Iron Acyl Complexes Research Articles

Synthesis and reactivity of (pyrazol-1-yl)acyl iron complexes

Treatment of 1-methyl-3,5-dialkylpyrazoles with n-BuLi, and subsequently with iron carbonyl and iodine yielded (pyrazol-1-yl)acyl iron complexes CH2(CO) (3,5-R2Pz)Fe(CO)3I (R = Me or Pri, Pz = pyrazol-1-yl). Reaction of CH2(CO) (3,5-Me2Pz)Fe(CO)3I with PhSNa gave a dimeric complex [CH2(CO) (3,5-Me2Pz)Fe(CO)2(SPh)]2, while similar reactions of CH2(CO) (3,5-R2Pz)Fe(CO)3I with PySNa (Py = 2-pyridyl) gave mononuclear complexes CH2(CO) (3,5-R2Pz)Fe(CO)2(SPy), which exhibited an isomerization in solution. Treatment of the dimeric complex with PPh3 at room temperature resulted in the decomposition of the starting material. Furthermore, this dimeric complex readily underwent reductive elimination to generate CH2(COSPh) (3,5-Me2Pz) when heated at relatively low temperature, and thermal decomposition reaction to give PhSSPh in refluxing toluene solution. Reaction of mononuclear complexes with PPh3 caused one carbonyl to be replaced by phosphine ligand to give complexes CH2(CO) (3,5-R2Pz)Fe(CO) (PPh3) (SPy). All these acyl iron complexes were fully characterized by IR and NMR spectroscopy, and their structures were unambiguously determined by X-ray crystallography.

Theoretical study of iron acyl complexes modeling the active site of [Fe]-hydrogenase: Solvation effects play a significant role

In this work, density functional theory (DFT) calculations were carried out to study the role of solvation effects on the reaction of diiron dithiolate complex with CO to form [Fe]-hydrogenase model complex. In the gas phase, the energy barrier of the first transition state TS1 species is ca. 6.1kcal/mol higher than the second transition state TS2 species. However, when the solvation effects were included, the energy order was reversed, i.e., the energy barrier of TS1 falls ca. 1.2kcal/mol lower than TS2, indicating that the insertion of the second CO to iron is the rate-determining step in the whole transformation process. The initial insertion of the CO plays an important role in increasing the reaction barrier of the binding of a second CO, which prevented the second step transformation. Thus, the solvation effects play a significant role in determining the reaction mechanism. In addition, the energy of PC species is lower than RC species, demonstrating that this transformation is a significantly exothermic process.

Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)[dbnd]C(OMe)CH[dbnd]CHR

The conjugate additions of alkyllithium reagents to alkoxycarbene cations of the iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)C(OMe)CHCHR]+ proceeded with moderate to excellent diastereoselectivity. The resultant methoxyvinyl complexes were transformed into the corresponding iron acyl complexes following a sequence of protonation and demethylation. The overall transformation yields iron acyl complexes of opposite relative configuration to those which result from the conjugate addition of the same nucleophile to the corresponding α,β-unsaturated iron acyl complex.

Synthesis of acyl iron complexes based on bis(heteroaryl)methanes

Treatment of the lithium salts, derived from the lithiation of bis(pyrazol-1-yl)methanes, bis(1-methylimidazol-2-yl)methane [CH2(mim)2] and 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine [CH2(3,5-Me2Pz)(Py)] using n-BuLi at low temperature, with iron carbonyl and iodine resulted in significantly different acyl iron derivatives. Reaction of bis(pyrazol-1-yl)methanes with n-BuLi, and subsequently with iron carbonyl and iodine yielded bis(pyrazol-1-yl)acyl iron complexes, while similar reaction of CH2(mim)2 gave valeryl iron complex CH2(mim)2Fe(CO)2(COBu-n)I, which was also obtained by the sequential treatment of iron carbonyl with n-BuLi, CH2(mim)2 and iodine. Additionally, the consecutive reaction of CH2(3,5-Me2Pz)(Py) with n-BuLi, iron carbonyl and iodine yielded (3,5-dimethylpyrazol-1-yl)(2-pyridyl)acyl iron complex. The corresponding valeryl iron complex CH2(3,5-Me2Pz)(Py)Fe(CO)2(COBu-n)I was obtained when iron carbonyl was reacted with n-BuLi, and subsequently with CH2(3,5-Me2Pz)(Py) and iodine. However, analogous valeryl iron complexes supported by bis(pyrazol-1-yl)methanes could not be formed by these methods. The different electron-donating ability of these bis(heteroaryl)methanes and the distinct nucleophilicity of the bis(heteroaryl)methyl carbanions were possibly responsible for the diversification of reactivities. All these acyl iron complexes were fully characterized by IR and NMR spectroscopy, and their structures were unambiguously determined by X-ray crystallography.

