542-18-7Relevant articles and documents
Liquid-Phase Reactions of CCl3 Radicals with Trimethylsilane and Triethylsilane
Baruch, G.,Horowitz, A.
, p. 2535 - 2539 (1980)
The γ-radiation-induced chain reactions in liquid solution of silane (R'3SiH) in CCl4-c-C6H12(RH) mixtures were investigated over the temperature range 303-423 K for R' = Me and 335-423 K for R' = Et.In both systems the main products are R'3SiCl, CHCl3, and RCl.By kinetic analyses of product distribution, the rate constants of hydrogen abstraction from the two silanes by CCl3 radicals were competitively determined vs. hydrogen abstraction from cyclohexane.The relative rate constants combined with the known Arrhenius parameters of the reference systems gave the following Arrhenius parameters for the reaction CCl3 + R'3SiH -> CHCl3 + R'3Si: log A4 (L mol-1 s-1) = 8.49 and E4 = 8.70 kcal mol-1 when R' = Me, and log A4 = 8.62 and E4 = 8.06 when R' = Et.These results indicate that alkyl-substituted silanes are considerably more reactive than Cl3SiH in the H-atom transfer reactions with CCl3 radicals.This observation is rationalized in terms of the polar effects of the alkyl substituents.
Oxidative aromatization of olefins with dioxygen catalyzed by palladium trifluoroacetate
Bercaw, John E.,Hazari, Nilay,Labinger, Jay A.
, p. 8654 - 8657 (2008)
(Chemical Equation Presented) Molecular oxygen can replace sacrificial olefins as the hydrogen acceptor in the palladium trifluoroacetate catalyzed dehydrogenation of cyclohexene and related cyclic olefins into aromatics. One of the major drawbacks of the homogeneous system is the tendency of the palladium trifluoroacetate to precipitate as palladium(0) at elevated temperatures. The use of better ligands affords catalysts that can operate at higher temperatures, although they are less reactive than palladium trifluoroacetate.
Non-Heme-Iron-Mediated Selective Halogenation of Unactivated Carbon?Hydrogen Bonds
Bleher, Katharina,Comba, Peter,Faltermeier, Dieter,Gupta, Ashutosh,Kerscher, Marion,Krieg, Saskia,Martin, Bodo,Velmurugan, Gunasekaran,Yang, Shuyi
supporting information, (2021/12/09)
Oxidation of the iron(II) precursor [(L1)FeIICl2], where L1 is a tetradentate bispidine, with soluble iodosylbenzene (sPhIO) leads to the extremely reactive ferryl oxidant [(L1)(Cl)FeIV=O]+ with a cis disposition of the chlorido and oxido coligands, as observed in non-heme halogenase enzymes. Experimental data indicate that, with cyclohexane as substrate, there is selective formation of chlorocyclohexane, the halogenation being initiated by C?H abstraction and the result of a rebound of the ensuing radical to an iron-bound Cl?. The time-resolved formation of the halogenation product indicates that this primarily results from sPhIO oxidation of an initially formed oxido-bridged diiron(III) resting state. The high yield of up to >70 % (stoichiometric reaction) as well as the differing reactivities of free Fe2+ and Fe3+ in comparison with [(L1)FeIICl2] indicate a high complex stability of the bispidine-iron complexes. DFT analysis shows that, due to a large driving force and small triplet-quintet gap, [(L1)(Cl)FeIV=O]+ is the most reactive small-molecule halogenase model, that the FeIII/radical rebound intermediate has a relatively long lifetime (as supported by experimentally observed cage escape), and that this intermediate has, as observed experimentally, a lower energy barrier to the halogenation than the hydroxylation product; this is shown to primarily be due to steric effects.
Aerobic Partial Oxidation of Alkanes Using Photodriven Iron Catalysis
Coutard, Nathan,Goldberg, Jonathan M.,Valle, Henry U.,Cao, Yuan,Jia, Xiaofan,Jeffrey, Philip D.,Gunnoe, T. Brent,Groves, John T.
, p. 759 - 766 (2022/01/11)
Photodriven oxidations of alkanes in trifluoroacetic acid using commercial and synthesized Fe(III) sources as catalyst precursors and dioxygen (O2) as the terminal oxidant are reported. The reactions produce alkyl esters and occur at ambient temperature in the presence of air, and catalytic turnover is observed for the oxidation of methane in a pure O2 atmosphere. Under optimized conditions, approximately 17% conversion of methane to methyl trifluoroacetate at more than 50% selectivity is observed. It is demonstrated that methyl trifluoroacetate is stable under catalytic conditions, and thus overoxidized products are not formed through secondary oxidation of methyl trifluoroacetate.
