Dynamics and structure of some tricarbonylferrole-iron tricarbonyl derivatives

A series of compounds of the formula Fe₂(CO)_6-x(PR₃)_x(R′C₂R″)₂ (x = 0, R′ and R″ = Ph, R′ and R″ = H, R′ = Ph and R″ = H; x = 1, K = Ph or n-Bu, and R′ and R″ = Ph) were studied by ¹³C NMR to observe their solution properties. The tricarbonylferrole unit was found to be static from ?125 to +95° C, while the π-Fe(CO)₃ group appeared to be fluxional over the same temperature range. Definite assignments of the carbonyl carbon and ferrole ring carbon resonances have been made. A low temperature single crystal X-ray study of Fe₂(CO)₅PPh₃(PhC₂Ph)₂ demonstrated that the phosphine ligand was attached to the ferrole iron contrary to previous belief based on chemical evidence.     

High Yield Synthesis,Molecular Structure,and Reactions of the 16‐Electron Norbornadiene Complex, [WI2(CO)2(nbd)]

Reaction of equimolar amounts of [WI₂(CO)₃(NCMe)₂] and norbornadiene (nbd) in toluene at 95 °C for 3h gave the 16‐electron crystallographically characterised complex, [WI₂(CO)₂(nbd)] (1) in 96 % yield. The structure of 1 has a distorted octahedral geometry, with the two cis‐ iodo ligands opposite to the two alkene groups in the equatorial plane, with the carbonyl groups in the axial sites. Treatment of 1 with two equivalents of PhC₂Ph in CH₂Cl₂ at room temperature afforded the bis(alkyne) complex [WI₂(CO)₂(η²—PhC₂Ph)₂] (2) . Equimolar quantities of 1 and 4, 4′‐bipyridine react in CH₂Cl₂ at room temperature to yield the seven‐coordinate complex, [WI₂(CO)₂(4, 4′‐bipyridine)(nbd)] (3) .     

Solid state13C NMR spectra of metal carbonyl clusters

The solid state¹³C NMR spectra of four¹³CO enriched carbonyl clusters having a tri-iron metallic core have been analyzed to provide structural and dynamic information. In Fe₃(CO)₁₂ (1), the high temperature spectra suggest the occurrence of large amplitude motions of the CO groups around their position at the vertexes of the coordination polyhedron in addition to the motion involving the Fe₃-triangle previously detected in the VT-¹³C MAS spectra.¹³C and³¹P NMR data of Fe₃(CO)₁₁PPh₃ (2) indicates the presence of one molecule in the asymmetric unit in apparent disagreement with the previously reported X-ray data. Furthermore, we show that structural information can be obtained from the chemical shift tensor components readily available from the analysis of the spinning sideband manifold.     

The formation of iron carbonyl radical anions in the reactions of iron carbonyls with trimethylamine N-oxide

The interaction of iron carbonyls, Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂ with Me₃NO occurs according to a one-electron redox-disproportionation scheme giving rise to iron carbonyl radical anions: Fe₂(CO)₈^·− (1), Fe₃(CO)₁₂^·− (2), Fe₃(CO)₁₁^·− (3) and Fe₄(CO)₁₃^·− (4). The role of Me₃NO, inducing CO-substitution, consists of the generation of reactive 17-electron species with a labile coordination sphere in which the substitution for other ligands occurs, resulting from fast ligand and electron exchange in the confines of the ETC-reaction.     

Solid state NMR spectroscopy of metal carbonyls. The influence of site symmetry on the solid state spectrum of cis-(η5-C5H5)2Fe2(CO)4

Solid state carbon-13 NMR spectra of metal carbonyls are readily obtained using commercial instrumentation. The observed isotropic chemical shifts are in good agreement with solution values. Furthermore there is a one-to-one correspondence between crystallographically unique carbonyls and magnetically distinguishable carbonyls in the absence of accidental degeneracies. For cis-(η⁵-C₅H₅)₂Fe₂(CO)₄ the site symmetry is C₁ while the molecular symmetry is C_2ν. The lower solid state symmetry gives rise to more resonances in the solid spectrum than in solution. Magic angle tuning and chemical shifts were obtained using hexamethylbenzene as a standard.     

