5402-29-9Relevant academic research and scientific papers
Rearrangement pathways of five-membered ring enlargement in carbocations: Quantum chemical calculations and deuterium kinetic isotope effects
Vrcek, Valerije,Saunders, Martin,Kronja, Olga
, p. 1859 - 1866 (2003)
Three plausible routes for the five-membered ring expansion in the equilibrating 2-cyclopentyl-2-propyl and 1-(2-propyl)cyclopentyl cations 1A/1B were located on the PES, all calculated at the MP4/6-31G(d)//MP2/6-31G(d) level of theory. In pathway I, the six-membered transition structure (TS-I) connects the less stable cyclopentyl cation 1A and the 1,2-dimethylcyclohexyl carbocation (2) via a barrier of 16.4 kcal/mol. In pathway II, which has a barrier of 16.3 kcal/mol, the methyl migration occurs first in the more stable 1B via transition structure TS-II. Pathway III involves the uphill hydride shift and formation of the secondary cation 3, which undergoes Wagner-Meerwein 1,2-isopropyl shift via a transition structure TS-III and the protonated carbocation intermediate 4. The barrier pathway III is for 17.0 kcal/mol. Experimental secondary deuterium isotope effects of the rearrangement were measured for the hexadeuterated 1A-d6/1B-d6 (kH/kD = 2.40) and tetradeuterated 1A-d4/1B-d4 (kH/kD = 0.18) cations by means of 1H NMR. Comparison of the experimental data with the theoretical values (kH/kD = 2.40 for 1B-d6 and kH/kD = 0.24 for 1B-d4, respectively) obtained with QUIVER revealed that pathway II is a major reaction route.
Phenoxazinone synthase-like catalytic activity of novel mono- And tetranuclear copper(ii) complexes with 2-benzylaminoethanol
Bondarenko, Olena E.,Nesterov, Dmytro S.,Nesterova, Oksana V.,Pombeiro, Armando J. L.
, p. 4710 - 4724 (2020/04/27)
Three novel coordination compounds, [Cu(ca)2(Hbae)2] (1), [Cu(va)2(Hbae)2] (2) and [Cu4(va)4(bae)4]·H2O (3), have been prepared by self-assembly reactions of copper(ii) chloride (1 and 2) or tetrafluoroborate (3) and CH3OH (1 and 3) or CH3CN (2) solution of 2-benzylaminoethanol (Hbae) and cinnamic (Hca, 1) or valeric (Hva, 2 and 3) acid. Crystallographic analysis revealed that both 1 and 2 have mononuclear crystal structures, wherein the complex molecules are H-bonded forming extended supramolecular chains. The tetranuclear structure of 3 is based on the {Cu4(μ3-O)4} core, wherein the metal atoms are bound together by μ3 oxygen bridges from 2-benzylaminoethanol forming an overall cubane-like configuration. The strong hydrogen bonding in 1-3 leads to the joining of the neighbouring molecules into 1D chains. Concentration-dependent ESI-MS studies disclosed the equilibria between di-, tri- and tetranuclear species in solutions of 1-3. All three compounds act as catalysts for the aerobic oxidation of o-aminophenol to the phenoxazinone chromophore (phenoxazinone synthase-like activity), with the maximum reaction rates of 4.0 × 10-7, 2.5 × 10-7 and 2.1 × 10-7 M s-1 for 1, 2 and 3, respectively, supported by the quantitative yield of the product after 24 h. The dependence of the reaction rates on catalyst concentrations is evidence of reaction orders higher than one relative to the catalyst. Kinetic and ESI-MS data allowed us to assume that the tetranuclear species, originating from 1, 2 and 3 in solution, possess considerably higher activity than the species of lower nuclearity. Mechanistic and isotopic 18O-labelling experiments suggested that o-aminophenol coordinates to CuII species with the formation of reactive intermediates, while the oxygen from 18O2 is not incorporated into the phenoxazinone chromophore.
Highly Selective and Catalytic Oxygenations of C?H and C=C Bonds by a Mononuclear Nonheme High-Spin Iron(III)-Alkylperoxo Species
Ghosh, Ivy,Banerjee, Sridhar,Paul, Satadal,Corona, Teresa,Paine, Tapan Kanti
, p. 12534 - 12539 (2019/08/07)
The reactivity of a mononuclear high-spin iron(III)-alkylperoxo intermediate [FeIII(t-BuLUrea)(OOCm)(OH2)]2+(2), generated from [FeII(t-BuLUrea)(H2O)(OTf)](OTf) (1) [t-BuLUrea=1,1′-(((pyridin-2-ylmethyl)azanediyl)bis(ethane-2,1-diyl))bis(3-(tert-butyl)urea), OTf=trifluoromethanesulfonate] with cumyl hydroperoxide (CmOOH), toward the C?H and C=C bonds of hydrocarbons is reported. 2 oxygenates the strong C?H bonds of aliphatic substrates with high chemo- and stereoselectivity in the presence of 2,6-lutidine. While 2 itself is a sluggish oxidant, 2,6-lutidine assists the heterolytic O?O bond cleavage of the metal-bound alkylperoxo, giving rise to a reactive metal-based oxidant. The roles of the urea groups on the supporting ligand, and of the base, in directing the selective and catalytic oxygenation of hydrocarbon substrates by 2 are discussed.
