- ENDO ADDITION TO DIENYLIUM METAL COMPLEXES
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Various mechanistic studies have been carried out on reactions of 5-exo-substituted tricarbonyl(η-cyclohexa-1,3-diene)iron and the tricarbonyl(1-5-η-cyclohexadienylium)iron cation.These have shown that the corresponding endo complexes can be prepared prov
- Burrows, Aubrey L.,Hine, Ken,Johnson, Brian F. G.,Lewis, Jack,Parker, David G.,et al.
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- 1,4-diaryl-1-azabuta-1,3-diene-catalyzed complexation of cyclohexa-1,3-diene by the tricarbonyliron fragment: Development of highly efficient catalysts, optimization of reaction conditions, and proposed mechanism
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The 1,4-diaryl-1-azabuta-1,3-diene-catalyzed complexation of cyclohexa-1,3-diene with either nonacarbonyldiiron or pentacarbonyliron is reported to provide high yields of the tricarbonyl(η4-cyclohexa-1,3-diene)iron complex. This procedure enables exploitation of both tricarbonyliron fragments of nonacarbonyldiiron for the complexation of dienes for the first time. Using 12.5 mol % of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene and optimized reaction conditions (nonacarbonyldiiron, dimethoxyethane, reflux, 16.5 h, or pentacarbonyl-iron, dioxane, reflux, 45 h), a quantitative catalytic complexation of cyclohexa-1,3-diene is feasible with both reagents. An extensive study with a broad range of 1,4-diaryl-1-azabuta-1,3-dienes shows that the efficiency of the catalysts strongly depends on the substituents of the two aryl rings. Remarkably high activities are found for those catalysts deriving from condensation of cinnamaldehyde and ortho-methoxy-substituted arylamines. A hexacarbonyldiiron complex of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene is obtained as a byproduct of the catalytic complexation and is structurally confirmed by X-ray crystallography. A mechanism supported by the experimental findings is proposed.
- Kn?lker, Hans-Joachim,Baum, Elke,Gonser, Peter,Rohde, Guy,R?ttele, Herbert
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- Addition reactions of lithiodimethylphenylsilane to (η4-1,3-diene)-Fe(CO)3 and (η6-arene)Cr(CO)3 complexes
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Treatments of (η4-cyclohexa-1,3-diene)Fe(CO)3 complex with 1.2 equivalents of PhMe2SiLi, followed by quenching the reactive intermediate with CF3COOH generated 1-dimethyl(phenyl)silylcyclohex-1-ene and with 2-(p
- Yeh, Ming-Chang P.,Sheu, Peng-Yu,Ho, Jin-Xuan,Chiang, Yi-Lin,Chiu, Dai-Yu,Narasimha Rao
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- Synthesis, Molecular Structure, Fluxional Behavior, and Tricarbonyliron Transfer Reactions of (η4-1-Azabuta-1,3-diene)tricarbonyliron Complexes
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The η4-1-azabuta-1,3-diene)tricarbonyliron complexes 10 are easily prepared in high yield by condensation of the corresponding arylamines 7 with the cinnamaldehydes 8 and subsequent ultrasound-promoted complexation of the resulting 1-azabuta-1,3-dienes 9 with nonacarbonyldiiron. The complexes 10 are shown to represent excellent reagents for the transfer of the tricarbonyliron fragment onto cyclohexa-1,3-diene (1a). The structural characterization for the complexes 10 is achieved by IR, 1H-NMR, and 13C-NMR spectroscopy, as well as X-ray crystallography of 10b, 10c, and 101. Using variable temperature 13C-NMR spectroscopy the fluxionality of the complexes 10a, 10b, 10c, 10e, and 2 is investigated and the activation barrier for the turnstile rotation of the tricarbonyliron fragment is determined. The transfer reaction and the structural factors influencing the transfer of the tricarbonyliron fragment are extensively investigated.
