- ELECTRON TRANSFER FROM AROMATIC HYDROCARBONS AND THEIR pi -COMPLEXES WITH METALS. COMPARISON OF THE STANDARD OXIDATION POTENTIALS AND VERTICAL IONIZATION POTENTIALS.
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The energetics of electron transfer from an extensive series of alkyl-substituted benzenes are measured both in solution and in the gas phase. The standard oxidation potentials E//A//r degree stem from the reversible cyclic voltammograms (CV) in trifluoroacetic acid using the recently developed microvoltammetric electrodes. These values show an excellent correlation with the vertical ionization potentials I//p of the same aromatic hydrocarbons in the gas phase. Thermochemical analysis indicates that the slope of less than unity for the correlation arises mainly from solvation differences, particularly in the highly substituted polyalkylbenzenes.
- Howell,Goncalves,Amatore,Klasinc,Wightman,Kochi
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- NAPHTHALENE COMPLEXES. V. ARENE EXCHANGE REACTIONS IN NAPHTHALENECHROMIUM COMPLEXES
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Di-η6-naphthalenechromium(0) (1) reacts at 150 deg C with benzene to yield (η6-naphthalene)(η6-benzene)chromium(0) (3) in 76percent yield.In the presence of THF, 1 undergoes Lewis base catalyzed arene exchange at 80 deg C.Reactions of 1 with substituted arenes yield the mixed sandwich complexes 4 and 6-10 (arene=1,4-C6H4Me2, 1,3,5-C6H3Me3, C6Me6, 1,4-C6H4(OMe)2, 1,4-C6H4F2 and 1,4-C10H6Me2).In all but one case (witih 1,4-dimethylnaphthalene) exchange of a single naphthalene ligand is observed.In marked contrast to the lability of 1, dimesitylenechromium(0) (5) is inert to arene diplacement in benzene up to 240 deg C.The molecular structure of 3 has been determined by X-ray crystallography.The crystal data are as follows: a 7.784(1), b 13.411(2), c 22.772(5) Angstroem, Z=8, space group Pbca.The structure was refined to a RW value of 0.043.The naphtahlene ligand in 3 is nearly planar and parallel to the approximately eclipsed benzne ring.Metal atom-ring distances are 1.631(9) and 1.611(4) Angstroem for naphthalene and benzene, respectively.Catalyzed and uncatalyzed naphtahlene exchanges in the sandwich complex are compared to the analogous reactions with the Cr(CO)3 complex 2.Naphthalene exchange in 2 in benzene is 1E3 to 1E4 times fastere than arene exchange in other arenetricarbonylchromium compounds.The mild conditions for Lewis base catalyzed naphthalene exchange make 2 a good precursor of other arenetricarbonylchromium compounds.Examples include the Cr(CO)3 complexes of styrene, benzocyclobutene, 1-ethoxybenzocyclobutene, 1,8-diemthoxy-9,10-dihydroanthracene and 1,4-dimethylnaphthalene.
- Kuendig, E. P.,Perret, C.,Spichiger, S.,Bernardinelli, G.
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- Intramolecular vibrational relaxation in n-alkyl benzene chromium tricarbonyls: State selective production of chromium atoms
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We have measured one color multiphoton dissociation/ionization (MPD/MPI) spectra for a series of n-alkyl substituted arene chromium tricarbonyls (ACTs) .Our data indicate that intramolecular vibrational relaxation (IVR) rates for methyl, ethyl, and propyl ACTs increase relative to the benzene analog in the ratio of 3:6:34.In contrast, the net relaxation rates of the p-xylene (dimethyl) and mesitylene (trimethyl) analogs are two and three times faster than benzene, respectively.The behavior of these latter analogs probably also reflects differences in electronic structure relative to the benzene ACT.Taken with the results of experiments on other analogs and the independently obtained results on the uncomplexed arenes, we have found a strong correlation between the presence of low frequency vibrations and the rate of IVR.The rate of IVR determines the distribution of neutral chromium atoms formed by MPD of the n-alkyl ACTs.
- Hossenlopp, Jeanne M.,Samoriski, Brian,Rooney, Dan,Chaiken, J.
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- Stereoselective synthesis and some reactions of β-(η6-arene)Cr(CO)3 complexes of podocarpic acid derivatives
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The stereoselective synthesis of a number of (η6-arene)tricarbonylchrorniurn(0) complexes derived from podocarpic acid has been achieved in good to excellent yield. The stereochemistry of complexes 36 and 37 was established by X-ray crystallography. Reactions of some of the deprotonated complexes with electrophiles were investigated.
- Clark, George R.,Kuipers, Bianca,Metzler, Michael R.,Nguyen, Manh H.,Woodgate, Paul D.
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- UV Laser Photolysis of (η6-C6H6)Cr(CO)3: Time-Resolved Infrared Studies of Gas-Phase (η6-C6H6)Cr(CO)x (x = 2 and 1)
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The time-resolved infrared absorption spectra of the coordinatively unsaturated (η6-C6H6)Cr(CO)x (x = 2 and 1) species generated via UV laser photolysis of the gas-phase (η6-C6H6)Cr(CO)3 are presented and discussed.The photofragments produced upon 355- and 266-nm photolysis are identified. (η6-C6H6)Cr(CO)2 is the predominant product upon 355-nm photolysis, while both (η6-C6H6)Cr(CO)2 and (η6-C6H6)Cr(CO) are produced upon 266-nm photolysis with a ratio of (η6-C6H6)Cr(CO)2:(η6-C6H6)Cr(CO) of about 2:5.The rate constants for reactions of (η6-C6H6)Cr(CO)2 and (η6-C6H6)Cr(CO) with CO are measured and found to be (6.3 +/- 0.3) * 1012 and (1.4 +/- 0.2) * 1012 cm3 mol-1 s-1, respectively.The rate constant for reaction of (η6-C6H6)Cr(CO)2 with CO lies between the corresponding values for spin-allowed and spin-disallowed reactions of other coordinatively unsaturated metal carbonyl species with CO.
- Wang, Wenhua,Jin, Pei,Liu, Yanwei,She, Yongbo,Fu, Ke-Jian
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- Investigating the reactivity of the (η6-C6H 5R)Cr(CO)2-(η2-C6H5R) [R = H, CH3, CF3] bond: A laser flash photolysis study with infrared detection
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The (η6-C6H5R)Cr(CO) 2-(η2-C6H5R) complexes (R = H, CH3, CF3) are generated upon photolysis of (η6-C6H5R)Cr(CO)3 in the appropriate arene. The energetics and mechanism of the displacement of the η2-coordinated arene from the metal center by piperidine are studied using the technique of laser flash photolysis. The substitution reaction is tentatively assigned as proceeding through an Id mechanism, and the activation enthalpy of 11.5 ± 0.9 kcal/mol provides a lower limit for the strength of the (η6-C6H6)Cr(CO) 2-(η2-C6H6) bond. The substitution rate decreases as the metal center becomes more electron poor or the arene electron rich, suggesting that L→M σ donation is the primary bonding interaction between the (η6-C6H 5R)Cr(CO)2 fragment and the arene ligand. This reactivity is different from that of the Cr - (η2-alkene) bond, where it was found that increasing the electron density on the metal center decreased the rate of substitution of cyclooctene from the (η6-C 6H5R)Cr(CO)2-(η2-cyclooctene) complex by pyridine.
