Effects of phenoxide ligation on iron-sulfur clusters. Preparation and properties of [Fe4S4 (OAr) 4] 2-ions and the structure of bis (tetraethylammonium) tetrakis (phenolatosulfidoferrate)([(C2H5) 4N] 2 [Fe4S4 (OC6H5) 4]) (original) (raw)
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Inorganic Chemistry, 1984
The phenoxide-ligated dinuclear ironsulfur clusters [Fe2S2(OAr),12-(I, Ar = phenyl; 11, Ar = p-tolyl; 111, Ar = p-C6H4C1) have been synthesized by two methods: (i) reaction of FeCI3, NaOAr, and Li2S in acetonitrile; (ii) reaction of [FeZS2C1,]*with NaOAr in acetonitrile. The preparation, reactivity, and electronic properties of these compounds are described.
1992
New thioether complexes of iron(tt) have been prepared: [Fe(MeCN),([14]aneS4)] [Fel,] ([14]aneS, = 1,4,8,11 -tetrathiacyclotetradecane), [Fe( [l 6]aneS,)]X, ([l GIaneS, = 1 5 9 . 1 3-tetrathiacyclohexadecane) and [Fe(MeSCH,CH,SMe),X,] (X = Br or I). The crystal structure of [Fe([lG]aneS,)]I, and Mossbauer properties of [Fe ( [l 6]aneS,) JX, are consistent with their formulation as unusual squareplanar, high-spin iron(ii) complexes. This peculiarity is ascribed to the size of [16]aneS, which forces longer than normal Fe-S bonds on the system. The possibility that iron rather than molybdenum might be at the active centre of nitrogenase has stimulated us to attempt to reproduce the dinitrogen chemistry exhibited by molybdenum, but on iron.' We have previously explored the chemistry of iron(ir) halides with diphosphines to establish a suitable basis for this research.' However, we are all too frequently made aware that metal ions in biological systems are never ligated by tertiary phosphines, and that sulfur (generally as sulfide) is likely to be the predominant ligand species. There is an extensive (mainly cluster) chemistry of iron ligated by sulfide and/or thi~late,~ which we did not wish to enter. We report here on iron(i1) complexes with thioethers, which were intended to be a first step towards preparing iron@) thioether dinitrogen complexes.
Inorganic Chemistry, 2003
Tetrahedral FeCl[N(SiMe 3) 2 ] 2 (THF) (2), prepared from FeCl 3 and 2 equiv of Na[N(SiMe 3) 2 ] in THF, is a useful ferric starting material for the synthesis of weak-field iron−imide (Fe−NR) clusters. Protonolysis of 2 with aniline yields azobenzene and [Fe 2 (µ-Cl) 3 (THF) 6 ] 2 [Fe 3 (µ-NPh) 4 Cl 4 ] (3), a salt composed of two diferrous monocations and a trinuclear dianion with a formal 2 Fe(III)/1 Fe(IV) oxidation state. Treatment of 2 with LiCl, which gives the adduct [FeCl 2 {N(SiMe 3) 2 } 2 ]-(isolated as the [Li(TMEDA) 2 ] + salt), suppresses arylamine oxidation/iron reduction chemistry during protonolysis. Thus, under appropriate conditions, the reaction of 1:1 2/LiCl with arylamine provides a practical route to the following Fe−NR clusters: [Li 2 (THF) 7 ][Fe 3 (µ-NPh) 4 Cl 4 ] (5a), which contains the same Fe−NR cluster found in 3; [Li(THF) 4 ] 2 [Fe 3 (µ-N-p-Tol) 4 Cl 4 ] (5b); [Li(DME) 3 ] 2 [Fe 2 (µ-NPh) 2 Cl 4 ] (6a); [Li 2 (THF) 7 ][Fe 2 (µ-NMes) 2 Cl 4 ] (6c). [Li(DME) 3 ] 2 [Fe 4 (µ 3-NPh) 4 Cl 4 ] (7), a trace product in the synthesis of 5a and 6a, forms readily as the sole Fe−NR complex upon reduction of these lower nuclearity clusters. Products were characterized by X-ray crystallographic analysis, by electronic absorption, 1 H NMR, and Mössbauer spectroscopies, and by cyclic voltammetry. The structures of the Fe−NR complexes derive from tetrahedral iron centers, edge-fused by imide bridges into linear arrays (5a,b; 6a,c) or the condensed heterocubane geometry (7), and are homologous to fundamental iron−sulfur (Fe−S) cluster motifs. The analogy to Fe−S chemistry also encompasses parallels between Fe-mediated redox transformations of nitrogen and sulfur ligands and reductive core conversions of linear dinuclear and trinuclear clusters to heterocubane species and is reinforced by other recent examples of iron− and cobalt−imide cluster chemistry. The correspondence of nitrogen and sulfur chemistry at iron is intriguing in the context of speculative Fe-mediated mechanisms for biological nitrogen fixation.
