Formation of paramagnetic mononuclear iron nitrosyl complexes from diamagnetic di- and tetranuclear iron-sulphur nitrosyls: characterisation by EPR spectroscopy and study of thiolate and nitrosyl ligand exchange reactions

The diamagnetic Roussin esters Fe₂(SR)₂(NO)₄ readily underwent exchange with thiols R′SH to yield Fe₂(SR′)₂(NO)₄: the exchange was faster in polar, coordinating solvents where paramagnetic, mononuclear complexes of types [Fe(NO)₂(solvent)₂]⁺ and Fe(NO) ₂(SR)(solvent) were formed. With the corresponding thiolate anions RS^-, the esters Fe₂(SR)₂(NO)₄ formed the mononuclear complexes [Fe(SR)₂(NO)₂]^-, which were fully characterised by EPR spectroscopy for R = H, Me, Et, i-Pr, t-Bu and PhCH₂: assignments of hyperfine couplings were confirmed by use of ¹⁵N. With Fe₂(SR)₂(NO)₄ and a different set of thiolate anion, R′S ^-, in excess, thiol exchange occurred to give [Fe(SR′)₂(NO)₂]^-. A mechanism for formation of Fe₂(SR′)₂(NO)₄ from Fe₂(SR)₂(NO)₄ has been proposed. The paramagnetic mononuclear complexes [Fe(SR)₂(NO)₂] were also readily formed from the diamagnetic clusters [Fe₄S₃(NO)₇]^- and Fe₄S₄(NO)₄, together with [Fe(SR)₃(NO)]^-, and additionally from [Fe(CO)₃NO]^-. [Fe(SMe)₂(NO)₂]^-. was found to be a precursor of isolable Fe₂(SMe)₂(NO)₄, and [Fe(SH)₂ (NO)₂]^- to be the common precursor of both Roussin′s red anion [Fe₂S₂(NO)₄]^- and Roussin's black anion [Fe₄S₃ (NO)₇]^- interconvertible by appropriate adjustment of pH. The nitrosyl groups in these complexes were freely labile, and mononitrosyliron and dinitrosyliron fragments were readily interconvertible: FE(NO) fragments were favoured by the dimethyldithiocarbamate ligand (Me₂NCS ₂) and Fe(NO)₂ fragments by thiolate ligands, RS^-, regardless of the origin of the Fe(NO)_x(x = 1,2) fragment: both mono- and dinitrosyliron complexes persisted with [(i-PrO)₂S₂]^- as ligand. Isotopic labelling showed the occurrence of rapid exchange of nitrogen between nitrosyl ligands and added nitrite in Fe(NO)(S₂CNMe₂)₂ and [Fe(SR)₂(NO)₂]^-     

Reactions of bis-μ-iodo-bis(dinitrosyliron) with halide ions and with thiols: An electron paramagnetic resonance study

Solutions of Fe₂(NO)₄I₂ in DMF exhibit EPR spectra characteristic of [Fe(NO)₂]⁺ at concentrations of 2 x 10^?4 mol dm^?3, and of an equilibrium mixture of [Fe(NO)₂⁺, Fe(NO)₂I, and [Fe(NO)₂I₂]^? at higher concentrations: in THF solutions only Fe(NO)₂I is observed, regardless of concentration. Addition of excess halide ions X^? (X=Cl, Br, I) to the DMF solution yields [Fe(NO)₂X₂]^?, but addition of excess I^? or Br^? to the THF solution yields [Fe(NO)₂I₂^? or Fe₂(NO)₄Br₂ respectively. In mixed THF/Et₃N solutions, mixtures of [Fe(NO)₂]⁺, Fe(NO)₂I, and [Fe(NO)₂I₂]^? are again formed, and subsequent addition of a thiol RSH causes formation of [Fe(NO)₂(SR)₂]^?, a precursor of Fe₂(NO)₄(SR)₂. A scheme is suggested to describe the steps in the preparatively useful conversion of Fe₂(NO)₄I₂ into Fe₂(NO)₄(SR)₂.     

Electron‐Rich Diferrous–Phosphane–Thiolates Relevant to Fe‐only Hydrogenase: Is Cyanide “Nature's Trimethylphosphane”?

