- Doped Complex Bases, a New Consequence of Aggregative Activation
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According to the basic principles of aggregative activation, it has been shown that the efficiency of the complex base NaNH2-ButONa can be improved by simple addition of a potassium salt.
- Jamart-Gregoire, Brigitte,Fort, Yves,Quirin, Marie-Jeanne,Caubere, Paul
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- Multifaceted chelating μ-(η3:η3-antifacial)-(cis-C4R2H2) coordination motif in binuclear complexes
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A novel μ-C4R2H2 core structure (formed by an unprecedented regioselective, redox-neutral C(sp2)-C(sp2) coupling process) in binuclear group 4 complexes displays adaptable coordination and accommodates different metal sizes, and is sufficiently robust to promote interesting catalytic reactivity at the bimetallic centers.
- Liu, Cham-Chuen,Chan, Michael C. W.,Lo, Po-Kam,Lau, Kai-Chung,Yiu, Shek-Man
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supporting information
p. 11056 - 11059
(2016/09/19)
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- Activation of heteroallenes by coordinatively unsaturated nickel(II) alkyl complexes supported by the hydrotris(3-phenyl-5-methyl)pyrazolyl borate (TpPh,Me) ligand
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Activation of sulfur containing heteroallenes by nickel(ii) alkyl complexes supported by the bulky hydrotris(3-phenyl-5-methylpyrazolyl)borate (TpPh,Me) ligand is described. Exposure of TpPh,MeNiCH2Ph (1a) and TpPh,MeNiCH2Si(CH3)3 (1b) to CS2 resulted in formation of the insertion products TpPh,MeNi(η2-CS2)CH2Ph (2a) and TpPh,MeNi(η2-CS2)CH2Si(CH3)3 (2b) in moderate yields. Reaction of 1a and MeNCS produced two species in a 1:1 ratio, identified as TpPh,MeNi(η2-MeNC)CH2Ph (3) and TpPh,MeNi(η2-MeNCS)SCH2Ph (4). Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a-b in the presence of isocyanides (i.e.tBuNC), which resulted in isolation of TpPh,MeNi(η2-tBuNC)CH2Ph (5a) and TpPh,MeNi(η2-tBuNC)CH2Si(CH3)3 (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare example of a Ni(i) carbonyl species TpPh,MeNiCO (6). Alternatively, complex 6 was also formed by exposure of 1a-b to an atmosphere of CO. Isolation of the intermediate species (TpPh,MeNi(η2-CO)CH2TMS (7b) and TpPh,MeNi(CO)(C(O)R, (8a-b) with R = Ph, TMS)) shed light on the formation of such species.
- Abubekerov, Mark,Eymann, Léonard Y. M.,Gianetti, Thomas L.,Arnold, John
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p. 14581 - 14590
(2016/10/03)
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- Nucleophilicity of Alkyl Zirconocene and Titanocene Precatalysts, and Kinetics of Activation by Carbenium Ions and by B(C6F5)3
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Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6F5)3were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal–carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal–alkyl bond cleavage (M=Zr, Ti) were studied and structure–reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis.
- Berionni, Guillaume,Kurouchi, Hiroaki,Eisenburger, Lucien,Mayr, Herbert
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supporting information
p. 11196 - 11200
(2016/08/03)
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- On the structural diversity of [K(18-crown-6)EPh3] complexes (E = C, Si, Ge, Sn, Pb): Synthesis, crystal structures and NOESY NMR study
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A series of homologous potassium triphenylelement complexes [K(18-crown-6)EPh3] 6a-e of group 14 elements (E = C, Si, Ge, Sn, Pb) was synthesised by alkoxide induced heterolytic cleavage of boron-element compounds. The complexes 6a-e are isolated as storable solids possibly useful as sources of nucleophilic [EPh3]- moieties. The solid state structures of 6a-e were established by X-ray crystal structure determination. Whilst all structures can be described as polymeric chains consisting of alternating [K(18-crown-6)]+ and [EPh3]- units, the interaction within each chain varies systematically with the coordination properties of E. For Si and Ge, classical E-K coordination along with secondary phenyl-K interactions are characteristic, whilst for Sn and Pb, potassium coordination via the phenyl π-system is observed due to inefficient coordination by the free electron pair localised in an 'inert' s-orbital. The carbon derivative is exceptional as the central sp2-hybridised carbon atom gives rise to extensive charge delocalisation and coordination via these partially charged π-systems. A 1H-1H NOESY NMR spectroscopic study in THF-d8 suggests appreciable anion/cation interactions for Si to Pb and hence the presence of contact ion pairs.