Organometallics, 1991
Reaction of Fe(dppe)Cl (dppe = 1,2-bis(diphenylphosphino)ethane) with LiCp* (Cp* = q5-pentamethylcylopentadienyl) in %HF yields Fe(Cp*)(dppe)Cl (1). The X-ray crystal structure of 1 shows that it crystallizes in the triclinic space group P1 with unit cell parameters a = 10.410(7) A, b = 10.987(3) A, c = 16.872 (4) A, a = 80.43 (2)O, 0 = 94.28 (5)O, y = 70.92 (5)O, and 2 = 2. The structure was solved and refined (5732 reflections) to the final residual values R = 0.37 and R, = 0.36. Compound 1 reacts with LiI and LiCH3 to afford respectively Fe(Cp*)(dppe)I (2) and Fe(Cp*)(dppe)CH3 (4). The hydride Fe-(Cp*)(dppe)H (3) can be obtained by reaction of 1 with LiA1H4 or by direct preparation in 50% yield from Cp*H and Fe(dppe)C12 reduced by a sonochemically (20 kHz) activated colloidal dispersion of potassium metal. The alkyl derivatives (Fe(Cp*)(dppe)R (R = CH3 (4) and CHzOCH3 (5)) are synthesized from FeCp*(C0)2R upon CO displacement by ultraviolet (UV) photolysis and trapping with dppe. Cyclic voltammetry (CV) reveals a reversible one-electron oxidation process for all these neutral iron(I1) compounds including the hydride (3). Ferrocenium and trityl salts as well as molecular oxygen can be used to synthesize the halide and alkyl 17-electron [Fe(Cp*)(dppe)X]PF, complexes in 9045% yield. ESR, Mdssbauer, and NMR experiments indicate that the Cp* ring and the alkyl or halide ligands contribute significantly to the delocalization of the odd electron. EHMO calculations on the [F~(CP)(PH~)~CH OH]'+ model are fully consistent with this finding: the singly occupied HOMO, of predominantly x2 -$character, is found to be 52% localized on the metal, 28% on Cp, and 15% on CHzOH. Magnetic susceptibility obeys the modified CurieWeiss expression, and the important values of pB observed are attributed to an orbital contribution. The low and negative values observed for 8 characterize these complexes as having short-distance dominant antiferromagnetic interactions. (1) (11) (a) Roger, C.; Marseille, P.; Salus, C.; Hamon, J.-R.; Lapinte, C. J. Organornet. Chem. 1987, 336, C13. (b) Morrow, J.; Catheline, D.; Desbois, M. H.; Manriquez, J. M.; Ruiz, J.; Astruc, D. Organometallics 1987. 6. 2605. (c) Desbois. M. H.; Nunn. C. M.: Cowlev, A. H.; Astruc, D.
Journal of The Chemical Society-dalton Transactions, 1992
New thioether complexes of iron(tt) have been prepared: [Fe(MeCN),([14]aneS4)] [Fel,] ([14]aneS, = 1,4,8,11 -tetrathiacyclotetradecane), [Fe( [l 6]aneS,)]X, ([l GIaneS, = 1 5 9 . 1 3-tetrathiacyclohexadecane) and [Fe(MeSCH,CH,SMe),X,] (X = Br or I). The crystal structure of [Fe([lG]aneS,)]I, and Mossbauer properties of [Fe ( [l 6]aneS,) JX, are consistent with their formulation as unusual squareplanar, high-spin iron(ii) complexes. This peculiarity is ascribed to the size of [16]aneS, which forces longer than normal Fe-S bonds on the system. The possibility that iron rather than molybdenum might be at the active centre of nitrogenase has stimulated us to attempt to reproduce the dinitrogen chemistry exhibited by molybdenum, but on iron.' We have previously explored the chemistry of iron(ir) halides with diphosphines to establish a suitable basis for this research.' However, we are all too frequently made aware that metal ions in biological systems are never ligated by tertiary phosphines, and that sulfur (generally as sulfide) is likely to be the predominant ligand species. There is an extensive (mainly cluster) chemistry of iron ligated by sulfide and/or thi~late,~ which we did not wish to enter. We report here on iron(i1) complexes with thioethers, which were intended to be a first step towards preparing iron@) thioether dinitrogen complexes.
