6708-17-4Relevant academic research and scientific papers
A structure-activity study of Ni-catalyzed alkyl-alkyl kumada coupling. Improved catalysts for coupling of secondary alkyl halides
Ren, Peng,Vechorkin, Oleg,Von Allmen, Kim,Scopelliti, Rosario,Hu, Xile
supporting information; experimental part, p. 7084 - 7095 (2011/06/26)
A structureactivity study was carried out for Ni catalyzed alkylalkyl Kumada-type cross coupling reactions. A series of new nickel(II) complexes including those with tridentate pincer bis(amino)amide ligands (RN2N) and those with bidentate mixed amino-amide ligands (RNN) were synthesized and structurally characterized. The coordination geometries of these complexes range from square planar, tetrahedral, to square pyramidal. The complexes had been examined as precatalysts for cross coupling of nonactivated alkyl halides, particularly secondary alkyl iodides, with alkyl Grignard reagents. Comparison was made to the results obtained with the previously reported Ni pincer complex [( MeN2N)NiCl]. A transmetalation site in the precatalysts is necessary for the catalysis. The coordination geometries and spin-states of the precatalysts have a small or no influence. The work led to the discovery of several well-defined Ni catalysts that are significantly more active and efficient than the pincer complex [(MeN2N)NiCl] for the coupling of secondary alkyl halides. The best two catalysts are [(HNN)Ni(PPh3)Cl] and [(HNN)Ni(2,4-lutidine)Cl]. The improved activity and efficiency was attributed to the fact that phosphine and lutidine ligands in these complexes can dissociate from the Ni center during catalysis. The activation of alkyl halides was shown to proceed via a radical mechanism.
Mono- and disubstituted N,N-dialkylcyclopropylamines from dialkylformamides via ligand-exchanged titanium - Alkene complexes
De Meijere, Armin,Williams, Craig M.,Kourdioukov, Alexandre,Sviridov, Sergei V.,Chaplinski, Vladimir,Kordes, Markus,Savchenko, Andrei I.,Stratmann, Christian,Noltemeyer, Mathias
, p. 3789 - 3801 (2007/10/03)
Dibenzylformamide was treated with cyclohexylmagnesium bromide in the presence of either titanium tetraisopropoxide or methyltitanium triisopropoxide and a variety of cyclic and acyclic alkenes and alkadienes to give new mono- and disubstituted as well as bicyclic dialkylcyclopropylamines (Tables 1-3) in yields ranging from 18 to 90% (in most cases around 55%). 3-Benzyl-6-(N,N-dibenzylamino)-3-azabicyclo[3.1.0]hexane (10a) and the orthogonally bisprotected 3-tert-butoxycarbonyl-6-(N,N-dibenzyl)- 3-azabicyclo[3.1.0]hexane (10d) as well as the analogous 6-(N,N-dibenzylamino)bicyclo[3.1.0]hexane (12) were obtained as pure exo diastereomers in particularly high yields (87, 90, and 88%, respectively) from N-benzylpyrroline (15a), N-Boc-pyrroline (15d; Boc = tert-butyloxycarbonyl) and cyclopentene (19). 1,3-Butadiene (52) and substituted 1,3-butadienes were also aminocyclopropanated quite well to give 2-ethenylcyclopropylamines in good yields (51-64%). Except for alkenyl and aryl-substituted compounds, N,N-dibenzylcyclopropylamines can be debenzylated by catalytic hydrogenation to the primary cyclopropylamines as demonstrated for 10a and 10d to yield the fully deprotected 10e (93%) and mono-Boc-protected 10f (98%), respectively. The latter are interesting templates for combinatorial syntheses of libraries of small molecules with a well defined distance of 4.3 A between two nitrogen atoms.
Radiolysis of Cyclooctane with γ-Rays and Helium Ions
Wojnarovits, Laszlo,LaVerne, Jay A.