- Knoelker, Hans-Joachim,Baum, Gerhard,Foitzik, Norbert,Goesmann, Helmut,Gonser, Peter,Jones, Peter G.,Roettele, Herbert
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p. 993 - 1007
(2007/10/03)
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- FTIR studies of organometalcarbonyl-tagged enzymes
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Attachment of organometaltricarbonyl tags to enzymes is revealed by changes in the vibrational modes of the carbonyl groups. Shoulders on νsym(CO) and νasym(CO) bands in the FTIR spectrum of an organometallic tag derived from tricarbonyl[1-{(2,3,4,5-η)-2,4-cyclohexadien-1-yl}pyridinium]iron(1 + ) hexafluorophosphate(1 - ) were detected on binding to enzymes (α-chymotrypsin, ribonuclease A, alkaline phosphatase and a triacylglycerol lipase). By comparison with tagging reactions between the tricarbonyliron moiety and model compounds, the new spectral features were attributed to an iron complex covalently bonded to the NH2 groups of the amino acid residues of the enzymes. FTIR spectroscopy was used to monitor deprotonation of tagged amino groups on the enzyme surface. Interactions between the organometalcarbonyl tag and other side-chain groups of the amino acid residues were also investigated.
- Anson, Christopher E.,Creaser, Colin S.,Egyed, Orsolya,Stephenson, G. Richard
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p. 1867 - 1877
(2007/10/03)
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- Construction of bridged and fused bicyclic skeletons via intramolecular addition of nucleophiles to (η4-diene)Fe(CO)3 complexes bearing functionalized side chains
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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, whereas larger rings cannot be obtained in this series. 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 iron-mediated intramolecular nucleophilic addition allows for the direct stereocontrol of four stereogenic centers of these fused bicyclic skeletons.
- Yeh, Ming-Chang P.,Sheu,Fu,Tau,Chuang
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p. 5941 - 5952
(2007/10/02)
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- The reaction of [(η5-cyclohexadienyl)Fe(CO)3]BF4 with fluoride revisited. Formation of (η4-5-fluorocyclohexa-1,3-diene)Fe(CO)3 and the mechanism of the decomposition pathway to give the carbon-carbon linked dimer (η4-C6H7)2Fe 2(CO)6
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The complex (η4-C6H7F)Fe(CO)3 has been prepared in situ in CD2Cl2 from the reaction of [(η5-C6H7)Fe(CO)3]BF4 with either KF/18-crown-6 or [(Me2N)3S][Me3SiF2]. On standing, (η4-C6H7F)Fe(CO)3 decomposes to give the C-C linked dimer (η4-C6H7)2Fe 2(CO)6 as the major product together with significant amounts of benzene and Fe(III) species. A mechanism is proposed to account for the formation of (η4-C6H7)2Fe 2(CO)6 from (η4-C6H7F)Fe(CO)3 and the mechanism extended to the reaction of [(η5-C6H7)Fe(CO)3]BF4 with hydroxide. Exposure of (η4-C6H7F)-Fe(CO)3 to H2O rapidly gives the diiron ether complex {(η4-C6H7)2O}Fe 2(CO)6.
- Powell, John,Horvath, Michael J.
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p. 4073 - 4076
(2008/10/08)
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- Enthalpies of reaction of (diene)- and (enone)iron tricarbonyl complexes with monodentate and bidentate ligands. Solution thermochemical study of ligand substitution in the L2Fe(CO)3 complexes
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The enthalpies of reaction of (BDA)Fe(CO)3 (BDA = (C6H5)CH=CHO(CH3), benzylideneacetone) with a series of mono- and multidentate ligands, leading to the formation of (η4-L)Fe(CO)3, (L′)2Fe(CO)3, and (L″)Fe(CO)3 complexes (L = diene, enone; L′ = monodentate arsines; L″ = bidentate ligands), have been measured by solution calorimetry in THF at 50°C. The range of reaction enthalpies spans some 44 kcal/mol. The overall relative order of stability established is as follows: for monodetate ligands, AsPh3 3 a relative order of complex stability for these compounds in the iron tricarbonyl system. These data allow the calculation of the enthalpy associated with the geometric isomerization process (axial-equatorial/ diaxial) present in the (L′)2Fe(CO)3 system (5.4 ± 0.5 kcal/mol) as well as for a quantitative analysis of ring strain energies in the (L″)Fe(CO)3 system. The four-membered metallacycle is the only cyclic structure exhibiting significant strain energy (12.6 kcal/mol). Comparisons with other organometallic systems and insight into factors influencing the Fe-L bond disruption enthalpies are also discussed.