The two‐step one‐pot oxidative decarbonylation of [Fe₂(S₂C₂H₄)(CO)₄(PMe₃)₂] ( 1 ) with [FeCp₂]PF₆, followed by addition of phosphane ligands, led to a series of diferrous dithiolato carbonyls 2 – 6 , containing three or four phosphane ligands. In situ measurements indicate efficient formation of 1 ²⁺ as the initial intermediate of the oxidation of 1 , even when a deficiency of the oxidant was employed. Subsequent addition of PR₃ gave rise to [Fe₂(S₂C₂H₄)(μ‐CO)(CO)₃(PMe₃)₃]²⁺ ( 2 ) and [Fe₂(S₂C₂H₄)(μ‐CO)(CO)₂(PMe₃)₂(PR₃)₂]²⁺ (R=Me 3 , OMe 4 ) as principal products. One terminal CO ligand in these complexes was readily substituted by MeCN, and [Fe₂(S₂C₂H₄)(μ‐CO)(CO)₂(PMe₃)₃(MeCN)]²⁺ ( 5 ) and [Fe₂(S₂C₂H₄)(μ‐CO)(CO)(PMe₃)₄(MeCN)]²⁺ ( 6 ) were fully characterized. Relevant to the H_red state of the active site of Fe‐only hydrogenases, the unsymmetrical derivatives 5 and 6 feature a semibridging CO ligand trans to a labile coordination site.     

Synthesis, crystal structures, Mössbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

The iron-sulfur nitrosyl complexes A[Fe₄S₃(NO)₇], where A=Na⁺, NH₄ ⁺, or N(Bu ⁿ )₄ ⁺, and B₂[Fe₂S₂(NO)₄], where B=Na⁺, Cs⁺, or N(Buⁿ)₄ ⁺, were synthesized. Their structures and properties were studied by X-ray diffraction analysis, Mössbauer spectroscopy, and cyclic voltammetry. The effect of the crystal packing on the geometry of the tetranuclear NH₄[Fe₄S₃(NO)₇]·H₂O and binuclear Cs₂[Fe₂S₂(NO)₄]·2H₂O complexes was analyzed. The changes in the Fe⁵⁷ Mössbauer spectral parameters of the anion in the B₂[Fe₂S₂(NO)₄] series depend on the size of the B cation and agree with variations in the structural parameters of the Fe[S₂(NO)₂] chromophores as well as in the stretching vibrations of the NO groups caused by changes in intermolecular contacts. The presence of electronic states delocalized through the Fe?Fe bonds explains the fact that the electronic states of the Fe_a(S₃NO) and Fe_b(S₂(NO)₂) chromophores in the [Fe₄S₃(NO)₇]^? anion are nearly identical. The binuclear clusters are unstable upon storage in the solid phase and decompose in solutions to form the tetranuclear [Fe₄S₃(NO)₇]^? complexes, sulfur, and nitrogen oxides. The redox properties of the [Fe₄S₃(NO)₇]^? and [Fe₂S₂(NO₄)]^2? anions in CH₃CN and THF solutions were studied. The mechanism of reduction of the anion in the tetranuclear cluster is proposed.     

Nanoscale ensembles using building blocks inspired by the [FeFe]-hydrogenase active site

The hydrogenase model [Fe₂(S₂C₃H₆)(CN)₂(CO)₄]²⁻ was employed as a molecular tecton for the construction of supramolecular aggregates. IR spectroscopy indicated that cyanide bridged aggregates are formed when [Fe₂(S₂C₃H₆)(CN)₂(CO)₄]²⁻ was treated with Lewis acids such as Zn(tetraphenylporphyrinate), [Cu(NCMe)(2,2′-bipyridine)]PF₆ and [Cu(NCMe)₄]PF₆. Condensation of [Fe₂(S₂C₃H₆)(CN)₂(CO)₄]²⁻ with the tritopic Lewis acid [Cp¹Rh]²⁺ afforded the novel expanded tetrahedron cage, {[Fe₂(S₂C₃H₆)(CN)₂(CO)₄]₆[Cp¹Rh]₄}⁴⁻. The tetrahedron cage was characterized crystallographically as the PPN salt.     

