Iron Acyl Complexes Research Articles

Sugar Acyl Iron Complexes: Synthesis and Conformational Studies in Solution and in the Solid State1

A synthetic strategy based on a combination of a sugar electrophile and a transition metal nucleophile allows a metal acyl functionalization at the C-1 carbon atom of acyclic carbohydrates. Following this methodology the per-O-acetylated acyl iron complexes dicarbonylcyclopentadienyl[2,3,4,5,6-penta-O-acetyl-D-galactonyl]iron(II) (6), dicarbonyl cyclopentadienyl[2,3,4,5,6-penta-O-acetyl-D-gluconyl]iron(II) (7), dicarbonylcyclopentadienyl[2,3,4,5-tetra-O-acetyl-L-arabinonyl]iron(II) (8), and dicarbonylcyclopentadienyl-[2,3,4,5-tetra-O-acetyl-D-ribonyl]iron(II) (9) are accessible in high yields. 1H NMR studies indicate that in solution the galacto and arabino (6, 8) complexes adopt planar zigzag conformations, whereas the gluco and ribo (7, 9) analogs prefer non-extended (“sickle”) conformations. A similar conformational preference is observed for the solid state as established by X-ray studies on the galacto and gluco derivatives 6 and 7, underlining the strong impact of syn-1,3-interactions of the protecting groups on the conformation adopted. cPermanent address: Department of Chemistry, University of Jyväskylä P. O. Box 35, Fin-40351 Jyväskylä, Finland 1. Organotransition Metal Modified Sugars, Part 3. - For Part 2, see: K. H. Dotz, 0. Neuß and M. Nieger, Synlert, 1996, 995. Dedicated to Professor Dr. Peter Welzel on the occasion of his 60th birthday

Cathodic carbonylation. Synthesis of aliphatic aldehydes using an electroreductively generated iron-carbonyl anion

Alkyl halides are electroreductively coupled with pentacarbonyliron to generate the acyliron complexes. After hydrolytic work-up, these anionic acyl compounds produce aldehydes in good yields. The best results were obtained with the bromide as starting halide. The first step in the formation of acyliron complexes is the direct cathodic reduction of [Fe(CO)5] to the anionic species. Synthetic and mechanistic aspects of the reaction are discussed.

Synthesis of Novel Alkynyl-substituted Iron Acyl and Carbene Complexes via Mixed Anhydrides

The synthesis of novel (alkynyl)-substituted iron acyl complexes has been achieved via a mixed anhydride procedure starting from the carboxylic acids. Aminolysis studies of the corresponding cationic (alkynyl)methoxycarbene iron complexes are described.

A Convenient Synthesis of β,γ-Unsaturated Carboxylic Acid Derivatives via Carbonylation of (η3-Allyl)Fe(CO2NO Complexes

One-pot reaction of allyl halides with [Bu 4 N] + °Fe(CO) 3 (NO)] - follo- wed by treatment with 1,2-bis(diphenylphosphino)ethane gave β,γ-unsatu- rated acyl iron complexes in good yields via regioselective carbonyla- tion with retention of configuration of the allylic double bond. β,γ-Un- saturated carboxylic acid esters and amides were prepared upon treat- ment of the acyl iron complexes with alcohols and amines in the presence of iodine

ChemInform Abstract: Asymmetric Synthesis of (S)‐(‐)‐Methyl Tropinate: Application of the Iron Acyl Complex (S)‐(+)‐((η5‐C5H5)Fe(CO)(PPh3)COCH2Ph) as a Homochiral Phenylacetate Enolate Equivalent.

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Multicarbonylation of Cyclopentadienyl and Cycloheptatrienyl Anions by Fe(CO)5

Abstract The reaction of cyclopentadienyl anions with Fe(CO)5 in the presence of acyl chlorides or carboxylic anhydrides gave cyclic acyliron complexes [η5-C5H4C(OCOR)=C(OCOR)CO]Fe(CO)2 via triple carbonylation of the anions and a double acylation. The structure of [η5-C5H4C(OCOCH2CH3)=C(OCOCH2CH3)CO]Fe(CO)2 thus obtained was confirmed by the X-ray analysis. Diastereomers of indenyl derivative [η5-C9H6C(OCOCH2CH3)=C(OCOCH2CH3)CO]Fe(CO)(P(OCH3)3) were prepared by substitution of CO ligand with trimethyl phosphite and the structure of the diastereomers were characterized by NMR spectroscopy using 2D technique. Treatment of cycloheptatrienyl anion with Fe(CO)5 and acyl chloride resulted in double carbonylation to give [η5-C7H6C(OCOR)=C(OCOR)]Fe(CO)2. The mechanism of the reaction is proposed.