Site Selective Chlorination of C(sp3)?H Bonds Suitable for Late-Stage Functionalization
Fawcett, Alexander,Keller, M. Josephine,Herrera, Zachary,Hartwig, John F.
supporting information, p. 8276 - 8283 (2021/03/15)
C(sp3)?Cl bonds are present in numerous biologically active small molecules, and an ideal route for their preparation is by the chlorination of a C(sp3)?H bond. However, most current methods for the chlorination of C(sp3)?H bonds are insufficiently site selective and tolerant of functional groups to be applicable to the late-stage functionalization of complex molecules. We report a method for the highly selective chlorination of tertiary and benzylic C(sp3)?H bonds to produce the corresponding chlorides, generally in high yields. The reaction occurs with a mixture of an azidoiodinane, which generates a selective H-atom abstractor under mild conditions, and a readily-accessible and inexpensive copper(II) chloride complex, which efficiently transfers a chlorine atom. The reaction's exceptional functional group tolerance is demonstrated by the chlorination of >30 diversely functionalized substrates and the late-stage chlorination of a dozen derivatives of natural products and active pharmaceutical ingredients.
Photocatalytic C-H activation and the subtle role of chlorine radical complexation in reactivity
Yang, Qiaomu,Wang, Yu-Heng,Qiao, Yusen,Gau, Michael,Carroll, Patrick J.,Walsh, Patrick J.,Schelter, Eric J.
, p. 847 - 852 (2021/05/28)
The functionalization of methane, ethane, and other alkanes derived from fossil fuels is a central goal in the chemical enterprise. Recently, a photocatalytic system comprising [CeIVCl5(OR)]2- [CeIV, cerium(IV); OR, -OCH3 or -OCCl2CH3] was disclosed. The system was reportedly capable of alkane activation by alkoxy radicals (RO·) formed by CeIV-OR bond photolysis. In this work, we present evidence that the reported carbon-hydrogen (C-H) activation of alkanes is instead mediated by the photocatalyst [NEt4]2[CeCl6] (NEt4+, tetraethylammonium), and RO· are not intermediates. Spectroscopic analyses and kinetics were investigated for C-H activation to identify chlorine radical (Cl·) generation as the ratelimiting step. Density functional theory calculations support the formation of [Cl·][alcohol] adducts when alcohols are present, which can manifest a masked RO· character. This result serves as an important cautionary note for interpretation of radical trapping experiments.
Enthalpy-Entropy Compensation Effect in Oxidation Reactions by Manganese(IV)-Oxo Porphyrins and Nonheme Iron(IV)-Oxo Models
Guo, Mian,Zhang, Jisheng,Zhang, Lina,Lee, Yong-Min,Fukuzumi, Shunichi,Nam, Wonwoo
supporting information, p. 18559 - 18570 (2021/11/22)
"Enthalpy-Entropy Compensation Effect"(EECE) is ubiquitous in chemical reactions; however, such an EECE has been rarely explored in biomimetic oxidation reactions. In this study, six manganese(IV)-oxo complexes bearing electron-rich and -deficient porphyrins are synthesized and investigated in various oxidation reactions, such as hydrogen atom transfer (HAT), oxygen atom transfer (OAT), and electron-transfer (ET) reactions. First, all of the six Mn(IV)-oxo porphyrins are highly reactive in the HAT, OAT, and ET reactions. Interestingly, we have observed a reversed reactivity in the HAT and OAT reactions by the electron-rich and -deficient Mn(IV)-oxo porphyrins, depending on reaction temperatures, but not in the ET reactions; the electron-rich Mn(IV)-oxo porphyrins are more reactive than the electron-deficient Mn(IV)-oxo porphyrins at high temperature (e.g., 0 °C), whereas at low temperature (e.g., -60 °C), the electron-deficient Mn(IV)-oxo porphyrins are more reactive than the electron-rich Mn(IV)-oxo porphyrins. Such a reversed reactivity between the electron-rich and -deficient Mn(IV)-oxo porphyrins depending on reaction temperatures is rationalized with EECE; that is, the lower is the activation enthalpy, the more negative is the activation entropy, and vice versa. Interestingly, a unified linear correlation between the activation enthalpies and the activation entropies is observed in the HAT and OAT reactions of the Mn(IV)-oxo porphyrins. Moreover, from the previously reported HAT reactions of nonheme Fe(IV)-oxo complexes, a linear correlation between the activation enthalpies and the activation entropies is also observed. To the best of our knowledge, we report the first detailed mechanistic study of EECE in the oxidation reactions by synthetic high-valent metal-oxo complexes.
