multidentate naphthyridine-based ligands were used to prepare a series of diiron(II) complexes. The compound [Fe(2)(BPMAN)(mu-O(2)CPh)(2)](OTf)(2) (1), where BPMAN = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine, exhibits two reversible oxidation waves with E(1/2) values at +310 and +733 mV vs Cp(2)Fe(+)/Cp(2)Fe, as revealed by cyclic voltammetry. Reaction with O(2) or H(2)O(2) affords a product with optical and M?ssbauer properties that are characteristic of a (mu-oxo)diiron(III) species. The complexes [Fe(2)(BPMAN)(mu-OH)(mu-O(2)CAr(Tol))](OTf)(2) (2) and [Fe(2)(BPMAN)(mu-OMe)(mu-O(2)CAr(Tol))](OTf)(2) (3) were synthesized, where Ar(Tol)CO(2)(-) is the sterically hindered ligand 2,6-di(p-tolyl)benzoate. Compound 2 has a reversible redox wave at +11 mV, and both 2 and 3 react with O(2), via a mixed-valent Fe(II)Fe(III) intermediate, to give final products that are also consistent with (mu-oxo)diiron(III) species. The paddle-wheel compound [Fe(2)(BBAN)(mu-O(2)CAr(Tol))(3)](OTf) (4), where BBAN = 2,7-bis(N,N-dibenzylaminomethyl)-1,8-naphthyridine, reacts with dioxygen to yield benzaldehyde via oxidative N-dealkylation of a benzyl group on BBAN, an internal substrate. In the presence of bis(4-methylbenzyl)amine, the reaction also produces p-tolualdehyde, revealing oxidation of an external substrate. A structurally related compound, [Fe(2)(BEAN)(mu-O(2)CAr(Tol))(3)](OTf) (5), where BEAN = 2,7-bis(N,N-diethylaminomethyl)-1,8-naphthyridine, does not undergo N-dealkylation, nor does it facilitate the oxidation of bis(4-methylbenzyl)amine. The contrast in reactivity of 4 and 5 is attributed to a difference in accessibility of the substrate to the diiron centers of the two compounds. The M?ssbauer spectroscopic properties of the diiron(II) complexes were also investigated. 相似文献
7.
The synthesis, structural characterization, and NO reactivity of carboxylate-bridged dimetallic complexes were investigated. The diiron(II) complex [Fe(2)(mu-O(2)CAr(Tol))(4)(Ds-pip)(2)] (1), where O(2)CAr(Tol) = 2,6-di(p-tolyl)benzoate and Ds-pip = dansyl-piperazine, was prepared and determined by X-ray crystallography to have a paddlewheel geometry. This complex reacts with NO within 1 min with a concomitant 4-fold increase in fluorescence emission intensity ascribed to displacement of Ds-pip. Although the diiron complex reacts with NO, as revealed by infrared spectroscopic studies, its sensitivity to dioxygen renders it unsuitable as an atmospheric NO sensor. The air-stable dicobalt(II) analogue was also synthesized and its reactivity investigated. In solution, the dicobalt(II) complex exists as an equilibrium between paddlewheel [Co(2)(mu-O(2)CAr(Tol))(4)(Ds-pip)(2)] (2) and windmill [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(Ds-pip)(2)] (3) geometric isomers. Conditions for crystallizing pure samples of each of these isomers are described. Reaction of 2 with excess NO proceeds by reductive nitrosylation giving [Co(mu-O(2)CAr(Tol))(2)(NO)(4)] (5), which is accompanied by release of the Ds-pip fluorophore that is N-nitrosated in the process. This reaction affords an overall 9.6-fold increase in fluorescence emission intensity, further demonstrating the potential utility of ligand dissociation as a strategy for designing fluorescence-based sensors to detect nitric oxide in a variety of contexts. 相似文献
8.
