共查询到20条相似文献,搜索用时 406 毫秒
1.
Manganese(I)‐Catalyzed C−H Activation: The Key Role of a 7‐Membered Manganacycle in H‐Transfer and Reductive Elimination 下载免费PDF全文
Dr. Nasiru P. Yahaya Kate M. Appleby Magdalene Teh Conrad Wagner Erik Troschke Joshua T. W. Bray Prof. Simon B. Duckett L. Anders Hammarback Dr. Jonathan S. Ward Jessica Milani Dr. Natalie E. Pridmore Dr. Adrian C. Whitwood Dr. Jason M. Lynam Prof. Ian J. S. Fairlamb 《Angewandte Chemie (International ed. in English)》2016,55(40):12455-12459
Manganese‐catalyzed C?H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered MnI intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at MnI by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C?H bond activation, serving as a valuable system for probing the mechanistic features of Mn C?H bond activation chemistry. 相似文献
2.
Ming‐Hsiu Yang Jordan R. Hunt Dr. Niusha Sharifi Prof. Dr. Ryan A. Altman 《Angewandte Chemie (International ed. in English)》2016,55(31):9080-9083
A palladium‐catalyzed decarboxylative benzylation reaction of α,α‐difluoroketone enolates is reported, in which the key C(α)?C(sp3) bond is generated by reductive elimination from a palladium intermediate. The transformation provides convergent access to α‐benzyl‐α,α‐difluoroketone‐based products, and should be useful for accessing biological probes. 相似文献
3.
A Preliminary Study of Diastereoselectivity in the PdII‐Catalyzed C(sp3)‐H Alkoxylation of Cyclic Systems 下载免费PDF全文
Xinglin Yang Tian‐Yu Sun Prof. Yu Rao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3273-3277
Primary mechanism of a PdII‐catalyzed 8‐aminoquinoline‐directed C?H alkoxylation was investigated. It was understood that the PdII‐catalyzed C(sp3)?O bond formation proceeded through a concerted reductive elimination from the PdIV intermediate in the cyclic system. Deuteration experiments and related computational studies elucidate that intrinsic conformation determined the diastereoselectivity of the PdII‐catalyzed C?H alkoxylation of cyclic carboxylic acids. 相似文献
4.
RhV‐Nitrenoid as a Key Intermediate in RhIII‐Catalyzed Heterocyclization by CH Activation: A Computational Perspective on the Cycloaddition of Benzamide and Diazo Compounds 下载免费PDF全文
Tao Zhou Wei Guo Dr. Yuanzhi Xia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9209-9218
A mechanistic study of the substituent‐dependent ring formations in RhIII‐catalyzed C?H activation/cycloaddition of benzamide and diazo compounds was carried out by using DFT calculations. The results indicated that the decomposition of the diazo is facilitated upon the formation of the five‐membered rhodacycle, in which the RhIII center is more electrophilic. The insertion of carbenoid into Rh?C(phenyl) bond occurs readily and forms a 6‐membered rhodacycle, however, the following C?N bond formation is difficult both kinetically and thermodynamically by reductive elimination from the RhIII species. Instead, the RhV‐nitrenoid intermediate could be formed by migration of the pivalate from N to Rh, which undergoes the heterocyclization much more easily and complementary ring‐formations could be modulated by the nature of the substituent at the α‐carbon. When a vinyl is attached, the stepwise 1,3‐allylic migration occurs prior to the pivalate migration and the 8‐membered ring product will be formed. On the other hand, the pivalate migration becomes more favorable for the phenyl‐contained intermediate because of the difficult 1,3‐allylic migration accompanied by dearomatization, thus the 5‐membered ring product was formed selectively. 相似文献
5.
