Density functional theory investigation of the active site of Fe-hydrogenases. systematic study of the effects of redox state and ligands hardness on structural and electronic properties of complexes related to the [2Fe](H) subcluster

Density functional theory has been used to investigate complexes related to the [2Fe](H) subcluster of [Fe]-hydrogenases. In particular, the effects on structural and electronic properties of redox state and ligands with different sigma-donor pi-acceptor character, which replace the cysteine residue coordinated to the [2Fe](H) subcluster in the enzyme, have been investigated. Results show that the structural and electronic properties of fully reduced Fe(I)Fe(I) complexes are strongly affected by the nature of the ligand L, and in particular, a progressive rotation of the Fe(d)(CO)(2)(CN) group, with a CO ligand moving from a terminal to a semibridged position, is observed going from the softest to the hardest ligand. For the partially oxidized Fe(I)Fe(II) complexes, two isomers of similar stability, characterized either by a CO ligand in a terminal or bridged position, have been observed. The switching between the two forms is associated with a spin and charge transfer between the two iron atoms, a feature that could be relevant in the catalytic mechanism of dihydrogen activation. The structure of the fully oxidized Fe(II)Fe(II) models is extremely dependent on the nature of the L ligand; one CO group coordinated to Fe(d) switches from terminal to bridging position going from complexes characterized by neutral to anionic L ligands.     

Iron complexes of (e)- and (z)-1,2-dichlorodisilenes

Novel disilene-iron complexes [(E)- (1E) and (Z)-(eta2-R3SiClSi=SiClSiR3)Fe(CO)4 (1Z), SiR3 = tBu2MeSi] were synthesized by the reaction of the corresponding tetrachlorodisilane with an excess amount of K2Fe(CO)4, and the structures of 1E and 1Z were determined by X-ray crystallography. These complexes constitute not only the first transition-metal complexes with E,Z-isomerism but also the first complexes with halogen-substituted disilene ligands. The initial formation of 1Z during the synthetic reaction and the slow one-way isomerization of 1Z to 1E are rationalized by the intervention of the corresponding silylene complex (R3SiCl2Si)(R3Si)Si=Fe(CO)4.     

Iron(II) carbonyl complexes containing xanthate,dithiocarbamate or dithiophosphate ligands

Summary Starting from Fe(CO)₄I₂, octahedral Fe^II carbonyl derivatives of the types Fe(CO)₂(xan)₂, Fe(CO)₃(xan)I and Fe(CO)₃(dtc)I were prepared (xan = xanthate, dtc = dithiocarbamate). Infrared evidence was obtained for the formation of Fe(CO)₂(dtp)₂ complexes (dtp = dithiophosphate). The dixanthate complexes are also formed from Fe^II salts and potassium xanthates by CO absorption in MeOH/H₂O solution.     

手性羰基铁体系催化酮的不对称氢转移氢化

手性羰基铁络合物很少被用于芳香酮的不对称氢转移氢化.利用不同的羰基铁络合物与手性双胺双膦配体现场络合,形成手性胺膦铁催化体系.考察了它们对多种芳香酮的不对称氢转移催化氢化性能.结果表明,三核的手性胺膦铁簇合物是催化芳香酮不对称氢转移氢化的较好体系.当用三核的铁簇合物[Et₃NH]⁺[HFe₃(CO)₁₁]^-体系催化1,1-二苯基丙酮的氢化时,最高可获得98%的对映选择性.通过现场红外光谱测定,揣测羰基铁簇合物Fe₃(CO)₁₂在催化反应过程中保持三核的簇合物的簇骼不变.     

Stable Salts of Heteroleptic Iron Carbonyl/Nitrosyl Cations

The oxidation of Fe(CO)₅ with the [NO]⁺ salt of the weakly coordinating perfluoroalkoxyaluminate anion [F‐{Al(OR^F)₃}₂]^? (R^F=C(CF₃)₃) leads to stable salts of the 18 valence electron (VE) species [Fe(CO)₄(NO)]⁺ and [Fe(CO)(NO)₃]⁺ with the Enemark–Feltham numbers of {FeNO}⁸ and {FeNO}¹⁰. This finally concludes the triad of heteroleptic iron carbonyl/nitrosyl complexes, since the first discovery of the anionic ([Fe(CO)₃(NO)]^?) and neutral ([Fe(CO)₂(NO)₂]) species over 80 years ago. Both complexes were fully characterized (IR, Raman, NMR, UV/Vis, scXRD, pXRD) and are stable at room temperature under inert conditions over months and may serve as useful starting materials for further investigations.     