Journal of the Chemical Society, Dalton Transactions
The compound [NMe4],[Fe,S4(SCH,CH20H),] is triclinic, space group P i , with a = 10.686(9), b = 11.288(8), c = 15.021(11) A, a = 99.0(1), (3 = 91.8(1), y = 108.4(1)",andZ = 2. 2 115 Independentreflections measured on a diffractometer have been refined to R = 0.088. The anion contains the Fe, S, cubane-like cluster core distorted from Td symmetry such that four approximately parallel Fe-S bonds are shorter (mean 2.239 A) than the other eight (mean 2.306 A). There are two strong intermolecular 0-* * H-0 hydrogen bonds (0 * 0 2.63, 2.70 A) and there may be an intermolecular S H-0 hydrogen bond(S-0 3.16 A). Carbon-13 n.m.r. (90 MHz) spectra have been recorded for the title compound in dimethyl sulphoxide solution between 31 7 and 363 K; the resonance position of thiolate carbon was observed between 103.3 and 106.4 p.p.m. downfield of SiMe,. The anion [Fe,S,-(SCH2CH,0H),l3-, generated by dithionite treatment of the title compound in buffered aqueous solution containing excess of 2-hydroxyethanethiol and stabilised by rapid freezing, exhibits an axially symmetric e.s.r. spectrum with 9 1 1 = 2.045 and gl = 1.929 (5 = 1.967) ; similar treatment of the title compound with K,[Fe(CN),] also generated a species having an axially symmetric e.s.r. spectrum, with gll = 1.963 and gl = 2.006. M13 9PL COMPLEXES of the type [Fe4S4(SR),l2-, the synthetic analogues of the four-and eight-iron ferredoxin proteins, continue to be studied in detail and the variation in the redox potentials of [4Fe-4S] centres in proteins is of particular interest. The midpoint reduction potential of the (equivalent of the) 2-13-couple has been observed to vary from-280 mV (vs. standard hydrogen electrode, s.h.e.) in Bacillus stearothermophilus ferredoxin to-490 mV in Chromatiurn vinosum 2[4Fe-4S] f e r r e d~x i n .~ The potential of this couple in C. vinosum high-potential iron-sulphur protein (HiPIP) is presumably even lower and has not been measured in aqueous s~l u t i o n .~ Clostridium pasteurianum 2 [4Fe-4S] protein had midpoint reduction potentials of ca.-405 mV, similar to those of the corresponding couples of Peptococcus aerogenes 2[4Fe-4S] f e r r e d~x i n ,~ and the former protein has been shown6 to have very similar redox potentials to [Fe,S4(SR),I2-{R = CH,CH,OH or R,S)-CH,CH[NH(COMe)]CONHMe) complexes in water-dmso (dmso = dimethyl sulphoxide) media. These observations together with the near structural congruency of the [4Fe4S] centres of P. aerogenes ferredoxin and [Fe,S,(SR),]"-(n = 2, R = P h or CH,Ph; n = 6, R = CH,CH,CO, lo) complexes suggest that those ferredoxins employing the 2-/3-couple at a potential significantly different from-400 mV do so due to structural and/or electronic influences of the protein. One important influence could be the hydrogen bonding, detected in P. aerogenes ferredoxin l1 C. vinosum
Inorganica Chimica Acta, 2003
The synthesis and characterization of the trifluoromethanesulfonato derivatives of bis(dimethylphenylphosphonite)tetrakis(phenyl)chlorinatoiron(III), and bis(diethylphenylphosphonite)tetrakis(phenyl)chlorinatoiron(III) are reported: [Fe(TPC)(P-Ph(OMe) 2) 2 ]CF 3 SO 3 (1) and [Fe(TPC)(PPh(OEt) 2) 2 ]CF 3 SO 3 (2). The 1 H NMR isotropic shifts at 20 8C of the different pyrrole protons of 1 varied from 10.9 and 5.55 ppm to (/11.5 ppm rather than the expected 0.6 ppm to (/57.8 ppm, based on previously studied dimethylphenylphosphine complexes of low-spin iron chlorins. The EPR spectrum of [Fe(TPC)(PPh(OMe) 2) 2 ]CF 3 SO 3 (1) in solution is rhombic and shows the principal g-values g 1 0/2.44, g 2 0/2.16 and g 3 0/1.82, ag 2 0/13.9. These spectroscopic observations are indicative of a metal-based electron for 1 with a (d xz , d yz) 4 (d xy) 1 ground state at any temperature in contrast to [Fe(TPC) (PPh(Me) 2) 2 ]CF 3 SO 3 complex which showed a (d xy) 2 (d xz d yz) 3 ground state at any temperature.