The synthesis and characterization of carboxylate-bridged dimetallic complexes are described. By using m-terphenyl-derived carboxylate ligands, a series of dicobalt(II), dicobalt(III), dinickel(II), and dizinc(II) complexes were synthesized. The compounds are [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (1), [Co(2)(mu-OH(2))(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (2a-c), [Co(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (3), [Ni(2)(mu-O(2)CAr(Tol))(4)L(2)] (4), [Ni(2)(mu-HO...H)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (5), and [Zn(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (6), where Ar(Tol)CO(2)H = 2,6-di(p-tolyl)benzoic acid and L = pyridine, THF, or N,N-dibenzylethylenediamine. Structural analysis of these complexes revealed that additional bridging ligands can be readily accommodated within the [M(2)(mu-O(2)CAr(Tol))(2)](2+) core, allowing a wide distribution of M...M distances from 2.5745(6) to 4.0169(9) A. Unprecedented bridging units [M(2)(mu-OH(2))(2)(mu-O(2)CR)(2)](n+) and [M(2)(mu-HO...H)(2)(mu-O(2)CR)(2)](n+) were identified in 2a-c and 5, respectively, in which strong hydrogen bonding accommodates shifts of protons from bridging water molecules toward the dangling oxygen atoms of terminal monodentate carboxylate groups. Such a proton shift along the O...H...O coordinate attenuates the donor ability of the anionic carboxylate ligand, which can translate into increased Lewis acidity at the metal centers. Such double activation of bridging water molecules by a Lewis acidic metal center and a metal-bound general base may facilitate the reactivity of metallohydrolases such as methionine aminopeptidase (MAP). 相似文献
9.
The syn coordination of histidine residues at the active sites of several carboxylate-rich non-heme diiron enzymes has been difficult to reproduce with small molecule model compounds. In this study, ligands derived from 1,8-naphthyridine, phthalazine, and 1,2-diethynylbenzene were employed to mimic this geometric feature. The preassembled diiron(II) complex [Fe(2)(micro-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(THF)(2)] (1), where Ar(Tol)CO(2)(-) is the sterically hindered carboxylate 2,6-di(p-tolyl)benzoate, served as a convenient starting material for the preparation of iron(II) complexes, all of which were crystallographically characterized. Use of the ligand 2,7-dimethyl-1,8-naphthyridine (Me(2)-napy) afforded the mononuclear complex [Fe(O(2)CAr(Tol))(2)(Me(2)-napy)] (2), whereas dinuclear [Fe(2)(micro-DMP)(micro-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(THF)] (3) resulted when 1,4-dimethylphthalazine (DMP) was employed. The dinuclear core of compound 3 is kinetically labile, as evidenced by the formation of [Fe(O(2)CAr(Tol))(2)(vpy)(2)] (4) upon addition of 2-vinylpyridine (vpy). The diiron analogue of 4, [Fe(2)(micro-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(vpy)(2)] (5), was prepared directly from 1. When the sterically more demanding ligand 2,6-di(4-tert-butylphenyl)benzoate (Ar(4-tBuPh)CO(2)(-)) was used, mononuclear [Fe(O(2)CAr(4)(-)(tBuPh))(2)(THF)(2)] (6) and [Fe(O(2)CAr(4)(-)(tBuPh))(2)(DMP)(2)] (7) formed. The difficulty in stabilizing a dinuclear core with these simple (N)(2)-donor ligands was circumvented by preparing a family of 1,2-diethynylbenzene-based ligands, from which were readily assembled the complexes [Fe(2)(Et(2)BCQEB(Et))(micro-O(2)CAr(Tol))(3)](OTf) (15) and [Cu(2)(Et(2)BCQEB(Et))(micro-I)(2)] (16), where Et(2)BCQEB(Et) is 1,2-bis(3-ethynyl-8-carboxylatequinoline)benzene ethyl ester. The Et(2)BCQEB(Et) framework provides both structural flexibility and the desired syn nitrogen donor geometry, thus serving as a good first-generation ligand in this class. 相似文献
10.