- Kleeberg, Christian
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p. 8276 - 8287
(2013/07/28)
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- Reduction of carbonyl to methylene: Organosilane-Ga(OTf)3 as an efficient reductant system
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Direct carbonyl reduction to methylene has been achieved by mild reductant system obtained from the combination of organosilane and gallium (III) trifluoromethanesulfonate {Ga(OTf)3}, a water tolerant, recyclable, catalyst. Among a series of organosilanes studied, dimethylchlorosilane (Me 2SiHCl, DMCS) showed the highest efficiency. Both aromatic and aliphatic ketones were effectively reduced to the corresponding methylene products with high functional groups tolerance, under very mild conditions in a relatively short period of time with good to excellent yields. Graphical Abstract: [Figure not available: see fulltext.]
- Surya Prakash,Do, Clement,Mathew, Thomas,Olah, George A.
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experimental part
p. 507 - 511
(2012/01/04)
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- Thermolysis of N-tetramethylpiperidinyl triphenylacetate: Homolytic fragmentation of a TEMPO ester
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Thermolysis of N-tetramethylpiperidinyl triphenylacetate (7, Ph 3CCO2T, T = 2,2,6,6-tetramethylpiperidinyl) in benzene at 146 °C leads to the formation of triphenylmethane (Ph3CH, 80%), tetramethylpiperidine (TH, 91%), and tetraphenylmethane (Ph4C, 9%). First-order rate constants for the decomposition at 132.8 and 150.0 °C were 2.20 × 10-6 and 2.88 × 10-5 s-1, respectively. In benzene-d6 solvent the triphenylmethane was formed as Ph3CD to the extent of 20%, as determined by 1H NMR and mass spectrometry. The results are interpreted as showing that Ph 3CCC2T undergoes thermolysis by concerted two-bond scission with formation of Ph3C., tetramethylpiperidinyl radicals and CO2. The formation of Ph4C occurs by addition of Ph3C. to benzene, followed by hydrogen atom abstraction from the resulting adduct. Calculations using DFT methods at the B3LYP/6-311++G** level were used to elucidate the bond fission of HCO2T (2), and indicate that cleavage to HCO2. and T. is favored by 7.8 kcal mol-1 relative to cleavage to HC(·)=O and TO., in agreement with the experimental results. Copyright
- Henry-Riyad, Huda,Tidwell, Thomas T.
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p. 559 - 563
(2007/10/03)
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- Zinc-Promoted Reactions. 1. Mechanism of the Clemmensen Reaction. Reduction of Benzophenone in Glacial Acetic Acid
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The mechanism of the Clemmensen reduction of diaryl ketones was investigated by reducing benzophenone, benzhydryl chloride, and dichlorodiphenylmethane in AcOH under a variety of conditions.Besides diphenylmethane, dimeric products were isolated that were indicative of the formation of radical species.Different product distributions were obtained from reactions run under different conditions.The reduction of deuteriated benzhydryl chloride was also performed.A quite complicated mechanistic pattern, involving ionic and nonionic reactions, emerged from the experimental p icture.Two pathways, connected through the protonated substrate, were recognized.According to the first pathway the reduction is promoted by a SET from Zn to the substrate, leading to the formation of a carbon radical having one zinc atom bound to the oxygen of the carbonyl group.Benzhydryl chloride, benzhydryl acetate, and dichlorodiphenylmethane are involved in the process.The product distributions suggest the occurrence of several SETs, which involve the formation of different radical species.Ionic reactions are responsible for the second route to the reduced products.Nucleophilic displacements also participate to the complex mechanism.
- Vona, Maria Luisa Di,Rosnati, Vittorio
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p. 4269 - 4273
(2007/10/02)
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- Photolysis of 1,1,1,2-Tetraarylalkanes in the Presence of 1,4-Dicyanobenzene. A Photochemical C-C Bond Cleavage Reaction of Radical Cations in Solution
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Irradiation of acetonitrile-methanol (1:1) solutions of 1,1,1,2-tetraarylalkanes or 1,1,1-triphenyl-2-methoxyethane containing 1,4-dicyanobenzene led to the formation of triarylmethane and triarylmethyl methyl ethers in good yields.This C-C bond cleavage reaction is thought to proceed via a radical cation intermediate.