Reactivity of a Nickel(II) Bis(amidate) Complex with meta-Chloroperbenzoic Acid: Formation of a Potent Oxidizing Species
Corona, Teresa,Pfaff, Florian F.,Acu?a-Parés, Ferran,Draksharapu, Apparao,Whiteoak, Christopher J.,Martin-Diaconescu, Vlad,Lloret-Fillol, Julio,Browne, Wesley R.,Ray, Kallol,Company, Anna
, p. 15029 - 15038 (2015/10/20)
Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a NiII precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., CH bonds, CC bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic OO bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a NiIII-oxyl compound. A highly reactive nickel-oxygen species has been spectroscopically trapped after heterolytic OO bond cleavage during the reaction of a NiII precursor with meta-chloroperbenzoic acid (HmCPBA). This species is used to carry out the oxidation of different substrates, such as olefins, sulfides, and CH bonds (see scheme).
Catalytic Oxidation of Alkanes and Alkenes by H2O2 with a μ-Oxido Diiron(III) Complex as Catalyst/Catalyst Precursor
Das, Biswanath,Al-Hunaiti, Afnan,Haukka, Matti,Demeshko, Serhiy,Meyer, Steffen,Shteinman, Albert A.,Meyer, Franc,Repo, Timo,Nordlander, Ebbe
, p. 3590 - 3601 (2015/08/06)
A new μ-oxo diiron(III) complex of the lithium salt of the pyridine-based unsymmetrical ligand 3-[(3-{[bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino]propanoate (LiDPCPMPP), [Fe2(μ-O)(LiDPCPMPP)2](ClO4)2, has been synthesized and characterized. The ability of the complex to catalyze oxidation of several alkanes and alkenes has been investigated by using CH3COOH/H2O2 (1:1) as an oxidative system. Moderate activity in cyclohexane oxidation (TOF = 33 h-1) and good activity in cyclohexene oxidation (TOF = 72 h-1) were detected. Partial retention of configuration (RC = 53%) in cis- and trans-1,2-dimethylcyclohexane oxidation, moderate 3/2 selectivity (4.1) in adamantane oxidation, and the observation of a relatively high kinetic isotope effect for cyclohexane oxidation (KIE = 3.27) suggest partial metal-based oxidation, probably in tandem with free-radical oxidation. Low-temperature UV/Vis spectroscopy and mass spectrometric studies in the rapid positive detection mode indicate the formation of a transient peroxido species, [Fe2(O)(O2)(LiDPCPMPP)2]2+, which might be an intermediate in the metal-based component of the oxidation process. A μ-oxido diiron(III) complex, [Fe2(μ-O)(LiDPCPMPP)2](ClO4)2, was synthesized and characterized. This complex was used as catalyst in C-H bond oxidation with CH3COOH-H2O2 as chemical oxidant. Reactivity studies indicate that the oxidation process goes through a metal-based mechanism concomitant with a radical process.
Catalytic oxidation of alkanes by iron bispidine complexes and dioxygen: Oxygen activation versus autoxidation
Comba, Peter,Lee, Yong-Min,Nam, Wonwoo,Waleska, Arkadius
supporting information, p. 412 - 414 (2014/01/06)
Organic substrates (specifically cis-1,2-dimethylcyclohexane, DMCH) are oxidized by O2 in the presence of iron(ii)-bispidine complexes. It is shown that this oxidation reaction is not based on O2 activation by the nonheme iron catalysts as in Nature but due to a radical-based initiation, followed by a radical- and ferryl-based catalytic reaction.
