19 research outputs found

    <i>para</i>-Selective Alkylation of Sulfonylarenes by Cooperative Nickel/Aluminum Catalysis

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    A method for the <i>para</i>-selective alkylation of a variety of arenesulfonamides and aromatic sulfones with 1-alkenes by cooperative nickel/aluminum catalysis has been developed. Taking advantage of the sulfornyl functionality serving as a removable <i>ortho</i>-directing group, the reaction can be applied to facile access to 1,3-dialkyl-substitued benzenes

    Arylboration of Alkenes by Cooperative Palladium/Copper Catalysis

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    Arylboration of vinylarenes and methyl crotonate with aryl halides and bis­(pinacolato)­diboron by cooperative Pd/Cu catalysis has been developed, giving 2-boryl-1,1-diarylethanes and an α-aryl-β-boryl ester in a regioselective manner. The reaction is compatible with a variety of functionalities and amenable to be scaled-up to a gram scale with no detriment to the yield. A short synthesis of the biologically active compound CDP840 was performed using the present reaction as a key step

    Reductive Denitration of Nitroarenes

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    The Pd-catalyzed reductive denitration of nitroarenes has been achieved via a direct cleavage of the C–NO<sub>2</sub> bonds. The catalytic conditions reported exhibit a broad substrate scope and good functional-group compatibility. Notably, the use of inexpensive propan-2-ol as a mild reductant suppresses the competitive formation of anilines, which are normally formed by other conventional reductions. Mechanistic studies have revealed that alcohols serve as efficient hydride donors in this reaction, possibly through β-hydride elimination from palladium alkoxides

    Aromatic C–H σ‑Bond Activation by Ni<sup>0</sup>, Pd<sup>0</sup>, and Pt<sup>0</sup> Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism

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    C–H σ-bond activation of arene (represented here by benzene) by the Ni<sup>0</sup> propene complex Ni<sup>0</sup>(IMes)­(C<sub>3</sub>H<sub>6</sub>) (IMes = 1,3-dimesitylimidazol-2-ylidene), which is an important elementary step in Ni-catalyzed hydroarylation of unactivated alkene with arene, was investigated by DFT calculations. In the Ni<sup>0</sup> complex, the C–H activation occurs through a ligand-to-ligand H transfer mechanism to yield Ni<sup>II</sup>(IMes)­(C<sub>3</sub>H<sub>7</sub>)­(Ph) (C<sub>3</sub>H<sub>7</sub> = propyl; Ph = phenyl). In Pd<sup>0</sup> and Pt<sup>0</sup> analogues, the activation occurs through concerted oxidative addition of the C–H bond to the metal. Analysis of the electron redistribution during the C–H activation highlights the difference between the two mechanisms. In the ligand-to-ligand H transfer, charge transfer (CT) occurs from the metal to the benzene. However, the atomic population of the transferring H remains almost constant, suggesting that different CT simultaneously occurs from the transferring H to the LUMO of propene. The electron redistribution contrasts significantly with that found for Pd<sup>0</sup> and Pt<sup>0</sup>, in which CT occurs only from the metal to the benzene. Preference for ligand-to-ligand H transfer over concerted oxidative addition in the Ni<sup>0</sup> complex is shown to be due to the smaller atomic radius of Ni in comparison to those of Pd and Pt and the smaller Ni<sup>II</sup>–H bond energy relative to the Pd<sup>II</sup>–H and Pt<sup>II</sup>–H energies. Interestingly, the bulky ligand accelerates the ligand-to-ligand H transfer in the Ni<sup>0</sup> complex by decreasing the distance between the coordinated benzene and alkene substrates. Thus, the Gibbs activation energy (Δ<i>G</i>°<sup>⧧</sup>) decreases in the case of cyclic-alkylaminocarbene with bulky substituents (CACC-K3), while the Δ<i>G</i>°<sup>⧧</sup> values are similar in X-Phos, IMes, and nonsubstituted cyclic alkylaminocarbene (CAAC-K0). An electron-withdrawing substituent on the arene accelerates the C–H activation by favoring the metal to arene CT