Carboxylate-bridged diiron(II) centers activate dioxygen for the selective oxidation of hydrocarbon substrates in bacterial multicomponent monooxygenases. Synthetic analogues of these systems exist in which substrate fragments tethered to the diiron(II) core through attachment to an N-donor ligand are oxidized by transient species that arise following the introduction of O2 into the system. The present study describes the results of experiments designed to probe mechanistic details of these oxidative N-dealkylation reactions. A series of diiron(II) complexes with ligands N,N-(4-R-Bn)Bnen, where en is ethylenediamine, Bn is benzyl, and R-Bn is benzyl with a para-directing group R = Cl, F, CH3, t-Bu, or OCH3, were prepared. A Hammett plot of the oxygenation product distributions of these complexes, determined by gas chromatographic analysis, reveals a small positive slope of rho = +0.48. Kinetic isotope effect (KIE(intra)) values for oxygenation of [Fe2(mu-O2CAr(Tol))2(O2CAr(Tol))2(N,N-(C6H5CDH)2en)2] and [Fe2(mu-O2CAr(Tol))2(O2CAr(Tol))2(N,N-(C6H5CD2)(C6H5CH2)en)2] are 1.3(1) and 2.2(2) at 23 degrees C, respectively. The positive slope rho and low KIE(intra) values are consistent with a mechanism involving one-electron transfer from the dangling nitrogen atom in N,N-Bn2en to a transient electrophilic diiron intermediate, followed by proton transfer and rearrangement to eliminate benzaldehyde. 相似文献
11.
Carboxylate-rich diiron(II) compounds with varying numbers of water ligands have been characterized, including the first complex with a {Fe2(mu-OH2)2(mu-O2CArTol)}3+ unit. The isolation of these complexes reveals how water can alter the structural properties of carboxylate-bridged diiron(II) core similar to those that occur in a variety of dioxygen-activating metalloenzyme cores. M?ssbauer and variable temperature, variable field magnetic susceptibility experiments indicate that the compound [Fe2(mu-OH2)2(mu-O2CAr4F-Ph)(O2CAr4F-Ph)3(THF)2(OH2)] has a high-spin diiron(II) core with little significant magnetic exchange coupling. 相似文献
12.
A dinucleating macrocycle, H(2)PIM, containing phenoxylimine metal-binding units has been prepared. Reaction of H(2)PIM with [Fe(2)(Mes)(4)] (Mes = 2,4,6-trimethylphenyl) and sterically hindered carboxylic acids, Ph(3)CCO(2)H or Ar(Tol)CO(2)H (2,6-bis(p-tolyl)benzoic acid), afforded complexes [Fe(2)(PIM)(Ph(3)CCO(2))(2)] (1) and [Fe(2)(PIM)(Ar(Tol)CO(2))(2)] (2), respectively. X-ray diffraction studies revealed that these diiron(II) complexes closely mimic the active site structures of the hydroxylase components of bacterial multicomponent monooxygenases (BMMs), particularly the syn disposition of the nitrogen donor atoms and the bridging μ-η(1)η(2) and μ-η(1)η(1) modes of the carboxylate ligands at the diiron(II) centers. Cyclic voltammograms of 1 and 2 displayed quasi-reversible redox couples at +16 and +108 mV vs ferrocene/ferrocenium, respectively. Treatment of 2 with silver perchlorate afforded a silver(I)/iron(III) heterodimetallic complex, [Fe(2)(μ-OH)(2)(ClO(4))(2)(PIM)(Ar(Tol)CO(2))Ag] (3), which was structurally and spectroscopically characterized. Complexes 1 and 2 both react rapidly with dioxygen. Oxygenation of 1 afforded a (μ-hydroxo)diiron(III) complex [Fe(2)(μ-OH)(PIM)(Ph(3)CCO(2))(3)] (4), a hexa(μ-hydroxo)tetrairon(III) complex [Fe(4)(μ-OH)(6)(PIM)(2)(Ph(3)CCO(2))(2)] (5), and an unidentified iron(III) species. Oxygenation of 2 exclusively formed di(carboxylato)diiron(III) compounds, a testimony to the role of the macrocylic ligand in preserving the dinuclear iron center under oxidizing conditions. X-ray crystallographic and (57)Fe M?ssbauer spectroscopic investigations indicated that 2 reacts with dioxygen to give a mixture of (μ-oxo)diiron(III) [Fe(2)(μ-O)(PIM)(Ar(Tol)CO(2))(2)] (6) and di(μ-hydroxo)diiron(III) [Fe(2)(μ-OH)(2)(PIM)(Ar(Tol)CO(2))(2)] (7) units in the same crystal lattice. Compounds 6 and 7 spontaneously convert to a tetrairon(III) complex, [Fe(4)(μ-OH)(6)(PIM)(2)(Ar(Tol)CO(2))(2)] (8), when treated with excess H(2)O. 相似文献
13.
