共查询到20条相似文献,搜索用时 10 毫秒
1.
We have previously postulated a serine gated electron transfer hypothesis (Inorg. Chem, 2002, 41, 1281-1291) to possibly be involved in gating electron transfer between the Mo(V) and Mo(IV) states. In this study we explored the effect of solvent dielectric upon the rate and mechanism of isomerization of an oxo-Mo(V) core in attempt to understand the effect of solvent polarity to the isomerization reaction. To this end, the data suggests that there may be significant entropic contributions to the reorganization of metal center as a function of the local dielectric constant. Furthermore, we note that there is a change in the observed rate as well as the mechanism of the geometric rearrangement when it is examined in polar and non-polar environments. More specifically, in low dielectric media, the reaction proceeds either via a fast dissociation which is then followed by a twist mechanism or by a dissociation that is synchronized with the twist mechanism. 相似文献
2.
Coordination by at least four sulfur donors to an embedded molybdenum center has been found to be a common feature in the crystal structures of many mononuclear molybdenum enzymes. In an effort to model embedded molybdenum centers, we have synthesized dendritic thiolate ligands and their oxo-molybdenum complexes containing a [Mo(V)OS(4)](-) core. These compounds have been isolated in pure form as blue solids or gummy materials, and the molecular nature of these compounds has been confirmed by electrospray ionization mass spectrometry and infrared, electron paramagnetic resonance, and UV-vis spectroscopies. The dendritic complexes exhibit little variation in their broad S --> Mo charge transfer band (lambda(max) approximately 600 nm; epsilon approximately 6000 M(-)(1) cm(-)(1)), Mo=O vibration energy (941-943 cm(-)(1)), and EPR g-values (g( parallel ) approximately 2.02; g( perpendicular ) approximately 1.98; g(av) approximately 1.99). The spectroscopic data confirm the integrity of the square pyramidal [Mo(V)OS(4)](-) core with little geometric distortions, suggesting that the electronic structure at the metal center is not perturbed by the ligand architecture. The electronic structure of these complexes, calculated by the density functional theory, demonstrates a similar composition of the HOMO. In complexes 6 and 7a, the energy of the HOMO orbital might be modulated by the difference in the electronic structure of the ligands. The Mo(V/IV) reduction potentials vary as a function of the dielectric constant and the donor number of the solvent. The kinetics of the reduction is influenced by the reorganization of the geometry and the encapsulating effect. We suggest that protein structure imposed microenvironments may control the dielectric properties and hence the redox properties of the metal center in many metallobiomolecules. 相似文献
3.
Crystal structures of DMSO reductases isolated from two different sources and the crystal structure of related trimethylamine-N-oxide reductase indicate that the angle between the terminal oxo atom on the molybdenum and the serinato oxygen varies significantly. To understand the significance of this angular variation, we have synthesized two isomeric compounds of the heteroscorpionato ligand (L1OH) (cis- and trans-(L1O)Mo(V)OCl(2)), where the phenolic oxygen mimics the serinato oxygen donor. Density functional and semiempirical calculations indicate that the trans isomer is more stable than the cis. The lower stability of the cis isomer can be attributed to two factors. First, a strong antibonding interaction between the phenolic oxygen with molybdenum d(xy) orbital raises the energy of this orbital. Second, the strong trans influence of the terminal oxo group in the trans isomer places the phenol ring, and hence the bulky tertiary butyl group, in a less sterically hindered position. In solution, the cis isomer spontaneously converts to the thermodynamically favorable trans isomer. This geometric transformation follows a first-order process, with an enthalpy of activation of 20 kcal/mol and an entropy of activation of -9 cal/mol K. Computational analysis at the semiempirical level supports a twist mechanism as the most favorable pathway for the geometric transformation. The twist mechanism is further supported by detailed mass spectral data collected in the presence of excess tetraalkylammonium salts. Both the cis and trans isomers exhibit well-defined one-electron couples due to the reduction of molybdenum(V) to molybdenum(IV), with the cis isomer being more difficult to reduce. Both isomers also exhibit oxidative couples because of the oxidation of molybdenum(V) to molybdenum(VI), with the cis isomer being easier to oxidize. This electrochemical behavior is consistent with a higher-energy redox orbital in the cis isomer, which has been observed computationally. Collectively, this investigation demonstrates that by changing the O(t)-Mo-O(p) angle, the reduction potential can be modulated. This geometrically controlled modulation may play a gating role in the electron-transfer process during the regeneration steps in the catalytic cycle. 相似文献
4.