Benzoylformyl Complexes of Iron and Molybdenum

Benzoylformyl complexes CpMo(COCOPh)(CO)₃ (1) and CpFe(COCOPh)(CO)₂ (2) were prepared by the reactions of [CpMo(CO)₃]^? and [CpFe(CO)₂]^? ions with PhCOCOCl, respectively. The single-crystal structure of complex 1 has been determined by X-ray diffraction with crystal data: P2₁/c, a = 6.674 (3) Å, b = 13.301 (4) Å, c= 16.903(6) Å, β = 90.82 (5)°,V = 1500(1) ų, Z = 4. Least-squares refinement on 894 reflections with I ≥ 2.0 σ(I) led to R = 0.041, R_W = 0.042. Complex 1 contains a near perpendicular s-trans oxalyl moiety in the benzoylformyl ligand with the torsional angle O4-C4-C5-O5 being 104 (1)°. The iron complex suffers spontaneous decarbonylation at 25 °C to yield CpFe(COPh)(CO)₂.     

Use of a methoxy substituent in controlling the stereochemistry of intramolecular iron-mediated diene/olefin cyclocoupling

A methodology for stereocontrol during the intramolecular coupling between cyclohexadiene--Fe(CO)(3) complexes and pendant alkenes is presented. Introduction of a methoxy group at the C(3) position of the diene moiety controls pre- and postcyclization rearrangements of the diene Fe(CO)(3) unit, allowing the preparation of spirolactams with defined relative stereochemistry and with a cyclohexenone framework, thus making this reaction a potentially valuable tool for the construction of quaternary carbon centers.     

Stereospecific 1,3-migration of an Fe(CO)3 group on acyclic conjugated polyenes: application to remote and iterative asymmetric induction

The stereochemical outcome of the 1,3- and 1,5-migration of an Fe(CO)3 group on (acyclic polyene)Fe(CO)3 complexes and their application to stereoselective construction of remote and contiguous stereogenic centers are described. Treatment of the [(eta(4)-4-7)triene]Fe(CO)3 complexes 1a-d bearing an electron-withdrawing group on the terminal position of an uncomplexed olefin with a base such as KN(SiMe3)2 (KHMDS) and LiCH2CN induced the 1,3-migration reaction of the Fe(CO)3 group, giving the [(eta4-2-5)triene]Fe(CO)3 complexes 2a-d in moderate to good yields, depending on the electron-withdrawing groups. From an experiment using the chiral (trienenitril)Fe(CO)3 complex 5, it is revealed that the 1,3-migration proceeds with inversion of configuration. Similarly, the 1,5-migration reaction of the[(eta4-6-9)tetraenone]Fe(CO)3 complexes 9 occurred with a catalytic amount of KHMDS, giving the [(eta4-2-5)tetraenone]Fe(CO)3 complexes 10 with retention of configuration. Furthermore, we have succeeded in the first regio- and stereoselective nucleophilic substitution of the (3,5-diene-1,2-diol) Fe(CO)3 complexes (15 --> 24a-h) with various nucleophiles via the ortho esters 21. By using iterative manipulation of the above two reactions, remote stereocontrol of the terminal substituents on acyclic polyene (9 --> 12) and construction of contiguous stereogenic centers (19, 28) have been achieved.     

