Cyclopentadienyl Iron Research Articles

Redox properties of 17-electron thiolate complexes of cyclopentadienyl iron (III)

The redox electrochemistry of iron (III) thiolate complexes of the type [CpFe(dppe)-SR]PF 6 R = CH 3, C 3H 7, C 6H 5, p-C 6H 4Br and thiobenzothiazole has been examined by cyclic voltammetry, coulometry and spectroelectrochemistry methods. Four redox waves were observed in the range −1.5 to +1.5 V (S.C.E.) in CH 2Cl 2. Around 0.0 V the metal centered reduction Fe ( III)→Fe ( II) process was observed, while that around +0.5 V the wave observed was attributed to a ligand centered oxidation. Strongly irreversible waves of oxidation near 1.3 V were assigned to the oxidation of RSSR while a reduction wave also strongly irreversible at very high negative potential was attributed to the reduction of the RSSR free ligand, RSSR + 2 e → 2RS −. The redox wave observed for the disulphides compounds are discussed in terms of a reductive elimination of RSSR. Chemical and electrochemical reduction of the complexes [CpFe(dppe)-SR]PF 6 was accomplished by the color changes blue → red-brown characteristic of the redox change 17e → 18e.

Metallo-carbonyl complexes based on the CpFe(CO)2(η1-N-imidato) system as protein labelling reagents: reactivity and selectivity studies using bovine serum albumin as a model protein

Transition metallo-carbonyl complexes are useful bioprobes to study molecular recognition processes such as ligand-receptor interactions, owing to their intense absorption bands in the mid-IR spectral range, which enable their detection at the picomole level with FT-IR spectrometers. New chemical methods for the introduction of cyclopentadienyl iron dicarbonyl fragments into proteins have been developed. Synthesis of a maleimide and of an N-succiminidyl ester and their reactivity with a model protein, namely bovine serum albumin (BSA), are described here. Results show that BSA can be labelled by both reagents at neutral to basic pH, and, as for the maleimide, side-chain selectivity can be tuned as a function of experimental coupling conditions.

An application of arene-iron chemistry in the synthesis of a novel liquid crystalline polymer

Arene–iron chemistry was applied in the synthesis of a novel liquid crystalline polymer. The chemistry, which is based on iron cyclopentadienyl (FeCp) arene complexes, allows sequential nucleophilic substitution of the chlorides from 1,3-dichlorobenzene–FeCp complex and photolytic decomplexation of the products to afford asymmetrical aryl ethers. This methodology provides easy access to novel polyether-esters, and is potentially useful in the synthesis of various functional polyarylates. © 1997 John Wiley & Sons, Inc.

Sulfur-hydrogen bond activation of thiols by the fragment CpFe(dppe) +: cyclopentadienyl iron(III) thiolate complexes

Oxidative addition of thiols RSH, R  CH 3, CH 2CH 2CH 3, CH 2C 6H 5, C(CH 3) 3 and C 6H 4Br, by the complex [CpFe(dppe)l] afforded the oxidized thiolate complexes [CpFe(dppe)-SR]PF 6. The reaction of [CpFe(dppe)l] with HSC 6H 4NH 2 produces the diamagnetic [CpFe(dppe)HSC 6H 4NH 2]PF 6 instead of the expected thiolate product. The reaction of the dithiol HS(CH 2) 4SH with the same iron fragment, gives the binuclear complex [CpFe(dppe)-S(CH 2) 2S-CpFe(dppe)][PF 6] 2. The formation of the thiol-containing complexes as intermediates in the activation of the SH bonds is discussed.

A Specific π-Ligand Transfer Reaction via Triple-Decker Sandwich Complex Intermediates

Photochemically generated cationic cyclopentadienyl iron fragments [FeCp]+ allow a specific stacking reaction of [(t-Bu3C3P2)Fe(t-Bu2C2P3)]. This results in the transient formation of an unstable cationic Fe-Fe triple-decker sandwich complex which decomposes by deliberating the neutral sandwich complex [CpFe(t-Bu2C2P3)], and is stacked again by a second [FeCp]+-unit, yielding the moderately stable cationic triple-decker sandwich complex [CpFe(t-Bu2C2P3)FeCp]+ with a central mi-eta5:eta5-triphospholyl ligand. Air exposure or storage of solutions at room temperature leads to a destacking and the neutral triphosphaferrocene derivative [CpFe(t-Bu2C2P3)] is formed again almost quantitatively in respect to the pentaphospha-ferrocene educt.

