Fe CH Research Articles

SYMMETRY BREAKING IN HF WAVE FUNCTIONS OF FE(CH)2

HF and CAS calculations for linear geometry of Fe(CH)2 with \(D_{\infty h}\) symmetry have been performed. The basis sets used were DZ and DZ + P with ECP on the iron atom. Two closed‐shell and one quintet RHF wave functions have been found, \(\Phi _1^{{\text{RHF}}} ,\Phi _2^{{\text{RHF}}}\) and \(\Phi _3^{{\text{RHF}}\left( {\text{Q}} \right)}\). All of them are singlet and triplet unstable in the wide range of Fe–CH distances. Singlet instability leads to the Charge Density Wave (CDW) broken‐symmetry wave function with two electrons on carbon \(p_x\) or \(p_y\) orbital in the dissociation limit. Triplet instabilities lead to two broken‐symmetry HF wave functions of Axial Spin Density Wave (ASDW) type, ASDW1 and ASDW2. In the dissociation limit they give carbon atoms with two electrons on \(p_x\) and \(p_y\) orbitals coupled to singlet and triplet, respectively. The stability conditions for CDW, ASDW1 and ASDW2 instabilities have been derived. Other HF wave functions with spin symmetry unrestricted have been also found. CAS(8,8), CAS(10,10) and CAS(12,12) calculations for singlet, triplet and quintet states of Fe(CH)2 have been carried out. In all CAS calculations the singlet state has the lowest energy. The Fe–CH equilibrium distances obtained from closed‐shell RHF wave functions are much shorter and from broken‐symmetry wave functions are much longer than those obtained from CAS calculations.

Investigation of the iron–carbon bonding for alkyl, alkynyl, carbene, vinylidene, and allenylidene complexes using 57Fe Mössbauer spectroscopy

The synthesis of the iron allenylidene [Cp*(dppe)Fe(CCC(OCH 3)CH 3)][BPh 4] ( 7) was achieved in one step, from the reaction of the Cp*(dppe)FeCl ( 8) with 1 equiv. of Me 3–Si–CC–CCH. By working in methanol and in the presence of NaBPh 4, the complex 7 was isolated in 85% yield as a dark green powder. Comparison of the Mössbauer parameters of a series of 16 compounds having the same Cp*(dppe)Fe backbone and a end-bound hydrocarbon ligand shows that it is possible to identify both the oxidation state of the metal (Fe II vs. Fe III) and the metal–carbon bonding (single vs. double bond) of the terminal hydrocarbon ligands using Mössbauer spectroscopy.

Oxidation of ferrocenyl ketones using selenium(IV) oxide: Crystal and molecular structures of racemic 2,3-diferrocenyl-1,4-diphenylbutane-1,4-dione, racemic and meso 2,3-diferrocenyl-1,4-bis(4-biphenylyl)butane-1,4-dione, and ferrocenylmethyl(4-biphenylyl)ketone

Oxidation of the ferrocenyl ketones FcCH 2COR 1 [Fe  (C 5H 5)Fe(C 5H 4); a R  Ph, b R  C 6H 4Ph-4] with selenium(IV) oxide provides only modest yields of the corresponding 1,2-diketones FeCOCOR 2, but substantial yields of the 1,4-butanediones RCOCH(Fe)CH(Fe)COR 3 resulting from CC coupling. Compounds 3 exist in two diastereoisomeric form, racemic and meso, and crystal structures are reported for rac- 3a, rac- 3b and meso- 3b, as well as for 1b.

Ferrocenyl salts as synthons: new ferrocenyl-1,3-dikentones

Reaction of (ferrocenylmethyl)trimethylammonium iodide with the mono-sodium salts of a range of acyclic 1,3-diketones leads smoothly to 2-(ferrocenylmethyl)-1,3-diketones [(C5H5)Fe(C5H4)CH2]CH(COR1)(COR2), but with the corresponding tetrabutylammonium salts deacylation occurs. With the sodium salt of cyclohexane-1,3-dione, disubstitution occurs to give (2,6-dioxocyclohexane-1,1-diyl)bismethyleneferrocene, [(C5H5)Fe(C5H4CH2)]2C[(CO)2(CH2)3]. The lithium salt of acetylferrocene reacts with a range of monocarboxylic esters to provide 1-ferrocenyl-1,3-diketones [(C5H5)Fe(C5H4)]COCH2COR, but simple esters of dicarboxylic acids either do not react, or undergo only monosubstitution.