Oxidation of alkane using Pt/Eu2O3/TiO 2/SiO2 catalyst with O2 and H2 in acetic acid under mild conditions
Yamanaka, Ichiro,Suzuki, Yuta,Toida, Masashi
experimental part, p. 286 - 290 (2011/01/04)
A new solid catalyst of Pt/Eu2O3/TiO 2/SiO2 for oxidation of alkane was developed. Oxidation of adamantane using the multi-components supported catalyst with O2 and H2 was studied in acetic acid at 313 K. Several multi-components supported catalysts were prepared and tested the oxidation activity. It is found that loading order of Eu2O3, TiO2 and Pt on the SiO2 support strongly affected the oxidation catalysis. The active catalysts model was proposed from TEM-EDS analysis that very small Pt particles well dispersed on amorphous Eu2O3 and TiO 2 on the SiO2 support. Eu and Ti oxides concertedly activated O2 with electrons supplied from H2 on Pt, and active oxygen species efficiently oxidized adamantane and other alkanes to oxygenated compounds. Active oxygen species could not be identified but its reactivity was studied. It showed radical nature for oxidation of alkanes and a cleavage of C-H bond was the rate-determining step during the oxidation.
Alkane oxidation by the H2O2-NaVO3-H2SO4 system in acetonitrile and water
Shul'pina, Lidia S.,Kirillova, Marina V.,Pombeiro, Armando J.L.,Shul'pin, Georgiy B.
experimental part, p. 2424 - 2429 (2009/07/25)
A simple system is described, which oxidizes saturated hydrocarbons either in acetonitrile or (less efficiently) in water. The system consists of 50% aqueous hydrogen peroxide as an oxidant, sodium metavanadate, NaVO3, as a catalyst and sulfuric (or oxalic) acid as a co-catalyst. The reactions were carried out at 20-50 °C. In the oxidation of cyclohexane in acetonitrile, the highest yield (37% based on cyclohexane) and turnover number (TON=1700) were attained after 3 h at 50 °C. The corresponding parameters were 16% and 1090 for n-heptane oxidation under the same conditions. The oxidation of higher alkanes, RH, in acetonitrile gives almost exclusively the corresponding alkyl hydroperoxides, ROOH. Light alkanes (n-butane, propane, ethane, and methane) have been also oxygenated by the system under consideration. The highest TON (200) was attained for ethane and the highest yield (19%) was obtained in the case of n-butane. The selectivity parameters measured for the oxidation of linear and branched alkanes are low, the reaction with cis- and trans-1,2-dimethylcyclohexanes is not stereoselective. These facts lead us to conclude that the oxidation occurs with the formation of hydroxyl radicals in the crucial step.
Alkane oxidation by the system 'tert-butyl hydroperoxide-[Mn 2L2O3][PF6]2 (L = 1,4,7trimethyl-1,4,7-triazacyclononane)-carboxylic acid'
Kozlov, Yuriy N.,Nizova, Galina V.,Shul'pin, Georgiy B.
, p. 119 - 126 (2008/09/20)
The kinetics of cyclohexane (CyH) oxygenation with terf-butyl hydroperoxide (TBHP) in acetonitrile at 50°C catalysed by a dinuclear manganese(IV) complex 1 containing 1,4,7-trimethyl-1,4,7-triazacyclononane and co-catalysed by oxalic acid have been studied. It has been shown that an active form of the catalyst (mixed-valent dimeric species 'MnIIIMnIV,) is generated only in the interaction between complex 1 and TBHP and oxalic acid in the presence of water. The formation of this active form is assumed to be due to the hydrolysis of the Mn - O - Mn bonds in starting compound 1 and reduction of one MnIV to MnIII. A species which induces the CyH oxidation is radical tert-BuO generated by the decomposition of a monoperoxo derivative of the active form. The constants of the equilibrium formation and the decomposition of the intermediate adduct between TBHP and 1 have been measured: k = 7.4mol-1dm3 and k = 8.4 × 10 -2s-1, respectively, at [H2O] = 1.5 mol dm -3 and [oxalic acid] = 10-2 mol dm-3. The constant ratio for reactions of the monomolecular decomposition of tert-butoxy radical (tert-BuO → CH3COCH3+ CH3) and its interaction with the CyH (terf-BuO + CyH → fert-BuOH + Cy) was calculated: 0.26 mol dm-3. One of the reasons why oxalic acid accelerates the oxidation is due to the formation of an adduct between oxalic acid and 1 (K ≈ 103 mol-1 dm3). Copyright
Alkane hydroxylation by a nonheme iron catalyst that challenges the heme paradigm for oxygenase action
Company, Anna,Gomez, Laura,Gueell, Mireia,Ribas, Xavi,Luis, Josep M.,Que Jr., Lawrence,Costas, Miquel
, p. 15766 - 15767 (2008/09/19)
A nonheme iron catalyst catalyzed stereoselective oxidation of alkanes with H2O2 with remarkable efficiency and exhibiting an unprecedented high incorporation of water into the oxidized products. The present results challenge the canonical description of oxygenases, the standard oxo-hydroxo tautomerism that applies to heme systems and serves as a precedent for alternative pathways for the oxidation of hydrocarbons at nonheme iron oxygenases. Copyright
