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1.
Monomeric imidozirconocene complexes of the type Cp2(L)Zr=NCMe3 (Cp = cyclopentadienyl, L = Lewis base) have been shown to activate the carbon-hydrogen bonds of benzene, but not the C-H bonds of saturated hydrocarbons. To our knowledge, this singularly important class of C-H activation reactions has heretofore not been observed in imidometallocene systems. The M=NR bond formed on heating the racemic ethylenebis(tetrahydro)indenyl methyl tert-butyl amide complex, however, cleanly and quantitatively activates a wide range of n-alkane, alkene, and arene C-H bonds. Mechanistic experiments support the proposal of intramolecular elimination of methane followed by a concerted addition of the hydrocarbon C-H bond. Products formed by activation of sp2 C-H bonds are generally more thermodynamically stable than those formed by activation of sp3 C-H bonds, and those resulting from reaction at primary C-H bonds are preferred over secondary sp3 C-H activation products. There is also evidence that thermodynamic selectivity among C-H bonds is sterically rather than electronically controlled. 相似文献
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This communication describes the Pd(OAc)2-catalyzed intermolecular amidation reactions of unactivated sp2 and sp3 C-H bonds using primary amides and potassium persulfate. The substrates containing a pendent oxime or pyridine group were amidated with excellent chemo- and regioselectivities. It is noteworthy that reactive C-X bonds were well-tolerated and a variety of primary amides can be effective nucleophiles for the Pd-catalyzed C-H amidation reactions. For the reaction of unactivated sp3 C-H bonds, beta-amidation of 1 degrees sp3 C-H bonds versus 2 degrees C-H bonds is preferred. The catalytic reaction is initiated by chelation-assisted cyclopalladation involving C-H bond activation. Preliminary mechanistic study suggested that the persulfate oxidation of primary amides should generate reactive nitrene species, which then reacted with the cyclopalladated complex. 相似文献
4.
Inagaki A Takemori T Tanaka M Suzuki H 《Angewandte Chemie (International ed. in English)》2000,39(2):404-406
The successive activation of alkane C-H bonds on a trinuclear ruthenium cluster enables cleavage of six C-H bonds and the formation of a closo-ruthenacyclopentadiene complex (the structure of the complex obtained with hexane is shown). 相似文献
5.
Iodination of remote aryl C-H bonds has been achieved using palladium acetate as the catalyst and iodoacetate (IOAc) as the oxidant. Systematic kinetic isotope studies imply a mechanistic regime shift as the number of bonds separating the directing heteroatom and the target C-H bond increases. Both isotope and electronic effects observed in remote C-H bond activation are consistent with an electrophilic palladation pathway in which the initial palladation is slower than the C-H bond cleavage. 相似文献
6.
Zaitsev VG Shabashov D Daugulis O 《Journal of the American Chemical Society》2005,127(38):13154-13155
A new palladium-catalyzed arylation process based on C-H activation has been developed. The utilization of pyridine-containing directing groups allows the beta-arylation of carboxylic acid derivatives and gamma-arylation of amine derivatives. Both primary and secondary sp3 C-H bonds, as well as sp2 C-H bonds, are reactive. 相似文献
7.
Qinhua Huang 《Tetrahedron letters》2009,50(52):7235-401
A novel synthesis of cyclopropanes has been developed via palladium-catalyzed C-H activation in which two new carbon-carbon bonds are formed in a single step. This method involves palladium-catalyzed activation of normally unreactive secondary alkyl C-H bonds and provides an efficient way to access cyclopropapyrrolo[1,2-a]indoles, analogues of mitomycin and cyclopropamitosenes. 相似文献
8.
Nakao Y Kashihara N Kanyiva KS Hiyama T 《Journal of the American Chemical Society》2008,130(48):16170-16171
Nickel/P(c-C(5)H(9))(3) (PCyp(3)) catalyst effects the addition reactions of fluoroarenes across alkynes, 1,3-dienes, and vinylarenes via the activation of C-H bonds over C-F bonds. The acidic C-H bonds located ortho to fluorine are exclusively activated to afford a range of alkenylated and alkylated fluoroarenes. 相似文献
9.