- Bengali, Ashfaq A.,Grunbeck, Amy R.
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- Protodeboronation of arylboronic acids and triarylboroxines in Bu2O/THF
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The arylboron compounds Ph3B3N3Me3, Ar3B3O3, or ArB(OH)2 (Ar = Ph, p-BrC6H4, p-MeC6H4, m-NH2C6H4) react with in refluxing Bu2O/THF (9:1) to afford the η6-arene)tricarbonylchromium(0) complexes of the protodeboronated substrates in yie
- Beckett, Michael A.,Gilmore, Robert J.,Idrees, Khalid
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- Photochemical synthesis of arenetricarbonylchromium(0) complexes: scope and limitations
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Two photochemical methods for the preparation of arenetricarbonylchromium(0) complexes are described.The first involves irradiation of a solution of hexacarbonylchromium(0) and arene in THF at room temperature with a medium pressure mercury lamp.In the se
- Kostermans, G. B. M.,Bobeldijk, M.,Kwakman, P. J.,Wolf, W. H. de,Bickelhaupt, F.
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- Dimeric boroles: Effective sources of monomeric boroles for heterocycle synthesis
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Monomeric boroles have been gaining attention as reagents for the synthesis of heterocycles due to their ability to insert atoms into the BC4 ring in a single step. Although unique boron frameworks can be accessed via this methodology, the products feature aryl substitution on the carbon centers as steric bulk is required to preclude borole dimerization. This work demonstrates that insertion chemistry is possible with Diels-Alder dimeric boroles and that such reactivity is not exclusive to monomeric boroles with bulky groups. With 1-phenyl-2,3,4,5-tetramethylborole dimer, the formal 1,1-insertion of a nitrene and sulfur generate the six-membered aromatic 1,2-azaborine and 1,2-thiaborine, respectively. The isolation of the 1,2-thiaborine enabled the synthesis of an η6-chromium complex. Benzophenone and diphenylketene readily insert a CO unit to generate BOC5 seven-membered rings confirming dimeric boroles can serve as monomeric synthons in 1,2-insertion reactions. An epoxide did not furnish the anticipated eight-membered BOC6 ring, instead provided a bicyclic system with a BOC3 ring. The insertion chemistry was demonstrated with two other borole dimers featuring different substitution with diphenylketene as a substrate. This work elevates borole insertion chemistry to a new level to access products that do not require bulky substitution.
- Su, Xiaojun,Baker,Martin, Caleb D.
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- Tetracarbonyl Ferrate Derivatives of (η6-arene)Cr(CO)3: New Reagents for Carbon-Carbon Bond Formation
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The reaction of Na2 and (η6-ClC6H5)Cr(CO)3 in tetrahydrofuran N-methylpyrrolidinone (THF/NMP) produces Na6-C6H5)Cr(CO)3>, while various (η6-o-LiXC6H4)Cr(CO)3 derivatives react with Fe(CO)5 to produce L
- Heppert, Joseph A.,Thomas-Miller, M. Elizabeth,Swepston, Paul N.,Extine, Michael W.
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- Rotational barriers in substituted (cycloheptatriene)Cr(CO)3 complexes
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The barriers of rotation about the cycloheptatriene-Cr axis have been determined for six (7-substituted cycloheptatriene)Cr(CO)3 complexes. The barriers were determined from a complete line-shape analysis of the 13C spectra for the carbonyl region as a function of temperature. The values of ΔH? for the cycloheptatriene (CHT), 7-exo-MeCHT, 7-endo-MeOCHT, and 7,7-di-MeOCHT complexes are essentially identical (9.9 ± 0.2,10.4 ± 0.5, 9.9 ± 0.3, and 9.9 ± 0.4 kcal/mol, respectively) and the values of ΔS? cluster around zero. On the other hand, ΔH? values for 7-exo-CNCHTCr(CO)3 (8.9 ± 0.2 kcal/mol) and 7-exo-t-BuCHTCr(CO)3 (10.9 ± 0.3 kcal/mol) are, respectively, slightly lower and higher than these values. This appears to be consistent with arguments concerning the electronic origin of these rotational barriers, namely, that the magnitude of the barrier is related to the cycloheptatriene-norcaradiene equilibrium. Estimates of the rotational barriers in three (1,6-methanoannulene)Cr(CO)3 complexes are also consistent with this theory. Finally the barrier in (tropone)Cr(CO)3 was found to be very small (~6 kcal/mol); extended Hu?ckel molecular orbital calculations predict a barrier of 5.8 kcal/mol. A rationale why the barrier in this complex is much lower than the other cycloheptatriene complexes is given.
- Reynolds, Stephen D.,Albright
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- Mechanisms of Arene Exchange in (Arene)tricarbonylchromium Compounds: Intermolecular and Intramolecular Exchanges in Complexes of Propenylbenzene, Stilbenes, and 1,1-Diphenylethylene
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Kinetic studies of arene exchange of (trans-propenylbenzene)tricarbonylchromium with benzene reveal intramolecular and intermolecular participation by the propenyl substituent.Intramolecular participation via direct bonding of Cr(CO)3 to the alkene portion of the ligand is supported by the observed "internal" exchange in Cr(CO)3 complexes of the three isomers of diphenylethene.The magnitudes of the internal exchange rate constants and the effect of added donor catalysts on internal exchange indicate that the geometry of the unsaturated hydrocarbon influences the movement of Cr(CO)3 along ? systems.
- Traylor T. G.,Stewart, Kevin J.
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- THE HEATS OF IODINATION OF CHROMIUM TRICARBONYL COMPLEXES OF ARENES AND CYCLOHEPTATRIENE
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The heats of iodination of chromium tricarbonyl complexes of benzene, toluene, mesitylene, and cycloheptatriene have been measured by solution calorimetry in tetrahydrofuran at 25 deg C.The order of the Cr-ligand strength is: mesitylene > cycloheptatriene
- Hoff, Carl D.
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- FTIR study of the adsorption of chromium carbonyl complexes on silica
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IR spectra are reported of Cr(CO)6, (C6H6)Cr(CO)3 and (Me4C6H2)Cr(CO)3 adsorbed on silica which had been pretreated in vacuum at temperatures in the range 250-800°C or in H2O or D2O vapour at 700°C. Surface isolated silanol groups formed hydrogen bonds with arene rings in Cr complexes which also interacted with the surfaces via ligation involving carbonyl groups. The generation of active adsorption sites was promoted by increasing pretreatment temperature. Several types of site were involved and resulted from dehydroxylation of the silica surface. Adsorbed bridging carbonyl species resulted from interactions with active Siδ+Oδ- surface sites. There was negligible evidence for the loss of CO ligands from adsorbed molecules and the supported complexes were inactive for the polymerisation of ethene. However, some loss of benzene occurred for (C6H6)Cr(CO)3 on silica pretreated at 800°C. Pretreatment of silica in H2O or D2O at 700°C promoted hydrothermal surface reorganisation of silica and destroyed a high proportion of the active adsorption sites generated at 700°C on silica in vacuum.
