Synthetic studies relating to acetylergosterol-(tricarbonyl)iron

Acetylergosterol(tricarbonyl)iron has been prepared in good yield using benzylideneacetone(tricarbonyl)iron. The steroidal complex may be hydroborated or subject to osmolysis, to yield potential vitamin D precursors.     

Protonation of homotroponeiron tricarbonyl and cyclooctatrienoneiron tricarbonyl complexes

2,3-Homotroponeiron tricarbonyl, 8-methyl- and 8,8-dimethyl-2,3-homotroponeiron tricarbonyl complexes have been shown to undergo O-protonation in trifluoroacetic (TFA) and 96% sulfuric acids. In the latter acid the O-protonated cations rearrange to give the thermodynamically more stable C-protonated isomers. Cyclooctatrienoneiron tricarbonyl undergoes protonation H₂SO₄ to give the same cation as was obtained from the protonation of the homotroponeiron tricarbonyl complex in H₂SO₄. On the basis of reaction in D₂SO₄, it is suggested that the kinetically preferred site of protonation of the cyclooctatrienone complex is at C(2) one of the coordinated carbon atoms.     

New tricarbonyl(amido-substituted-1,3-diene)iron complexes

X-substituded benzamides (X = H; 2-OH; 4-MeO; 3-MeO; 3,5-(MeO)₂; 4-Cl and 2,4-Cl₂) have been shown to add reversibly to the dienyl rings of the organometallic compounds [(dienyl)Fe(CO)₃]BF₄ (dienyl = C₆H₇, 2-MeOC₆H₆ or C₇H₉) to give the corresponding cationic tricarbonyl(substituted-diene)iron complexes.     

Synthesis of cyclic hydrocarbons via intramolecular coupling of bis-pentadienyl iron tricarbonyl cations

A general synthesis for the preparation of medium sized cycloalkanes having 1,2-butadienyl substituents is described. The reaction sequence involved acylation of butadiene-iron tricarbonyl with a diacid chloride, reduction of the resultant diketone to a diol derivative and conversion with HBF₄ to an acyclic bis-pentadienyl Fe(C0)₃ dicationic complex. Upon treatment with zinc the dication undergoes intramolecular ring closure to afford the bis-Fe(C0)₃ complex of the 1,2-dibutadienyl cycloalkane. Five-, six- and ten-membered cyclolalkene derivatives have been prepared in this manner.     

The diphenylmethylbis(π-chromium tricarbonyl) carbonium ion. Isolation of a stable hexafluorophosphate salt

Reaction of diphenylmercurybis(π-chromium tricarbonyl) with dicobalt octacarbonyl in THF gave benzophenonebis(π-chromium tricarbonyl). Reduction of the latter with NaBH₄ in methanol resulted in formation of the expected alcohol which was treated with hexafluorophosphoric acid in propionic anhydride to give the title carbonium ion salt as a blue solid. This salt was found to alkylate ethanol, diethylamine and pyrrole.     

The unusual iron complex with a trimethylenemethane type ligand, (η5-cyclopentadienyldicarbonylmanganese)- (phenylmethylene)carbomethaneiron tricarbonyl [Cp(CO)2 MnC(CO)CHPh]Fe(CO)3

The binuclear complex with composition [Cp(CO)₂ MnC(CO)CHPh]Fe(CO)₃ is obtained by interaction of CpMn(CCHPh)(CO)₂ with Fe₂C0)₉. An X-ray study of this complex has shown that besides three carbonyl groups the iron atom is covalently bonded to four atoms, viz. the carbon of a phenylmethylene group, the carbon of a bridging CO group, the manganese atom and the central carbon of the organomanganese ligand lying just above iron. It seems to be the first example of a heteroatomic analogue of trimethylenemethane complexes.     

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.     

Fluorimetric determination of iron(III) by a kinetic method

A sensitive and relatively interference-free method for the kinetic determination of iron(III) is described. The method is based on the catalytic action of this ion on the autoxidation process of 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulfonate (disodium salt), to produce a strong pink fluorescence that increases with time. The reaction is monitored at 585 nm, when excited at 525 nm, and the initial rate method is applied to perform the analytical procedure. The influence of reaction variables and the effect of foreign ions are discussed. Iron(III) contents between 0.1 and 1 μg ml^?1 can be determined with R.S.D. of ± 3.7%.     