    How to Control Inversion vs Retention Transmetalation between Pd<sup>II</sup>–Phenyl and Cu<sup>I</sup>–Alkyl Complexes: Theoretical Insight

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    Transmetalation between Pd­(Br)­(Ph<sup>A</sup>)­(PCyp<sub>3</sub>)<sub>2</sub> (Ph = phenyl, Cyp = cyclopentyl) and Cu­(C<sup>a</sup>HMePh<sup>B</sup>)­(NHC) (NHC = 1,3-bis­(2,6-diisopropylphenyl)-imidazolidin-2-ylidene) is an important elementary step in recently reported catalytic cross-coupling reaction by Pd/Cu cooperative system. DFT study discloses that the transmetalation occurs with inversion of the stereochemistry of the C<sup>a</sup>HMePh<sup>B</sup> group. In its transition state, the C<sup>a</sup>HMePh<sup>B</sup> group has almost planar structure around the C<sup>a</sup> atom. That planar geometry is stabilized by conjugation between the π* orbital of the Ph<sup>B</sup> and the 2p orbital of the C<sup>a</sup>. Another important factor is activation entropy (Δ<i>S</i>°<sup>‡</sup>); retention transmetalation occurs through Br-bridging transition state, which is less flexible than that of the inversion transmetalation because of the Br-bridging structure, leading to a smaller activation entropy in the retention transition state than in the inversion transition state. For C<sup>a</sup>HMeEt group, transmetalation occurs in a retention manner. In the planar C<sup>a</sup>HMeEt group of the inversion transition state, the C<sup>a</sup> 2p orbital cannot find a conjugation partner because of the absence of π-electron system in the C<sup>a</sup>HMeEt. Transmetalation of C<sup>a</sup>HMe­(CHCH<sub>2</sub>) occurs in a retention manner because the vinyl π* is less effective for the conjugation with the C<sup>a</sup> 2p because of its higher orbital energy than the Ph π*. The introduction of electron-withdrawing substituent on the Ph<sup>B</sup> is favorable for inversion transmetalation. These results suggest that the stereochemistry of the C<sup>a</sup> atom in transmetalation can be controlled by electronic effect of the C<sup>a</sup>HMeR (R = phenyl, vinyl, or alkyl) and sizes of the substituent and ligand

    How to Control Inversion vs Retention Transmetalation between Pd<sup>II</sup>–Phenyl and Cu<sup>I</sup>–Alkyl Complexes: Theoretical Insight

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    Transmetalation between Pd­(Br)­(Ph<sup>A</sup>)­(PCyp<sub>3</sub>)<sub>2</sub> (Ph = phenyl, Cyp = cyclopentyl) and Cu­(C<sup>a</sup>HMePh<sup>B</sup>)­(NHC) (NHC = 1,3-bis­(2,6-diisopropylphenyl)-imidazolidin-2-ylidene) is an important elementary step in recently reported catalytic cross-coupling reaction by Pd/Cu cooperative system. DFT study discloses that the transmetalation occurs with inversion of the stereochemistry of the C<sup>a</sup>HMePh<sup>B</sup> group. In its transition state, the C<sup>a</sup>HMePh<sup>B</sup> group has almost planar structure around the C<sup>a</sup> atom. That planar geometry is stabilized by conjugation between the π* orbital of the Ph<sup>B</sup> and the 2p orbital of the C<sup>a</sup>. Another important factor is activation entropy (Δ<i>S</i>°<sup>‡</sup>); retention transmetalation occurs through Br-bridging transition state, which is less flexible than that of the inversion transmetalation because of the Br-bridging structure, leading to a smaller activation entropy in the retention transition state than in the inversion transition state. For C<sup>a</sup>HMeEt group, transmetalation occurs in a retention manner. In the planar C<sup>a</sup>HMeEt group of the inversion transition state, the C<sup>a</sup> 2p orbital cannot find a conjugation partner because of the absence of π-electron system in the C<sup>a</sup>HMeEt. Transmetalation of C<sup>a</sup>HMe­(CHCH<sub>2</sub>) occurs in a retention manner because the vinyl π* is less effective for the conjugation with the C<sup>a</sup> 2p because of its higher orbital energy than the Ph π*. The introduction of electron-withdrawing substituent on the Ph<sup>B</sup> is favorable for inversion transmetalation. These results suggest that the stereochemistry of the C<sup>a</sup> atom in transmetalation can be controlled by electronic effect of the C<sup>a</sup>HMeR (R = phenyl, vinyl, or alkyl) and sizes of the substituent and ligand