《Journal of Coordination Chemistry》2012,65(15):1387-1393
Complexes of general formula [ReOX2{(C5H4N)CH(O)CH2(C5H4N)}] (X?=?Cl,?I) were prepared by reaction of trans-[ReOCl3(PPh3)2] and trans-[ReOI2(OEt)(PPh3)2] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. The coordinated DPE ligand undergoes addition of water at the ethylenic carbon atoms, and the (C5H4N)CH(O)CH2(C5H4N) moiety acts as a uninegative terdentate N,O,N-donor ligand. X-ray crystal structures of both complexes have been determined and show distorted octahedral geometry at the rhenium(V) centre. 相似文献
5.
Kanney JA Noll BC Rakowski DuBois M 《Journal of the American Chemical Society》2002,124(33):9878-9886
The thermal reactions of the Re(V) dithiolate complex Cp'ReCl2(SCH2CH2S), 1 (where Cp' = EtMe4C5), and related derivatives have been studied. When 1 is heated in toluene in a sealed evacuated tube at 100 degrees C, a dehydrogenation reaction occurs to form a new rhenium complex with a dithiolene ligand, Cp'ReCl2(SCHCHS), 6, in ca. 40% yield. The structure of 6 has been confirmed by an X-ray diffraction study. Under the thermal conditions studied, 1 also undergoes an olefin extrusion reaction. Free ethene is detected in the NMR spectrum of the products, and insoluble rhenium products are also formed. When 1 is reacted with excess ethene under mild conditions, a new organic product, 1,4-dithiane, is formed. Complex 1 is also found to react with oxidants, such as O2 and S8, under mild conditions to form the dehydrogenation product 6. Kinetic studies of the thermal reaction of 1 and related derivatives have been completed, and possible mechanisms for the thermally induced dehydrogenation reaction are discussed. 相似文献
6.
Kundu S Thompson JV Ryabov AD Collins TJ 《Journal of the American Chemical Society》2011,133(46):18546-18549
Ferric tetraamido macrocyclic ligand (TAML)-based catalysts [Fe{C(6)H(4)-1,2-(NCOCMe(2)NCO)(2)CR(2)}(OH(2))]PPh(4) [1; R = Me (a), Et (b)] are oxidized by m-chloroperoxybenzoic acid at -40 °C in acetonitrile containing trace water in two steps to form Fe(V)oxo complexes (2a,b). These uniquely authenticated Fe(V)(O) species comproportionate with the Fe(III) starting materials 1a,b to give μ-oxo-(Fe(IV))(2) dimers. The comproportionation of 1a-2a is faster and that of 1b-2b is slower than the oxidation by 2a,b of sulfides (p-XC(6)H(4)SMe) to sulfoxides, highlighting a remarkable steric control of the dynamics. Sulfide oxidation follows saturation kinetics in [p-XC(6)H(4)SMe] with electron-rich substrates (X = Me, H), but changes to linear kinetics with electron-poor substrates (X = Cl, CN) as the sulfide affinity for iron decreases. As the sulfide becomes less basic, the Fe(IV)/Fe(III) ratio at the end of reaction for 2b suggests a decreasing contribution of concerted oxygen-atom transfer (Fe(V) → Fe(III)) concomitant with increasing electron transfer oxidation (Fe(V) → Fe(IV)). Fe(V) is more reactive toward PhSMe than Fe(IV) by 4 orders of magnitude, a gap even larger than that known for peroxidase Compounds I and II. The findings reinforce prior work typecasting TAML activators as faithful peroxidase mimics. 相似文献
7.