Coordination of alane and aluminum alkyls to the N-donor atom of side chain functionalized cyclopentadienyl iron and nickel complexes; structure of {[(C 5H 5)(C 5H 4CH 2NMe 2)]Fe} 2AlH 3

The synthesis of iron and nickel complexes with interaction of aiane and trialkylaluminum compounds to the amino group is described. Treatment of [2-( N,N-dimethyIamino)methyl] ferrocene {[(C 5H 5)(C 5H 4CH 2NMe 2)]Fe ( 1) with trimethylaminealane (H 3AlNMe 3), leads to the formation of the iron alane complex {[(C 5H 5)(C 5H 4CH 2NMe 2)]Fe} 2AlH 3 ( 2), with a five-coordinated aluminum center. The structure of 2 has been determined by single-crystal X-ray diffraction. The reaction of FeCl 2 with two equivalents of {(C 5H 4CH 2CH 2NMe 2)Li} leads to the formation of [(C 5H 4CH 2CH 2CH 2NMe 2) 2Fe] ( 3). Complex 3 reacts quantitatively with two equivalents of trimethylaluminum to the compound [(C 5H 4CH 2CH 2NMe 2) 2Fe](AlMe 3) 2 ( 4). Addition of trimethylaluminum or triethylaluminum to the nickel complex [(C 5H 4CH 2CH 2NMe 2) 2Ni]Ni ( 5) give the paramagnetie nickel aluminum compounds [(C 5H 4CH,CH 2NMe 2) 2Ni](AlMe 3) 2 ( 6a) and [(C 5H 4CH 2CH 2NMe 2) 2Ni](AlEt 3) 2 ( 6b), respectively. These compounds were characterized by 1H, 13C and 27Al NMR, elemental analysis and mass spectroscopy. Studies to deposit intermetallic thin films using these compounds as bimetallic single source precursors revealed that aluminum was deposited, only.

The molecular structure of ferrocene

The vertical iron–cyclopentadienyl distance in ferrocene has been determined using ab initio coupled-cluster theory. At the CCSD level, a TZV2P basis set yields a metal–ligand distance of 1.664 Å with all 96 electrons correlated and 1.672 Å with 66 electrons correlated. With 66 electrons correlated at the CCSD(T) level the equilibrium distance is 1.660 Å, in agreement with experiment (1.66 Å).

Preparation of Functionalized p-Phenylenediamine Derivatives Using Arene−Iron Chemistry

Selective displacement of chloride from cyclopentadienyl(1,4-dichlorobenzene)iron(1+) by a series of cyclic secondary amine nucleophiles is described. This selectivity, in combination with further manipulation of the complexes, allows access to a series of unsymmetrical and/or functionalized tetraalkyl-p-phenylenediamine complexes. A series of demetalated phenylenediamines were shown by CV to have redox potentials distributed over a range of 320 mV, as a consequence of remote functionality. Preliminary fluorescence studies on a series of electron acceptor-substituted phenylenediamines indicated quenching of the phenylenediamine fluorescence, attributable to rapid electron transfer.

Cyclopentadienyl(iron)arene-bis-(p-N,N-dimethylaminobenzylidene)-cyclopentanone Photoinitiated Polymerization of Methyl Methacrylate and Styrene

Abstract Polymerization of methyl methacrylate and styrene can be effectively photoinitiated by a binary photoinitiator system consisting of cyclopentadienyl(iron)arene hexafluorophosphonate salt and bis(p-N, N-dimethylaminobenzylidene)cyclopentanone in the spectral range of 400–500 nm. The amine-type radical formed from the exciplex of the binary photoinitiator system is probably responsible for the radical polymerization of vinyl monomers. A probable mechanism of initiation of polymerization is discussed.

Synthesis, characterization and electrochemical properties of an iron cyclopentadienyl complex of poly(n-hexylphenylene)

Abstract An iron cyclopentadienyl complex of a conducting polymer, poly(n-hexylphenylene) (abbreviated as PHP), was prepared by a reaction of PHP with ferrocene, Al and AlCl 3 followed by an anion exchange using NH 4 PF 6 . Cyclic voltammetry of the complex thus formed with a formula, {(C 6 H 3 C 6 H 13 )1.6[(η 6 -C 6 H 3 C 6 H 13 )Fe(η 5 -C 5 H 5 )]PF 6 } n (abbreviated as PHP-[FeCp]PF 6 , Cp = η 5 -cyclopentadienyl), has indicated that it is reduced with a moderate chemical reversibility in Bu 4 NBF 4 -THF at E 0 ′ = − 1.7 V versus Ag/Ag + . Spectroelectrochemical measurements have suggested that the chemical reaction of the reduced form is a coupling reaction of phenylene rings coordinated to iron, resulting in a formation of insoluble thin network polymer film on the electrode surface. Photoluminescence of PHP is modified in intensity and maximum emission wavelength by coordinating the FeCp moiety.