The synthesis and characterization of [Fe(2)(micro-O(2)CAr(Tol))(4)L(2)] complexes, where L is benzylamine or 4-methoxybenzylamine (BA(p)()(-)(OMe)), are described. The reaction of the latter diiron(II) complex with dioxygen at -78 degrees C affords a metastable mixed-valent Fe(II)Fe(III) green intermediate. When O(2) is introduced at ambient temperature, N-dealkyation occurs to yield anisaldehyde, eliminating N-oxidation as a viable pathway for the reaction. Use of [Fe(2)(micro-O(2)CAr(T)(omicron)(l))(4)(alpha-d(1)-BA(p)()(-)(OMe))(2)] allowed a deuterium kinetic isotope of approximately 3 to be determined. 相似文献
14.
The {Fe2(mu-OH)2(mu-O2CR)}3+ and {Fe2(mu-O)(mu-O2CR)}3+ cores of the carboxylate-bridged diiron(III) centers in the enzyme active sites were reproduced by small molecule model complexes that were prepared through direct oxygenation of the mononuclear iron(II) complexes. Upon oxygenation of [Fe(O2CArTol)2(Hdmpz)2], where -O2CArTol is 2,6-di(p-tolyl)benzoate and Hdmpz is 3,5-dimethylpyrazole, [Fe2(mu-OH)2(mu-O2CArTol)(O2CArTol)3(OH2)(Hdmpz)2] was generated and characterized to share close physical properties with sMMOHox, including delta = 0.45 (2) mm/s, DeltaEQ = 1.21 (2) mm/s, and J = -7.2 (2) cm-1. The compound [Fe2(mu-O)(mu-O2CAr4-FPh)(O2CAr4-FPh)3(Hdmpz)3], where -O2CAr4-FPh is 2,6-di(4-fluorophenyl)benzoate, with delta = 0.51 (2) mm/s, DeltaEQ = 1.26 (2) mm/s, and J = -117.4 (1) cm-1, was isolated as the oxygenation product of [Fe(O2CAr4-FPh)2(Hdmpz)2]. 相似文献
15.
Lee D DuBois JL Pierce B Hedman B Hodgson KO Hendrich MP Lippard SJ 《Inorganic chemistry》2002,41(12):3172-3182
The synthesis, molecular structures, and spectroscopic properties of a series of valence-delocalized diiron(II,III) complexes are described. One-electron oxidation of diiron(II) tetracarboxylate complexes afforded the compounds [Fe(2)(mu-O(2)CAr(Tol))(4)L(2)]X, where L = 4-(t)BuC(5)H(4)N (1b), C(5)H(5)N (2b), and THF (3b); X = PF(6)(-) (1b and 3b) and OTf(-) (2b). In 1b-3b, four mu-1,3 carboxylate ligands span relatively short Fe...Fe distances of 2.6633(11)-2.713(3) A. Intense (epsilon = 2700-3200 M(-1) cm(-1)) intervalence charge transfer bands were observed at 620-670 nm. EPR spectroscopy confirmed the S = (9)/(2) ground spin state of 1b-3b, the valence-delocalized nature of which was probed by X-ray absorption spectroscopy. The electron delocalization between paramagnetic metal centers is described by double exchange, which, for the first time, is observed in diiron clusters having no single-atom bridging ligand(s). 相似文献
16.