Mixed-metal cluster chemistry. 26 . Proclivity for “all-terminal” or “plane-of-bridging-carbonyls” ligand disposition in tungsten-triiridium clusters

Reaction of WH(CO)₃(η-C₅Me₅) with IrCl(CO)₂(4-H₂NC₆H₄Me) affords WIr₃(μ-CO)₃(CO)₈(η-C₅Me₅) in low yield. A structural study reveals a WIr₂-centred plane of bridging carbonyls, in contrast to the crystal structure of WIr₃(CO)₁₁(η-C₅H₅) (all-terminal carbonyl distribution). DFT calculations reveal an increasing proclivity to adopt an all-terminal CO disposition for clusters MIr₃(CO)₁₁(η-C₅H₅) in the gas phase on proceeding from M=Cr to Mo and then W, consistent with structural studies in the solid state for which the tungsten-containing cluster is the only all-terminal example. Increasing electron donation from the ligands in the tungsten system (either from phosphine substitution or cyclopentadienyl permethylation) suffices to impose a plane of bridging carbonyls in the ground state structure. ¹³C NMR fluxionality studies reveal that CO exchange mechanism(s) for WIr₃(CO)₁₁(η-C₅H₅) and the related tetrahedral cluster W₂Ir₂(CO)₁₀(η-C₅H₅)₂ are very fast and involve all carbonyls on the clusters. DFT calculations on MIr₃(CO)₁₁(η-C₅H₅) (M=Cr, Mo) substantiate a ‘merry-go-round’ mechanism for carbonyl scrambling in these systems, a result which is consistent with the scrambling behaviour seen in the NMR fluxionality studies on the W-containing congener.     

The crystal and molecular structure of μ(1,2,6-η: 3-5-ηbicyglo[6.10]nona-1,3,5-triene)hexacarbonyldiiron (FEFe), and comment on its temperature-dependent 1H NMR spectrum

The crystal and molecular structure of (C₉H₁₀)Fe₂(CO)₆6 has been determined from a three-dimensional, X-ray crystal-structure analysis. The structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares. With all atoms located and refined the conventional R factor is 0.034, based on 2651 reflections measured with an automated General Electric XRD-6 diffractometer utilizing Mo-Kα radiation. Crystallographic data are: space group P$\text{1}$ with a = 7.229(4), b = 14.699(4) and c = 7.696(2) Å, α = 87.53(2)°, β = 113.48(3)° and γ = 102.08(2)°, Z = 2 and ?_calcd = 1.80 g/cm₃, ?_obsd = 1.78 g/cm₃. Contrary to previous claims the structure of the molecule is of the asymmetric type already established for (C₈H₁₀)Fe₂(CO)₆ and (C₁₀H₁₂)Fe₂(CO)₆. The almost identical bond parameters amongst the three structures are noted. The lengthening of the FeC(carbonyl) trans to FeC σ bond is attributed to the trans-influence of the σ-carbon atom. The fluxional nature of the molecule is also demonstrated by extending the variable temperature ¹H NMR study down to ?127°.     

Unexpectedly complex structure and dynamic behavior of bis [(η5-cyclopentadienyl)dicarbonyl molybdenum ]-μ-pent-3-yne (MoMo)

The title compound, (η⁵-C₅H₅)₂Mo₂(CO)₄ (μ-EtCCEt) in its crystalline form, has a molecular structure that lacks symmetry. Two (ηs-C₅H₅)Mo groups are connected by an MoMo bond 2.977(1) Å in length with the usual sort of crosswise acetylene bridge. There are two terminal CO groups on Mo(1) and one on Mo(2). The fourth CO group is in a semi-bridging posture with Mo(2)—C = 1.936(6) and Mo(1)—C = 2.826(6). The ¹³CO NMR spectrum at ?126°C has six lines, indicative of the presence of two isomers, in each of which two CO's are either statically or dynamically equivalent. Complex changes occur in the spectrum as the temperature is increased so that at ?40°C there is only a single line. A detailed interpretation of these spectra is not yet available.     