- Hunter, Geoffrey,Rochester, Colin H.,Wilkinson, Anthony G.,Paton, John
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- KINETIC CH-ACIDITY OF BENZENETRICARBONYLCHROMIUM AND ITS DERIVATIVES
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Kinetic acidities of aryl and benzyl CH-bonds for complexes of benzene and its methoxy and alkyl derivatives with tricarbonylchromium are determined in a solution of lithium tert-butoxide in N,N-dimethylacetamide.Complexation of alkyl-aromatic compounds t
- Antonova, M. V.,Moiseev, S. K.,Kalinin, V. N.,Shapiro, I. O.
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- Experimental and theoretical study of the substituted (η6-arene)Cr(CO)3 complexes
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Synthesis of arenetricarbonylchromium(0) complexes, [(η6-arene)Cr(CO)3], has been carried out, wherein arene were benzene (Ph), chlorobenzene (PhCl), phenyl trimethyl silane (PhSiMe3), and acenaphthene (PhNp). Characterization of the compounds was carried out using NMR, IR and UV-visible spectrophotometers. Electronic absorption of these complexes were measured in various solvents namely methanol, methylene chloride, chloroform, benzene, and isooctane. The complexes showed the electronic absorption of the lowest in the energy range of 313-320 nm, with a relatively high intensity. Density functional theory at the B3LYP/LanL2DZ level of theory was also used to study the geometry parameters, binding energy (BE), vibrational spectra, electronic spectra, frontier molecular orbital (NBO analysis), charge transfer (CT) of the complexes. It was found that the order of the complex stability is: (PhSiMe3)Cr(CO)3> (Ph)Cr(CO)3> (PhNp)Cr(CO)3> (PhCl)Cr(CO)3. The NBO analysis showed that the stability of the complexes arising from intramolecular interactions and electron delocalization in which synergistic interaction occurs in the arene hyper conjugative orbital ring for metal antibonding orbital and back donation (via metal bonding orbital to bond antibonding orbital ring). The electronic spectrum shows the charge transfer is dominated by ligand to metal charge transfer (LMCT) transition, except for (PhNpe) Cr(CO)3 that is dominated by metal to ligand charge transfer (MLCT) and only a small portion is set to d-d transition.
- Purwoko, Agus Abhi,Hadisaputra, Saprizal
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- A halogenophilic pathway in the reactions of transition metal carbonyl anions with [(η6-iodobenzene)Cr(CO)3]
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The paper provides the first example of formal nucleophilic substitution by the halogenophilic pathway in Cr(CO)3 complexes of haloarenes with metal carbonyl anions. All metal carbonyl anions examined attack [(η6-iodobenzene)Cr(CO)3] at halogen, which is shown by aryl carbanion scavenging with t-BuOH. The reaction with K[CpFe(CO) 2] gives only the dehalogenated arene, but the reaction with K[Cp*Fe(CO)2] (Cp* = η5-C 5Me5) results in nucleophilic substitution to give [(η6-C6H5FeCp*(CO) 2)Cr(CO)3]. Reaction with Na[Re(CO)5] quantitatively gives the iodo(acyl)rhenate anion Na[(η6-C 6H5C(O)ReI(CO)4)Cr(CO)3] and in the case of K[Mn(CO)5] a mixture of σ-aryl complexes [(η6-C6H5Mn(CO)5)Cr(CO) 3] and K[(η6-C6H5Mn(CO) 4I)Cr(CO)3]. An analogous rhenium complex Na[(η6-C6H5Re(CO)4I)Cr(CO) 3] is formed from the initial iodo(acyl)rhenate upon prolonged standing at 20 °C, and its structure (in the form of [NEt4] + salt) is established by X-ray diffraction analysis. The reaction of [(η6-chlorobenzene)Cr(CO)3] with K[CpFe(CO) 2], in contrast, proceeds by the common SN2Ar mechanism.
- Sazonov, Petr K.,Ivushkin, Vasiliy A.,Khrustalev, Victor N.,Kolotyrkina, Natal'Ya G.,Beletskaya, Irina P.
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p. 13392 - 13398
(2014/11/07)
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- Arene-metal π-complexation as a traceless reactivity enhancer for C-H arylation
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Current approaches to facilitate C-H arylation of arenes involve the use of either strongly electron-withdrawing substituents or directing groups. Both approaches require structural modification of the arene, limiting their generality. We present a new approach where C-H arylation is made possible without altering the connectivity of the arene via π-complexation of a Cr(CO)3 unit, greatly enhancing the reactivity of the aromatic C-H bonds. We apply this approach to monofluorobenzenes, highly unreactive arenes, which upon complexation become nearly as reactive as pentafluorobenzene itself in their couplings with iodoarenes. DFT calculations indicate that C-H activation via a concerted metalation-deprotonation transition state is facilitated by the predisposition of C-H bonds in (Ar-H)Cr(CO)3 to bend out of the aromatic plane.
- Ricci, Paolo,Kraemer, Katrina,Cambeiro, Xacobe C.,Larrosa, Igor
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supporting information
p. 13258 - 13261
(2013/09/24)
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- [2+4] Cycloaddition of η6-(styrene)chromium tricarbonyl and conjugated dienes
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Cycloaddition of η6-(styrene)chromium tricarbonyl to hexa-2,4-diene or cyclopentadiene afford the Diels-Alder adducts with retention of the Cr(CO)3 group, whereas cyclohexa-1,3-diene undergoes aromatization to give η6-(ben
- Artemov,Sazonova,Revin,Rybkin,Lazarev,Faerman
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p. 2103 - 2106
(2012/09/22)
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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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- Characterization and reactions of previously elusive 17-electron cations: Electrochemical oxidations of (C6H6)Cr(CO)3 and (C5H5)Co(CO)2 in the presence of [B(C6F5)4]
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The electrochemical oxidations of (C6H6)Cr(CO)3, 1, and (C5H5)Co(CO)2, 2, when carried out in CH2Cl2/[NBu4][B(C6F5)4], allow the physical or chemical characterization of the 17-electron cations 1+ and 2+ at room temperature. The generation of 1+ on a synthetic time scale permits an electrochemical switch process involving facile substitution of CO by PPh3 as a route to (C6H6)Cr(CO)2PPh3. The radical 2+ undergoes a second-order reaction to give a product assigned as the metal-metal bonded dimer dication [Cp2Co2(CO)4]2+. The new anodic chemistry of these often-studied 18-electron compounds is made possible by increases in the solubility and thermal stability of the cation radicals in media containing the poorly nucleophilic anion [B(C6F5)4]-, TFAB. Copyright
- Camire, Nicole,Nafady, Ayman,Geiger, William E.