Über Chalkogenolate. 179. Kupfer(I)-thioxanthate und Thioxanthatocuprate(I)

On Chalcogenolates. 179. Copper(I) Thioxanthates and Thioxanthatocuprates(I) Copper(I) thioxanthates Cu[S₂C? SR], where R = C₂H₅, ⁿC₄H₉, and CH₂? C₆H₅, have been prepared by two procedures and studied by means of diverse methods. They are soluble in ethanolic and acetonic solutions containing the corresponding [S₂C? SR]^? ions in excess to yield thioxanthatocuprates(I) [Cu_n(S₂C? SR)_n+1]^?. The compounds [(C₆H₅)₄P][Cu_n(S₂C? SC₂H₅)_n+1] with n = 1, 4, 6 have been isolated. The existence of [(C₆H₅)₄P][Cu₄(S₂C? SC₄H₉)₅] and [(C₆H₅)₄P][Cu₆(S₂C? SCH₂? C₆H₅)₇] has been ascertained.     

Variable-temperature and solvent NMR study of bis(μ2-methanethiolato)-bis(dinitrosyliron) and bis(μ2-methaneselenolato)-bis(dinitrosyliron)

The ¹H NMR spectrum of Fe₂(SMe)₂(NO)₄ has been measured in a total of 22 solvents, and the activation barrier ΔG^≠ for the C_2h?C_2v isomerisation in nine of these solvents. In aromatic solvents, the solvent-induced shifts are consistent with the formation of charge-transfer complexes, either 1:1 or 1:n; in non-aromatic, non-halogenated solvents of high dipolarity/polarizability the solvent-induced shifts follow the variation of the solvatochromic parameter, π*. The behaviour of Fe₂(SeMe)₂(NO)₄ in a limited range of solvents is similar. The activation barrier ΔG^≠ in Fe₂(SMe)₂(NO)₄ is ca 78 kJ mol^?1 in the majority of solvents, but that for Fe₂(SeMe)₂(NO)₄ is significantly higher.     

The thiolate anion as a nucleophile Part IX. Reactions of some fluoroaromatics

The reactions of some halogenoaromatic compounds, mainly fluoroaromatics C₆F_xH_6-x with the methanethiolate anion have been studied in DMF or an HMPA/THF mixture. Complete replacement of fluorine occurred forming C₆(SMe)_xH_6-x. Attempts to prepare C₆(SEt)₆ and compounds such as C₆(SEt)₂(SMe)₄ are described. Other new compounds isolated included C₆(SMe)₅SH and C₆F₂(SMe)₂(SEt)₂. Details of the spectra, particularly NMR, are given.     

Reactions of Distibanes with [Fe2(CO)9]: Synthesis,Structure and DFT Calculations of [(Et2Sb)4Fe4(CO)14], [(nPr2Sb)4Fe3(CO)10], [{(Me3SiCH2)2Sb}4Fe2(CO)6], and [2‐(Me2NCH2)C6H4SbFe2(CO)8]

The iron complexes [(Et₂Sb)₄Fe₄(CO)₁₄] ( 1 ), [(nPr₂Sb)₄Fe₃(CO)₁₀] ( 2 ), [{(Me₃SiCH₂)₂Sb}₄Fe₂(CO)₆] ( 3 ), and [2‐(Me₂NCH₂)C₆H₄SbFe₂(CO)₈] ( 4 ) were prepared by reactions of distibanes with Fe₂(CO)₉. Compounds 1 – 4 were characterized by X‐ray diffraction, ¹H NMR and IR spectroscopy as well as mass spectrometry; complex 1 was additionally characterized by density functional calculations.     

Trinuclear π-cyclopentadienyl bridging sulphido derivatives of iron

The reaction of [Fe(π-C₅H₅)(CO)₂]₂ with the dialkyl disulphides R₂S₂ (R = CH₃, C₂H₅, t-C₄H₉ or CH₂C₆H₅) affords, as well as dinuclear derivatives of the type [Fe(π-C₅H₅)(CO)SR]₂, trinuclear species of formula [Fe₃(π-C₅H₅)₃(CO)₂(S)SR].     