Diironhexacarbonyl clusters with imide and amine ligands: hydrogen evolution catalysts

The reaction of Fe₃(CO)₁₂ and N-(4-thiolphenyl)-1,8-naphthalimide afforded a new diironhexacarbonyl complex (3). The integrity and electronic structure of 3 has been determined by elemental analysis and spectroscopy (NMR and infrared). Infrared spectrum of 3 shows peaks at 2000, 2040, and 2075?cm^?1 ascribed to stretching frequencies of the terminal metal carbonyls. Compound 4 was obtained from the reaction of Fe₃(CO)₁₂ and 4-aminothiolphenol. A comparison of the electronic, electrochemical, and electrocatalytic properties of 3 and 4 are discussed. Cyclic voltammetric studies show that 3 and 4 catalyze the reduction of acetic acid to produce hydrogen at ?2.19?V and ?1.88?V versus Fc/Fc⁺, respectively.     

Syntheses,crystal structures,and electrochemical studies of Fe2(CO)6(μ-PPh2)(μ-L) (L = OH,OPPh2, PPh2)

Reaction of Fe₃(CO)₁₂ and Ph₂PH in the presence of Et₃N in THF at 0?°C immediately forms Fe₂(CO)₆(μ-PPh₂)(μ-OH) (1), Fe₂(CO)₆(μ-PPh₂)(μ-k²O,P-OPPh₂) (2), and Fe₂(CO)₆(μ-PPh₂)₂ (3) in yields of 25, 14, and 19%, respectively. Experiments confirm that Et₃N shortens the reaction time. The absence of O₂ hinders the formation of 2. The presence of H₂O can increase the yield of 1. Their structures have been determined by X-ray crystallography and the complexes have been completely characterized by EA, IR, and ¹H, ¹³C, ³¹P NMR. Electrochemical studies reveal that they exhibit catalytic H₂-producing activities.     

[Fe2(μsb‐CO)(CO)3(NO)(μ‐PtBu2)(μ‐Ph2PCH2PPh2)]: Synthese,Kristallstruktur und Koordinationsisomerie

[Fe₂(μ_sb‐CO)(CO)₃(NO)(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)]: Synthesis, X‐ray Crystal Structure and Isomerization Na[Fe₂(μ‐CO)(CO)₆(μ‐P^tBu₂)] ( 1 ) reacts with [NO][BF₄] at —60 °C in THF to the nitrosyl complex [Fe₂(CO)₆(NO)(μ‐P^tBu₂)] ( 2 ). The subsequent reaction of 2 with phosphanes (L) under mild conditions affords the complexes [Fe₂(CO)₅(NO)L(μ‐P^tBu₂)], L = PPh₃, ( 3a ); η‐dppm (dppm = Ph₂PCH₂PPh₂), ( 3b ). In this case the phosphane substitutes one carbonyl ligand at the iron tetracarbonyl fragment in 2 , which was confirmed by the X‐ray crystal structure analysis of 3a . In solution 3b loses one CO ligand very easily to give dppm as bridging ligand on the Fe‐Fe bond. The thus formed compound [Fe₂(CO)₄(NO)(μ‐P^tBu₂)(μ‐dppm)] ( 4 ) occurs in solution in different solvents and over a wide temperature range as a mixture of the two isomers [Fe₂(μ_sb‐CO)(CO)₃(NO)(μ‐P^tBu₂)(μ‐dppm)] ( 4a ) and [Fe₂(CO)₄(μ‐NO)(μ‐P^tBu₂)(μ‐dppm)] ( 4b ). 4a was unambiguously characterized by single‐crystal X‐ray structure analysis while 4b was confirmed both by NMR investigations in solution as well as by means of DFT calculations. Furthermore, the spontaneous reaction of [Fe₂(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 5 ) with NO at —60 °C in toluene yields a complicated mixture of products containing [Fe₂(μ‐CO)(CO)₄(μ‐H)(μ‐P^tBu₂)(μ‐dppm)] ( 6 ) as main product beside the isomers 4a and 4b occuring in very low yields.     