Synthesis and second-order nonlinear optical properties of three coordinate organoboranes with diphenylphosphino and ferrocenyl groups as electron donors: crystal and molecular structures of ( E)-DCHCHB(mes) 2 and DCCB(mes) 2 [D  P(C 6H 52, (η-C 5H 5)Fe(η-C 5H 4); mes = 2,4,6-(CH 3) 3C 6H 2

We report the synthesis and characterization of five π-electron conjugated diphenylphosphino and ferrocenyl dimesitylboranes ( E)-Ph 2PCHCHB(mes) 2 ( 3a) crystallizes in space group P2 12 12 1 and exhibits a powder second harmonic generation (SHG) efficiency, χ (2), approximately equal to that of urea. First molecular hyperpolarizabilities, β, of 3a, Ph 2PCCB(mes) 2 ( 5a), ( E)-(η-C 5H 5)Fe(η-C 5H 4)CHCHB(mes) 2 ( 3b) and (η-C 5H 5)Fe(η-C 5H 4)CCB(mes) 2 ( 5b) have been measured and the values are comparable to those for small organic compounds. Ground-state charge-transfer interactions have been examined for compounds 3a, b, 5a, b via analysis of their crystal and molecular structures. It is significant that the vinyl group rotates out of the BC 3 plane by 16.8° for 3a and 12.0° for 5a, whereas mesityl groups are typically rotated by 50–70° with respect to the boron valence plane. This indicates that the best π-conjugation is along the desired pathway, i.e. from π-donor through the vinyl and ethynyl group to the vacant p-orbital on boron. In addition, the BC(vinyl) bond distance in 3b is somewhat shorter than the average BC(mes) bond length, and the PC(vinyl) bond length is shorter than the average PC(phenyl) bond distance in 3a, also supporting a certain degree of π-conjugation in these systems. For the phosphine derivatives, the sum of angles about phosphorus is 308–309°, typical of a pyramidal configuration. As a result, π-electronic interaction between boron and phosphorus is probably weak and a large angle exists between the ground-state and excited-state dipole moments. Related arguments also apply to the ferrocenyl boranes. The large β value ( − 24 × 10 −30 esu) measured for 3b is probably the result of a low-lying charge transfer from electron-rich iron to electron-deficient boron. The effect of crystal packing on the observed structures is discussed.

Activation of dithioformate by iron complexes: insertion of alkynes into the coordinated CS bond. X-ray structures of [formula omitted](SMe)H](CO)(PMe 3) 2 and [formula omitted]HCH(SMe)](CO)(PMe 3) 2

BH 3 containing iron complexes Fe(η 3-HB(H) 2SC HSR′)(CO)(PR 3) 2 ( 3) were prepared by reduction of Fe(η 2- CS 2R′)(X)(CO)(PR 3) 2 derivatives ( 2) with NaBH 4. The X-ray structure of 3a (R′R Me) shows the cis addition of the H − and BH 3 fragments to the coordinated dithioformate CS bond and that one BH bond is coordinated to the iron atom. The removal of BH 3 from 3, on treatment with pyridine, generates a 16-electron iron moiety which can trap two-electron ligands (CO, PR 3) or react with alkynes HCCR (RPh, H, C(Me)CH 2) to give the insertion of the alkyne into the dithioformate coordinated CS bond and Fe(η 3- SC(R)CHCHSMe)(CO)(PR 3) 2 complexes. The latter are stable for RPh ( 6), for which the structure has been determined by X-ray diffraction, and RH ( 8); the cleavage of their FeCH bond leads to new sulfur- containing metallacycles 7 (RPh) and 10 (RCMeCH 2).

The synthesis of ferrocenyl compounds with second-order optical non-linearities

A series of new donor-acceptor compounds of the form (η-C 5H 5)Fe(η-C 5H 4) CHCHR, where R is a π-acceptor group and the ferrocenyl moiety is a donor has been synthesized. Reaction of the ylide (η-C 5H 5)Fe(η-C 5H 4)CHP(C 6H 5) 3 ( 3), generated in situ with various aldehydes, proceeds smoothly. The ferrocenyl compounds were screened for second harmonic generation efficiencies using 1.907μm light generated by Raman shifting the 1.064μm light from an Nd-YAG laser, using a high pressure hydrogen cell. Several of the compounds had efficiencies greater than the urea reference standard.