Recently, we reported the synthesis of a carboxylate-rich non-heme diiron enzyme model compound [Fe2(mu-O2CAr(Tol))4(4-CNPy)2] (1), where (-)O(2)CAr(Tol) is 2,6-di-p-tolylbenzoate and 4-CNPy is 4-cyanopyridine (Yoon, S.; Lippard, S. J. J. Am. Chem. Soc. 2005, 127, 8386-8397). A metal-to-ligand charge-transfer band in the visible region of the optical absorption spectrum involving the nitrogen-donor ligand endowed this complex with a distinctive red color that facilitated analysis of its chemistry. Following this strategy, we prepared and characterized two related isomeric complexes, windmill (3) and paddlewheel (4) species having the formula [Fe2(O2CAr(Tol))4(4-AcPy)2], where 4-AcPy is 4-acetylpyridine. In anhydrous solvents, 1 and 4 adopt paddlewheel structures, but upon the addition of water, they convert to aquated forms, windmill structures having the composition [Fe2(mu-O2CAr(Tol))2(O2CAr(Tol))2(4-RPy)2(H2O)2]. This conversion is favored at low temperature and was studied by NMR spectroscopy. A kinetic analysis of the aquation reaction was undertaken by stopped-flow measurements between 198 and 223 K for both 1 and 4, which revealed a first-order dependence on both the diiron compound and water. The oxygenation rates for the water-containing complexes are much faster than those for the corresponding anhydrous complexes, being 20-fold faster for 4 and 10-fold more rapid for 1. The presence or absence of water had little effect on the activation enthalpies, suggesting that the loss of water may not be necessary prior to dioxygen binding in the transition state. 相似文献
17.
A kinetic study of the reaction between a diiron(II) complex [Fe(II)(2)(mu-OH)(2)(6-Me(3)-TPA)(2)](2+) 1, where 6-Me(3)-TPA = tris(6-methyl-2-pyridylmethyl)amine, and dioxygen is presented. A diiron(III) peroxo complex [Fe(III)(2)(mu-O)(mu-O(2))(6-Me(3)-TPA)(2)](2+) 2 forms quantitatively in dichloromethane at temperatures from -80 to -40 degrees C. The reaction is first order in [Fe(II)(2)] and [O(2)], with the activation parameters DeltaH(double dagger) = 17 +/- 2 kJ mol(-1) and DeltaS(double dagger) = -175 +/- 20 J mol(-1) K(-1). The reaction rate is not significantly influenced by the addition of H(2)O or D(2)O. The reaction proceeds faster in more polar solvents (acetone and acetonitrile), but the yield of 2 is not quantitative in these solvents. Complex 1 reacts with NO at a rate about 10(3) faster than with O(2). The mechanistic analysis suggests an associative rate-limiting step for the oxygenation of 1, similar to that for stearoyl-ACP Delta(9)-desaturase, but distinct from the probable dissociative pathway of methane monoxygenase. An eta(1)-superoxo Fe(II)Fe(III) species is a likely steady-state intermediate during the oxygenation of complex 1. 相似文献
18.
The catalytic oxidation of triphenylphosphine in the presence of dioxygen by the diiron(II) complex [Fe(2)(micro-O(2)CAr(Tol))(2)(Me(3)TACN)(2)(MeCN)(2)](OTf)(2) (1), where (-)O(2)CAr(Tol) = 2,6-di(p-tolyl)benzoate and Me(3)TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane, has been investigated. The corresponding diiron(III) complex, [Fe(2)(micro-O)(micro-O(2)CAr(Tol))(2)(Me(3)TACN)(2)](OTf)(2) (2), the only detectable iron-containing species during the course of the reaction, can itself promote the reaction. Phosphine oxidation is coupled to the catalytic oxidation of THF solvent to afford, selectively, the C-C bond-cleavage product 3-hydroxypropylformate, an unprecedented transformation. After consumption of the phosphine, solvent oxidation continues but results in the products 2-hydroperoxytetrahydrofuran, butyrolactone, and butyrolactol. The similarities of the reaction pathways observed in the presence and absence of catalyst, as well as (18)O labeling, solvent dependence, and radical probe experiments, provide evidence that the oxidation is initiated by a metal-centered H-atom abstraction from THF. A mechanism for catalysis is proposed that accounts for the coupled oxidation of the phosphine and the THF ring-opening reaction. 相似文献
19.