Syntheses of the new trinuclear ions [Ru3(CO)11]2− and [Os3(CO)11]2−

Stoichiometric reduction of Os₃CO)₁₂ and Ru₃(CO)₁₂ with K and Ca, respectively; yields the two new cluster dianions [Os₃(CO)₁₁]^2? and [Ru₃(CO)₁₁]^2? which have been isolated and characterized. Temperature-dependent ¹³C NMR spectra for [Os₃(CO)₁₁]^2? and infrared spectra of [Os₃(CO)₁₁]^2? and [Ru₃(CO)₁₁]^2? suggest a similar structure for these dianions in which there is a single edge-bridging carbonyl.     

Binuclear metal carbonyl dab complexes : VII. A 13C NMR investigation of MM′(CO)6(DAB) complexes (M = M ′ = Fe,Ru; M = Mn,Re and M′ = Co; DAB = 1,4-diazabutadiene). Dynamic behaviour of σ2-N, σ2-N′, η2-C=N coordinated dab in MnCo(CO)6(DAB) and local scrambling of the carbonyl groups

The ¹³C NMR spectra of MM′(CO)₆(DAB) complexes (M = M′ = Fe, Ru; M = Mn, Re and M′ = Co; DAB = 1,4-diazabutadiene) show very characteristic features which are directly related with the bonding mode of the DAB ligand to the binuclear metal carbonyl fragment. In these complexes the DAB ligand is σ²-N, μ²-N′, η²-C=N or σ²-N, σ²-N′, η²-C=N coordinated. Chemical shifts of about 175 ppm are observed for the σ-coordinated imine fragments and about 60 or 80 ppm for the η²-C=N coordinated imine fragments.In MnCo(CO)₆[diacetylbis(cyclopropylimine)] the DAB ligand is fluxional, and the changes in the spectra when recorded at various temperatures can be interpreted in terms of an exchange between the σ- and π-coordinated part of the DAB ligand.The homodinuclear M₂(CO)₆(DAB) complexes (M = Fe or Ru) contain M(CO)₃ fragments on which the carbonyl groups are involved in a local scrambling process with very different activation parameters (T_c = ?50°C and +85°C).MCo(CO)₆(DAB) complexes (M = Mn, Re), which contain a semi-bridging carbonyl group according to the crystal structure, show rapid interchange of this carbonyl group with the terminal carbonyl groups on cobalt. The electronic balance is kept in equilibrium by an internal compensation within the DAB ligand.     

Binuclear Iron(I) Complex Containing Bridging Phenanthrene‐4,5‐dithiolate Ligand: Preparation,Spectroscopy, Crystal Structure,and Electrochemistry