- Luo, Lubin,Nolan, Steven P.
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p. 2410 - 2415
(2008/10/08)
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- Bromination and alkylation of tricarbonyl(η1,η2-but-3-en-1-yl)iron(0) anion complexes
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Reactive carbon nucleophiles add to tricarbonyl(η4-1,3-diene)iron(0) complexes at -78 deg D to produce putative internally coordinated tricarbonyl(η1,η2-but-3-en-1-yl)iron(0) anion complexes.Treatment of the reactive inter
- Yeh, Ming-Chang P.,Hwu, Chong-Chen
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p. 341 - 355
(2007/10/02)
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- The reactions of nitrosoarenes with cationic cyclohexadienyl complexes of iron tricarbonyl: an ESR study
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The reactions of nitrosoarenes with the (cyclohexadienyl)Fe(CO)3 cation have been investigated by using electron spin resonance spectroscopy.The radicals produced are nitroxides of the type (OC)3Fe(C6H7)(Ar)N-O* but, in some cases, disproportionation and loss of the metal carbonyl fragment leads to the corresponding C6H5(Ar)N-O* radical.With bulky nitrosoarenes, such as C6Me5NO, isomers are observed in which the aryl ring rotation is slow on the ESR time scale.The analogous reactions with the cyclohexadienyl cation derived from the B ring of (ergosteryl acetate)Fe(CO)3 lead to initial attack not at one of the termini of the delocalized system but rather at the central carbon, i.e., at C-7.Subsequent hydrogen migration leads to the (5,7-diene)Fe(CO)3 complex bearing the arylnitroxide at the 7-position.The mechanisms of these reactions are discussed.Key words: nitrosoarenes, iron cations, ESR.
- Li, Lijuan,Perrier, Richard E.,Eaton, Donald R.,McGlinchey, Michael J.
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p. 1868 - 1877
(2007/10/02)
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- THE KINETICS AND MECHANISM OF DIENE EXCHANGE IN (η4-ENONE)Fe(CO)2L COMPLEXES (L = PHOSPHINE, PHOSPHITE)
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Kinetic data for the exchange of 1,3-cyclohexadiene with (η4-benzylideneacetone)Fe(CO)2L complexes (L = CO, PPh3-xMex (x = 0-2) or P(OPh)3) to give (η4-1,3-cyclohexadiene)Fe(CO)2L derivatives indicate a mechanism involving stepwise competing D and Id opening of the ketonic M-CO ?-bond.Rates increase in the order CO>>PPh3P(OPh)3>PPh2Me>>PPhMe2, and both steric and electronic factors appear to be important. (η4-1,3-cyclohexadiene)Fe(CO)2L complexes of potential use in enantioselective synthesis (L = (+)-Ph2P(menthyl) or (+)-Ph2PCH2CH(Me)Et) may be preparedvia their (η4-benzylideneacetone)Fe(CO)2L complexes.
- Howell, James A. S.,Kola, John C.,Dixon, Denis T.,Burkinshaw, Philip M.,Thomas, Marion J.
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- TRICARBONYLBIS( eta 2-CIS-CYCLOOCTENE)IRON: PHOTOCHEMICAL SYNTHESIS OF A VERSATILE Fe(CO)3 SOURCE FOR OLEFIN ISOMERIZATION AND PREPARATIVE APPLICATIONS.