《Angewandte Chemie (International ed. in English)》2017,56(13):3635-3639
Metal–metal bonds play a vital role in stabilizing key intermediates in bond‐formation reactions. We report that binuclear benzo[h ]quinoline‐ligated NiII complexes, upon oxidation, undergo reductive elimination to form carbon–halogen bonds. A mixed‐valent Ni(2.5+)–Ni(2.5+) intermediate is isolated. Further oxidation to NiIII, however, is required to trigger reductive elimination. The binuclear NiIII–NiIII intermediate lacks a Ni−Ni bond. Each NiIII undergoes separate, but fast reductive elimination, giving rise to NiI species. The reactivity of these binuclear Ni complexes highlights the fundamental difference between Ni and Pd in mediating bond‐formation processes. 相似文献
6.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(13):3689-3693
Metal–metal bonds play a vital role in stabilizing key intermediates in bond‐formation reactions. We report that binuclear benzo[h ]quinoline‐ligated NiII complexes, upon oxidation, undergo reductive elimination to form carbon–halogen bonds. A mixed‐valent Ni(2.5+)–Ni(2.5+) intermediate is isolated. Further oxidation to NiIII, however, is required to trigger reductive elimination. The binuclear NiIII–NiIII intermediate lacks a Ni−Ni bond. Each NiIII undergoes separate, but fast reductive elimination, giving rise to NiI species. The reactivity of these binuclear Ni complexes highlights the fundamental difference between Ni and Pd in mediating bond‐formation processes. 相似文献
7.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(6):1557-1560
Single‐crystal X‐ray characterization of cationic (α‐diimine)Ni‐ethyl and isopropyl β‐agostic complexes, which are key intermediates in olefin polymerization and oligomerization, are presented. The sharp Ni‐Cα‐Cβ angles (75.0(3)° and 74.57(18)°) and short Cα−Cβ distances (1.468(7) and 1.487(5) Å) provide unambiguous evidence for a β‐agostic interaction. An inverse equilibrium isotope effect (EIE) for ligand coordination upon cleavage of the agostic bond highlights the weaker bond strength of Ni−H relative to the C−H bond. An Eyring plot for β‐hydride elimination–olefin rotation–reinsertion is constructed from variable‐temperature NMR spectra with 13C‐labeled agostic complexes. The enthalpy of activation (ΔH ≠) for β‐H elimination is 13.2 kcal mol−1. These results offer important mechanistic insight into two critical steps in polymerization: ligand association upon cleavage of the β‐agostic bonds and chain‐migration via β‐H elimination. 相似文献
8.
A DFT Study on the Conversion of Aryl Iodides to Alkyl Iodides: Reductive Elimination of R−I from Alkylpalladium Iodide Complexes with Accessible β‐Hydrogens 下载免费PDF全文
Wei Hao Junnian Wei Yue Chi Prof. Dr. Patrick J. Walsh Prof. Dr. Zhenfeng Xi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3422-3429
DFT calculations have been performed on the palladium‐catalyzed carboiodination reaction. The reaction involves oxidative addition, alkyne insertion, C?N bond cleavage, and reductive elimination. For the alkylpalladium iodide intermediate, LiOtBu stabilizes the intermediate in non‐polar solvents, thus promoting reductive elimination and preventing β‐hydride elimination. The C?N bond cleavage process was explored and the computations show that PPh3 is not bound to the Pd center during this step. Experimentally, it was demonstrated that LiOtBu is not necessary for the oxidative addition, alkyne insertion, or C?N bond cleavage steps, lending support to the conclusions from the DFT calculations. The turnover‐limiting steps were found to be C?N bond cleavage and reductive elimination, whereas oxidative addition, alkyne insertion, and formation of the indole ring provide the driving force for the reaction. 相似文献
9.
Palladium‐Catalyzed Intermolecular Acylation of Aryl Diazoesters with ortho‐Bromobenzaldehydes 下载免费PDF全文
Yinghua Yu Dr. Qianqian Lu Prof. Dr. Gui Chen Prof. Dr. Chunsen Li Prof. Dr. Xueliang Huang 《Angewandte Chemie (International ed. in English)》2018,57(1):319-323
In this work, we describe a palladium‐catalyzed intermolecular O acylation of α‐diazoesters with ortho‐bromobenzaldehydes. The C(sp2)?H bond activation of the aldehyde is enabled by migratory insertion of a palladium carbene intermediate. The diazoesters act as modular three‐atom units to build up key seven‐membered palladacycles, which are transformed into a variety of isocoumarin derivatives upon reductive elimination. Mechanistic experiments and DFT calculations provide insight into the reaction pathway. 相似文献
10.