The rhenium(V) monooxo complexes (hoz)2Re(O)Cl (1) and [(hoz)2Re(O)(OH2)][OTf] (2) have been synthesized and fully characterized (hoz = 2-(2'-hydroxyphenyl)-2-oxazoline). A single-crystal X-ray structure of 2 has been solved: space group = P1, a = 13.61(2) A, b = 14.76(2) A, c = 11.871(14) A, alpha = 93.69(4) degrees, beta = 99.43(4) degrees, gamma = 108.44(4) degrees, Z = 4; the structure was refined to final residuals R = 0.0455 and Rw = 0.1055. 1 and 2 catalyze oxygen atom transfer from aryl sulfoxides to alkyl sulfides and oxygen-scrambling between sulfoxides to yield sulfone and sulfide. Superior catalytic activity has been observed for 2 due to the availability of a coordination site on the rhenium. The active form of the catalyst is a dioxo rhenium(VII) intermediate, [Re(O)2(hoz)2]+ (3). In the presence of sulfide, 3 is rapidly reduced to [Re(O)(hoz)2]+ with sulfoxide as the sole organic product. The transition state is very sensitive to electronic influences. A Hammett correlation plot with para-substituted thioanisole derivatives gave a reaction constant rho of -4.6 +/- 0.4, in agreement with an electrophilic oxygen transfer from rhenium. The catalytic reaction features inhibition by sulfides at high concentrations. The equilibrium constants for sulfide binding to complex 2 (cause of inhibition), K2 (L x mol(-1)), were determined for a few sulfides: Me2S (22 +/- 3), Et2S (14 +/- 2), and tBu2S (8 +/- 2). Thermodynamic data, obtained from equilibrium measurements in solution, show that the S=O bond in alkyl sulfoxides is stronger than in aryl sulfoxides. The Re=O bond strength in 3 was estimated to be about 20 kcal x mol(-1). The high activity and oxygen electrophilicity of complex 3 are discussed and related to analogous molybdenum systems. 相似文献
8.
Pilar Alonso Isabel de Frutos Teresa Gutiérrez Antonio Doadrio López 《Transition Metal Chemistry》1987,12(2):133-136
Summary The synthesis and the dinuclear or mononuclear nature of several molybdenum(VI) and molybdenum(V) oxocomplexes derived from 1,3-diphenyl-1,3-propanedione (HLL) are described. These complexes were identified by i.r. and electronic spectra, magnetic susceptibility and analytical data, and are assigned the following formulae: [MoO2(LL)2], [Mo2O5(LL)2], [Mo2O4(LL)2], [MoOCl(LL)2], [MoCl2(LL)] and [MoO(OH)(LL)2)]. The low magnetic moments of the dinuclear complexes are due, in part, to intramolecular interactions. The i.r. data show that the dionate is bound by two oxygen atoms forming a chelate six-membered ring. 相似文献
9.
Schweinfurth D Demeshko S Khusniyarov MM Dechert S Gurram V Buchmeiser MR Meyer F Sarkar B 《Inorganic chemistry》2012,51(14):7592-7597
The 'Click'-derived tripodal ligand tris[(1-benzyl-1H-1,2,3-triazole-4-yl)methyl]amine, tbta, was used to synthesize the complexes [Fe(tbta)Cl]BF(4), 1, and [Co(tbta)Cl]BF(4), 2. Both complexes were characterized by (1)H NMR spectroscopy and elemental analysis. Single-crystal X-ray structural determination of 2 shows a 4 + 1 coordination around the cobalt(II) center with a rather long bond between Co(II) and the central amine nitrogen atom of tbta. Such a coordination geometry is best described as capped tetrahedral. 1 and 2 are thus the first examples of pseudotetrahedral coordinated Fe(II) and Co(II) complexes with tbta. A combination of SQUID susceptometry, EPR spectroscopy, M?ssbauer spectroscopy, and DFT calculations was used to elucidate the electronic structures of these complexes and determine the spin state of the metal center. Comparisons are made between the complexes presented here with related complexes of other ligands such as tris(2-pyridylmethyl)amine, tmpa, hydrotris(pyrazolyl) borate, Tp, and tris(2-(1-pyrazolyl)methyl)amine, amtp. 1 and 2 were tested as precatalysts for the homopolymerization of ethylene, and both complexes delivered distinctly different products in this reaction. Blind catalyst runs were carried out with the metal salts to prove the importance of the tripodal ligand for product formation. 相似文献
10.