A correlation between spin state and electrochemical electron-transfer rate for tris(N,N-disubtituted dithiocarbamato) iron(III) complexes

The electrochemical electron-transfer rate constants for the redox systems Fe(IV)L₃⁺/Fe(III)L₃ (L=N,N-disubstituted dithicarbamate ion) and Fe(III)L₃/Fe(II)L₃^? with a variety of substituents were measured at a platinum electrode in acetonitrile with the galvanostatic double-pulse method. It is known that each of the Fe(III) complexes exists both in a highspin state ⁶A₁ and a low-spin state ²T₂ in equilibirium of which position is widely changed by a subtle change in substituent. The standard rate constants for Fe(IV)L₃⁺/Fe(III)L₃ were larger or smaller than those for Fe(III)L₃/Fe(II)L₃^? according as the Fe(III)L₃ complexes are predominantly low- or high-spin complexes. Since the Fe(IV) and Fe(II) complexes are low-and high-spin complexes respectively, these findings suggest that electrochemical electron-transfer reactions accompanied by a spin-state change are slower than those without it. Such spin-state effect on electrode reactions has rarely been discussed so far.     

Isomerization of bicyclo[5.1.0]-2,4-octadieneiron tricarbonyl to bicyclo[4.2.0]-2,4-octadieneiron tricarbonyl

It has been shown that bicyclo[5.1.0]-2,4-octadieneiron tricarbonyl undergoes thermal isomerization to bicyclo[4.2.0]-2,4-octadieneiron tricarbonyl. The first-order rate constant for this process at 120.6° was determined to be 1.8 X 10^?5 s^?1 which corresponds to ΔF³ = 31.8 kcal/mol. Gas chromatographic results coupled with a kinetic analysis very strongly suggest that 1,3,5-cyclooctatrieneiron tricarbonyl is an intermediate in this isomerization. Two plausible mechanisms are offered to explain this rearrangement.     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

The vibrational spectrum of (maleic anhydride)iron tetracarbonyl

On the basis of solid-phase IR and Raman spectra, with some solution data for the IR, a reasonably complete vibrational assignment has been made for the modes of maleic anhydride in (maleic anhydride)iron tetracarbonyl. Shifts in v(C=C) and δ(CH) are consistent with a strong interaction with the metal, but relatively little coupling between the modes. More restricted assignments were made for modes associated with the (maleic anhydride)iron and Fe(CO)₄ fragments.     

Separation of trans-1,2-cyclohexanediaminetetra-acetic acid chelates of bismuth(III), iron(III) and copper(II) by reversed-phase paired-ion chromatography

Trans-1,2-cyclohexanediaminetetra-acetic acid (DCTA) chelates of bismuth(III), iron(III) and copper(II) have been separated by two techniques using reversed-phase paired-ion chromatography. In one, the chelates in aqueous solution were separated within 20 min on a 6.0 × 300 mm ERC-ODS column with 10⁻²M tetrabutylammonium ion (TBA⁺) in methanoi-water mixture (45:55 v/v) as eluent. In the other, the metal ions in aqueous solution were separated within 10 min by direct injection into an ERC-ODS column with 10⁻²M TBA⁺/10⁻³M DCTA in methanoi-water mixture (40:60 v/v) as eluent.     

Electrochemical reduction of tricarbonyl compounds: Reduction mechanism of alloxan on a mercury electrode

A study has been carried out on the reduction mechanism of alloxan over a DME corresponding to the first two-electron transfer over the pH range 0–12.Polarographic and voltammetric results show the reduction process to be kinetically controlled. Rate and equilibrium constant data for the prior chemical reaction have been evaluated and several reaction mechanisms for different pH zones have been proposed.     

Low temperature spectroscopic observation of oxygen-protonated troponeiron tricarbonyl complexes

Troponeiron tricarbonyl and 7-methyltroponeiron tricarbonyl undergo kinetically controlled oxygen protonation at low temperatures to give the corresponding hydroxytropyliumiron tricarbonyl cations, observable by ¹C and ¹H NMR spectroscopy. At higher temperatures, the oxygen-protonated species isomerize to yield the thermodynamically more stable carbon-protonated pentadienyliron tricarbonyl cations.     