Reactions of transition-metal η1-ally and propargyl complexes with ketenes and some new nonoxidative transition-metal-carbon bond cleaving reactions of the ketene cycloadducts which yield cyclopentenones

Reactions of cyclopentadienyl iron 2-alkynyl and allyl complexes with ketenes or ketene precursors yield transition-metal substituted cyclopentenones in some cases and new transition-metal substituted allyl complexes in others. The transition metals can subsequently be cleaved from the cyclopentenone containing complexes under a variety of oxidative and nonoxidative reaction conditions.

Preparation of some organic precursors via photolytic demetallation of their iron complexes

Nucleophilic aromatic substitution (SNAr) of chloroarenes complexed to the cyclopentadienyl iron moiety with ethyl cyanoacetate or phenylsulfonylacetonitrile in the presence of potassium carbonate in DMF resulted in the formation of arylated ethyl cyanoacetate or phenylsulfonylacetonitrile complexes. Photolytic demetallation of these complexes led to the liberation of the substituted arene ligands in high yield. This synthetic route is more advantageous than those previously reported and is a practical way to synthesise heterocycles and alkanoic acid precursors.

Dicarbonyl(h5-cyclopentadienyl)iron-(II)-h1-complexes of Carbohydrates

Dicarbonyl(η 5 -cyclopentadienyl)iron(II) η 1 -complexes of carbohydrates are prepared by reaction of 2-deoxy-2-halosugars with sodium dicarbonyl(η 5 -cyclopentadienyl)ferrate via a single-electron-transfer mechanism. Evidence for the in situ conversion of these compounds into the corresponding thermo-labile dicarbonyl(η 5 -cyclopentadienyl)iron(II) η 2 -complexes, is presented

Oxidatively induced nucleophilic capture vs. degradation of cyclopentadienyl iron derivatives of simple carboxylic acids and of α-amino acids. A comparative study

The electrochemical behaviour and the chemical oxidation of various cyclopentadienyl iron complexes of simple carboxylic acids and of amino-protected α-amino acids have been studied in relation to several factors including the nature of the ligands on the metal (Cp, Cp★, CO, PPh 3), the nature of the oxidizing agent (one-electron oxidants such as Cu(OTf) 2, FcOTf and CAN or a two-electron oxidant such as NBS) and the medium effects (especially the presence or absence of nucleophilic species). With simple carboxylic acid derivatives either homolytic dissociation (leading to alkyl radicals) or nucleophilic capture of the first-formed iron radical cations is observed, depending on the reaction conditions. With α-amino acid derivatives, an oxidative degradation to aldehyde is observed invariably, which is likely to proceed through the successive and transient formation of N-acyl α-amino radicals and N-acyl iminium ions.

Palladium-catalysed enantioselective Grignard cross coupling with use of a new ferrocenylaminophosphine ligand

A new ferrocenylaminophosphine ligand, cyclopentadienyl(7-dimethylamino-1-diphenylphosphino-4,5,6,7-tetrahydroindenyl)iron (ptfa), and its palladium dichloride complex have been synthesised, structurally characterised by X-ray analysis of the palladium complex, and shown to be effective in the enantioselective Grignard cross coupling reaction of phenethylmagnesium chloride and vinyl bromide giving 3-phenylbut-1-ene with 79% enantiomeric excess.

Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 4. A survey of the effect of methyl substitution on the bonding in some iron sandwich complexes

A series of methylated benzene complexes of the type [Fe(η6-C6HnMe6–n)(η5-C5H4X)]PF6(n= 0–6) have been synthesised where X = H, Me or COPh. Iron-57 Mossbauer data are presented and quadrupole splittings (q.s.) correlated with the degree of methylation (n) of the arene moiety. Fox X = H, a linear correlation between q.s. and n was found. For X = Me, a similar correlation was obtained but with a significantly lower slope whereas for X = COPh the plot showed a minimum at n= 1. These results are discussed in relation to the bonding in other iron sandwich complexes {ferrocenes and [Fe(η6-arene)2]2+ salts}. This has enabled a rationalisation of Mossbauer parameters for a wide range of iron sandwich complexes to be made.

Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 3. Carbon-13 nuclear magnetic resonance and iron-57 Mössbauer spectroscopic studies on [(η-cyclohexadienyl)(η-cyclopentadienyl)]iron(II) complexes

A series of [Fe(η-C5H4X)(η-C6H7–nXn)](X = H or Me, n= 0–6) complexes has been prepared. A detailed analysis of their 13C NMR spectra is presented, the assignments being confirmed using distortionless enhancement by polarisation transfer (DEPT) techniques. The co-ordination shift of the cyclohexadienyl ligand shifts are not uniform and these anomalies are discussed in terms of possible bonding schemes. The effect of substitution by chlorine and methyl groups is also included. For the case where X = Me, evidence is presented for the occurrence of conformational isomers due to restricted rotation of the ligands. The 57Fe Mössbauer parameters are reported as well as a temperature-dependence study. The results are discussed in terms of the somewhat distorted nature of the cyclohexadienyl ligand in these complexes.