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p. 7260 - 7261
(2007/10/03)
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- Asymmetric synthesis of sulfinyl-substituted arene chromium tricarbonyl complexes
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The synthesis of (SRSs[(phenylsulfinyl)benzene] chromium tricarbonyl 5 and (SRSs)-[(p-tolylsulfiny))benzene] chromium tricarbonyl 6 is achieved via a nucleophilic displacement reaction between the anion derived from (benzene) chromium tricarbonyl 9 and a suitable sulfinate ester. Replacing the sulfinate ester with a chiral sulfinyl-transfer reagent allows the isolation of the non-racemic sulfinyl-substituted complexes with good enantioselectivities (ee 80-89%) under optimised conditions. The use of Kagan's cyclic sulfite methodology for the synthesis of an enantiomerically pure tert-butylsulfinyl complex is unsuccessful, but results in the identification of a novel fragmentation - isomerisation process of the intermediate sulfinate. The Royal Society of Chemistry 1999.
- Davies, Stephen G.,Loveridge, Tracey,Teixeira, M. Fatima C. C.,Clough, John M.
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p. 3405 - 3412
(2007/10/03)
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- Photochemical synthesis of new (η6-arene)Cr-hydrido stannyl and (η6-arene)Cr-bis-stannyl complexes. Ligand effects on the Sn-H interaction in the hydrido stannyl compounds
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Hydrido stannyl compounds containing the η2-H-SnPh3 ligand and bis-stannyl compounds containing two SnPh3 ligands have been obtained from the photolysis of (η6-arene)Cr(CO)3 and HSnPh3. New complexes with different arenes (mesitylene, trifluorotoluene and 1,4-dimethoxybenzene) have been obtained and characterized by X-ray diffraction: (η6-C6H4(OCH3) 2)Cr(CO)2(HSnPh3) (3a), (η6-C6H4(OCH3) 2)Cr(CO)2(SnPh3)2 (3b). Structural data for 3a: monoclinic; space group P21/c (No. 14); a=17.445(3), b=9.820(3) and c=16.302(5) A; Z=4; V=2539.2(12) A3; 3b: monoclinic; space group P21/n (No. 14); a=13.904(3), b=20.567(5) and c=13.911(3) A; Z=4; V=3994(2) A3. 1H-NMR as well as X-ray provided evidence for the existence of three-center two-electron bonds in the hydrido stannyl complexes. The effects of different ligands on bonding and spectroscopic parameters were studied. Arene exchange reactions of the bis-stannyl complexes, as well as reactions of some of these compounds with P(C2H5)3 and CO, were also investigated.
- Khaleel, Abbas,Klabunde, Kenneth J.,Johnson, Alison
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- Photochemical synthesis of (η6-arene)chromium hydrido stannyl and (η6-arene)chromium bis(stannyl) complexes
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Photolysis of (η6-arene)Cr(CO)3 complexes and HSnPh3 in aromatic solvents at room temperature has led to two classes of complexes: hydrido stannyl compounds containing the η2-H-SnPh3 ligand and bis(stannyl) compounds containing two SnPh3 ligands. The ratio between the two complexes simultaneously produced depends on the choice of the arene. Complexes with different arenes (mesitylene, toluene, benzene, fluorobenzene, and difluorobenzene) have been obtained and characterized including X-ray structures for (η-6C6H3(CH3) 3)Cr(CO)2 (H)(SnPh3) (1a). (η6-C6H3)3)(η 6CH3)3)Cr(CO)2(SnPhs 3)2 (1b), (η-C6-H6H3F)Cr(CO)2(SnPh 3)2 (4b), and (η-C6C6H4 (CO)2(SnPh3)2 (5b). X-ray crystallography of the last three compounds has given the following results: 1b, monoclinic, space group P21/c (No. 14), a = 13.905(4) A?, b = 18.499(2) A?, c = 17.708(2) A?, Z = 4, V = 4285(1) A?3; 4b, orthorhombic, space group Pca21 (No. 29), a = 16.717(2) A?, b = 18.453(2) A?, c = 25.766(2) A?, Z = 8, V = 7948(2) A?3; 5b, monoclinic, space group P21/c (No. 14), a = 13.756(2) A?, b = 18.560(2) A?, c = 17.159(2) A?, Z = 4, V = 4372(2) A?3. The relatively high J(119Sn-Cr-H) and J(117Sn-Cr-H) values as well as the X-ray structural data provide evidence for the existence of three-center two-electron bonds in the hydrido stannyl complexes. The 1H NMR data of the complexes are compared with chromium-arene bond distances, and a sensible trend is observed and discussed.
- Khaleel, Abbas,Klabunde, Kenneth J.
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p. 3223 - 3227
(2008/10/09)
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- Synthesis and reactions of [(((η6)-2-acylaryl)-C,O) tetracarbonylmanganese]-tricarbonylchromium complexes: Enhancement of diastereoselection during cyclopentaannulation
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Cyclomanganation reactions of [(η6)-acylaryl]tricarbonylchromium complexes have been investigated. Three novel heterobimetallic complexes have been synthesised in moderate to good yield, with one being characterised by X-ray crystallography. Several modes of activating these bimetallic complexes towards coupling reactions with substituted alkenes and alkynes were investigated, including oxidative decarbonylation at room temperature, and thermal promotion. The stereochemistry of one of the cyclopentaannulated adducts has been established by X-ray crystallography. Thermal displacement of one of the CO ligands of the bimetallic complex 27 in the presence of PPh3 afforded a single adduct, the structure of which was established by X-ray crystallography. The chemistry of this novel bimetallic system was investigated.
- Clark, George R.,Metzler, Michael R.,Whitaker, Giles,Woodgate, Paul D.
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p. 109 - 134
(2007/10/03)
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- Nucleophilic aromatic substitutions: Hydrodealkoxylation, hydrodehalogenation, and hydrodeamination of alkoxy, halogeno, and amino (η6-arene)tricarbonylchromium complexes
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Hydrodealkoxylation, -dehalogenation, and -deamination, occur while lithium triethylborohydride is added to [η6-alkoxy-, halogeno-, and -(dimethylamino)benzene]tricarbonylchromium complexes. In the case of (η6-benzene)tricarbonylchromium, addition of deuteride to the benzene ring gives reversibly an anionic tricarbonyl(η5-cyclohexadienyl)chromium complex which can be trapped by triphenyltin chloride to yield the neutral binuclear complex (η5-C6H6D)(CO)3Cr-Sn(C 6H5)3. The latter complex molecular structure has been confirmed by single-crystal X-ray diffraction analysis. Empirical formula C27H21DCrO3Sn: triclinic system, space group P1, z = 2, a = 8.961(4) A?, b = 10.853(5) A?, c = 12.713(2) A?, α = 85.15(3)°, β = 86.26(2)°, γ = 72.40(4)°, R = 0.033, Rw = 0.037 (unit weight).