Palladium‐Catalyzed Cascade CH Trifluoroethylation of Aryl Iodides and Heck Reaction: Efficient Synthesis of ortho‐Trifluoroethylstyrenes 下载免费PDF全文
Hao Zhang Dr. Pinhong Chen Prof. Dr. Guosheng Liu 《Angewandte Chemie (International ed. in English)》2014,53(38):10174-10178
A palladium‐catalyzed selective C? H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho‐trifluoroethyl‐substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key PdIV intermediate, which is generated through the rate‐determining oxidative addition of CF3CH2I to a palladacycle; the bulky nature of CF3CH2I influences the reactivity. Reductive elimination from the PdIV complex then leads to the formation of the aryl–CH2CF3 bond. 相似文献
11.
Computational Insight into Nickel‐Catalyzed Carbon–Carbon versus Carbon–Boron Coupling Reactions of Primary,Secondary, and Tertiary Alkyl Bromides 下载免费PDF全文
Dr. Man Sing Cheung Fu Kit Sheong Prof. Dr. Todd B. Marder Prof. Dr. Zhenyang Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(20):7480-7488
The nickel‐catalyzed alkyl–alkyl cross‐coupling (C?C bond formation) and borylation (C?B bond formation) of unactivated alkyl halides reported in the literature show completely opposite reactivity orders in the reactions of primary, secondary, and tertiary alkyl bromides. The proposed NiI/NiIII catalytic cycles for these two types of bond‐formation reactions were studied computationally by means of DFT calculations at the B3LYP level. These calculations indicate that the rate‐determining step for alkyl–alkyl cross‐coupling is the reductive elimination step, whereas for borylation the rate is determined mainly by the atom‐transfer step. In borylation reactions, the boryl ligand involved has an empty p orbital, which strongly facilitates the reductive elimination step. The inability of unactivated tertiary alkyl halides to undergo alkyl–alkyl cross‐coupling is mainly due to the moderately high reductive elimination barrier. 相似文献
12.
Dr. Randa K. Gabr Prof. Dr. Takuji Hatakeyama Prof. Dr. Kazuhiro Takenaka Prof. Dr. Shinobu Takizawa Yoshihiro Okada Prof. Dr. Masaharu Nakamura Prof. Dr. Hiroaki Sasai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(29):9518-9525
The reaction pathway of an enantioselective 5‐endo‐trig‐type cyclization of 3‐alkenoic acids catalyzed by a chiral palladium–spiro‐bis(isoxazoline) complex, Pd–SPRIX, has been studied by density functional theory calculations. The most plausible pathway involves intramolecular nucleophilic attack of the carboxylate moiety on the C?C double bond activated by Pd–SPRIX and β‐H elimination from the resulting organopalladium intermediate. The enantioselectivity was determined in the cyclization step through the formation of a π‐olefin complex, in which one of the two enantiofaces of the olefin moiety was selected. The β‐H elimination occurs via a seven‐membered cyclic structure in which the acetate ligand plays a key role in lowering the activation barrier of the transition state. In the elimination step, the SPRIX ligand was found to behave as a monodentate ligand due to the hemilability of one of the isoxazoline units thereby facilitating the elimination. Natural population analysis of this pathway showed that the more weakly electron‐donating SPRIX ligand, compared with the bis(oxazoline) ligand, BOX, facilitated the formation of the π‐olefin complex intermediate, leading to a smaller overall activation energy and a higher reactivity of the Pd–SPRIX catalyst. 相似文献
13.
Yu‐Li Sun Xing‐Ben Wang Feng‐Na Sun Qian‐Qian Chen Jian Cao Zheng Xu Li‐Wen Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(20):6819-6823
A palladium‐catalyzed enantioselective intramolecular σ‐bond cross‐exchange between C?I and C?C bonds is realized, providing chiral indanones bearing an alkyl iodide group and an all‐carbon quaternary stereocenter. Pd/TADDOL‐derived phosphoramidite is found to be an efficient catalytic system for both C?C bond cleavage and alkyl iodide reductive elimination. In addition to aryl iodides, aryl bromides can also be used for this transformation in the presence of KI. Density‐functional theory (DFT) calculation studies support the ring‐opening of cyclobutanones occuring through an oxidative addition/reductive elimination process involving PdIV species. 相似文献
14.