Pressure effects on the photoreactions of the iron acyl complex (.eta.5-C5H5)Fe(CO)2(COCH3). Mechanistic implications regarding competitive reactions of the solvento intermediate (.eta.5-C5H5)Fe(CO)(Sol)(COCH3)

Author(s): Ryba, DW; van Eldik, R; Ford, PC | Abstract: Photolysis of CpFe(CO)2(COCH3) (Cp = η5-C5H5) plus P(OCH3)3(L) in n-heptane solutions leads to the competitive decarbonylation to give CpFe(CO)2CH3 and ligand substitution to give CpFe(CO)L(COCH3). The application of hydrostatic pressure changes the relative quantum yields of the two processes, higher pressure strongly favoring the ligand photosubstitution pathway. These differences are interpreted in terms of the competitive reactions of the solvento intermediate CpFe(CO)(Sol)(COCH3) (S), shown previously (J. Am. Chem. Soc. 1991, 113, 9524–9528) to be formed by the initial photolysis step, i.e., the labilization of CO. The much more negative apparent activation volume for the ligand substitution pathway suggests that this proceeds via an associative mechanism of S, while the competing methyl migration to the metal may require simultaneous dissociation of the coordinated solvent molecule, Sol. © 1993, American Chemical Society. All rights reserved.

Asymmetric synthesis of (S)-(−)-methyl tropinate: application of the iron acyl complex (S)-(+)-[(η 5-C 5H 5)Fe(CO)(PPh 3)COCH 2Ph] as a homochiral phenylacetate enolate equivalent.

Treatment of the lithium enolate derived from homochiral ( S)-[(η 5-C 5H 5)Fe(CO)(PPh 3)COCH 3 5 with benzyne afforded the homochiral phenylacetyl complex ( S)-[(η 5-C 5H 5)Fe(CO)(PPh 3)COCH 2Ph] 4. Treatment of the lithium enolate derived from 4 with ClCH 2OCH 2Ph furnished the homochiral α-substituted complex ( S, S)-(−)-[(η 5-C 5H 5)-Fe(CO)(PPh 3)COCH(CH 2OCH 2Ph)Ph] 14 (d.e. > 98%), which on decomplexation and debenzylation afforded ( S)-(−)-methyl tropinate ( S)- 2 (e.e. > 98%).

Reactions of acyl(carbonyl)ruthenium(II) and acyl(carbonyl)iron(II) complexes with amines. Preparation of novel propionyl(carbamoyl)ruthenium(II) complexes

Treatment of Ru(COEt)Cl(CO)(PPh 3) 2 ( 1) with secondary amines (R 2NH) under pressure of CO and / or ethylene gives propionyl-carbamoyl complexes Ru(COEt)(CONR 2)(CO)(PPH 3) 2 (NR 2 = NEt 2 ( 4a), N(CH 2) 4CH 2 ( 4b), NMe, ( 4c)) together with the ammonium salt R 2NH 2Cl. Complexes 4a–c have been isolated as pale yellow crystals and characterized by means of NMR and IR spectroscopy and elemental analysis. Reactions of Fe(COMe)I(CO) 2(PMe 3) 2 and [Fe(COMe)(CO) 3(PMe 3) 2]BF 4 with nucleophiles (HNEt 2, LiNMe 2, EtOH (in conjunction with Et 3N) and NaOMe) give the corresponding acetamides and acetic acid esters. The carbonyl(propionyl)ruthenium complex 1 in solution under CO pressure was found to undergo nucleophilic attack of secondary amines on the coordinated CO ligand to give isolable acyl(carbamoyl)ruthenium complexes 4 in a parallel behavior with the previously reported acyl(carbonyl) palladium complexes [4g,h]. However, the isolated acyl(carbamoyl)ruthenium complexes differ in their behavior from the palladium analogs in their inactivity to release α-keto amide. The exact reason for the different behavior is not clear. A possible explanation for the reluctance of reductive elimination from the acyl(carbamoyl)ruthenium complex is that the acyl and the carbamoyl ligands are situated at unfavorable sites for a concerted reductive elimination to occur. In a theoretical treatment of reductive elimination of two organic groups from a five-coordinated nickel complex, it has been discussed that (i) the organic ligands both situated at equatorial positions in a trigonal-bipyramidal complex are symmetrically forbidden to undergo the reductive elimination process, and (ii) kinetic barriers for pseudorotation to bring the concerned organic ligands to axial and equatorial sites are very high [13]. A similar argument might be advanced in the present case but we would rather defer from advancing the discussion further until more bis-acyl type complexes are prepared and their behavior examined.