    Intramolecular Aminocyanation of Alkenes by Cooperative Palladium/Boron Catalysis

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    A cooperative palladium/triorganoboron catalyst to accomplish the intramolecular aminocyanation of alkenes through the cleavage of N–CN bonds is reported. 4,5-Bis­(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) is found to be crucial as a ligand for palladium to effectively catalyze the transformation with high chemo- and regioselectivity. A range of substituted indolines and pyrrolidines with both tetra- or trisubstituted carbon and cyano functionalities are readily furnished by the newly developed cyanofunctionalization reaction. A preliminary example of enantioselective aminocyanation is also described

    Aromatic C–H σ‑Bond Activation by Ni<sup>0</sup>, Pd<sup>0</sup>, and Pt<sup>0</sup> Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism

    No full text
    C–H σ-bond activation of arene (represented here by benzene) by the Ni<sup>0</sup> propene complex Ni<sup>0</sup>(IMes)­(C<sub>3</sub>H<sub>6</sub>) (IMes = 1,3-dimesitylimidazol-2-ylidene), which is an important elementary step in Ni-catalyzed hydroarylation of unactivated alkene with arene, was investigated by DFT calculations. In the Ni<sup>0</sup> complex, the C–H activation occurs through a ligand-to-ligand H transfer mechanism to yield Ni<sup>II</sup>(IMes)­(C<sub>3</sub>H<sub>7</sub>)­(Ph) (C<sub>3</sub>H<sub>7</sub> = propyl; Ph = phenyl). In Pd<sup>0</sup> and Pt<sup>0</sup> analogues, the activation occurs through concerted oxidative addition of the C–H bond to the metal. Analysis of the electron redistribution during the C–H activation highlights the difference between the two mechanisms. In the ligand-to-ligand H transfer, charge transfer (CT) occurs from the metal to the benzene. However, the atomic population of the transferring H remains almost constant, suggesting that different CT simultaneously occurs from the transferring H to the LUMO of propene. The electron redistribution contrasts significantly with that found for Pd<sup>0</sup> and Pt<sup>0</sup>, in which CT occurs only from the metal to the benzene. Preference for ligand-to-ligand H transfer over concerted oxidative addition in the Ni<sup>0</sup> complex is shown to be due to the smaller atomic radius of Ni in comparison to those of Pd and Pt and the smaller Ni<sup>II</sup>–H bond energy relative to the Pd<sup>II</sup>–H and Pt<sup>II</sup>–H energies. Interestingly, the bulky ligand accelerates the ligand-to-ligand H transfer in the Ni<sup>0</sup> complex by decreasing the distance between the coordinated benzene and alkene substrates. Thus, the Gibbs activation energy (Δ<i>G</i>°<sup>⧧</sup>) decreases in the case of cyclic-alkylaminocarbene with bulky substituents (CACC-K3), while the Δ<i>G</i>°<sup>⧧</sup> values are similar in X-Phos, IMes, and nonsubstituted cyclic alkylaminocarbene (CAAC-K0). An electron-withdrawing substituent on the arene accelerates the C–H activation by favoring the metal to arene CT