An investigation of steric effects along a cyclopentadienyl substituent: a study by 1H, 13C and 29Si NMR spectroscopy of bis(trimethylsilyl)cyclopentadienyl iron complexes

The syntheses of a range of complexes, [(η 5-C 5H 3(SiMe 3) 2)Fe(CO)(L)I], (L  tBuNC, 2,6-Me 2C 6H 3NC (xylNC), P(OMe) 3, PMe 2Ph, P(O- o-tol) 3 PPh 3, P( m-tol) 3, P( p-tol) 3, and P(CH 2Ph) 3) are reported. Three separate cyclopentadienyl ring proton resonances were observed in the NMR spectra of the iron complexes, and their assignments determined from NOE experiments (L  P(OMe) 3, P(O- o-tol) 3). The 13C NMR spectra were recorded and assignments made from a knowledge of the 1H spectra by use of CH correlated spectroscopy. 29Si and 31P NMR data were also obtained. Three-dimensional correlations were observed between separations of pairs of NMR resonances ( 29Si, 13C and 1H) and (i) steric effects as measured by the Tolman cone angle, θ, and (ii) electronic effects as measured by ν CO, the stretching frequency of the carbonyl group. The degree of correlation varied with the distance of the NMR-active nuclei from the iron atom (ring C and Si(CH 3) 3 Si, C and H atoms), and the result is taken as an indication of the best region, in space, in which the Tolman cone angle concept is most appropriate. The best correlation occurred between the chemical shift difference of the two 29Si resonances and θ and ν(CO) ( R 2 = 0.96, mse = 0.00640). Conformational data obtained from the NOE spectra suggest that the Group 15 donor ligand resides close to a SiMe 3 group and near the two adjacent ring protons. The steric demand of the two bulky SiMe 3 groups hinders rotation of the P(OMe) 3 and P(O- o-tol) 3 ligands around the ring, resulting in a windscreen wiper motion of the ligand between the two SiMe 3 groups.

Isolation of cationic cyclopentadienyl iron complexes containing phosphinite and formation of metallaphosphineoxide complexes by the Arbuzov-like dealkylation reaction

Reaction of (η 5-C 5H 5)(CO) 2FeCl with PPh 2(OR) yields an isolable cationic complex [(η 5-C 5H 5)(CO) 2Fe{PPh 2(OR)}]Cl (R  Et, Ia; Me, Ib), which reacts with NaOMe to give [(η 5-C 5H 5)(CO)Fe(COOMe){PPh 2(OR)}] and with PPh 2(OR) to afford [(η 5-C 5H 5)(CO)Fe{PPh 2(OR)} 2]Cl (R  Et, IVa; Me, IVb). Complexes Ib and IVb undergo the Arbuzov-like dealkylation reaction in benzene at room temperature to give metallaphosphineoxide complexes, [(η 5-C 5H 5)(CO) 2Fe{P(O)Ph 2}] and (η 5-C 5H 5)(CO)Fe{PPh 2(OMe)}{P(O)Ph 2}], respectively, whereas Ia and IVa do not undergo the reaction. This difference in reactivity is discussed from electronic and steric points of view.

Flash vacuum pyrolysis study of iron cyclopentadienyl complexes and the crystal structure of O-acetyl- N-(1-ferrocenylpropylidene)hydroxylamine

Under flash vacuum pyrolysis (FVP) conditions the acylferrocene FcCOCMe 3 ( 1e) [Fe  (C 5H 5)Fe(C 5H 4)] cracks to provide isobutene, but other acylferrocenes FcCOR (R  H, Me, Et, Me 2CH, Ph or PhCH 2) ( 1a–d, f, g) either were recovered unchanged or underwent total decomposition. The oxime FCCHNOH yielded both FcCN and FcCHO while the oxime acetate yielded FcCHO and acetic acid. Other oximes FcCRNOH were too involatile for FVP while of the oxime acetates FcCR=NOCOCH 3, no pyrolysis was observed when R  Me or Me 2CH, but when R  Et, rearrangement to FcCOEt occurred. The structure of FcC(Et)NOCOCH 3 has been determined by an X-ray diffraction study; the crystals are made up of isolated molecules with no short inter- or intra-molecular contacts.