CC Bond Formation via Carbon‐Centered Radicals Generated from Dicarbonyl(η5‐cyclopentadienyl) organoiron Complexes

AbstractIrradiation of benzyldicarbonyl(η5‐cyclopentadienyl)iron complex (2) leads to hemolytic cleavage of the FeC bond. In the presence of activated alkenes, radical addition occurs and both saturated and unsaturated addition products 7–9 are formed. Photolysis of alkyliron complexes 2,3 and 20 in the presence of acrylonitrile leads to the same products as the irradiation of the respective acyliron complexes 28–30. This indicates that, under photolytical conditions, alkyl and acyl complexes are in equilibrium with each other.

Exploration of the [3 + 2] Cycloaddition Reaction Between Allylstannanes and α,β-Unsaturated Acyliron Complexes

The reaction between allylstannanes and α,β-unsaturated acyliron complexes has been investigated. Contrary to the behavior of other α,β-unsaturated carbonyl compounds, α,β-unsaturated acyliron complexes react with allylstannanes to produce predominately cyclopentane derivatives with a high degree of stereoselectivity. The initial cycloadducts contain acyliron and trialkylstannyl functionalities, which are readily converted to ester and alcohol groups, respectively, with complete retention of stereochemistry. Transition state models involving a synclinal orientation of reactants have been proposed to explain the observed stereochemistry. Studies of cyclization reactions of 5-hexenylstannanes have also been described. 1. Introduction 2. Why Examine the Reaction Between Allylstannanes and α,β-Unsaturated Acyliron Complexes in the First Place? 3. Optimization of the Reaction Between Allyltributyltin and Acryloyldicarbonyl(η-cyclopentadienyl)iron (2). 4. Will Allyltributyltin React with Other α,β-Unsaturated Acyliron Complexes in the Same Manner? 5. Will Acryloyliron Complex 2 React Similarly with Other Allylic Tributylstannanes? 6. Reactions in which Both Cycloaddition Partners Bear Additional Substituents 7. What Do Other Allylmetal Complexes Do? 8. Development of Methods for Conversion of the Metals to Simpler Functional Groups 9. Development of New C-Sn Bond Cleavage Reactions 10. Assignment of Stereochemistry 11. What Is the Mechanism of the Reaction? 12. How Do We Explain the Observed Stereoselectivity? 13. What's So Great About This Model? 14. Why Do α,β-Unsaturated Acyliron Complexes Behave So Differently from Other α,β-Unsaturated Carbonyl Compounds? 15. How Do We Explain Those Cases Where Open-Chain Products Are Obtained? 16. Summary and Outlook

ChemInform Abstract: Reaction of Allylstannanes with Cationic α,β‐Unsaturated Alkoxycarbeneiron Complexes.

AbstractMethylation of the acyliron complexes (I) with dimethoxycarbenium hexafluorophosphate, generated in situ from triphenylcarbenium hexafluorophosphate (III) and trimethyl orthoformate (II), yields the carbene complexes (IV) which are coupled in situ with the allylstannanes (V) and then demethylated to produce the hexenoyliron complexes (VII).

Reaction of allylstannanes with .alpha.,.beta.-unsaturated acyliron complexes: stereoselective synthesis of cyclopentane derivatives

The reaction between allylstannanes and α,β-unsaturated acyliron complexes has been examined. When the reaction is conducted in the presence of Lewis acids, [3+2] cycloaddition products are obtained with extremely high degrees of stereoselectivity. The [3+2] cycloadducts contain acyliron and organotin functionalities. The acyliron group is easily converted to the corresponding ester by treatment with N-bromosuccinimide in the presence of alcohols. The tributyltin group can be converted to a hydroxy group by treatment with bromine followed by treatment with peracids and amine bases; this transformation occurs with complete retention of stereochemistry

ChemInform Abstract: Chiral Recognition in the Reaction of the Enolate Derived from ((η5‐C5H5)Fe(CO)(PPh3)COCH2OCH2Ph) with 1‐Phenylethyl Bromide.