Permetalloplumbanes: Preparation of [Pb{Co(CO)3(L)}4] and [Pb{Fe(CO)2(NO)(L)}4].: Complexes containing four transition metal to lead bonds (L = tertiary arsine,phosphine or phosphite).

The sole and unexpected products from the reactions of a variety of lead (II) and lead (IV) compounds with [Co₂(CO)₆(L)₂] complexes (L = tertiary arsine, phosphine, or phosphite) in refluxing benzene solution are the blue, air-stable percobaltoplumbanes [Pb{Co(CO)₃(L)}₄]. These have also been obtained from the reaction of Na[Co(CO)₃(L)] (L  PBu₃ⁿ) with lead (II) acetate which with Na[Fe(CO)₂(NO)(L)] forms the isoelectronic [Pb{Fe(CO)₂(NO)(L)}₄] [L  P(OPh)₃]. The IR spectra of the complexes in the v(CO) and v(NO) regions are consistent with tetrahedral PbCo₄ or PbFe₄ fragments, trigonal bipyramidal coordination about the cobalt or iron atoms and linear PbCoAs, PbCoP, or PbFeP systems. Unlike [Pb{Co(CO)₄}₄], our complexes do not dissociate to [Co(CO)₃(L)]^? or [Fe(CO)₂(NO)(L)]^? ions when dissolved in donor solvents.     

Metallkomplexe mit anionischen Liganden von Elementen der 4. Hauptgruppe. IX. Zum komplexchemischen Verhalten von Trichlorstannid-und Trichlorgermid-Ionen gegenüber Komplexen von Übergangsmetallen in niedrigen Oxydationsstufen

Metal Complexes with Anionic Ligands of the Main Group IV Elements. IX. Reactions of Trichlorostannide and Trichlorogermide Ions with Complexes of Transition Metals in Low Oxidation States Carhonyl trichlorostannido- and carbonyl trichlorogermido-metalate complexes have been synthesized both by photochemical and thermical substitution reactions of [ECl₃]^? ions (E = Sn, Ge) with M(CO)₆, (M = Cr, Mo, W), Fe(CO)₅ Fe₃(CO)₁₂, Co₂(CO)₈, as well as with the metalcarbonyl derivatives (π-arene)M(CO)₃, (M = Cr, Mo), (h⁵-C₅,H₅,)V(CO)₄, Mn(CO)₅,Cl, Co(NO)(CO)₃, and Fe(NO)₂,(CO)₂. Mainly the bonding properties of the [ECl₃]^? ligands are discussed by means of i.r. spectroscopic investigations. The progress of the reactions and the necessary reaction conditions show that the nucleophilic properties oft both anions [ECl₃]^? are unexpectedly small. The slightly weaker hasicity of [SnCl₃]^? compared with [GeC1₃]^? arreared, when both anions were reacted with Co₂,(CO)₈, forming the substitution product. [Co₂,(CO)₇,SnCl₃]^? and the products of a “base reaction” Cl₃GcCo(CO)₄, and [Co(CO)₄]^?.     

The solution constitution of the roussin ester Fe2(SBu-t)2(NO)4

The¹H and¹⁵N NMR spectra of the Roussin ester Fe₂(SBu-t)₂(NO)₄ show that in solution it exists as a mixture of two isomeric forms (I andII), of C_2h- and C_2v- symmetry, respectively. Unlike other similar esters, Fe₂(SR)₂(NO)₄, the isomers are present in non-equal proportions: the equilibrium constant K = [II]/[I] is unchanged in the temperature range 220–298 K, indicating that entropy factors are primarily responsible for the unequal abundance ofI andII.     

Synthesis and characterization of new heterometallic iron sulfur nitrosyl clusters

The reactivity of the (PPN)₂[Fe₈S₆(NO)₈] and (PPN)₂[Fe₆S₆(NO)₆] clusters is explored and new derivative clusters have been synthesized and structurally characterized. The unique (PPN)₂Fe₄S₄(NO)₆ “open-cubane” cluster with a chair like Fe₄S₄ core is obtained along with the mixed metal pentandite-like clusters (PPN)₂[Mo₂Fe₆S₆(NO)₆(CO)₆], (PPr₃)₂Cu₂Fe₆S₆(NO)₆, (PPr₃)₄Cu₄Fe₄S₆(NO)₄, (PPr₃)₂Ni₂Fe₆S₆(NO)₆, (PPr₃)₃Ni₃Fe₄S₆(NO)₄. The rich electrochemistry of the mixed metal clusters is presented as well.     