- Djukic, Jean-Pierre,Rose-Munch, Francoise,Rose, Eric,Simon, Frederic,Dromzee, Yves
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p. 2027 - 2038
(2008/10/09)
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- Ground-state versus transition-state effects in arene displacement reactions of the complexes (η6-arene)Cr(CO)s: Linear dependence of transition-state energies and resonance energies of the arene ligands
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The rates of displacement of arene and thiophene ligands by P(n-Bu)3 in decalin and PPh3 in toluene have been studied. The reactions are first order in complex and incoming ligand. Rates of reaction increase in the order benzene dimethylthiophene > triphenylene > phenanthrene > thiophene > naphthalene > anthracene > pyrene and spans about 7 kcal/mol. The combination of kinetic and thermodynamic data is used to construct reaction profiles for these reactions. On the basis of the assumption that the transition state occurs on the way to formation of (η4-arene)Cr(CO)3(L) a linear correlation exists between the enthalpy of formation of the transition-state complex and changes in resonance energy of the fused arene ligands attributable to localization of the π bonds of the proposed η4 intermediate. The rate of binding of C6H6 to (THF)3Cr(CO)3 is 10% slower than for C6D6, implicating the importance of (η1-C6H6)Cr(CO)3(THF) 2 as an intermediate on the pathway to formation of (η6-C6H6)-Cr(CO)3.
- Zhang, Songshen,Shen, Jian Kun,Basolo, Fred,Ju, Telvin D.,Lang, Russell F.,Kiss, Gabor,Hoff, Carl D.
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p. 3692 - 3702
(2008/10/08)
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- The diastereoselectivity of the addition of tricarbonyl(η6-2-lithiothiophene)chromium(0) complexes on aldehydes
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It has been shown that the reactions of tricarbonyl(η6-2-lithiothiophene)chromium(0) with various arene carboxaldehydes yields mixtures of unequal amounts of diastereoisomers, which can be separated by flash chromatography.The structures of the products have been established by 1H NMR spectroscopy and by independent synthesis.A novel synthesis of tricarbonyl(η6-thiophene)chromium(0) (1) is described.Key words: Chromium; Thiophene; Carbonyl; Aldehyde
- Struharik, Milan,Toma, Stefan
-
-
- Laser pulse photolysis and transient infrared investigation into the effect of solvent or substituents (X) on the reactivity of photogenerated (η6-C6H6-yXy)Cr(CO)2 intermediates
-
Time-resolved infrared spectroscopy identified the first observable species following nanosecond laser photolysis of (benzene)Cr(CO)3 in alkane solution as (benzene)Cr(CO)2(alkane). UV/ vis-monitored laser flash photolysis was used to observe the reaction of this species with CO. The reactivity toward CO of the primary photoproducts derived from related arene complexes (arene = C6H5Cl, C5H5Me, p-ClC6H4Me, C6H5Et, C6H5But, o- and p-C6H4Me2, C6H3Me3, C6Me6, C6Et6) were also determined by this technique. The rate of reaction with CO was found to depend on the alkane solvent and on the nature and degree of substitution of the arene ligand. The enthalpies of activation for all reactions were constant (24 ± 2 kJ mol-1), while the entropy of activation increased upon methyl substitution of the arene and upon a change in the solvent from cyclohexane to a linear alkane.
- Creaven, Bernadette S.,George, Michael W.,Ginzburg, Allan G.,Hughes, Catherine,Kelly, John M.,Long, Conor,McGrath, Irene M.,Pryce, Mary T.
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p. 3127 - 3131
(2008/10/08)
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- Transition Metal Stannyl Complexes, 7. - Preparation of Carbene Complexes (?-Arene)(CO)2CrCR2 by the Reaction of the Anionic Stannyl Complexes - with R2CX2 or Y
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Carbene complexes (?-arene)(CO)2Cr=CR2 are formed in substitution/elimination reactions from the anionic stannyl complexes K and organic dihalides R2CX2 containing activated C-X bonds or ionic halides Y.Bis(stannyl)complexes (?-arene)(CO)2Cr(SnPh3)2 (3) and hydrido(stannyl)complexes (?-arene)(CO)2Cr(H)SnPh3 are formed as byproducts due to the reaction of the eliminated Ph3SnCl with the anionic starting complexes or electron transfer reactions, respectively.The portion and ration of the byproducts is largely influenced by the steric properties of both the (?-arene)(CO)2Cr fragment and the organic halide.Pyridinylidene complexes 2 are only obtained from 2-chloro-N-methylpyridinium tetrafluoroborate with 1a-c, but not with 1d.With the sterically less demanding halides Cl (n=3,4)> or 3,3-dichloro-1,2-diphenylcyclopropene the carbene complexes (?-arene)(CO)2Cr=C(H)NR2 or are obtained with all employed ?-arene ligands. Key Words: Carbene Complexes / Stannyl complexes / Chromium complexes / Anionic complexes
- Schubert, Juergen,Mock, Stefan,Schubert, Ulrich
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p. 657 - 664
(2007/10/02)
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- Bimetallic activation in homogeneous catalysis. 3. Mechanistic study of the methoxycarbonylation of tricarbonyl(chlorobenzene)chromium: Isolation and reactivity of possible reaction intermediates
-
The coordination of the Cr(CO)3 moiety to the aromatic ring allows the carbonylation of chlorobenzene, catalyzed by palladium complexes, to esters, aldehydes, amides or α-oxo-amides. The mechanism of methoxycarbonylation of tricarbonyl(chlorobenzene)chromium, (η6-C6H5Cl)Cr(CO)3, and the role of the Cr(CO)3 moiety are now investigated. Tricarbonyl(chlorobenzene)chromium reacts at room temperature with Pd(PPh3)4 or Pd(dba)2 and PR3 via an oxidative addition to give aryl-palladium complexes of the type {Pd[(η6-C6H5)Cr(CO)3](Cl)L y}2/y, which are monomers (L = PPh3 (1), PEt2Ph (4), PPh2Et (5)) or dimers (L = PPh3 (2), PCy3 (3)). By comparison, the oxidative addition of PhCl to Pd(PPh3)4 is known to proceed at 140 °C, indicating that the coordination of Cr(CO)3 to PhCl greatly enhances the rate of this reaction. However, this reaction does not proceed with L2 = dppe or dpph, but the same complexes can be prepared by Cl-bridge cleavage and/or phosphine exchange with PR3 on Pd2[(η6-C6H5)Cr(CO) 3]2(μ-Cl)2(PPh3)2 to give the monomers (L = PEt2Ph (4), PPh2Et (5); L2 = dppe (6), dpph (7)) and the dimer (L = PCy3 (3)). The X-ray structures of complexes trans-Pd2[(η6-C6H5)Cr(CO) 3]2(μ-Cl)2(PCy3)2 (3) and cis-Pd[(η6-C6H5)Cr(CO)3]Cl (dppe) (6) have been determined. Crystal data for 3: orthorhombic with the space group Pccm; a = 18.486 (8) A?, b = 20.401 (7) A?, c = 17.255 (6) A?, V = 6508 A?3, Z = 8. Crystal data for 6: monoclinic with the space group P21/n, a = 9.841 (2) A?, b = 12.783 (5) A?, c = 28.377 (2) A?, β = 92.23 (1)°, V = 3567 A?3, Z = 4. These aryl-palladium complexes react at room temperature with CO under atmospheric pressure (L = PPh3, PEt2Ph; L2 = dpph) or 5 bar (L = PCy3) to give the corresponding monomeric or dimeric acyl-palladium complexes of the type {Pd[(η6-C6H5CO)Cr(CO) 3](Cl)Ly}2/y (y = 2: L = PPh3 (8), PEt2Ph (9), L2 = dpph (10); y = 1: L = PPh3 (11), PCy3 (12)). The reaction does not proceed with L2 = dppe even under 30 bar of CO; Cl-bridge cleavage and phosphine exchange with dppe on Pd2[(η6-C6H5CO)-Cr(CO) 3]2(μ-Cl)2(PPh3)2 enable the formation of cis-Pd[(η6-C6H5CO)Cr(CO) 3]Cl(dppe) (13). Methanolysis of complexes Pd[(η6-C6H5CO)Cr(CO) 3]Cl(PPh3)2 (8) and Pd2[(η6-C6H5CO)Cr(CO) 3]2(μ-Cl)2(PPh3)2 (11) in the presence of triethylamine at room temperature proceeds rapidly and leads to the formation of (η6-C6H5COOMe)Cr(CO)3, which is the product of methoxycarbonylation of (η6-C6H5Cl)Cr(CO)3. Complexes {Pd[(η6-C6H5)Cr(CO)3]Cl(PPh 3)y}2/y (1, 2) and {Pd[(η6-C6H5CO)Cr(CO) 3]Cl(PPh3)y}2/y (8, 11) then appear to be reasonable intermediates in the catalytic cycle of methoxycarbonylation of (η6-C6H5Cl)Cr(CO)3. A possible mechanism for this reaction is discussed.