Yamamoto T Toganoh M Furuta H 《Dalton transactions (Cambridge, England : 2003)》2012,41(30):9154-9157
N-Confused porphyrin oxorhenium(V) complexes were prepared and their X-ray structures were elucidated. The oxorhenium(V) complexes can transfer oxygen atom from pyridine N-oxide to triphenylphosphine, in which unique cooperation between metal and ligand was observed. 相似文献
11.
The mechanism of nitrogen atom transfer from four-coordinate tris(carbene)borate iron(IV) nitrido complexes to phosphines and phosphites has been investigated. In the absence of limiting steric effects, the rate of nitrogen atom transfer to phosphines increases with decreasing phosphine σ-basicity. This trend has been quantified by a Hammett study with para-substituted triarylphosphines, and is contrary to the expectations of an electrophilic nitrido ligand. On the basis of electronic structure calculations, a dual-nature transition state for nitrogen atom transfer is proposed, in which a key interaction involves the transfer of electron density from the nitrido highest occupied molecular orbital (HOMO) to the phosphine lowest unoccupied molecular orbital (LUMO). Compared to analogous atom transfer reactions from a 5d metal, these results show how the electronic plasticity of a 3d metal results in rapid atom transfer from pseudotetrahedral late metal complexes. 相似文献
12.
A. A. Markov S. P. Dolin N. I. Moiseeva A. E. Gekhman I. I. Moiseev 《Russian Journal of Inorganic Chemistry》2011,56(5):738-744
The addition of a water molecule to mono-, di-, and triperoxovanadium(V) complexes has been studied at the density functional theory (B3LYP/6-31G**) and Møller-Plesset perturbation theory (MP2/6-31G**) levels. It has been demonstrated that the H2O…V donor-acceptor interaction cannot compete with hydrogen bonds and becomes weaker with an increase in the number of peroxo groups in the complex. In the most stable isomers of aquaperoxo complexes, water is mainly held by intermediate hydrogen bonds. The energy of addition of a water molecule to peroxovanadate is lower than or close to the heat of evaporation of water; i.e., the formation of stable aquaperoxovanadium complexes in aqueous solutions is improbable. This conclusion is consistent with the mass spectra of aqueous solutions of peroxovanadates, which show that the concentration of water-free peroxo complexes considerably exceeds the concentration of complexes with a coordinated water molecule. The coordination of the water molecule through the V…OH2 donor-acceptor interaction is prevented by the cis effect of the peroxo group, which has the HOMO orbital of symmetry suitable for interaction with the LUMO orbital of the VO group. 相似文献
13.
14.
Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H2L1) in methanol with aqueous NH4VO3 solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL1(MeOH)]·ClO4 (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H2L1) with aqueous solution of VOSO4 leads to the formation of di-(μ-oxo) bridged vanadium(V) complex [VO2L2]2 (2) as green solid where HL2 = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL2 is generated in situ by the hydrolysis of one of the imine bonds of HL1 ligand during the course of formation of complex [VO2L2]2 (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H2O2 and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by 1H NMR spectroscopic studies. 相似文献
15.