Combining a Nitrogenase Scaffold and a Synthetic Compound into an Artificial Enzyme

Nitrogenase catalyzes substrate reduction at its cofactor center ([(Cit)MoFe₇S₉C]^n?; designated M‐cluster). Here, we report the formation of an artificial, nitrogenase‐mimicking enzyme upon insertion of a synthetic model complex ([Fe₆S₉(SEt)₂]^4?; designated Fe₆^RHH) into the catalytic component of nitrogenase (designated NifDK^apo). Two Fe₆^RHH clusters were inserted into NifDK^apo, rendering the conformation of the resultant protein (designated NifDK^Fe) similar to the one upon insertion of native M‐clusters. NifDK^Fe can work together with the reductase component of nitrogenase to reduce C₂H₂ in an ATP‐dependent reaction. It can also act as an enzyme on its own in the presence of Eu^IIDTPA, displaying a strong activity in C₂H₂ reduction while demonstrating an ability to reduce CN^? to C₁–C₃ hydrocarbons in an ATP‐independent manner. The successful outcome of this work provides the proof of concept and underlying principles for continued search of novel enzymatic activities based on this approach.     

Mössbauer study of some Fe-containing M6 and M5 clusters

Isomer shift (δ) and quadrupole splitting (Δ) parameters have been assigned to the iron sites in [FeRh₅(CO)₁₆]⁻, trans- and cis-[Fe₂Rh₄(CO)₁₆]²⁻, [Fe₃-Rh₃(CO)₁₇]³⁻, [FeRh₄(CO)₁₅]²⁻, [Fe₃Pt₃(CO)₁₅]²⁻ and [Fe₄M(CO)₁₆]²⁻ (M = Pd or Pt) from ⁵⁷Fe Mössbauer spectra recorded at 78 K. The data for the closo compounds [FeRh₅(CO)₁₆]⁻ and [Fe₂Rh₄(CO)₁₆]²⁻ are compared with those for [Fe₆(CO)₁₆C]²⁻. In [Fe₃Rh₃(CO)₁₇]³⁻, the three major Fe sites were identified. For both [Fe₄M(CO)₁₆]²⁻ compounds two isomers were shown to be present in the solid state.     

The Electronic Ground State of [Fe(CO)3(NO)]−: A Spectroscopic and Theoretical Study

During the past 10 years iron‐catalyzed reactions have become established in the field of organic synthesis. For example, the complex anion [Fe(CO)₃(NO)]^?, which was originally described by Hogsed and Hieber, shows catalytic activity in various organic reactions. This anion is commonly regarded as being isoelectronic with [Fe(CO)₄]^2?, which, however, shows poor catalytic activity. The spectroscopic and quantum chemical investigations presented herein reveal that the complex ferrate [Fe(CO)₃(NO)]^? cannot be regarded as a Fe^?II species, but rather is predominantly a Fe⁰ species, in which the metal is covalently bonded to NO^? by two π‐bonds. A metal–N σ‐bond is not observed.     

Aromatic Osmacyclopropenefuran Bicycles and Their Relevance for the Metal‐Mediated Hydration of Functionalized Allenes

The aromatic osmacyclopropenefuran bicycles [OsTp{κ³‐C¹,C²,O‐(C¹H₂C²CHC(OEt)O)}(PⁱPr₃)]BF₄ (Tp=hydridotris(1‐pyrazolyl)borate) and [OsH{κ³‐C¹,C²,O‐(C¹H₂C²CHC(OEt)O)}(CO)(PⁱPr₃)₂]BF₄, with the metal fragment in a common vertex between the fused three‐ and five‐membered rings, have been prepared via the π‐allene intermediates [OsTp(η²‐CH₂=CCHCO₂Et)(OCMe₂)(PⁱPr₃)]BF₄ and [OsH(η²‐CH₂=CCHCO₂Et)(CO)(OH₂)(PⁱPr₃)₂]BF₄, and their aromaticity analyzed by DFT calculations. The bicycle containing the [OsH(CO)(PⁱPr₃)₂]⁺ metal fragment is a key intermediate in the [OsH(CO)(OH₂)₂(PⁱPr₃)₂]BF₄‐catalyzed regioselective anti‐Markovnikov hydration of ethyl buta‐2,3‐dienoate to ethyl 4‐hydroxycrotonate.     