- Dufaud, Véronique,Thivolle-Cazat, Jean,Basset, Jean-Marie,Mathieu, René,Jaud, Jo?l,Waissermann, Jacqueline
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p. 4005 - 4015
(2008/10/08)
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- The study of catalyst effects on the complexation of arenes with Cr(CO)6. An overview
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New results from our thorough investigation of different catalystic effects on the rate and yields of complexation of arenes with Cr(CO) are presented with a short review of the subject.With decalin as solvent the following substances were found to be the best catalysts: butyl acetate, ethyl formate, and dimethyl succinate.Butyl acetate proved to be the catalyst also in di-n-butyl ether.Special attention was paid to the complexation of naphthalene, and chlorobenzene.Some unsuccessful attempts at asymmetric induction of complexation are also described.
- Hudecek, Milan,Gajda, Vladimir,Toma, Stefan
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p. 155 - 160
(2007/10/02)
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- A simple route to (η6-arene)tricarbonylchromium complexes and a systematic study of different catalysts for complexation of arenes with Cr(CO)6
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A systematic investigation was made of the catalytic effect of different substances on complexation of toluene with Cr(CO)6. 1-3 molar equivalents of butyl acetate in refluxing decalin was found to be the best catalyst, providing that the complexation was carried out in a special apparatus described earlier.Comparable yields were obtained also in butyl acetate as a solvent, but the reaction time was more than doubled.The utility of the method was verified by complexation of 7 different benzene derivatives.
- Hudecek, Milan,Toma, Stefan
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p. 147 - 151
(2007/10/02)
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- Acid catalysed complexation of arenes with Cr(CO)6
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Several acids were tested as potential catalysts for complexation of arenes with Cr(CO)6 in boiling decalin.Acetic acid was found to be an efficient catalyst for complexation of acyl- and acyloxybenzenes.A mixture of butanone or cyclohexanone and acetic acid, with THF and acetic acid was found to be an efficient catalytic system or complexation of other arenes.The complex (η2-acenaphthylene)4Cr(CO)2 was isolated during an attempt on acetic acid catalysed complexation of acenaphthylene with Cr(CO)6.
- Hrnciar, Peter,Toma, Stefan
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p. 161 - 164
(2007/10/02)
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- An improved method for the synthesis of η6-arenetricarbonylchromium complexes
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A novel apparatus for the complexation of arenes with Cr(CO)6 is described.This, and the modification of the reaction procedure shortens the reaction time, and improves the yields of η6-arenetricarbonylchromium complexes.The method was tested f
- Hudecek, Milan,Toma, Stefan
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p. 115 - 118
(2007/10/02)
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- Competitive nucleophilic aromatic substitution and haloarene reduction in the synthesis of bimetallic π-arene complexes: The structural characterization of [Et4N][(η6-{(CO)5W}C6H 5)Cr(CO)3]
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Collman's reagent, [Fe(CO)4]2-, reacts with (η-ClC6H5)Cr(CO)3 to produce [(η6-{(CO)4Fe}C6H5)Cr(CO) 3]- in THF/N-methyl-2-pyrrolidinone solvents, while [M(CO)5]2- (M = Cr or W) reacts with (η6-FC6H5)Cr(CO)3 in THF at 0°C to form analogous [(η6-{(CO)5M}C6H5)Cr(CO) 3]- complexes. The products are isolated as yellow-orange crystalline [Et4N]+ salts from acetone or methylene chloride and are somewhat air sensitive in both solution and the solid state. Spectroscopic data indicate that the molecules adopt a classical η6-arene structure, as opposed to the alternate possible η5-cyclohexadienide carbene valence form. This supposition is confirmed by an X-ray crystallographic study of [Et4N][(η6-{(CO)5W}C6H 5)Cr(CO)3], which displays a typical W-CAr σ-bond interaction and a minimal distortion of the planarity of the arene. The reaction of [M(CO)5]2- (M = Cr or W) with (η6-ClC6H5)Cr(CO)3 results in the exhaustive reductive dehalogenation of the chlorobenzene substrate to (η6-C6H6)Cr(CO)3. This later reaction is in keeping with anticipated higher reactivity and reducing power of the [M(CO)5]2- anions. Crystal data for [Et4N][(η6-{(CO)5W}C6H 5)Cr(CO)3] at 20°C: a = 11.599 (3) A?, b = 10.562 (2) A?, c = 20.369 (5) A?, Z = 4, Dcalcd = 1.782, space group Pca21 and R(F) = 0.0352, Rw(F) = 0.0583 for 1698 reflections.
- Heppert, Joseph A.,Thomas-Miller, M. Elizabeth,Scherubel, Devin M.,Takusagawa, Fusao,Morgenstern, Mark A.,Shaker, Mohammad R.