The reaction of Re(NC6H4R)Cl3(PPh3)2 (R = H, 4-Cl, 4-OMe) with 1,2-bis(diphenylphosphino)ethane (dppe) is investigated in refluxing ethanol. The reaction produces two major products, Re(NC6H4R)Cl(dppe)(2)2+ (R = H, 1-H; R = Cl, 1-Cl; R = OMe, 1-OMe) and the rhenium(III) species Re(NHC6H4R)Cl(dppe)2+ (R = H, 2-H; R = Cl, 2-Cl). Complexes 1-H (orthorhombic, Pcab, a = 22.3075(10) A, b = 23.1271(10) A, c = 23.3584(10) A, Z = 8), 1-Cl (triclinic, P1, a = 11.9403(6) A, b = 14.6673(8) A, c = 17.2664(9) A, alpha = 92.019(1) degrees, beta = 97.379(1) degrees, gamma = 90.134(1) degrees, Z = 2), and 1-OMe (triclinic, P1, a = 11.340(3) A, b = 13.134(4) A, c = 13.3796(25) A, alpha = 102.370(20) degrees, beta = 107.688(17) degrees, gamma = 114.408(20) degrees, Z = 1) are crystallographically characterized and show an average Re-N bond length (1.71 A) typical of imidorhenium(V) complexes. There is a small systematic decrease in the Re-N bond length on going from Cl to H to OMe. Complex 2-Cl (monoclinic, Cc, a = 24.2381(11) A, b = 13.4504(6) A, c = 17.466(8) A, beta = 97.06900(0) degrees, Z = 4) is also crystallographically characterized and shows a Re-N bond length (1.98 A) suggestive of amidorhenium(III). The rhenium(III) complexes exhibit unusual proton NMR spectra where all of the resonances are found at expected locations except those for the amido protons, which are at 37.8 ppm for 2-Cl and 37.3 ppm for 1-H. The phosphorus resonances are also unremarkable, but the 13C spectrum of 2-Cl shows a significantly shifted resonance at 177.3 ppm, which is assigned to the ipso carbon of the phenylamido ligand. The extraordinary shifts of the amido hydrogen and ipso carbon are attributed to second-order magnetism that is strongly focused along the axially compressed amido axis. The reducing equivalents for the formation of the Re(III) product are provided by oxidation of the ethanol solvent, which produces acetal and acetaldehyde in amounts as much as 30 equiv based on the quantity of rhenium starting material. Equal amounts of hydrogen gas are produced, suggesting that the catalyzed reaction is the dehydrogenation of ethanol to produce acetaldehyde and hydrogen gas. Metal hydrides are detected in the reaction solution, suggesting a mechanism involving beta-elimination of ethanol at the metal center. Formation of the amidorhenium(III) product possibly arises from migration of a metal hydride in the imidorhenium(V) complex. 相似文献
16.
17.
18.
19.
Six new organoantimony(V) complexes containing various isomers of fluoromethylbenzoate ligands [RC6H3COO]2SbPh3 and [RC6H3COO]SbPh4 [R = 3-F-4-(CH3) (1, 4), 4-F-2-(CH3) (2, 5), 5-F-2-(CH3) (3, 6)] have been synthesized by the reactions of triphenylantimony(V) dichloride or tetraphenylantimony(V) bromide with various isomers of fluoromethylbenzoate ligands in 1:2 or 1:1 stoichiometries. All the complexes have been characterized by elemental analysis, IR and NMR [1H, 13C and 19F] studies. The crystal structures of complexes 1, 3, 4, 5 and 6 have been determined by X-ray single crystal diffraction. The structure of complexes show that the five-coordinated antimony(V) atom adopts a distorted trigonal bipyramidal geometry. Furthermore, weak but significant intermolecular C–H···O, C–H···F hydrogen bonds, C–H···pi stacking lead to aggregation and assembly of these complexes into 1D and 2D supramolecular frameworks. 相似文献
20.
AbstractVanadium complexes are attractive candidates for anticancer chemotherapy, although often suffering from rich aqueous chemistry and hydrolytic instability. We have introduced an LVO family of vanadium oxo complexes, L being a diaminotris(phenolato) chlelating ligand, demonstrating high hydrolytic stability in water along with promising in vitro and in vivo efficacy. Herein we analyzed mechanistic aspects of the reactivity of such complexes in cellular environment. A representative complex exhibited high activity toward all lines in the NIH NCI-60 panel, with an average GI50 value of 0.7 ± 0.5 μM, and with a unique reactivity pattern implying a distinct mechanism. Free ligands demonstrated cytotoxicity similar to that of their vanadium complexes, were identified in cells treated with the complex, and induced apoptosis as did the parent complex, all implying their participation as active species. Cell cycle studies pointed to possible arrest mostly at the S phase, with some variations for the complex and ligand on the two lines analyzed. Nevertheless, the vanadium ion apparently accelerated cellular entry, as the activity was evident following markedly shorter periods of incubation with the extracellular complex when compared with the free ligand. The results displayed herein overall highlight the role of the vanadium complex as a pro-drug. 相似文献