Organometallic salts with large second-harmonic-generation powder efficiencies: (E)-1-ferrocenyl-2-(1-methyl-4-pyridiniumyl)ethylene salts

A series of salts of the form (E)-(η-C 5 H 5 )Fe(η-C 5 H 4 )CH=CH(4-C 5 H 4 N-1-CH 3 ) + X − has been synthesized. Variation of the counterion leads to materials with second-harmonic-generation powder efficiencies at 1907-nm fundamental as large as 220 times that of a urea reference standard. This is the largest value reported for an organometallic compound. The crystal structure of the nitrate salt, which had a powder SHG efficiency 110 times that of urea, was determined

Homogeneous reduction of carbon monoxide

Hydride additions to eighteen electron iron cations containing both cyclopentadienyl and carbonyl Ligands occur regioselectively onto coordinated carbon monoxide to generate formyls which undergo further reduction or disproportionate to iron methyls. Alternatively Ligand loss converts the iron formyls to carbonyl hydrides. The carbonyl hydride [(η 5-C 5H 5)Fe(Ph 2PCH 2CH 2PPh 2)(CO)H] exists in equilibrium with the corresponding formyl complex which in polar solvents disproportionates to the methyl complex [(η 5-C 5H 5)Fe(Ph 2PCH 2CH 2PPh 2)CH 3] but in non polar solvents rearranges to the cyclopentadiene complex [(η 4-C 5H 6)Fe(Ph 2PCH 2CH 2PPh 2)CO]. Deuterium labelling studies have shown this latter migration to be an intramolecular transfer of hydride from the iron to the endo-position of the cyclopentadiene. Hydride reduction of the cation [(η 5-C 5H 5)Fe(PMe 3)(CO) 2] +PF 6 − generates via the formyl [(η 5-C 5H 5)Fe(PMe 3)(CO)CHO] the methyl complex [(η 5-C 5H 5)Fe(PMe 3)(CO)CH 3]. Carbon monoxide insertion into this iron methyl generates the corresponding acetyl complex [(η 5-C 5H 5)Fe(PMe 3)(CO)COCH 3] which is reduced by BH 3.THF to the ethyl complex [(η 5-C 5H 5)Fe(PMe 3)(CO)CH 2CH 3]. Successive clean homologations by treatment with CO and BH 3.THF gives after four carbonylations [(η 5-C 5H 5)Fe(PMe 3)(CO)COCH 2CH 2CH 2CH 3] which on oxidation yields entirely CO-derived pentanoic acid. The carbonyl hydride [(η 5-C 5H 5)Fe(PMe 3)(CO)H] in the presence of carbon monoxide produces the cyclopentadiene complex [(η 4-C 5H 6)Fe(PMe 3)(CO) 2] via an intermolecular hydride transfer from an intermediate formyl which is catalysed by [(η 5-C 5H 5)Fe(PMe 3)(CO) 2] +PF 6 −.

Relative thermodynamic stabilities of acetyl and formyl complexes: a theoretical determination

Ab initio LCAO-MO-SCF calculations have been used to calculate the relative thermodynamic stabilities of the complexes [Fe(CO) 4(CH 3)(CHO)] and [Fe(CO) 4(COCH 3)H]; the results throw light on the relative ease of CO insertion into the FeH or FeCH 3 bond of [Fe(CO) 4(CH 3)H].

Ironcarbon bond formation during substrate activation by hemoproteins

Recent results point to the existence of an important organometallic chemistry of certain hemoproteins, with the formation of ironcarbon bonds during substrate activation. Evidence for such ironcarbon bond formation comes both from spectroscopic studies on the hemoproteins themselves and from model studies on iron-porphyrins. These ironcarbon bonds are formed either upon reduction or oxidation of several substrates [1]. Reduction of benzylhalides, ArCH 2X, by microsomal cytochrome P450 leads to σ-alkyl complexes of this cytochrome involving a Fe(III)CH 2Ar bond. Reduction of halothane,CF 3CHClBr, leads also to a σ-alkyl cytochrome P450Fe(III)CHClCF 3 complexes, whereas microsomal reduction of other polyhalogenated compounds such as CCl 4 or CCl 3CN leads to ironcarbene complexes, cytochrome P450Fe(II) ← CCl 2 (or CClCN). Similar reactions occur upon reduction of the same compounds by iron-porphyrins, the corresponding σ-alkyl or carbene complexes having been isolated and characterized [2]: ▪ Cytochrome P450iron(II)carbene complexes are also formed upon metabolic oxidation of the methylene group of 1,3-benzodioxole derivatives, suggesting a mechanism for CH bond activation by cytochrome P450 that involves the intermediate formation of an ironcarbon bond [3]. Very recently, it has been indicated that σ-alkyl (or -aryl) iron(III) complexes of cytochrome P450 [4] or hemoglobin [4, 5] are formed upon metabolic oxidation of various monosubstituted hydrazines by these hemoproteins. Most often, iron(II)diazene complexes are involved as intermediates in this reaction: ▪ Similar diazene and σ-alkyl complexes are formed upon reaction of RNHNH 2 with ironporphyrins; they have been isolated and characterized [6]. A general scheme for ironcarbon bond formation will be given; it involves a reductive or oxidative activation of the substrate leading to an organic free radical, and the combination of this radical with the hemoproteiniron. Most of these hemoproteinσ-alkyl or carbene complexes have also been detected in vivo; their biological implications will be discussed.