Revisiting Alkane Hydroxylation with m-CPBA (m-Chloroperbenzoic Acid) Catalyzed by Nickel(II) Complexes
Itoh, Mayu,Itoh, Shinobu,Kubo, Minoru,Morimoto, Yuma,Shinke, Tomoya,Sugimoto, Hideki,Wada, Takuma,Yanagisawa, Sachiko
, p. 14730 - 14737 (2021/09/29)
Mechanistic studies are performed on the alkane hydroxylation with m-CPBA (m-chloroperbenzoic acid) catalyzed by nickel(II) complexes, NiII(L). In the oxidation of cycloalkanes, NiII(TPA) acts as an efficient catalyst with a high yield and a high alcohol selectivity. In the oxidation of adamantane, the tertiary carbon is predominantly oxidized. The reaction rate shows first-order dependence on [substrate] and [NiII(L)] but is independent on [m-CPBA]; vobs=k2[substrate][NiII(L)]. The reaction exhibited a relatively large kinetic deuterium isotope effect (KIE) of 6.7, demonstrating that the hydrogen atom abstraction is involved in the rate-limiting step of the catalytic cycle. Furthermore, NiII(L) supported by related tetradentate ligands exhibit apparently different catalytic activity, suggesting contribution of the NiII(L) in the catalytic cycle. Based on the kinetic analysis and the significant effects of O2 and CCl4 on the product distribution pattern, possible contributions of (L)NiII?O. and the aroyloxyl radical as the reactive oxidants are discussed.
Aliphatic C–H hydroxylation activity and durability of a nickel complex catalyst according to the molecular structure of the bis(oxazoline) ligands
Hikichi, Shiro,Izumi, Takashi,Matsuba, Naki,Nakazawa, Jun
, (2021/07/13)
Applicability of the oxazoline-based compounds, bis(2-oxazolynyl)methane (BOX) and 2,6-bis(2-oxazolynyl)pyridine (PyBOX), as supporting ligands of nickel(II) complexes for the catalysis of aliphatic C–H hydroxylation with m-CPBA (meta-chloroperoxybenzoic acid) was explored. Substituent groups at the fourth and fifth positions of oxazoline rings and the bridgehead carbon atom of the BOX derivatives affected the catalytic performances toward cyclohexane hydroxylation. Presence of dioxygen led to a reduced catalytic performance of the nickel complexes, except in the case of a fully substituted BOX ligand complex.
Mechanism of Ni-catalyzed oxidations of unactivated C(sp3)-H Bonds
Qiu, Yehao,Hartwig, John F.
supporting information, p. 19239 - 19248 (2020/11/13)
The Ni-catalyzed oxidation of unactivated alkanes, including the oxidation of polyethylenes, by meta-chloroperbenzoic acid (mCPBA) occur with high turnover numbers under mild conditions, but the mechanism of such transformations has been a subject of debate. Putative, high-valent nickel-oxo or nickel-oxyl intermediates have been proposed to cleave the C-H bond, but several studies on such complexes have not provided strong evidence to support such reactivity toward unactivated C(sp3)-H bonds. We report mechanistic investigations of Ni-catalyzed oxidations of unactivated C-H bonds by mCPBA. The lack of an effect of ligands, the formation of carbon-centered radicals with long lifetimes, and the decomposition of mCPBA in the presence of Ni complexes suggest that the reaction occurs through free alkyl radicals. Selectivity on model substrates and deuterium-labeling experiments imply that the m-chlorobenzoyloxy radical derived from mCPBA cleaves C-H bonds in the alkane to form an alkyl radical, which subsequently reacts with mCPBA to afford the alcohol product and regenerate the aroyloxy radical. This free-radical chain mechanism shows that Ni does not cleave the C(sp3)-H bonds as previously proposed; rather, it catalyzes the decomposition of mCPBA to form the aroyloxy radical.