Synthese und Struktur der Phosphor-verbrückten Übergangsmetallkomplexe [Fe2(CO)6(PR)6] (R = tBu,iPr), [Fe2(CO)4(PiPr)6], [Fe2(CO)3Cl2(PtBu)5], [Co4(CO)10(PiPr)3], [Ni5(CO)10(PiPr)6] und [Ir4(C8H12)4Cl2(PPh)4]

Synthesis and Structure of the Phosphorus-bridged Transition Metal Complexes [Fe₂(CO)₆(PR)₆] (R = ^tBu, ⁱPr), [Fe₂(CO)₄(PⁱPr)₆], [Fe₂(CO)₃Cl₂(P^tBu)₅], [Co₄(CO)₁₀(PⁱPr)₃], [Ni₅(CO)₁₀(PⁱPr)₆], and [Ir₄(C₈H₁₂)₄Cl₂(PPh)₄] (P^tBu)₃ and (PⁱPr)₃ react with [Fe₂(CO)₉] to form the dinuclear complexes [Fe₂(CO)₆(PR)₆] (R = ^tBu: 1 ; ⁱPr: 2 ). 2 is also formed besides [Fe₂(CO)₄(PⁱPr)₆] ( 3 ) in the reaction of [Fe(CO)₅] with (PⁱPr)₃. When PⁱPr(P^tBu)₂ and PⁱPrCl₂ are allowed to react with [Fe₂(CO)₉] it is possible to isolate [Fe₂(CO)₃Cl₂(P^tBu)₅] ( 4 ). The reactions of (PⁱPr)₃ with [Co₂(CO)₈] and [Ni(CO)₄] lead to the tetra- and pentanuclear clusters [Co₄(CO)₁₀(PⁱPr)₃] ( 5 ), [Ni₄(CO)₁₀(PⁱPr)₆] [2] and [Ni₅(CO)₁₀(PⁱPr)₆] ( 6 ). Finally the reaction of [Ir(C₈H₁₂)Cl]₂ with K₂(PPh)₄ leads to the complex [Ir₄(C₈H₁₂)₄Cl₂(PPh)₄] ( 7 ). The structures of 1–7 were obtained by X-ray single crystal structure analysis (1: space group P2₁/c (Nr. 14), Z = 8, a = 1 758.8(16) pm, b = 3 625.6(18) pm, c = 1 202.7(7) pm, β = 90.07(3)°; 2 : space group P1 (Nr. 2), Z = 1, a = 880.0(2) pm, b = 932.3(3) pm, c = 1 073.7(2) pm, α = 79.07(2)°, β = 86.93(2)°, γ = 72.23(2)°; 3 : space group Pbca (Nr. 61), Z = 8, a = 952.6(8) pm, b = 1 787.6(12) pm, c = 3 697.2(30) pm; 4 : space group P2₁/n (Nr. 14), Z = 4, a = 968.0(4) pm, b = 3 362.5(15) pm, c = 1 051.6(3) pm, β = 109.71(2)°; 5 : space group P2₁/n (Nr. 14), Z = 4, a = 1 040.7(5) pm, b = 1 686.0(5) pm, c = 1 567.7(9) pm, β = 93.88(4)°; 6 : space group Pbca (Nr. 61), Z = 8, a = 1 904.1(8) pm, b = 1 959.9(8) pm, c = 2 309.7(9) pm. 7 : space group P1 (Nr. 2), Z = 2, a = 1 374.4(7) pm, b = 1 476.0(8) pm, c = 1 653.2(9) pm, α = 83.87(4)°, β = 88.76(4)°, γ = 88.28(4)°).