AbstractThe racemic phenylethyl bromide (IV) reacts with the racemic lithium enolate (III) under chiral recognition to produce the diastereoisomerically pure iron acyl complex (V) which is oxidatively demetalated, yielding the dibenzyl acetal (VI).

Cyclopentannulation reactions with organoiron reagents. Facile construction of functionalized hydroazulenes

Troponeiron tricarbonyl, 2-methyltroponeiron tricarbonyl, and 4-methyltroponeiron tricarbonyl are converted to fluxional tropyliumiron tricarbonyl salts by treatment with either trimethylsilyl or di-n-butylboron triflate. These pentadienyliron cations react with (η 1 -allyl)-, (η 1 -propargyl)-, and (η 1 -allenyl)Fp complexes [Fp=C 5 H 5 Fe(CO) 2 ] to give ketohydroazulene cycloadducts derived, in each reaction, from a single tautomeric tropyllium cation. The further reaction of two such cycloadducts with lithium dimethyl cuprate gave tricyclic ketones, through a sequence depicted as involving initial formation of an anionic acyliron complex, followed by migratory insertion and an intramolecular aldol condensation

Organische Synthesen mit Übergangsmetallkomplexen, 42 Allene als Liganden in zweikernigen Eisencarbonyl‐Komplexen; Carbonylierungen von Allenen sowie deren Kupplung mit Alkinen und Allenen; dynamische “Keten‐Scheibenwischer”‐Komplexe

Organic Syntheses via Transition Metal Complexes, 42. - Allenes in Dinuclear Iron Carbonyl Complexes; their Carbonylation and Coupling with Alkynes and Allenes; Fluxional “Ketene Windshield-Wiper” Complexes On photochemically induced metallation with pentacarbonyl iron allenes H2C = C = CHR 1 (R = H, C6H5) give dinuclear acyl iron complexes 2, in which the central carbon of the C = C = C unit is attached to a carbonyl group. 2 on warming yield π-ally1,σ complexes 3 by loss of carbon monoxide. The reaction 2 ⇌ 3 + CO is reversibel. 3 add alkynes R1 - C = C - R24 (R1 = C6H5r, CH2OCH3; R2 = Hr C6H5) with insertion of the C = C triple bond into the M - C σ-bond to give dinuclear ketene complexes 5. The latter are fluxional, as was shown by NMR measurements. The ketene unit is moving back and forth like a windshield wiper. Thermolysis of 5 under normal pressure affords ferracyclopentadiene iron complexes 6 (by 1,3-hydrogen shifts) and 4-methylene-2-cyclopenten-1-one 7 (by cyclocarbonylation). Thermolysis of 5 under CO pressure gives 7 as the sole products. Complexes 3 also add allenes 1 with insertion into the M–C σ-bond and formation of a C–C bond between the central carbon atoms of both allene units to give dinuclear bis(allyl) complexes 8 and 8′.

Chiral recognition in the reaction of the enolate derived from [(η5-C5H5)Fe(CO)(PPh3)COCH2OCH2Ph] with 1-phenylethyl bromide

Chiral recognition to the extent of 30 : 1 has been observed in the reaction between the homochiral iron acyl complex [(η5-C5H5)Fe(CO)(PPh3)COCH2OCH2Ph] and racemic 1-phenylethyl bromide.

ChemInform Abstract: Asymmetric Synthesis of Differentially Protected α‐Alkyl Succinates.

AbstractThe chiral acyliron complexes (III), prepared by alkylation of the acetyl complex (I) with the iodides (II), are diastereoselectively coupled with the bromoacetate (IV) to produce the new iron succinoyl complexes (V).

ChemInform Abstract: The Asymmetric Synthesis of cis‐Substituted Cyclopropanecarboxylic Acid Derivatives.

AbstractCyclopropanation of the racemic α,β‐unsaturated acyliron complexes (±)‐(I) with methylene iodide (II) in the presence of diethylzinc/ZnCl2 or triethylaluminum gives the diastereomeric cyclopropanes (III) and (IV) with predominance of (III).

ChemInform Abstract: Palladium‐Catalyzed Reaction of Acyliron Complexes with Aryl Halides. A Convenient Synthesis of Aromatic Ketones.

Acyliron complexes, easily prepared from disodium tetracarbonylferrate and alkyl halides, reacted with aryl iodides in the presence of a catalytic amount of Pd(PPh3)4 and a cocatalyst, ZnCl2, to give aromatic ketones in good yields. (R)-2-Methyl-1-phenyl-1-octanone was prepared starting from (S)-2-bromooctane in an excellent optical yield.