ChemInform Abstract: [Fe]‐Hydrogenase and Models That Contain Iron—Acyl Ligation

AbstractReview: 39 refs.

Fe]‐Hydrogenase and Models that Contain IronAcyl Ligation

[Fe]-hydrogenase is a newly characterized type of hydrogenase. This enzyme heterolytically splits hydrogen in the presence of a natural substrate. The active site of the enzyme contains a mono-iron complex with intriguing iron-acyl ligation. Several groups have recently developed iron-acyl complexes as synthetic models of [Fe]-hydrogenase. This Focus Review summarizes the studies of this enzyme and its model compounds, with an emphasis on our own research in this area.

Carbonylation of alkyl halides with [Fe(CO)3(NO)]−: in silico identification of a common intermediate

The mechanism of carbonylation of alkyl halides using [Fe(CO)3(NO)](-) has been studied using density functional theory (DFT). Our results suggest an SN2 mechanism for the alkylation event followed by a well-defined oxidative addition and alkyl migration. An experimentally elusive common intermediate [Fe(CO)2NO(Ac)] has been identified in two isomers and reacted in silico with a number of ligands (CO, PH3 and PPh3) to give the corresponding iron acyl complexes. Pathways between the two isomers, including direct involvement of a solvent molecule (THF) or iodide, have been elucidated.

ChemInform Abstract: Reaction of Allylstannanes with α,β-Unsaturated Acyliron Complexes: Stereoselective Synthesis of Cyclopentane Derivatives.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Asymmetric Synthesis of β-Lactams and Pseudopeptides via Stereoselective Conjugate Additions of Lithium (α-Methylbenzyl)allylamide to α,β-Unsaturated Iron Acyl Complexes.

Lithium (α-methylbenzyl)allylamide 2 undergoes stereoselective conjugate additions to α,β-unsaturated iron acyl complexes 3a–c to afford β-amino iron acyl adducts 5a–c and 6a–c. These adducts may be deallylated smoothly using palladium(0) catalysis providing the corresponding homochiral secondary amines 7a–c which, upon oxidative decomplexation with bromine or N-bromosuccinimide, undergo direct β-lactam ring formation. The diastereoselectivity for the conjugate addition to 3a may be further improved by the use of magnesium amide 10. Oxidative decomplexation of one of the β-amino iron acyl adducts 5b in the presence of α-amino esters provides pseudopeptide fragments comprising an α-amino acid coupled to a β-amino acid.

Synthesis and Reactivity of Iron Acyl Complexes Modeling the Active Site of [Fe]-Hydrogenase

A [Fe(II)Fe(II)] dithiolate complex containing acyl and carbonyl ligands was synthesized. The diiron complex reacted with phosphine, cyanide, isocyanide, and CO to give monomeric Fe(II) complexes reproducing the first coordination sphere of the active site of [Fe]-hydrogenase (H(2)-forming methylene-tetrahydromethanopterin dehydrogenase, Hmd) in various states. All the acyl and carbonyl carbons in the diiron complex underwent facile isotopic exchange with (13)CO via monomeric Fe tricarbonyl intermediates.

Stereoselective conjugate addition reactions of lithium amides to α,β-unsaturated chiral iron acyl complexes [(η 5-C 5H 5)Fe(CO)(PPh 3)(COCH [dbnd]CHR)

Conjugate addition of achiral lithium dimethylamide to the chiral iron cinnamoyl complexes ( S, E)- and ( S, Z)-[(η 5-C 5H 5)Fe(CO)(PPh 3)(COCH CHPh)] proceeds with high diastereoselectivity, with this protocol being used to establish unambiguously the absolute configuration of Winterstein’s acid (3- N, N-dimethylamino-3-phenylpropanoic acid) as ( R). The highly diastereoselective conjugate addition of lithium N-benzyl- N-trimethylsilylamide to a range of α,β-unsaturated iron acyl complexes, followed by in-situ elaboration of the derived enolate by either alkylation or aldol reactions is also demonstrated, facilitating the stereoselective synthesis of both cis- and trans-β-lactams. This methodology has been used to effect the formal asymmetric syntheses of (±)-olivanic acid and (±)-thienamycin. Addition of chiral lithium amides derived from primary and secondary amines to the iron crotonyl complex [(η 5-C 5H 5)Fe(CO)(PPh 3)(COCH CHMe)] indicates that lithium N-α-methylbenzylamide shows low levels of enantiorecognition, while lithium N-3,4-dimethoxybenzyl- N-α-methylbenzylamide and lithium N-benzyl- N-α-methylbenzylamide show high levels of enantiodiscrimination. The high level of observed enantiorecognition was used to facilitate a kinetic resolution of ( RS)-[(η 5-C 5H 5)Fe(CO)(PPh 3)(COCH CHMe)] with homochiral lithium ( R)- N-3,4-dimethoxybenzyl- N-α-methylbenzylamide. Further mechanistic studies show that conjugate additions of ( RS)-lithium N-benzyl- N-α-methylbenzylamide to either the ( RS)- or homochiral iron crotonyl complex show 2:1 stoicheiometry, while homochiral lithium N-benzyl- N-α-methylbenzylamide shows 1:1 stoicheiometry.