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The photoreaction of pentacarbonyliron and cis-cyclooctene in alkane solvent at minus 40 degree C results in high yield formation of tricarbonylbis( eta **2-cis-cyclooctene)iron (1). Solid 1 can be handled at room temperature. In solution at approximately greater than minus 35 degree C the complex is substitutionally labile and serves as a versatile source of the Fe(CO)//3 unit. The thermal reaction of 1 with 1-pentene results in extensive isomerization of the alkene with turnover numbers up to 2000, thus establishing the role of Fe(CO)//3 as the repeating unit in the catalytic alkene isomerization. Turnover rates are 0. 48 min** minus **1 at minus 20 degree C, 12. 2 min** minus **1 at 0 degree C, and 173 min** minus **1 at 20 degree C. Ligand exchange with 1,3-dienes and vinyl-substituted aromatic compounds provides excellent yields of the corresponding ( eta **4-organic ligand)Fe(CO)//3 complexes. The reaction of 1 with 2-butyne demonstrates that alkyne coupling products are accessible under remarkably mild conditions.
- Fleckner,Grevels,Hess
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p. 2027 - 2032
(2007/10/02)
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- Approaches to Enantioselective Syntheses using Tricarbonyl(diene)iron Complexes
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Methods for the resolution of tricarbonyl(1-5-η-cyclohexadienyl)iron salts are described involving the separation of diastereoisomeric pairs obtained by nucleophilic attack using chiral phosphines, alkoxides, and amines.Nucleophilic attack by CN- on 5-C6H7)(CO)2L*>BF4 to give proceeds with significant asymmetric induction at the chiral carbon so formed.
- Howell, James A.S.,Thomas, Marian J.
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p. 1401 - 1410
(2007/10/02)
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- Preparation of Trimethylsilyl-substituted Tricarbonyl(cyclohexadiene)iron Complexes
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Reductive silylation of benzene yields cis/trans-3,6-bis(trimethylsilyl)-1,4-cyclohexadienes (1a/1b), which react with pentacarbonyliron to give tricarbonyliron complexes (2a/2b and 2c), respectively, in good yields.Reaction of 2a with triphenylmethyl tetrafluoroborate leads to isomeric monotrimethylsilylated cationic complexes 7 and 8.Protodesilylation of the isomeric mixture 2a/2b/2c with an excess of trifluoroacetic acid gives tricarbonyliron (10a).
- Keil, Michael,Effenberger, Franz
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p. 1103 - 1112
(2007/10/02)
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- Low-temperature matrix photochemistry of (1,3-diene)tricarbonyliron complexes
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UV photolysis of (η4-2,3-dimethylbutadiene)Fe(CO)3 and (η4-butadiene)Fe(CO)3 in inert matrices at 10 K was monitored by IR and UV spectroscopy. Elimination of CO is the predominant photoreaction. In the latter case we also observed the decomplexation of the butadiene ligand and hence the formation of (η2-butadiene)Fe(CO)3. This product is also obtained during the photolysis of (η2-butadiene)Fe(CO)4 which is subsequently transformed to (η4-butadiene)Fe(CO)3. For comparison, (η2-ethylene)Fe(CO)4 and (η2-1,3-cyclohexadiene)Fe(CO)4 were photolyzed under analogous conditions. Photolysis of (η4-1,3-diene)Fe(CO)3 complexes in nitrogen matrices gives (η4-1,3-diene)Fe(CO)2N2; formation of (η2-butadiene)Fe(CO)3N2 from (η2-butadiene)Fe(CO)4 requires annealing of the nitrogen matrix subsequent to irradiation.
- Ellerhorst, Gabriele,Gerhartz, Wolfgang,Grevels, Friedrich-Wilhelm
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- Kinetics and Mechanism of Mono- and Di-olefin Exchange at Five-co-ordinate Iron(0)
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Exchange of various mono-olefins with styrene in proceeds via a dissociative process, involving an Fe(CO)4 intermediate.Ligand exchange in system (i) (enone = benzylideneacetone, cinnamaldehyde, chalcone, or dypnone; polyene = cyclohexa- and cyclohepta-1,3-diene, cycloheptatriene, cyclo-octatetraene, 4-enone)> + polyene (*) 4-polyene)> + enone (i) or 1,4-diphenylbuta-1,3-diene) is stepwise, involving a rate-determining dechelation of the ?-bound CO moiety.Both associative and dissociative pathways are found.The influence of diene structure and enone substituent is discussed.
- Burkinshaw, Philip M.,Dixon, Denis T.,Howell, James A. S.
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p. 999 - 1004
(2007/10/02)
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