Journal of the American Chemical Society, 1993
Fe(I1) and Fe(1) u-alkynyl complexes of the general formula [(PP3)Fe(C=CR)]"+ (n = 1, 0) have been synthesized as BPh4-salts or neutral molecules and characterized by chemical, spectroscopic, X-ray, and electrochemical techniques [R = Ph, SiMe3, n-CjH7, n-C5HII, CMe3; PP3 = P(CH2CH*PPh2)3]. All of the compounds undergo electron-transfer reactions that encompass Fe(O), Fe(I), Fe(II), and Fe(II1) oxidation states of the metal. X-ray crystal structures of the 16-and 17-electron complexes [(PP3)Fe(C=-CPh)]BPhgC4H8O and [(PP3)Fe(C=CPh)] have been determined. The Fe(I1) compound crystallizes in the space group P2,/c, and the cation assumes an almost regular trigonal-bipyramidal structure with the alkynyl ligand trans to the bridgehead phosphorus atom of PP3 (P4-Fe-C7 bond angle = 177.2(6)'). The Fe(1) compound crystallizes in the space group P2,/n and assumes a strongly distorted trigonal-bipyramidal structure with the Pd-Fe-C, bond angle of 170.3(3)' and equatorial bond angles of 143.9(1)O, 102.4(1)O, and 1 1 1. 1 (1)O. A decrease in the Fe-P bond distances on going from Fe(I1) to Fe(1) is interpreted in terms of significant metalphosphorus r-back-bonding. In contrast, from a perusal of IR, structural, and electrochemical data, no significant d r (metal)r* (alkynyl) interaction occurs. All compounds are paramagnetic and have been characterized by X-band ESR spectroscopy (powder, frozen solution, fluid solution). The powder and frozen solution spectra of the Fe(1) alkynyls are interpreted in terms of S = ' / 2 and a rhombic g tensor. The fluid solution spectra show that the compounds exist in tetrahydrofuran solution as two isomeric formsexhibiting distorted trigonal-bipyramidal structures in a ratio that depends on the temperature. The ESR spectra of the Fe(1I) derivatives (powder and frozen solution) display unresolved line shape consistent with a S = 1 Hamiltonian with noticeable zero-field splitting effects at room temperature. q6-C6R6,5 q3-C8H136). To the best of our knowledge, no stable iron-(I) compound with a u-hydrocarbyl has ever been reported. In this paper, we describe the synthesis, the X-band ESR characterization, and the electrochemical behavior of a family of d7 low-spin u-alkynyl Fe(1) complexes of the general formula [(PP3)Fe(CWR)] (PP3 = P(CH2CH2PPh2)j; R = Ph, SiMe3, n-C3H7, n-CsHI I , CMe3).
Inorganic Chemistry, 2015
Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph 2 P) 2 N(CH 2 ) 3 SMe (1) and (Ph 2 P) 2 N(p-C 6 H 4 )SMe (2), the Fe(II) complexes [FeCl2(1)] n (3), [FeCl 2 (2)] 2 (4), [Fe(OAc)(1) 2 ]PF 6 (5), and [Fe(OAc)(2) 2 ]PF 6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,Ppseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe−P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl 2 (SR 2 ){R 2 1 PN(R 2 )P′R 2 3 }] (R = H, Me; R 1 , R 2 , and R 3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe−P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe−P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra-and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.