, p. 8014 - 8018 (2007/10/02)
Iodine scavenging techniques have been used to examine the role of the cyclooctyl radical in the radiolysis of cyclooctane with γ-rays and with 5-20-MeV helium ions.In γ-radiolysis about 70percent of the total yield of 6.6 cyclooctyl radicals/100 eV are scavenged with E-4 M iodine, which agrees well with other studies on cycloalkanes that show most of the radicals produced in these systems react in the bulk medium at times longer than 1 μs.However, it is found that 2.5 radicals/100 eV (38percent) are produced by H atom precursors as copmpared to a value of 1.5 cyclohexyl radicals/100 eV (25percent) in cyclohexane.With 10-MeV helium ions (average LET of 106 eV/nm), only 8percent of the cyclooctyl radicals survive longer than a few microseconds due to the increased initial radical concentration in the helium ion track.The yield of the cross-bridged product bicyclooctane (pentalane) was found to be independent of iodine concentration up to 0.03 M with both types of radiation.However, the pentalane yield found with 10-MeV helium ions was only one-third of that found in γ-radiolysis.The most likely reason for this result is the decreased yield of singlet-state formation due to the enhanced probability of cross combination reactions of electron-cation pairs in the high-density region of the helium ion track.
Roles of Surface Protanation on the Photodynamic, Catalytic, and Other Properties of Polyoxometalates Probed by the Photochemical Functionalization of Alkalies. Implications for Irradiated Semiconductor Metal Oxides
Renneke, Roman F.,Kadkhodayan, Miryam,Pasquali, Marzia,Hill, Craig L.
, p. 8357 - 8367 (2007/10/02)
This paper further addresses the photodynamic and redox properties of polyoxometalates and the legitimacy of these compounds as discrete molecular representations for semiconductor metal oxides. The effect of protonation on redox, photochemical, catalytic, and other basic properties of a representative polyoxometalate, decatungstate (W10O324-), in aprotic media has been examined in detail. Protonation results in minimal perturbation of the electronic absorption spectral features of W10O324- including the HOMO-LUMO gap (band gap in semiconductor formalism) but a shift of ～ 1 V in the ground-state redox potentials (two quasi-reversible one-electron waves at -1.2 and -1.8 V become one quasi-reversible two-electron wave at -0.1 V vs Ag/AgNO3). The quantum yields (Φ) for the photooxidation of several alkanes by W10O324- (homogeneous reactions in CH3CN solution, 25 °C, Ar atmosphere, 322-nm light) all increase substantially upon protonation, with the increases dependent on alkane (ΦH+/ΦnoH+ ≈ 6.9 for cyclooctane (least increase) to ～ 25 for most alkanes). The alkane oxidation products in these processes also change upon protonation from those largely derived from freely diffusing alkyl radical intermediates to those largely derived from carbocation intermediates. The EPR spectra (X band) obtained from photooxidation of alkanes by W10O324- in the absence and presence of acid in frozen CH3CN glasses at 10 K and at 25 °C along with evidence from UV-visible spectra and oxidative titration data establish that the one-electron (EPR-active, S = 1/2) and two-electron (EPR-silent, S = 0) reduced forms of decatungstate, W10O325- and W10O326-, respectively, are produced in a 3:7 mol ratio in the absence of acid while the two-electron reduced form is produced exclusively in the presence of acid. EPR spectra as a function of irradiation time and as a function of acid concentration further establish that the two forms of the one-electron-reduced decatungstate present under acidic conditions are W10O325- and HW10O324-. The quantum yields, organic product distributions, polyoxometalate product distributions, UV-vis spectra, and ground-state redox potentials have all been assessed as a function of the number of equivalents of acid added per equivalent of W10O324-. All change monotonically with added acid, are well correlated, and attain a limiting behavior when ～ 2.5 equiv of acid has been added. The addition of W10O324- to acidified CH3CN solutions of branched alkenes suppresses acid-catalyzed alkene isomerization, providing another independent confirmation of W10O324- protonation. Protonation significantly decreases the rate of reduced decatungstate reoxidation by dioxygen in line with the effect of protonation on the ground-state redox potentials. The rate laws of the protonated and unprotonated forms are very similar: Both are variable order in W10O324-, apparently first order in substrate, and first order in light intensity. A rate law consistent with all the data that covers both protonation phenomena and the important coupled thermal process of electron-transfer oxidation of intermediate radicals has been formulated. The ratios of the rate constant for total deactivation of the excited state to the specific rate constant for alkane photooxidation by the excited state, assessed by double reciprocal plots, are 0.86 and 3.4 for the acidified and nonacidified reactions, respectively. The ratios of the rate constant for radiationless decay to that specifically for alkane photooxidation are 0.095 and 1.63 for the acidified and nonacidified systems, respectively.