Reaction Behavior of Decacarbonyldimetalates(2‐) (M = Cr and Mo) towards the Nitrosyl Carbonyls of Iron and Cobalt

The reaction of the nitrosyl carbonyl complexes [Fe(NO)₂(CO)₂] and [Co(NO)(CO)₃] with the decacarbonyldimetalates [M₂(CO)₁₀]^2– (M = Cr and Mo) in THF as the solvent at room temperature was investigated. Thereby a substitution of one nitrosyl ligand towards carbon monoxide was observed in each case. Both reactions afforded the known metalate complexes [Fe(NO)(CO)₃]^– and [Co(CO)₄]^–, respectively. These species were isolated as their corresponding PPN salts [PPN⁺ = bis(triphenylphosphane)iminium cation] in nearly quantitative yields. The products were unambiguously identified by their IR spectroscopic and elemental analytic data as well as by their characteristic colors and melting points.     

Photoinduced Carbon Monoxide Release from Half‐Sandwich Iron(II) Carbonyl Complexes by Visible Irradiation: Kinetic Analysis and Mechanistic Investigation

Three half‐sandwich iron(II) complexes, [Fe(η⁵‐Cp)(cis‐CO)₂X] (X^?=Cl^?, Br^?, I^?), were synthesized and characterized. The kinetics of the CO‐releasing behaviour of these complexes upon illumination by visible irradiation in various media was investigated. Our results indicated that the CO release was significantly affected by the auxiliary ligands. Of the three light sources used (blue, green, and red), blue light exhibited the highest efficiency. In the photoinduced CO release, the solvents and exogenous nucleophiles in the media were involved, which allowed their CO‐releasing reaction to comply with pseudo first‐order model rather than the characteristic zero‐order model for a photochemical reaction. In aqueous media (D₂O), an intermediate bearing the core of {Fe^II(cis‐CO)₂} involving cleavage of cyclopentadiene was detected. Despite the non‐absorption of the red light, its illumination combined with nucleophilic substitution did cause considerable CO release. Assessment of the cytotoxicity of the three complexes indicated that they showed good biocompatibility.     

Transition Metal Cation Salts in Organic Synthesis

Reaction of lithium diisopropylamide (LDA) with (η⁴-1,3-cyclohexadiene)Fe(CO)₃ complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3,2,1]octene and bicyclo[3,3,1]nonene systems after electrophilic quenching. Under the same reaction conditions, intramolecular cyclization of acyclic (η⁴- 1,3-butadiene)Fe(CO)₃ complexes with functionalized side chains at the terminal position of the diene ligands furnishes fused bicyclo[3.3,0]octanone and bicyclo[4.3.0]nonanone derivatives after acid quenching. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)ZnI to the (η⁷-cycloheptatrienyl)Cr(CO) gives (η⁶-cyclohepta-1,3,5-triene)Cr(CO)₃ complexes with a functionalized side-chain at the C-7 position of the ring. Intramolecular cyclization of ester-subsbtuted adducts using lithium diisopropylamide generates fused bicyclo[5.3.0]decane and bicyclo[5.4.0]undecane derivatives. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)Znl to the (η⁴-cyclohexa-1,3-diene)Mo(CO)₂(Cp) at the terminus of the coordinated diene ligand gives [Mo(π-allyl)(CO)₂(Cp)](Cp = cyclopentadienyl) complexes with the functionalized side-chain at the C-4 position of the ring. Intramolecular cyclization of the (π-allyl)molybdenum complex containing a pendant propanoic acid unit generates the δ-lactone derivative.     