Redox Reltionship between Carbeneiron and σ‐Alkyliron Porphyrins

σ‐Alkyliron porphyrins, both with FeII as well as with FeIII can be generated from carbeneiron (II) porphyrins by cyclovoltammetric reduction. (TPP) Fe(HCCPh2)—a σ‐vinyl‐FeII complex–was also independently synthesized from (TPP)Fe(ClO4) and BrMgCHCPh2; its properties resemble those of the product of the (2e + H⊕)‐reduction of (TPP) Fe(:CCPh2).

A kinetic study of the cleavage of the ironcarbon σ bond in η 5-C 5H 5Fe(CO) 2R by halogenated acetic acids

The rates of the reaction of η 5-C 5H 5Fe(CO) 2R (R = alkyl and aryl) with CF 3CO 2H to give η 5-C 5H 5Fe(CO) 2OC(O)CF 3 and RH wre investigated in organic solvents, mostly at 25°C, by infrared spectroscopic, manometric and volumetric techniques. When R = alkyl, the cleavage in CH 2Cl 2 is first order in η 5-C 5H 5Fe(CO) 2R and first order in the CF 3CO 2H monomer at acid concentrations ⪆0.1 M, but first order in η 5-C 5H 5Fe(CO) 2R and second order in the CF 3CO 2H monemer at lower acid concentrations. The dependence of the second-order rate constant on R follows the order C 5H 5 > CH 5Si(CH 3) 3 (>110) > CH 3 (32) > n-C 4H 9 (15) > C 2H 5 (11) > CH 2C(CH 3) 3 (6.2) > CH 2CH 2C 6H 5 (5.3) > CH(CH 3)C 6H 5 (∼1.2) ⪆ CH 2C 6H 5 (1.0) > CH(CH 3) 2. The isotope effect, k 2/ k D, for the cleavage of η 5-C 5H 5Fe(CO) 2CH 3 by CF 3CO 2H and CF 3CO 2D is 4.7. Solvent influence on the rate of the FeCH 3 bond scission in CH 2Cl 2, CH 2ClCH 2Cl and C 6H 6 is very small. A mechanism is proposed which involves the formation of an Fe-H-OC(O)CF 3 hydrogen-bridged 1 1 adduct of the reactants in a reversible step. This adduct then affords [η 5-C 5H 5Fe(CO) 2(R)H][CF 3CO 2H·O 2CCF 3] with the assistance of a second molecule of CF 3CO 2H. Reductive elimination of RH and coordination to iron of CF 3CO 2 − complecte the reaction. The corresponding cleavage of a given FeR bond by CHCl 2CO 2H is substantially slower than that by CF 3CO 2H; for the aryl complexes it follows the order R = p-C 6H 4CH 3 > p-C 6H 4F > C 6H 5 > p-C 6H 4Cl, with p ∼ −5.4.

Synthesis and structure proof of a new ring system from the reaction of diironnonacarbonyl and naphtho[ b]-cyclopropene

The reaction of naphtho [ b] cyclopropene with Fe 2(CO) 9 in CH 2Cl 2 at 25°C yields at yellow crystalline product, I, in 27% yield. The identity and structure of I were ascertained by spectroscopic, and especially X-ray crystallographic means. The product can be formally regarded as resulting from the addition of an FeC bond of Fe(CO) 5 across one edge of the three-membered ring of naphtho [ b]-cyclopropene. Thus, the iron atom is coordinated in distorted octahedral fashion by four CO groups, the carbon atom of a carbonyl group at the 2 position of naphthalene and the carbon atom of a methylene group at the 3 position of naphthalene. The product, (C 12H 8O)Fe(CO) 4, crystallizes in space group P2 1/ n. The unit cell contains four molecules and has the dimensions a = 9.446(3), b = 6.383(2), c = 23.464(4) Å, β = 91.58(2)°. Using a total of 1731 reflections for which ¦ F 0¦ 2 exceeded 3 times the standard deviation of ¦ F 0¦ 2 the structure was solved and refined to convergence using anisotropic temperature factors for all atoms to give discrepency indices of R 1 = 0.064 and R 2 = 0.081. The CC distances in the naphthalene moeity agree very well with known values for naphthalene itself. The four FeCO distances are 1.815, 1.823, 1.831 and 1.844 Å, the FeCH 2 distance is 2.112(7) Å and the FeC(O) ring distance is 2.035(5) Å.