A series of iron(III) complexes of the tetradentate ligand BPMEN (N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine) were prepared and structurally characterized. Complex [Fe(2)(mu-O)(mu-OH)(BPMEN)(2)](ClO(4))(3) (1) contains a (mu-oxo)(mu-hydroxo)diiron(III) diamond core. Complex [Fe(BPMEN)(urea)(OEt)](ClO(4))(2) (2) is a rare example of a mononuclear non-heme iron(III) alkoxide complex. Complexes [Fe(2)(mu-O)(mu-OC(NH(2))NH)(BPMEN)(2)](ClO(4))(3) (3) and [Fe(2)(mu-O)(mu-OC(NHMe)NH)(BPMEN)(2)](ClO(4))(3) (4) feature N,O-bridging deprotonated urea ligands. The kinetics and equilibrium of the reactions of 1 with ligands L (L = water, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1,3,3-tetramethylurea, and acetamide) in acetonitrile solutions were studied by stopped-flow UV-vis spectrophotometry, NMR, and mass spectrometry. All these ligands react with 1 in a rapid equilibrium, opening the four-membered Fe(III)(mu-O)(mu-OH)Fe(III) core and forming intermediates with a (HO)Fe(III)(mu-O)Fe(III)(L) core. The entropy and enthalpy for urea binding through oxygen are DeltaH degrees = -25 kJ mol(-1) and DeltaS degrees = -53.4 J mol(-1) K(-1) with an equilibrium constant of K(1) = 37 L mol(-1) at 25 degrees C. Addition of methyl groups on one of the urea nitrogen did not affect this reaction, but the addition of methyl groups on both nitrogens considerably decreased the value of K(1). An opening of the hydroxo bridge in the diamond core complex [Fe(2)(mu-O)(mu-OH)(BPMEN)(2)] is a rapid associative process, with activation enthalpy of about 60 kJ mol(-1) and activation entropies ranging from -25 to -43 J mol(-1) K(-1). For the incoming ligands with the -CONH(2) functionality (urea, 1-methylurea, 1,1-dimethylurea, and acetamide), a second, slow step occurs, leading to the formation of stable N,O-coordinated amidate diiron(III) species such as 3 and 4. The rate of this ring-closure reaction is controlled by the steric bulk of the incoming ligand and by the acidity of the amide group. 相似文献
20.
Westerheide L Müller FK Than R Krebs B Dietrich J Schindler S 《Inorganic chemistry》2001,40(8):1951-1961
The iron(III) complexes [Fe(2)(HPTB)(mu-OH)(NO(3))(2)](NO(3))(2).CH(3)OH.2H(2)O (1), [Fe(2)(HPTB)(mu-OCH(3))(NO(3))(2)](NO(3))(2).4.5CH(3)OH (2), [Fe(2)(HPTB)(mu-OH)(OBz)(2)](ClO(4))(2).4.5H(2)O (3), [Fe(2)(N-EtOH-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3CH(3)OH.1.5H(2)O (4), [Fe(2)(5,6-Me(2)-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3.5CH(3)OH.C(2)H(5)OC(2)H(5).0.5H(2)O (5), and [Fe(4)(HPTB)(2)(mu-F)(2)(OH)(4)](ClO(4))(4).CH(3)CN.C(2)H(5)OC(2)H(5).H(2)O (6) were synthesized (HPTB = N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, N-EtOH-HPTB = N,N,N',N'-tetrakis(N' '-(2-hydroxoethyl)-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, 5,6-Me(2)-HPTB = N,N,N',N'-tetrakis(5,6-dimethyl-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane). The molecular structures of 2-6 were established by single-crystal X-ray crystallography. Iron(II) complexes with ligands similar to the dinucleating ligands described herein have been used previously as model compounds for the dioxygen uptake at the active sites of non-heme iron enzymes. The same metastable (mu-peroxo)diiron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1-6. Using stopped-flow techniques these reactions were kinetically investigated in different solvents and a mechanism was postulated. 相似文献