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p. 1199 - 1206
(2008/10/08)
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- Chromium tricarbonyl facilitated nucleophilic aromatic substitution by metal carbonyl anions: The synthesis and molecular structure of a new class of bimetallic π-arene complexes
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The highly nucleophilic metal carbonyl anions [CpFe(CO)2]- and [(C5Me5)Fe(CO)2]- (C5Me5 ≡ Cp*) react with (η-XRC6H4)Cr(CO)3 substrates in a previously unknown type of nucleophilic aromatic substitution to form (η6-{CpFe(CO)2}RC6H4)Cr(CO) 3 products. A variety of less reactive metal nucleophiles, including [CpMo(CO)3]-, [CpNi(CO)]-, [Mn(CO)5]-, and [Co(CO)4]-, fail to participate in the substitution reactions. The structure of (η-{CpFe(CO)2}ClC6H4)Cr(CO)3 has been determined by X-ray crystallography. The compound crystallizes in the space group P21/n with four molecules in the unit cell of dimensions a = 7.969 (2) A?, b = 18.982 (4) A?, c = 10.789 (2) A?, and β = 91.45 (3). Full-matrix least-squares refinement yielded R = 0.0353 for 2153 reflections. The structure shows that the conformation of the Cr(CO)3 fragment is determined by a cogging of the carbonyl ligands of the CpFe(CO)2 and Cr(CO)3 units to avoid steric interactions, although 1H and 13C NMR studies failed to show a perceptible barrier to Cr(CO)3 rotation about the Cr-Phcentroid vector. Certain haloarene substrates react predominantly through an apparent electron-transfer pathway to produce [CpFe(CO)2]2 and (η-RC6H5)Cr(CO)3. The fraction of reduced products formed is dependent on (1) the reducing power of the anion ([Cp*Fe(CO)2]- ? [CpFe(CO)2]-), (2) the electron-donating ability of the R group (electron donor ? electron acceptor), (3) the substitution pattern of the arene (in general ortho ? meta ? para), and (4) the identity of the halogen leaving group (I ? Cl > F).
- Heppert, Joseph A.,Morgenstern, Mark A.,Scherubel, Devin M.,Takusagawa, Fusao,Shaker, Mohammad R.
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p. 1715 - 1723
(2008/10/08)
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- Facile exchange of naphthalene for η4-benzene in [Cr(η4-C6H6)(CO)3]2-
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The η4-benzene in K2[Cr(Tη4-C6H6)(CO)3] (K22) exchanges with free naphthalene at room temperature to give [Cr(η4-C10H8)(CO)3]2- (52-), as established by oxidation to [Cr(η6-C10H8)(CO)3] (4), 1H NMR observation, and protonation to [Cr(η5-C10H9)(CO)3]- (6-). 1-Methylnaphthalene and 1,4-dimethylnaphthalene also exchange with 22~ if the corresponding naphthalenide is used as the reductant, and this leads to a single isomer of [Cr(η-C10H6Me2)(CO)3] (8) in which the Cr is bonded to the unsubstituted ring of the naphthalene.
- Leong, Voon S.,Cooper, N. John
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p. 2058 - 2060
(2008/10/08)
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- DERIVES HYDROSILYLES DES COMPLEXES (Η-ARENE) TRICARBONYLCHROME, DE TYPE (ΗC6R6)(CO)2Cr(H)SiHPh2; LIAISON A 2 ELECTRONS/3 CENTRES, Cr-H-Si
-
Diphenylsilane reacts photocemically, at low temperature, on the η(tricarbonylchromium)arenes, to give unstables hydrosilylcomplexes, (η-C6R6)(CO)2Cr(H)SiHPh2 with a three-center two electron bond, Cr-H-Si; according to 29Si NMR data, the degree of this bond is higher than both the degree of the Mn-H-Si bond in isoelectronic manganese compounds, (η-C5R5)L2Mn(H)SiHPh2, and the degree of the three-center Cr-H-Si bond in the permethylated complex, (η-C6Me6)(CO)2Cr(H)SiHPh2, of chromium.The variation of /2J(Si-Cr-H)/ depending on the electron density of the metal is discussed.
- Matarasso-Tchiroukhine, Elisabeth,Jaouen, Gerard
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p. 2157 - 2160
(2007/10/02)
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- Chemistry of the podocarpaceae LXXI. Preparation, structure, and reactions of some (arene)tricarbonylchromium(0) complexes. Crystal structure of α-tricarbonylchromium(0)
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Tricarbonylchromium(0) (7), tricarbonylchromium(0) (11) and (benzene)tricarbonylchromium(0) (10) were prepared and examined.Complex 7 was obtained as a mixture of diastereomers, an X-ray structural determination showing that the α-isomer possesses a near eclipsed conformation, in agreement with the conformation in solution deduced from 400 MHz 1H NMR analysis.Carbanions derived from 1,3-dithiane, 2-methyl-1,3-dithiane and 2-(2,2-dimethoxyethyl)-1,3-dithiane (24), and the dianion derived from 2,2'-methylenebis-1,3-dithiane (27) were prepared and brought into reaction with the complexes.Compounds 23 and 33 resulted from regioselective attack on 7 at the site predicted.Treatment with methyl electrophiles of the dithianyl η5-intermediate leading to 22 did not give products of acetyl incorporation.Arene lithiation-electrophilic quenching of 7 gave a mixture of compound 6 and its C(14) regioisomer along with the novel ketone 39 and its C(14) regioisomer.
- Cambie, Richard C.,Clark, George R.,Gallagher, Stewart R.,Rutledge, Peter S.,Stone, Martin J.,Woodgate, Paul D.
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p. 315 - 338
(2007/10/02)
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- Neighboring Group Participation in Organometallic Chemistry: Internal Exchange in (Diarylalkane)tricarbonylchromium Complexes
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The rates of internal and external exchange of (diarylalkane)tricarbonylchromium complexes in benzene/cyclohexane mixtures have been determined.Neighbouring group participation is demonstrated in all complexes and follows an order with respect to ring siz
- Traylor, Teddy G.,Goldberg, Martin J.
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p. 3968 - 3973
(2007/10/02)
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- Regioselective electrophilic substitution via lithiation and intramolecular arene exchange (haptotropic rearrangement) in (naphthalene)tricarbonylchromium
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The sequential reaction of (η6-naphthalene)tricarbonylchromium (1) with (tetramethylpiperidyl)lithium (TMPLi) and electrophiles (D+, ClSiMe3, CO2, MeI, EtOSO2CF3) is highly regioselective and exclusively yields (2-substituted naphthalene)tricarbonylchromium complexes bearing the substituent in the coordinated ring. With n-BuLi, the same sequence gives mixtures of the 1- and 2-substituted naphthalene complexes in the ratio of 3:7. [1-4a,8a-η-1,3-(SiMe3)2C10H 6]Cr(CO)3 (5) is obtained in reactions with excess TMPLi and ClSiMe3. The selectively labeled complexes (1-4a,8a-η-[2-D]naphthalene)Cr(CO)3 (3a) and (1-4a,8a-η-[1,3-8-D7]naphthalene)Cr(CO)3 (3b) were used in a kinetic study of the haptotropic rearrangement of (naphthalene)tricarbonylchromium. The rate constants and activation parameters of the rearrangement in cyclohexane-d12 and in benzene were determined by 1H and 2H NMR methods. In cyclohexane, the activation parameters for the intramolecular rearrangement in 3b were found to be ΔH? = 20.4 kcal mol-1 and ΔH? = -23 cal mol-1 K-1. Haptotropic rearrangement was found to proceed by first-order kinetics and, within experimental error limits, at the same rate in benzene as in cyclohexane. Addition of THF accelerated intra- as well as intermolecular arene exchange. In benzene, at 100°C, the intramolecular ring migration of 3b is 9 times faster than arene exchange. (1-4a,8a-η-2-Methylnaphthalene)Cr(CO)3 (3e) rearranges (ΔH? = 26.2 kcal mol-1) on heating in cyclohexane to an equilibrium mixture (65:35) of the two isomers, the major isomer being the one in which the metal is coordinated to the substituted ring.