Alkane Functionalization on a Preparative Scale by Mercury-Photosensitized Cross-Dehydrodimerization
Brown, Stephen H.,Crabtree, Robert H.
, p. 2946 - 2953 (2007/10/02)
Alkanes can be functionalized with high conversions and in high chemical and quantum yields on a multigram scale by mercury-photosensitized reaction between an alkane and alcohols, ethers, or silanes to give homodimers and cross-dehydrodimers.The separation of the product mixtures is often particulary easy because of a great difference in polarity of the homodimers and cross-dimers.It is also possible to bias the product composition when the ratio of the components in the vapor phase is adjusted by altering the liquid composition.This is useful either to maximize chemical yield or to ease separation by favoring the formation of the most easily separated pair of compounds.The mechanistic basis of the reaction is discussed and a number of specific types of syntheses, for example of 2,2-disubstituted carbinols, are described in detail.The selectivity of cross-dimerization is shown to exceed that for homodimerization and reasons are discussed.Relative reactivities of different compounds and classes of compound are MeOHp-dioxanecyclohexane1,3,5-trioxacyclohexaneethanolisobutaneTHFEt3SiH.The observed selectivities generally parallel those for homodimerization, reported in the preceding paper, but certain differences are noted, and reasons for the differences are proposed.The bond-dissociation energy of Et3SiH is estimated from the reactivity data to be 90 kcal/mol.Eleven new carbinols are synthesized.
Homogeneous Catalytic Photochemical Functionalization of Alkanes by α-Dodecatungstophosphate. Rate Behavior, Energetics, and General Characteristics of the Processes
Renneke, Roman F.,Hill, Craig L.
, p. 5461 - 5470 (2007/10/02)
The photochemical functionalization of saturated hydrocarbons catalyzed by the heteropolytungstate α-dodecatungstophospate in acetonitrile solution has been examined in detail.Under anaerobic conditions, the net processes involve oxidation of alkane, RH, and evolution of hydrogen (RH->R+1/2H2) with conversion of light into chemical energy (ΔHo>+30 kcal/mol of RH oxidized in some cases).The processes are catalytic in the polyoxotungstate with or without Pt(0) or other hydrogen evolution catalyst, but Pt(0) greatly accelerates the reoxidation of the photoreduced polyoxotungstate, the slow step, resulting in increased turnover rates.Two oxidative titration procedures adapted for these hydrophobic media, and the sizes and shapes of the electronic absorption chromophores generated as a function of time upon irradiation in the near-UV of α-H3PW12O40 (1) in acetonitrile solutions of representative alkanes, establish that the principal form of the photoreduced catalyst is the one-electron heteropoly blue species α-PW12O40(4-), in contrast to the case for photooxidation of alcohols and other organic substrates by 1.The product distributions have been established for the functionalization of representative branched alkanes and cycloalkanes.The relative yields of the initial alkane-derived oxidation products in these processes, alkene, N-alkylacetamide, alkylalkane dimer, and alkyl methyl ketone, vary with the alkane substrate, the form of the polyoxotungstate, and the reaction conditions.All these organic products are remarkably stable under the reaction conditions.Alcohols are not produced in these polyoxotungstate-based systems.The highest selectivities (ca. 100percent for alkene production) are seen with 1 in the absence of Pt(0).Quantum yields average 0.1 but vary with the form of the polyoxotungstate and the reaction conditions and can be considerably higher.For the exemplary system, substrate = cyclooctane and catalyst = 1, production of α-PW12O40(4-) is a one-photon process that is first order in alkane, inverse order in water for low concentrations of water, and zero order in 1 for high concentrations of 1.A rate law that involves the substrate, solvent, initial products, catalyst, and light intensity in accord with substantial kinetic data is derived.The relative observed rate constants for the production of α-PW12O40(4-) under optically dense conditions by photooxidation of several normal, branched, and cyclic alkanes by 1 are unlike those seen in radical, hydride abstraction, electrophilic, or any type alkane activation process documented for homogeneous liquid-phase reactions.These relative rates, the primary kinetic isotope effects kcyclohexane-h12/kcyclohexane-d12 = 1.38 and kcis-Decalin-h12/Kcis-Decalin-d12 = 1.39, and the product distribution studies are most compatible with electron transfer as the principal alkane activation process in the mechanism.These data also allow analysis...