Iron pyrrole‐based PNP pincer ligand complexes as catalyst precursors

The structure of a pincer ligand consists of a backbone and two `arms' which typically contain a P or N atom. They are tridentate ligands that coordinate to a metal center in a meridional configuration. A series of three iron complexes containing the pyrrole‐based PNP pincer ligand 2,5‐bis[(diisopropylphosphanyl)methyl]pyrrolide (PN^pyrP) has been synthesized. These complexes are possible precursors to new iron catalysts. {2,5‐Bis[(diisopropylphosphanyl)methyl]pyrrolido‐κ³P ,N ,P ′}carbonylchlorido(trimethylphosphane‐κP )iron(II), [Fe(C₁₈H₃₄NP₂)Cl(C₃H₉P)(CO)] or [Fe(PN^pyrP)Cl(PMe₃)(CO)], (I), has a slightly distorted octahedral geometry, with the Cl and CO ligands occupying the apical positions. {2,5‐Bis[(diisopropylphosphanyl)methyl]pyrrolido‐κ³P ,N ,P ′}chlorido(pyridine‐κN )iron(II), [Fe(C₁₈H₃₄NP₂)Cl(C₅H₅N)] or [Fe(PN^pyrP)Cl(py)] (py is pyridine), (II), is a five‐coordinate square‐pyramidal complex, with the pyridine ligand in the apical position. {2,5‐Bis[(diisopropylphosphanyl)methyl]pyrrolido‐κ³P ,N ,P ′}dicarbonylchloridoiron(II), [Fe(C₁₈H₃₄NP₂)Cl(CO)₂] or [Fe(PN^pyrP)Cl(CO)₂], (III), is structurally similar to (I), but with the PMe₃ ligand replaced by a second carbonyl ligand from the reaction of (II) with CO. The two carbonyl ligands are in a cis configuration, and there is positional disorder of the chloride and trans carbonyl ligands.     

Addition of Dialkyl Hydrogen Phosphites to Alkenes in the Presence of Carbonyl Complexes of Chromium Subgroup Metals and Iron

Depending on the reactant ratio and order of their mixing, reactions of dialkyl hydrogen phosphite with alkenes in the presence of catalytic amounts of homoligand carbonyl complexes of iron or chromium subgroup metals yield phosphonates by two pathways: reaction of dialkyl hydrogen phosphite with -coordinated alkene and addition to alkene of the product of reaction of dialkyl hydrogen phosphite with the transition metal carbonyl. The products of reactions of Fe(CO)₅ and W(CO)₆ with dialkyl hydrogen phosphites contain the phosphorus-metal bond.     

Gold cluster carbonyls: vibrational spectroscopy of the anions and the effects of cluster size, charge, and coverage on the CO stretching frequency

We report the vibrational spectra of the carbonyl complexes of anionic gold clusters in the range of the CO stretching frequency as measured in the gas phase using IR multiple photon dissociation spectroscopy. The investigated complexes contain between 3 and 14 Au atoms and up to 7 CO ligands. Special attention is given to the complexes that exhibit saturation CO coverage as well as to the monocarbonyl species. In conjunction with data from the corresponding cationic complexes we quantify how the CO stretching frequency varies with the charge state of the gold cluster. Our results provide a size- and charge-dependent basis to interpret values of the CO stretching frequency measured for CO on deposited gold clusters in terms of the charge states of the clusters.     

Iron(II) complexes of 1-benzyl-2-phenylbenzimidazole and 2-coumarinylbenzimidazole

Summary Iron(II) complexes of 1-benzyl-2-phenylbenzimidazole (BPBI) and 2-coumarinylbenzimidazole (CBI) have been prepared and characterised. The chloride, bromide, iodide and thiocyanate complexes have the general formula FeL₂X₂ (where L = BPBI or CBI) while the perchlorate complex of CBI has the composition [Fe(CBI)₃](CIO₄)₂. The perchlorate complex behaves as a 1 : 2 electrolyte in nitrobenzene and methanol; Fe(BPBI)₂I₂ shows considerable dissociation in nitrobenzene while the other complexes behave as nonelectrolytes. The i.r. spectra of the complexes suggest that N(3) of BPBI and N(3) together with the CO group of CBI are the coordination sites. The magnetic and spectral evidence suggests a regular octahedral geometry for the perchlorate complex and pseudotetrahedral configuration for the iodide and thiocyanate complexes. The other complexes appear to be distorted octahedral with halide bridging.Author to whom all correspondence should be addressed.     

Monocyclopentadienylhydride derivatives of ruthenium: stereoselective proton transfer and proton-hydride exchange in an extremely short dihydrogen bond

Diastereomerically pure complexes of formula CpRuCl(PP) and CpRuH(PP) with chiral ferrocenyl diphosphines were prepared and the selectivity of proton-transfer processes over the monohydride compounds with different acids was studied. With 1 equiv of HBF(4) the cis-dihydrogen and trans-dihydride complexes were formed while with 3 equiv of CF(3)CO(2)H the trans-dihydride derivative was the only product. However, the use of 1 equiv of CF(3)CO(2)H led to a dihydrogen bonded complex with an extremely short RuH...HO(2)CF(3) interaction that exhibits proton-hydride exchange. Using the labeled acid CF(3)CO(2)D, a stereoselective transference of the deuteron was demonstrated that implies the previous epimerization of the monohydride and the subsequent attack of the acid in the position previously occupied by the hydride.     

Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3− (A=As,Sb, Bi) Complexes

Heteronuclear transition‐metal–main‐group‐element carbonyl complexes of AsFe(CO)₃⁻, SbFe(CO)₃⁻, and BiFe(CO)₃⁻ were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass‐selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C_3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)₃⁻. Chemical bonding analyses on the whole series of AFe(CO)₃⁻ (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp–p) type of transition‐metal–main‐group‐element multiple bonding. The σ‐type three‐orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)₃⁻ (A=As, Sb, Bi) complexes.     

Synthesis and Reactivity of Mononuclear Iron Models of [Fe]‐Hydrogenase that Contain an Acylmethylpyridinol Ligand

[Fe]‐hydrogenase has a single iron‐containing active site that features an acylmethylpyridinol ligand. This unique ligand environment had yet to be reproduced in synthetic models; however the synthesis and reactivity of a new class of small molecule mimics of [Fe]‐hydrogenase in which a mono‐iron center is ligated by an acylmethylpyridinol ligand has now been achieved. Key to the preparation of these model compounds is the successful C?O cleavage of an alkyl ether moiety to form the desired pyridinol ligand. Reaction of solvated complex [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(CH₃CN)₂]⁺(BF₄)^? with thiols or thiophenols in the presence of NEt₃ yielded 5‐coordinate iron thiolate complexes. Further derivation produced complexes [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(SCH₂CH₂OH)] and [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(CH₃COO)], which can be regarded as models of FeGP cofactors of [Fe]‐hydrogenase extracted by 2‐mercaptoethanol and acetic acid, respectively. When the derivative complexes were treated with HBF₄?Et₂O, the solvated complex was regenerated by protonation of the thiolate ligands. The reactivity of several models with CO, isocyanide, cyanide, and H₂ was also investigated.     

Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3− (A=As,Sb, Bi) Complexes

Heteronuclear transition‐metal–main‐group‐element carbonyl complexes of AsFe(CO)₃^?, SbFe(CO)₃^?, and BiFe(CO)₃^? were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass‐selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C_3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)₃^?. Chemical bonding analyses on the whole series of AFe(CO)₃^? (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp–p) type of transition‐metal–main‐group‐element multiple bonding. The σ‐type three‐orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)₃^? (A=As, Sb, Bi) complexes.     

Iron borohydride pincer complexes for the efficient hydrogenation of ketones under mild, base-free conditions: synthesis and mechanistic insight

The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(η(1)-BH(4))] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1 atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH(3) scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H)(2)(CO)] (4a) and cis-[(iPr-PNP)Fe(H)(2)(CO)] (4b). The dihydrido complexes 4a and 4b do not react with acetophenone or benzaldehyde, indicating that these complexes are not intermediates in the catalytic reduction of ketones. NMR studies indicate that the tetrahydridoborate ligand in 1 dissociates prior to ketone reduction. DFT calculations show that the mechanism of the iron-catalyzed hydrogenation of ketones involves alcohol-assisted aromatization of the dearomatized complex [(iPr-PNP*)Fe(H)(CO)] (7) to initially give the Fe(0) complex [(iPr-PNP)Fe(CO)] (21) and subsequently [(iPr-PNP)Fe(CO)(EtOH)] (38). Concerted coordination of acetophenone and dual hydrogen-atom transfer from the PNP arm and the coordinated ethanol to, respectively, the carbonyl carbon and oxygen atoms, leads to the dearomatized complex [(iPr-PNP*)Fe(CO)(EtO)(MeCH(OH)Ph)] (32). The catalyst is regenerated by release of 1-phenylethanol, followed by dihydrogen coordination and proton transfer to the coordinated ethoxide ligand.