- Kündig,Desobry,Grivet,Rudolph,Spichiger
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p. 1173 - 1180
(2008/10/08)
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- Stereoelectronic effects in arene exchange of (arene)tricarbonylchromium complexes: Internal arene exchange and internal arene catalysis of external arene exchange
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Kinetics of internal and external arene exchanges in benzene as solvent have been studied with tricarbonylchromium complexes of ditolylmethane, ditolylcyclopropane, dimesitylmethane, and dibenzobicyclo[2.2.2]octadienes. These studies define the stereoelectronic requirements for arene exchange and document the stepwise process in which the bonding in the displaced arene proceeds from η6 to η4 to η2. A new intermediate, (arene)3Cr(CO)3, is indicated by the catalyzed exchange reactions of some of these compounds.
- Traylor, Teddy G.,Goldberg, Martin J.
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p. 2413 - 2416
(2008/10/08)
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- Neighboring group participation in organometallic chemistry: Anchimeric assistance in catalyzed arene exchange reactions of (diarylalkane)tricarbonylchromium complexes
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Nucleophilic catalysis of the migration of a tricarbonylchromium group from one ring to the other in diarylalkane tricarbonyl derivatives has been observed and compared with catalysis of external exchange. Internal catalysis by a neighboring tricarbonylchromium is also being reported. These results demonstrate the intermediacy of a chromium complex having three carbonyl groups, ketone, and two η2-bound arenes. The consequences of this result for metal exchange reactions are discussed.
- Traylor, Teddy G.,Goldberg, Martin J.
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p. 2531 - 2536
(2008/10/08)
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- Formation and characterization of [Cr(η-C6H6)(CO)2]2-, a dianionic η6-arene-substituted carbonylmetalate
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Naphthalenide reduction of [Cr(η-C6H6)(CO)2-(PV)] (1) (py = pyridine) gives [Cr(η-C6H6)(CO)2]2- (3), which reacts with Ph3SnCl to give [Cr(η-C6H6)-(CO)2SnPh3] - (1 equiv) or [Cr(η-C6H6)(CO)2(SnPh3) 2] (5) (excess). Addition of NH4PF6 (1 equiv) to 3 gives [Cr(η-C6H6)(CO)2H]- (6), and excess NH4PF6 gives [Cr(η-C6H6)(CO)2(NH3)] (8) and H2. Anion 6 reacts with Ph3SnCl to give a 1:1 mixture of 5 and 8.
- Leong, Voon S.,Cooper, N. John
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p. 2000 - 2002
(2008/10/08)
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- Electrophilic Substitution in (Arene)tricarbonylchromium Complexes. Part 1.
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The Friedel-Crafts acetylation of several (arene)tricarbonylchromium complexes have been investigated.From the results it is concluded that the tricarbonylchromium group deactivates to a small extent towards electrophilic substitution the ring to which it is attached.In the case of tricarbonyl(diphenylmethane)chromium (1; n=1), however, attack occurred on both rings to about an equal extent, possible explanations for this unexpected behaviour are advanced.
- von Rosenberg, Joseph L.,Pinder, A. Reginald
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p. 747 - 752
(2007/10/02)
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- Tricarbonylchromium Complexes of Aryltrimethylsilanes - Synthesis and Reactions
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Tricarbonylchromium (TCC) complexes 3, 12 of aryltrimethylsilanes are synthesized by reaction of aryltrimethylsilanes 2 and phenylenebis(trimethylsilanes) 11, resp., with hexacarbonylchrom (1).Under basic catalysis 3 and 12 react - caused by the acceptor effect of the tricarbonylchromium (TCC) group - with aldehydes and ketones to give the TCC-alkyl(trimethylsilyl) ether complexes 4, 9, 13.Hydrolysis of 4, 13 accomplish TCC complexes 5 of substituted benzyl alcohols.The oxidative removal of the TCC group with iodine or sodium dichromate was demonstrated with 4a yieldi ng benzhydrol (7) and benzophenone (8f), respectively.Nucleophiles can be added to the aromatic ring of 4, 9, 13 by known methods; the TCC complexes 3, 12, therefore, can be used for the straightforward synthesis of multiply substituted arenes by combination of electrophilic carbodesilylation and nucleophilic addition.
- Effenberger, Franz,Schoellkopf, Klaus
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p. 4356 - 4376
(2007/10/02)
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- Synthesis of (η6-arene)2Cr2(CO)3 Complexes Containing a Formal CrCr Triple Bond Starting from η6-areneCr(CO)2NCCH3
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The photochemical reaction of η6-ArCr(CO)3 (Ar = benzene, toluene, m-xylene, mesitylene, methyl benzoate, and fluorobenzene) with acetonitrile in hexane or p-tolunitrile in THF, resp., yields complexes η6ArCr(CO)2NCR (1-10).Solutions of the red acetonitrile complexes yield on warming or UV photolysis by dissoziation of the nitrile and one CO ligand in the presence of benzene the new black coordination compounds (η6-Ar)2Cr2(CO)3 (11-16).The spectra and an X-ray structure determination of the benzene derivative 11 verify a Cr2-unit with a formal triple bond bridged by three CO ligands.The asymmetric unit of 11 contains two halves of molecules with Cr-Cr distances of 222.6 and 221.6 pm.
- Kluefers, Peter,Knoll, Lothar,Reiners, Christiane,Reiss, Karl
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p. 1825 - 1835
(2007/10/02)
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- Self-catalysis in arene exchange reactions of (arene)tricarbonylchromium complexes
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The replacement of p-xylene from its tricarbonylchromium complex by benzene is catalyzed by (hexamethylbenzene)tricarbonylchromium without the replacement of hexamethylbenzene. This and other observations suggest that the bound carbonyl group acts as a nucleophilic catalyst in arene exchange.
- Traylor,Stewart, Kevin
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p. 325 - 327
(2008/10/08)
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- ELECTROCHEMICAL REDUCTION OF ?-TRICARBONYLCHROMIUM-PHENYLDIMETHYLSULFONIUM TETRAFLUOROBORATE IN DIMETHYL SULFOXIDE
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The mechanism of the electrochemical reduction of ?-tricarbonylchromium-phenyldimethylsulfonium tetrafluoroborate in anhydrous DMSO has been investigated, together with that of the free phenyldimethylsulfonium tetrafluoroborate.On varying the reduction potential and the protonating power of the medium the number of electrons transferred changes together with the nature and the yield of the products.It is suggested that formation of an intermediate sulfonium ylid by a two-electron process is followed by an acid-base reaction.
- Ceccon, Alberto,Gambaro, Alessandro,Romanin, Anna Maria
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p. 207 - 218
(2007/10/02)
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