Dr. Sarolta Pilbák Dr. Ödön Farkas Prof. Dr. László Poppe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(25):7793-7802
Quantum mechanics/molecular mechanics calculations in tyrosine ammonia lyase (TAL) ruled out the hypothetical Friedel–Crafts (FC) route for ammonia elimination from L ‐tyrosine due to the high energy of FC intermediates. The calculated pathway from the zwitterionic L ‐tyrosine‐binding state (0.0 kcal mol?1) to the product‐binding state ((E)‐coumarate+H2N? MIO; ?24.0 kcal mol?1; MIO=3,5‐dihydro‐5‐methylidene‐4H‐imidazol‐4‐one) involves an intermediate (IS, ?19.9 kcal mol?1), which has a covalent bond between the N atom of the substrate and MIO, as well as two transition states (TS1 and TS2). TS1 (14.4 kcal mol?1) corresponds to a proton transfer from the substrate to the N1 atom of MIO by Tyr300? OH. Thus, a tandem nucleophilic activation of the substrate and electrophilic activation of MIO happens. TS2 (5.2 kcal mol?1) indicates a concerted C? N bond breaking of the N‐MIO intermediate and deprotonation of the pro‐S β position by Tyr60. Calculations elucidate the role of enzymic bases (Tyr60 and Tyr300) and other catalytically relevant residues (Asn203, Arg303, and Asn333, Asn435), which are fully conserved in the amino acid sequences and in 3D structures of all known MIO‐containing ammonia lyases and 2,3‐aminomutases. 相似文献
15.
Understanding the Mechanisms of Unusually Fast HH,CH,and CC Bond Reductive Eliminations from Gold(III) Complexes 下载免费PDF全文
A. Nijamudheen Sharmistha Karmakar Prof. Dr. Ayan Datta 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14650-14658
Carbon–carbon bond reductive elimination from gold(III) complexes are known to be very slow and require high temperatures. Recently, Toste and co‐workers have demonstrated extremely rapid C?C reductive elimination from cis‐[AuPPh3(4‐F‐C6H4)2Cl] even at low temperatures. We have performed DFT calculations to understand the mechanistic pathway for these novel reductive elimination reactions. Direct dynamics calculations inclusive of quantum mechanical tunneling showed significant contribution of heavy‐atom tunneling (>25 %) at the experimental reaction temperatures. In the absence of any competing side reactions, such as phosphine exchange/dissociation, the complex cis‐[Au(PPh3)2(4‐F‐C6H4)2]+ was shown to undergo ultrafast reductive elimination. Calculations also revealed very facile, concerted mechanisms for H?H, C?H, and C?C bond reductive elimination from a range of neutral and cationic gold(III) centers, except for the coupling of sp3 carbon atoms. Metal–carbon bond strengths in the transition states that originate from attractive orbital interactions control the feasibility of a concerted reductive elimination mechanism. Calculations for the formation of methane from complex cis‐[AuPPh3(H)CH3]+ predict that at ?52 °C, about 82 % of the reaction occurs by hydrogen‐atom tunneling. Tunneling leads to subtle effects on the reaction rates, such as large primary kinetic isotope effects (KIE) and a strong violation of the rule of the geometric mean of the primary and secondary KIEs. 相似文献
16.
Yeonjin Ko Mark W. Ruszczycky Sei‐Hyun Choi Prof. Dr. Hung‐wen Liu 《Angewandte Chemie (International ed. in English)》2015,54(3):860-863
DesII is a radical S‐adenosylmethionine (SAM) enzyme that catalyzes the C4‐deamination of TDP‐4‐amino‐4,6‐dideoxyglucose through a C3 radical intermediate. However, if the C4 amino group is replaced with a hydroxy group (to give TDP‐quinovose), the hydroxy group at C3 is oxidized to a ketone with no C4‐dehydration. It is hypothesized that hyperconjugation between the C4 C? N/O bond and the partially filled p orbital at C3 of the radical intermediate modulates the degree to which elimination competes with dehydrogenation. To investigate this hypothesis, the reaction of DesII with the C4‐epimer of TDP‐quinovose (TDP‐fucose) was examined. The reaction primarily results in the formation of TDP‐6‐deoxygulose and likely regeneration of TDP‐fucose. The remainder of the substrate radical partitions roughly equally between C3‐dehydrogenation and C4‐dehydration. Thus, changing the stereochemistry at C4 permits a more balanced competition between elimination and dehydrogenation. 相似文献
17.
