- Comparison of the Reactivity of Paracyclophane and p-Xylene
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The relative abilities of paracyclophane (C16H16) and p-xylene (C6H4Me2-1,4) to form arene tricarbonyl complexes from chromium hexacarbonyl has been studied in dioxane using the Strohmeier reflux method, and the rate constants contrasted.The reactions are found to proceed more quickly with paracyclophane by ca. 25percent.Density functional molecular-orbital calculations have rationalised this observation, and indicate that the enhanced reactivity of the paracyclophane system relative to p-xylene is a consequence of repulsive interactions between the two arene decks in the former, which are relieved to some extent by co-ordination of the electron-withdrawing Cr(CO)3 fragment.
- Dyson, Paul J.,Humphrey, David G.,McGrady, John E.,Mingos, D. Michael P.,Wilson, D. James
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- Intervention by an η6-organochromium moiety switches chemoselectivity in palladium-catalyzed reactions with trialkyltin compounds
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The reaction of (chloroarene)tricarbonylchromium with hexaalkylditin under palladium catalysis does not proceed by the expected Stille reaction with addition of an SnR3 group but, instead, affords alkylarene complexes via a postulated chromium-assisted alkyl migration.
- Prim, Damien,Tranchier, Jean-Philippe,Chavignon, René,Rose-Munch, Fran?oise,Rose, Eric
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- Chromium carbonyl complexes with aryl mono- and oligogermanes: Ability for haptotropic rearrangement
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The intra- and intermolecular inter-ring η6 ? η6-haptotropic rearrangements (IRHR), occurring by involving interactions to Ge atoms in arylgermanes, were investigated theoretically and experimentally. The new methods for the synthesis of non-symmetrical polyaromatic Ge compounds were elaborated. Digermane Ph3GeGeMe2Cl (2) was obtained from Ph3GeGeMe2NMe2 (1) under action of Me3SiCl. Aryl digermane Ph3GeGeMe2(η6-C6H5)Cr(CO)3 (4) was obtained after lithiation of (η6-C6H6)Cr(CO)3 (3) with subsequent interaction with 2. It was established that thermally induced intramolecular IRHR in 4 is not observed experimentally; at similar reaction conditions in the presence of tetralin C10H12 (7) the bimolecular intermolecular IRHR occurs giving (η6-C10H12)Cr(CO)3 (8). DFT analysis of the intramolecular IRHRs for model germane (p-Tol)2Ge(H)(η6-Tol-p)Cr(CO)3 (MC1) and digermane Ph3GeGeH2(η6-C6H5)Cr(CO)3 (MC2) indicates a plausible effect of 3c-2e (agostic) Ge–H···Cr interaction on success of such rearrangement. The theoretical activation barrier is determined to be in the range of 35–37 kcal/mol. The model compound (η6-C6H3(GeHPh2)Me2-p)Cr(CO)3 (12) was obtained from (η6-C6H4Me2-p)Cr(CO)3 (11). The decomposition of 12 was observed under conditions of thermally induced IRHR. Molecular structures of 8, 11 and 12 in a crystal were investigated by XRD.
- Zaitsev, Kirill V.,Gloriozov, Igor P.,Oprunenko, Yuri F.,Lermontova, Elmira Kh,Churakov, Andrei V.
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- Palladium-catalyzed allylic substitution with (η6-Arene- CH2Z)Cr(CO)3-based nucleophiles
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Although the palladium-catalyzed Tsuji-Trost allylic substitution reaction has been intensively studied, there is a lack of general methods to employ simple benzylic nucleophiles. Such a method would facilitate access to "α-2-propenyl benzyl" motifs, which are common structural motifs in bioactive compounds and natural products. We report herein the palladium-catalyzed allylation reaction of toluene-derived pronucleophiles activated by tricarbonylchromium. A variety of cyclic and acyclic allylic electrophiles can be employed with in situ generated (η6-C 6H5CHLiR)Cr(CO)3 nucleophiles. Catalyst identification was performed by high throughput experimentation (HTE) and led to the Xantphos/palladium hit, which proved to be a general catalyst for this class of reactions. In addition to η6-toluene complexes, benzyl amine and ether derivatives (η6-C6H5CH 2Z)Cr(CO)3 (Z = NR2, OR) are also viable pronucleophiles, allowing C-C bond-formation α to heteroatoms with excellent yields. Finally, a tandem allylic substitution/demetalation procedure is described that affords the corresponding metal-free allylic substitution products. This method will be a valuable complement to the existing arsenal of nucleophiles with applications in allylic substitution reactions.
- Zhang, Jiadi,Stanciu, Corneliu,Wang, Beibei,Hussain, Mahmud M.,Da, Chao-Shan,Carroll, Patrick J.,Dreher, Spencer D.,Walsh, Patrick J.
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p. 20552 - 20560
(2012/02/13)
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- Benzylic functionalization of (η6-alkylarene)chromium tricarbonyl complexes
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A general method for the regioselective benzylic metallation of (η6-alkylarene)chromium tricarbonyl complexes on the action of lithium amides in THF under very mild conditions has been developed. Transmetallation reactions of the lithium derivatives thus obtained produce the corresponding benzylic organotin, zinc and copper chromium tricarbonyl complexes. Methods for the preparative benzylic functionalization of (η6-alkylarene)chromium tricarbonyl complexes have been developed, including carboxylation, α-hydroxyalkylation, γ-carbonylation, acylation, arylation, vinylation, heteroarylation and alkylation procedures. 5-Acetoxy-3-benzyl-1,4-methano-2,3,4,5-tetrahydro-1H-3-benzazepine has been prepared using the benzylic lithium derivative of the (η6-alkylarene)chromium tricarbonyl complex at the key step. This compound is a representative of the major class of physiologically active compounds known as C-norbenzomorphans.
- Kalinin, Valery N.,Cherepanov, Il'ya A.,Moiseev, Sergey K.
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p. 437 - 455
(2007/10/03)
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- 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
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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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- 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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p. 291 - 296
(2007/10/02)
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- Stability and the gas chromatography of alkyl-substituted η6-benzenetricarbonylchromium(0) complexes
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Thermoanalytical and gas chromatographic data are reported for benzenetricarbonylchromium(0) and nine of its methyl- and t-butyl-substituted derivatives.The distinct trends found for the volatilities, thermal stabilities, air stabilities and gas chromatog
- Patsalides, E.,Pratten, S. J.,Robards, K.
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p. 169 - 180
(2007/10/02)
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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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p. 3331 - 3337
(2007/10/02)
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- 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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p. 3968 - 3976
(2007/10/02)
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- METALLKOMPLEXE VON CYCLOPHANEN V. REAKTION VON 2,6,15,19-TETRATHIAPARACYCLOPHAN MIT Cr(CO)6. EINE NEUE MOEGLICHKEIT DER SCHWEFELEXTRUSION AUS EINEM THIAPHAN
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The reaction of 2,6,15,19-tetrathiaparacyclophane with Cr(CO)6 is described.The reaction products demonstrate the tendency of the 1,3-propanedithia unit to be cleaved off under the influence of the metal carbonyl.The reaction products allow a radical mechanism to be proposed for the elimination of the 1,3-propanedithia unit.
- Koray, Ali R.,Ziegler, Manfred L.
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