A diiron hexacarbonyl complex containing bridging phenanthrene‐4,5‐dithiolate ligand is prepared by oxidative addition of Phenanthro[4,5‐cde][1,2]dithiin to Fe₂(CO)₉. The complex is investigated as a model for the active site of the [Fe–Fe] hydrogenase enzyme. The compound, [(μ‐PNT)Fe₂(CO)₆]; (PNT = phenanthrene‐4,5‐dithiolate), was characterized by spectroscopic methods (IR, UV/Vis and NMR) and X‐ray crystallography. The IR and proton NMR spectra of [(μ‐PNT)Fe₂(CO)₆] ( 4 ) are in agreement with a PNT ligand attached to a Fe₂(CO)₆ core. The infrared spectrum of 4 recorded in dichloromethane contains three peaks at 2001, 2040, and 2075 cm^–1 corresponding to the stretching frequency of terminal metal carbonyls. X‐ray crystallographic study unequivocally confirms the structure of the complex having a butterfly shape with an Fe–Fe bond length of 2.5365 Å close to that of the enzyme (2.6 Å). Electrochemical properties of [(μ‐PNT)Fe₂(CO)₆] have been investigated by cyclic voltammetry. The cyclic voltammogram of [(μ‐PNT)Fe₂(CO)₆] recorded in acetonitrile contains one quasi‐irreversible reduction (E_1/2 = –0.84 V vs. Ag/AgCl, I_pc/I_pa = 0.6, ΔE_p = 131 V at 0.1 V · s^–1) and one irreversible oxidation (E_pa = 0.86 V vs. Ag/AgCl). The redox of [(μ‐PNT)Fe₂(CO)₆] at E_1/2 = –0.84 V can be assigned to the one‐electron transfer processes; [Fe^I–Fe^I] → [Fe^I–Fe⁰] and [Fe^I–Fe⁰] → [Fe^I–Fe^I].     

Observation of in-plane carbonyl scrambling in a derivative of dodecacarbonyltriosmium.

¹³C NMR spectra obtained for the norbornadiene complex Os₃(CO)₁₀(C₇H₈)indicate restricted equilibration of in-plane carbonyls via a triply bridged intermediate. Spectral assignments are facilitated by observation of significant ¹³C-¹³C coupling between nonequivalent trans carbonyls.     

Investigation of the kinetics of the chain-radical process in the system iron carbonyl–Lewis base

An ESR spectroscopy investigation of the kinetics of accumulation and consumption of iron carbonyl radical anions, Fe₃(CO)₁₂⁻ and Fe₃(CO)₁₁⁻, arising in the reaction of Fe₃(CO)₁₂ with (Et₄N)SEt in THF at 19.5°C, was carried out using the stopped-flow technique. The solution of the inverse kinetic problem showed a satisfactory agreement between calculated and experimental data. This supports the principal idea that chain radical processes including preliminary complex formation followed by one-electron redox-initiation lie at the heart of the interaction of iron carbonyls with Lewis bases, and that the following transformations are due to electron and ligand changes in the coordination sphere of seventeen-electron coordinatively unsaturated species.     

A MECHANISTIC STUDY OF THE FORMATION OF [Ru6C(CO)16]2− FROM [Ru6(CO)18]2−

Abstract

The kinetics of the transformation of [Ru₆(CO)₁₈]^2? into [Ru₆C(CO)₁₆]^2? in diglyme over the temperature range 130–160°C have been determined. The results are consistent with reversible loss of a carbonyl ligand from [Ru₆(CO)₁₈]^2?, followed by formation of carbon dioxide and reassociation of carbon monoxide to give the observed product. Mass spectral analysis of the evolved carbon dioxide trapped as barium carbonate supports an intramolecular pathway for the disproportionation of carbon monoxide.     

Perturbation of metal—metal stretching frequencies by the interaction of lewis acids with bridging carbonyls

Adduct formation on the oxygen of a bridging carbonyl causes a very small perturbation of metal—metal stretching frequencies of polynuclear carbonyls. This small shift contrasts with the large change in v(MM) when carbonyl groups are redistributed between terminal and bridging positions; therefore, using low frequency Raman spectroscopy, it is possible to infer the structural relation of C- and O-bonded adduct to the parent carbonyl. Structural inferences for Fe₃(CO)₁₂ · AlBr₃, Ru₃(CO)₁₂ · AlBr₃ and Fe₂(CO)₉ · AlBr₃ are given.     