Reaction of K[(π-C5H5)Fe(CO)(CN)2] with boranes and AlCl3: Preparation and investigation of iron(II) complexes containing isocyanoborate ligands

Iron(II) complexes containing CNBX^?₃ or CNBX₂NC^? ligands were prepared from the reaction of K[(π-C₅H₅)Fe(CO)(CN)₂] with boranes (BX₃; X = F, Cl, Br H, Ph). Stable, twelve-membered ring compounds containing Fe, C, N, and B atoms were formed involving CNBF₂NC^? and CNBBr₂NC^? ligands. The reaction of K[(π-C₅H₅)Fe(CO)(CN)₂] with AlCl₃ gave a four-center complex with two Fe and two Al atoms. The compounds were studied by infrared and mass spectroscopic methods.     

Thermally induced incomplete high-spin (5T2) ⇌ low-spin (1A1) transition in solid bis[2-(2-pyridylamino)-4-(2-pyridyl) thiazolato]iron (II)

The ⁵⁷Fe Mössbauer effect in two samples (A and B) of [Fe(papt)₂] and in its solvates with CHCl₃ and C₆H₆ has been studied between 4.2 and 343 K and clearly indicates a temperature induced high-spin (⁵T₂) ? low-spin (¹A₁) transition in these compounds [paptH = 2-(2-pyridylamino)-4-(2-pyridyl) thiazole]. At 343 K, sample B shows a doublet with ΔE_Q = 2.03 mm s^?1 and δIS = +0.87 mm s^?1, characteristic of a ⁵T₂ ground state. At 257 K, a second doublet, typical for a ¹A₁ ground state, is observed and its intensity increases as the transition progresses but levels off below ～ 100 K. At 4.2 K, 83% of the intensity is due to the ¹A₁ state, and ΔE_Q(¹A₁) = 1.56 mm s^?1 and δ^IS(¹A₁ = +0.32 mm s^?1. In an applied magnetic field, V_zz(¹A₁) < 0 and η ≈ 0.7 have been determined, whereas for the ^sT₂ ground state, V_zz(^sT₂) > 0, η ≈ 0.75, and an internal hyperfine field H_n ≈ ?13 kG have been observed. Similar results have been obtained with the other samples.Debye-Waller factors f5_T2 and f1_A1 were determined from the saturation corrected areas in the Mössbauer spectra, assuming Curie-Weiss dependence of the magnetic susceptibility for the ⁵T₂ and constant υ_cff for the ¹A₁ ground state. The temperature dependence of ?In f1_A1 closely follows the Debye model with Θ1_A1 = 165 K, whereas the same applies to ?ln f5_T2 only above ～ 210 K and Θ5_T2 = 134 K. The nature of the observed transition is discussed and the data presented are shown to be incompatible with a model based on a Boltzmann distribution between the two states.     

The redox properties of organotransition-metal complexes IV. The activation of cyclic polyolefiniron tricarbonyl derivatives by one-electron oxidation

Cyclic polyolefiniron tricarbonyl derivatives [Fe(CO)₂L(C_nH_m)] (L = CO or phosphorus donor) and oxidising agents such as Ag⁺ or [NO]⁺ in CH₂Cl₂ give reactive paramagnetic cations [Fe(CO)₂L(C_nH_m]⁺ which can abstract hydrogen from the solvent to give [Fe(CO)₂L(C_nH_{m + 1})]⁺.     

Co-nonsolvent systems for poly(ϵ-caprolactone) and poly(methyl methacrylate)

The cloud points for the co-nonsolvent systems (i) pyridine (PY) + formic acid (FA) towards poly(?-caprolactone) (PCL) or poly(methyl methacrylate) (PMMA) and (ii) pyridine + acetic acid (AA) towards PCL have been experimentally determined as a function of solvent composition at fixed polymer concentrations. Heats of mixing for the (FA + PY) system have also been measured. The single liquid approximation model correctly predicts for the (PY + FA) system the solvent composition at which the solvent power of the mixture is the poorest, provided it is recognized that the solvent system is comprised of pyridinium formate (PYFA) as one component and either PY or FA (depending on which is present in excess over 1:1 mole ratio) as the other. With the other co-nonsolvent system, the prediction is not as good. A possible reason for the discrepancy has been given.