Asymmetric synthesis of tetracyclic substructures of Strychnos indole alkaloids

The addition of the enolate of methyl 1-methyl-2-indoleacetate 1 and lithium 2-(lithiomethyl)indole-1-carboxylate 5 to pyridines and N-alkylpyridinium salts bearing a chiral auxiliary at the 3-position (tolylsulfinyl, acyl iron complexes, bornane-10,2-sultam), with subsequent acid cyclization of the resulting dihydropyridines, is investigated.

Metal complexes of anionic 3-borane-1-alkylimidazol-2-ylidene derivatives

Addition of BH 3·thf to 1-alkylimidazoles (alkyl=methyl, butyl) and 1-methylbenzimidazole leads to BH 3 adducts, which are deprotonated by BuLi to yield the organolithium compounds (L)Li +( 1b– d) −. In the solid state (thf)Li + 1b − is dimeric. The acyl–iron complexes (thf) 3Li +( 3b, d) − are formed from (thf)Li +( 1b, d) − and Fe(CO) 5. (L)Li +( 1a– c) − react with [CpFe(CO) 2X], however, the only complex obtained is [CpFe(CO) 2 1a] (5a). The analogous reaction of (L)Li + 1a − with the pentadienyl complex [(C 7H 11)Fe(CO) 2Br] yields the corresponding iron compound 6a. Their compositions follow from spectroscopic data. Treatment of Cp 2TiCl with (L)Li + 1a − leads to [Cp 2Ti 1a] ( 7a), which could not be oxidized with PbCl 2 to give the corresponding Ti(IV) complex. The compounds [Li(py) 4] + 9a − and [Li(L) 4] +( 10b– d) − are obtained when (L)Li + 1 − are reacted with VCl 3 and ScCl 3. The X-ray structure analysis of the vanadium complex reveals a distorted tetrahedron of the anion [V( 1a) 4] − with two smaller and four larger CVC angles. The scandium compound [Li(dme) 2 + 10c −] has a different structure: the distorted tetrahedron of the anion [Sc( 1c) 4] − contains two larger (140.2 and 142.9°) and four smaller CScC angles (93.9–98.7°). This arrangement allows the formation of four bridging BHSc 3c,2e bonds to give an eight-fold coordination. The anion 10c − is formally a 16e complex.

Remarkable Reactions of (η4-1-azadiene)Fe(CO)3 Complexes with Aryllithium Reagents. Syntheses and Structures of Novel Chelated Furanyl-Coordinated Alkoxy(amino)carbeneiron, η4-Azadiene-Coordinated 17e Acyliron, and Iron Inner Salt Complexes

The reactions of a (η4-1-azadiene)Fe(CO)3 complex, [(η4-C4H3OCHCHCHNC6H11)Fe(CO)3] (1), with aryllithium reagents, ArLi (Ar = C6H5, p-CH3C6H4, o-CH3OC6H4, p-CH3OC6H4, p-CF3C6H4), in ether at low temperature followed by alkylation with Et3OBF4 in aqueous solution at 0 °C or in CH2Cl2 at −60 °C gave novel chelated furanyl-coordinated alkoxy(amino)carbeneiron complexes [{η4-C4H3OCHCHCH(Ar)N(C6H5)C(OC2H5)}Fe(CO)2] (4, Ar = C6H5; 5, Ar = p-CH3C6H4; 6, Ar = o-CH3OC6H4; 7, Ar = p-CH3OC6H4; 8, Ar = p-CF3C6H4). The analogous reactions of compounds [(η4-C4H3OCHCHCHNC6H11)Fe(CO)3] (2) and [(η4-C6H5CHCHCHNC6H11)Fe(CO)3] (3) with ArLi (Ar = C6H5, o-, m-, p-CH3C6H4) afforded novel η4-azadiene-coordinated 17e acyliron complexes [{η4-C4H3OCHCHCHNC6H11}Fe(CO)2(COAr)] (9, Ar = C6H5; 10, Ar = o-CH3C6H4; 11, Ar = m-CH3C6H4; 12, Ar = p-CH3C6H4) and [(η4-C6H5CHCHCHNC6H11)Fe(CO)2(COAr)] (15, Ar = C6H5; 16, Ar = m-CH3C6H4; 17, Ar = p-CH3C6H4), respectively. Unexpectedly, 2 reacts similarly with p-CH3OC6H4Li and p-CF3C6H4Li to yi...