    Contemporary Literature of the Fantastic in China Tom Mieville's Projection

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    У статті наведено погляди Чайни Тома М’євіля щодо завдання фантастичної літератури з огляду на аналіз письменником різновекторних розгалужень антастики: «високого» фентезі зразка Дж. Р. Р. Толкіна та «бульварної» фантастики (pulp fiction) зразка Г. Ф. Лавкрафта. Зроблено висновок про творче кредо письменника, відповідно до якого фантастична література покликана представляти реалістичну проблематику, виражену в химерних формах.The article presents an overview of contemporary trends in Anglophone fantastic literature explored through China Miéville’s ideas on fantasy and weird fiction. It aims to show the driving force behind the generic transformations of the fantastic which are rooted in the objective need for the genre to evolve and individual creative needs of the writers who practice it. The objective reason is identified to be the repetitiveness of the fantastic canon which renders it ill-suited for accommodating visions, anxieties, and desires of the modern world. The individual reasons lie in the inability of the classical fantastic canon to express the author’s intentions for their writing. Maintaining dialogue between the fantasy and weird fiction tradition, China Mieville’s writing attempts to marry the realism of concern with the weird of expression in the secondary-world setting. The major points of fantasy criticism are overcome in the writer’s texts by abstaining from moralization, demythologizing heroism and allowing the plot to follow its own dynamics instead of the prescribed set of genre protocols which allow for a more realistic narrative. The deployment of weird fiction strategies for genre blending frees the literature of the fantastic from the genre constraints and adds to the atmosphere of estrangement essential to rethinking social and aesthetic conventions. Thus, China Mieville’s writing reflects the revitalization of the literature of the fantastic and facilitates in its making

    Theoretical Study of Nickel-Catalyzed Selective Alkenylation of Pyridine: Reaction Mechanism and Crucial Roles of Lewis Acid and Ligands in Determining the Selectivity

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    Selective alkenylation of pyridine is challenging in synthetic organic chemistry due to the poor reactivity and regioselectivity of the aromatic ring. We theoretically investigated Ni-catalyzed selective alkenylation of pyridine with DFT. The first step is coordination of the pyridine–AlMe<sub>3</sub> adduct with the active species Ni<sup>(0)</sup>(NHC)­(C<sub>2</sub>H<sub>2</sub>) <b>1</b> in an η<sup>2</sup>-fashion to form an intermediate <b>Int1</b>. After the isomerization of <b>Int1</b>, the oxidative addition of the C–H bond of pyridine across the nickel–acetylene moiety occurs via a transition state <b>TS2</b> to form a Ni<sup>(II)</sup>(NHC) pyridyl vinyl intermediate <b>Int3</b>. This oxidative addition is rate-determining. The next step is C–C bond formation between pyridyl and vinyl groups leading to the formation of vinyl-pyridine (<b>P1</b>). One of the points at issue in this type of functionalization is how to control the regioselectivity. With the use of Ni­(NHC)/AlMe<sub>3</sub> catalyst, the C<sup>4</sup>- and C<sup>3</sup>-alkenylated products (Δ<i>G</i>°<sup>⧧</sup> = 17.4 and 21.5 kcal mol<sup>–1</sup>, respectively) are formed preferably to the C<sup>2</sup> one (Δ<i>G</i>°<sup>⧧</sup> = 22.0 kcal mol<sup>–1</sup>). The higher selectivity of the C<sup>4</sup>-alkenylation over the C<sup>3</sup> and the C<sup>2</sup> ones is attributed to the small steric repulsion between NHC and AlMe<sub>3</sub> in the C<sup>4</sup>-alkenylation. Interestingly, with Ni­(P­(<i>i</i>-Pr)<sub>3</sub>)/AlMe<sub>3</sub> catalyst, the C<sup>2</sup>-alkenylation occurs more easily than the C<sup>3</sup> and C<sup>4</sup> ones. This regioselectivity arises from the smaller steric repulsion induced by P­(<i>i</i>-Pr)<sub>3</sub> than by bulky NHC. It is notable that AlMe<sub>3</sub> accelerates the alkenylation by inducing the strong CT from Ni to pyridine–AlMe<sub>3</sub>. In the absence of AlMe<sub>3</sub>, pyridine strongly coordinates with the Ni atom through the N atom, which increases Gibbs activation energy (Δ<i>G</i>°<sup>⧧</sup> = ∼27 kcal mol<sup>–1</sup>) of the C–H bond activation. In other words, AlMe<sub>3</sub> plays two important roles, acceleration of the reaction and enhancement of the regioselectivity for the C<sup>4</sup>-alkenylation
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