Photochemical Hydroxymethylation of Alicyclic and Aliphatic Alkenes Induced by a EuIII/EuII Photoredox System in Methanol
Ishida, Akito,Yamashita, Shinya,Toki, Susumu,Takamuku, Setsuo
, p. 1195 - 1200 (2007/10/02)
The photoirradiation of a methanol solution of EuCl3 and alkenes such as cyclohexene, cyclooctene, cyclododecene, and tetramethylene afforded (hydroxymethyl)alkane.The dihydro dimer of alkene,hydrogen, and ethylene glycol are also formed.Reactions proceed via a radical mechanism induced by hydrogen atoms and hydroxymethyl radicals, which are produced by a photoredoc reaction of EuIII/EuII in methanol.
DECOMPOSITION DU PERCARBONATE DE O,O-t-BUTYLE ET O-ISOPROPENYLE EN SOLUTION DANS DES CYCLANES
Jaouhari, R.,Filliatre, C.,Maillard, B.,Villenave, J.J.
, p. 3137 - 3142 (2007/10/02)
Thermolysis of O,O-t-butyl and O-isopropenyl percarbonate in cyclohexane involves free-radical acetonylation of solvent.Free radicals derived from solvent add to the percarbonate double bond and after a double β-scission reaction, cyclohexylacetone carbon dioxide and t-butoxy radicals are formed.Abstracting H atoms from the solvent, t-butoxy radicals regenerate free radicals from solvent, and the reaction becomes a chain process.Extending the study to other cycloalkanes it has been shown that the process is a general synthesis method for cycloalkylacetones.On the other hand, competitive reactions of pairs of solvents have shown that the reactivity of the substrates depends on H atom lability and on more complex phenomena like transfers between hydrocarbons and C-centred free-radicals.
UNIMOLECULAR H2 ELIMINATION DURING THE LIQUID PHASE RADIOLYSIS AND PHOTOLYSIS OF ALKANE-ALKANE MIXTURES
Wojnarovits, L.,Foeldiak, G.
, p. 27 - 38 (2007/10/02)
Unimolecular H2 elimination from alkanes was investigated in cyclopentane-cyclohexane, n-hexane-cyclohexane and cyclohexane-cyclooctane mixtures during radiolysis and 7.6 eV photolysis.During the radiolysis of all system, and when the fluorescence shift law allowed it, during the photolysis as well, inhibited H2 detachment was observed from the first component and sensitized hydrogen molecule elimination from the second.It has been concluded that the same excited state (the lowest singlet, S1) is responsible for the H2 elimination during radiolysis and photolysis and this is that one that gives rise to fluorescence in the experiments of other authors.The H2 and H elimination from alkanes generally have different excited precursors.The direct population of S1 by γ-irradiation is of limited importance and this intermediate is mainly produced in "charge neutralization" processes.