- Shi, Min,Okamoto, Yoshiki,Takamuku, Setsuo
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p. 1831 - 1840
(2007/10/02)
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- Thermolabile Hydrocarbons, 30. - Thermal Stability and Heat of Formation of 1,1,2,2- and 1,1,1,2-Tetraphenylethane. - Energy of Stabilisation of Benzhydryl and Triphenylmethyl Radicals
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Heat of combustion of symmetrical (3) and unsummetrical tetraphenylethane (4) were determined by combustion calorimetry: ΔHc0(c) (3) = -3249.5 +/- 0.8; (4) = -3252.0 +/- 0.6 kcal/mol.Enthalpies of sublimation of 3 ( ΔHsub,298K0 = 32.7 kcal/mol) and 4 ( 31.7 kcal/mol) were obtained from vapour-pressure-temperature relations, which were determined by gas-saturation method.The resulting heats of formationΔHf0(g) (3) = 85.4 +/- 1.3 and ΔHf0(g) (4) = 87.3 +/- 0.8 kcal/mol correspond to low strain energies: Hs(3) = 1.5 and Hs(4) = 4.6 kcal/mol.The thermolysis reactions above 200 deg C in solution with thiophenol as a scavenger are clean first order processes.The following activation parameters are obtained from kinetic measurements: ΔH(excit.) (3) = 47.3 +/- 0.3 , (4) = 45.0 +/- 0.3 kcal/mol, ΔS(excit.) (3) = 12.8 +/- 0.5 and (4) = 14.0 +/- 0.6 e.u.From the presented thermodynamic and kinetic data the stabilisation energies of the benzhydryl (1) and the trityl radical (2) have been derived by comparison with the corresponding data for the alkanes 7 and 9.As a result 1 is stabilysed by 12.9 +/- 0.9 and 2 by 20.0 +/- 1.7 kcal/mol, compared with a secondary or tertiary alkyl radical, respectively.Thus the substituent effect of two ( or three) phenyl rings in 1 ( or 2) is smaller than twice ( or thrice) the value for one phenyl group: 7.8 +/- 2.0 for a secondary and 8.4 +/- 1.2 kcal/mol for a tertiary benzyl radical.This can be explained by steric repulsion between the phenyl rings and steric inhibition of resonance.
- Beckhaus, Hans-Dieter,Dogan, Barbara,Schaetzer, Juergen,Hellmann, Siegrid,Ruechardt, Christoph
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p. 137 - 144
(2007/10/02)
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- THE EFFECT OF SOLVENT ON THERMAL CRACKING OF BIBENZYL AS A COAL MODEL
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The effect of solvent on bibenzyl conversion depends on the nature of solvent.Triphenylmethane, diphenylmethane, and diphenylamine are poor hydrogen donor solvents.But, when these compounds were used as solvent, bibenzyl conversion was markedly enhanced, and toluene, stilbene and adducts were formed.Moreover, when a proper amount of tetralin was mixed with the abowe solvent, toluene was solely obtained in reasonable yield.
- Chiba, Koji,Tagaya, Hideyuki,Yamauchi, Taku,Thukahara, Yoshitaro
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p. 945 - 948
(2007/10/02)
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- Configuration Determination of (R)-(-)-1,1,2-Triphenyl-3,3-dimethylbutane and the Stereochemistry of the Reaction of Benzhydryllithium with (R)-(+)-α-Phenylneopentyl Chloride
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A three-step synthesis of optically pure (R)-(-)-1,1,2-triphenyl-3,3-dimethylbutane from (R)-(-)-α-tert-butylphenylacetic acid has been accomplished.The synthesis of α-phenylneopentyl chloroformate from optically pure (R)-(+)-1-phenyl-2,2-dimethyl-1-propa
- Bright, Danielle Angrand,Mathisen, Donald E.,Zieger, Herman E.
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p. 3521 - 3524
(2007/10/02)
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- SELECTIVE COUPLING OF FREE RADICALS VIA ORGANOCHROMIUM COMPLEXES.
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Free radicals can be coupled in high yield to give either symmetric dimers or cross coupling products by reacting chromous chloride in THF with alkyl halides.
- Sustmann, Reiner,Altevogt, Rudolf
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p. 5167 - 5170
(2007/10/02)
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- THE IRON CARBONYL INDUCED DEOXYGENATION OF ALCOHOLS
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Alcohols, able to form stable carbanions, are deoxygenated to hydrocarbons by treatment with potassium, iron pentacarbonyl, and then hydrochloric acid.Use of an alkyl halide in place of HCl results in reductive alkylation.
- Alper, Howard,Salisova, Marta
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p. 801 - 804
(2007/10/02)
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