Vierkernige Clusterkomplexe vom Typ [MM′(AuPR3)2(μ‐H)(μ‐PCy2)(μ4‐PCy)(CO)6] (M,M′ = Mn,Re; R = Ph,Cy, Et): Synthese,Struktur und Topomerisierung

Tetranuclear Cluster Complexes of the Type [MM′(AuR₃)₂(μ‐H)(μ‐PCy₂)(μ₄‐PCy)(CO)₆] (M,M′ = Mn, Re; R = Ph, Cy, Et): Synthesis, Structure, and Topomerisation The dirhenium complex [Re₂(μ‐H)(μ‐PCy₂)(CO)₇(ax‐H₂PCy)] ( 1 ) reacts at room temperature in thf solution with each two equivalents of the base DBU and of ClAuPR₃ (R = Ph, Cy, Et) in a photochemical reaction process to afford the tetranuclear clusters [Re₂(AuPR₃)₂(μ‐H)(μ‐PCy₂)(μ₄‐PCy)(CO)₆] (R = Ph ( 2 ), Cy ( 3 ), Et ( 4 )) in yields of 35–48%. The homologue [Mn₂(μ‐H)(μ‐PCy₂)(CO)₇(ax‐H₂PCy)] ( 5 ) leads under the same reaction conditions to the corresponding products [Mn₂(AuPR₃)₂(μ‐H)(μ‐PCy₂)(μ₄‐PCy)(CO)₆] (R = Ph ( 6 ), Et ( 8 )). Also [MnRe(μ‐H)(μ‐PCy₂)(CO)₇(ax/eq‐H₂PCy)] ( 9 ) reacts under formation of [MnRe(AuPR₃)₂(μ‐H)(μ‐PCy₂)(μ₄‐PCy)(CO)₆] (R = Ph ( 10 ), Et ( 11 )). All new cluster complexes were identified by means of ¹H‐NMR, ³¹P‐NMR and ν(CO)‐IR spectroscopic measurements. 2 , 4 and 10 have also been characterized by single crystal X‐ray structure analyses with crystal parameters: 2 triclinic, space group P 1, a = 12.256(4) Å, b = 12.326(4) Å, c = 24.200(6) Å, α = 83.77(2)°, β = 78.43(2)°, γ = 68.76(2)°, Z = 2; 4 monoclinic, space group C2/c, a = 12.851(3) Å, b = 18.369(3) Å, c = 40.966(8) Å, β = 94.22(1)°, Z = 8; 10 triclinic, space group P 1, a = 12.083(1) Å, b = 12.185(2) Å, c = 24.017(6) Å, α = 83.49(29)°, β = 78.54(2)°, γ = 69.15(2)°, Z = 2. The trapezoid arrangement of the metal atoms in 2 and 4 show in the solid structure trans‐positioned an open and a closed Re…Au edge. In solution these edges are equivalent and, on the ³¹P NMR time scale, represent two fluxional Re–Au bonds in the course of a topomerization process. Corresponding dynamic properties were observed for the dimanganese compounds 6 and 8 but not for the related MnRe clusters 10 and 11 . 2 and 4 are the first examples of cluster compounds with a permanent Re–Au bond valence isomerization.     

Formation and structure of diruthenium complexes Ru2(CO)6−n (PPh3) n {μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} (n=1, 2)

Ruthenium carbonyl triphenylphosphine complexes Ru₂(CO)_6−n (PPh₃) _n {μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} (n=1, 2) were obtained by the reaction of complex Ru₂(CO)₆{μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} containing the ruthenacyclopentadiene moiety with PPh₃ in refluxing toluene. The complexes were characterized by IR and by¹H,¹³C, and³¹P NMR spectroscopy, and by X-ray analysis. The monophosphine derivative is identical to the complex formed by fragmentation of the Ru₃(CO)₈(PPh₃){μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} cluster and contains the PPh₃ ligand at the ruthenium atom of the ruthenacyclopentadiene moiety. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1836–1843, September, 1998