Novel organoiron compounds resulting from the attempted syntheses of dibenzofulvalene complexes

Thermal reaction of 2,2′-biindenyl with Fe(CO) 5 generates (η 4-2,2′-biindenyl)Fe(CO) 3 and a ferrole isomer of (μ,η 3:η 3-dibenzo[b,e]fulvalene)Fe 2(CO) 6. Reaction of the dianion of dibenzo[b,e]fulvalene with iron carbonyls produced a novel cyclized acyliron complex, whose structure was proven by X-ray crystallography; a mechanism is proposed for its formation. Reaction of the same dianion with (η 5-cyclopentadienyl)Fe(CO) 2Br generated another novel cyclic compound (C 18H 12)Fe(CO) 2(C 5H 4), probably via intramolecular radical attack on the η 5-bound cyclopentadienyl ring. Treatment of dibenzo[a,d]fulvalene with Fe 2(CO) 9 generates (η 2-dibenzo[a,d]fulvalene)Fe(CO) 4, (μ,η 2:η 2-dibenzo[a,d]fulvalene)Fe 2(CO) 8, and two compounds with bis(η 5) structures. These appear to have CO and Fe(CO) 4 groups inserted into the reactive Fe–Fe bond of (μ,η 5:η 5-dibenzo[a,d]fulvalene)Fe 2(CO) 4.

Formation of Acyliron Complexes CpFe(CO){P(OR′)3}COR′ by Reaction of Silyliron Complexes CpFe(CO)2SiR3 with Alkylphosphites P(OR′)3

Abstract Heating a toluene solution of CpFe(CO)2SiR3 (R3 = HMe2, HEt2, and FMe2) and excess P(OR′)3 (R′ = Me, Et, and Me-d3) at 80 °C resulted in the formation of an acyliron complex CpFe(CO){P(OR′)3}COR′ in 25–40% yield: Hence the alkyl group of phosphite is transferred to the carbon of a carbonyl ligand to give an acyl ligand during the reaction.

Asymmetric synthesis of β-lactams and pseudopeptides via stereoselective conjugate additions of lithium (α-methylbenzyl)allylamide to α,β-unsaturated iron acyl complexes

Lithium (α-methylbenzyl)allylamide 2 undergoes stereoselective conjugate additions to α,β-unsaturated iron acyl complexes 3a–c to afford β-amino iron acyl adducts 5a–c and 6a–c. These adducts may be deallylated smoothly using palladium(0) catalysis providing the corresponding homochiral secondary amines 7a–c which, upon oxidative decomplexation with bromine or N-bromosuccinimide, undergo direct β-lactam ring formation. The diastereoselectivity for the conjugate addition to 3a may be further improved by the use of magnesium amide 10. Oxidative decomplexation of one of the β-amino iron acyl adducts 5b in the presence of α-amino esters provides pseudopeptide fragments comprising an α-amino acid coupled to a β-amino acid.

Borane-Substituted Imidazol-2-ylidenes: Syntheses, Structures, and Reactivity⋆

Reactions of the Lewis acids BH3 and BEt3 with trimethylimidazole (1) lead to the borane adducts 2a and 2b. Deprotonation of 2a with n-butyllithium results in the formation of the novel N-borane-substituted imidazol-2-ylidene anion 3a– whereas deprotonated 2b rearranges unexpectedly to the anionic compound 3b–. This can be transformed into the carbene–borane adduct 4 by methylation. The reaction of 3a– with [Mn(CO)5Br] yields the carbene complex 5. Surprisingly, 3a– attacks Fe(CO)5 at a carbon atom which leads to the iron acyl complex anion 6–. The compositions of the products follow from spectroscopic and analytical data and from X-ray structure analyses for Li(thp)+3a–, Li(thf)2+3b– and Li(thp)3+6–.

Borane-Substituted Imidazol-2-ylidenes: Syntheses, Structures, and Reactivity

Reactions of the Lewis acids BH3 and BEt3 with trimethylimidazole (1) lead to the borane adducts 2a and 2b. Deprotonation of 2a with n-butyllithium results in the formation of the novel N-borane-substituted imidazol-2-ylidene anion 3a– whereas deprotonated 2b rearranges unexpectedly to the anionic compound 3b–. This can be transformed into the carbene–borane adduct 4 by methylation. The reaction of 3a– with [Mn(CO)5Br] yields the carbene complex 5. Surprisingly, 3a– attacks Fe(CO)5 at a carbon atom which leads to the iron acyl complex anion 6–. The compositions of the products follow from spectroscopic and analytical data and from X-ray structure analyses for Li(thp)+3a–, Li(thf)2+3b– and Li(thp)3+6–.

ChemInform Abstract: Organotransition Metal Modified Sugars. Part 3. Sugar Acyl Iron Complexes: Synthesis and Conformational Studies in Solution and in the Solid State.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.