Adiran deAguirre Ignacio Funes‐Ardoiz Feliu Maseras 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(12):3938-3942
The computational characterization of the full catalytic cycle for the synthesis of indoline from the reaction between iodoacetanilide and a terminal alkene catalyzed by a nickel complex and a photoactive ruthenium species is presented. A variety of oxidation states of nickel, Ni0, NiI, NiII, and NiIII, is shown to participate in the mechanism. Ni0 is necessary for the oxidative addition of the C?I bond, which goes through a NiI intermediate and results in a NiII species. The NiII species inserts into the alkene, but does not undergo the reductive elimination necessary for C?N bond formation. This oxidatively induced reductive elimination can be accomplished only after oxidation to NiIII by the photoactive ruthenium species. All the reaction steps are computationally characterized, and the barriers for the single‐electron transfer steps calculated using a modified version of the Marcus Theory. 相似文献
18.
The title compound is formed as a side‐product in the reaction of CF3CCl3 with Zn/DMF and dimethyl(thexyl)silyl chloride (=dimethyl(1,1,2‐trimethylpropyl)silyl chloride). The structure and the double‐bond configuration are deduced from its 13C‐NMR data. Its formation is discussed in terms of a Vilsmeier‐type formylation and a reductive elimination. 相似文献
19.
Exploring Bis(cyclometalated) Ruthenium(II) Complexes as Active Catalyst Precursors: Room‐Temperature Alkene–Alkyne Coupling for 1,3‐Diene Synthesis 下载免费PDF全文
Jing Zhang Dr. Angel Ugrinov Prof. Dr. Yong Zhang Prof. Dr. Pinjing Zhao 《Angewandte Chemie (International ed. in English)》2014,53(32):8437-8440
Described is the development of a new class of bis(cyclometalated) ruthenium(II) catalyst precursors for C? C coupling reactions between alkene and alkyne substrates. The complex [(cod)Ru(3‐methallyl)2] reacts with benzophenone imine or benzophenone in a 1:2 ratio to form bis(cyclometalated) ruthenium(II) complexes ( 1 ). The imine‐ligated complex 1 a promoted room‐temperature coupling between acrylic esters and amides with internal alkynes to form 1,3‐diene products. A proposed catalytic cycle involves C? C bond formation by oxidative cyclization, β‐hydride elimination, and C? H bond reductive elimination. This RuII/RuIV pathway is consistent with the observed catalytic reactivity of 1 a for mild tail‐to‐tail methyl acrylate dimerization and for cyclobutene formation by [2+2] norbornene/alkyne cycloaddition. 相似文献
20.
Regioselective reaction of a lithium organocuprate (R2CuLi) and a polyconjugated carbonyl compound affords a remote‐conjugate‐addition product. This reaction proceeds particularly cleanly when the conjugation is terminated by a C? C triple bond. The reaction pathways and the origin of the regioselectivity of this class of transformations are explored with the aid of density functional calculations. The outline of the reaction pathway is as follows. An initially formed β‐cuprio(III) enolate intermediate undergoes smooth copper migration along the conjugated system. This process takes place faster than reductive elimination of intermediary σ/π‐allylcopper(III) species, since the latter reaction disrupts the conjugation in the substrate and hence is not preferred. The copper migration to the acetylenic terminal affords a σ/π‐allenylcopper(III) intermediate, which undergoes facile and selective C? C bond forming reductive elimination at the terminal carbon atom. The present mechanistic framework shows good agreement with some pertinent experimental data, including 13C NMR chemical shifts and kinetic isotope effects. 相似文献