G. N. Boiko Yu. M. Shul’ga O. S. Roshchupkina A. S. Lobach N. F. Gol’dshleger 《Russian Journal of General Chemistry》2007,77(4):625-628
Coordinated fullerene acts as a hydrogen acceptor in reactions with compounds having weakened C-H bonds (1,4-dihydropyridine and 9,10-dihydroanthracene). Metal fullerides are the dehydrogenation catalysts. They activate the C-H bonds of dihydroanthracene and diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate in positions 9,10 and 1,4, respectively. No activation of norbornane carbon-hydrogen bonds with metal fullerides was observed under mild conditions. 相似文献
10.
The combination of directed C-H activation, batch-wise addition of tetraalkyltin reagents, and rate enhancement by benzoquinone and microwave irradiation provides a promising strategy for the direct coupling of C-H bonds with organometallic reagents. A variety of tetraalkyltins were coupled to C-H bonds to give the alkylated products in good yields by using 5 mol % Pd(OAc)2 as the catalyst. Benzoquinone was shown to be essential for the C-H activation when substrates containing non-pi-conjugated chelating groups are used. Monitoring the formation and reductive elimination of the Pd(Ar)(Me)L2 complex also revealed that benzoquinone promotes the reductive elimination step. Microwave irradiation enhances the reaction rate drastically. The versatility of this protocol was demonstrated by using substrates containing either oxazoline or pyridine as directing groups. 相似文献
11.
A novel Pummerer-type reaction was developed via o-chloranil-mediated C-H bond oxidation. The reaction provides a simple and efficient method to construct sulfide derivatives. A Knoevenagel-type reaction was also achieved via multiple C-H bonds activation under neutral reaction conditions. 相似文献
12.
Xiao B Li YM Liu ZJ Yang HY Fu Y 《Chemical communications (Cambridge, England)》2012,48(40):4854-4856
A practical Pd-catalyzed reaction was developed to achieve C-H activation/C-B cross-coupling of acetanilides under acidic conditions. The new reaction shows a good functional group tolerance and an exclusive mono-selectivity. This C-H borylation method may provide a generally applicable route for the conversion of C-H moieties into many other types of bonds. 相似文献
13.
Jones WD 《Inorganic chemistry》2005,44(13):4475-4484
Over the past 20 years, substantial progress has been made in the understanding of the activation of C-H and other strong bonds by reactive metal complexes in low oxidation states. This paper will present an overview of the use of pentamethylcyclopentadienyl and trispyrazolylborate rhodium complexes for the activation of arene and alkane C-H bonds. Insights into bond strengths, kinetic and thermodynamic selectivities, and the nature of the intermediates involved will be reviewed. The role of eta-2 arene complexes will be shown to be critical to the C-H activation reactions. Some information about the fleeting alkane sigma-complexes will also be presented. In addition, use of these complexes with thiophenes has shown the ability to cleave C-S bonds. Mechanistic information has been obtained indicating coordination through sulfur prior to cleavage. Relevant examples of nickel-based C-S cleavage will also be given. 相似文献
14.
Various anilides have been directly ortho-acetoxylated through a Pd(OAc)2-catalyzed C-H bond activation process. The amide group in anilides was found to functionalize as an elegant directing group to convert aromatic sp(2) C-H bonds into C-O bonds in high regioselectivity with acetic acid as the acetate source and K(2)S(2)O(8) as the oxidant. 相似文献
15.
A (PNP)Ir fragment undergoes facile, room-temperature oxidative addition of C-H bonds in arenes and haloarenes in preference to aromatic carbon-halogen bonds. This preference, however, is determined to be kinetic in nature. Oxidative addition of C-Cl and C-Br is preferred thermodynamically. The products of the C-Cl or C-Br oxidative addition are separated from the C-H oxidative addition products by a high activation barrier and are only accessible at >100 degrees C. Of the C-H oxidative addition products of chlorobenzene, the isomer with the o-ClC6H4 ligand has the lowest energy. 相似文献
16.
An efficient strategy for the oxidative carbonylation of aromatic amides via C-H/N-H activation to form phthalimides using an Rh(III) catalyst has been developed. The reaction shows a preference for C-H bonds of electron-rich aromatic amides and tolerates a variety of functional groups. 相似文献
17.
Borovik AS 《Chemical Society reviews》2011,40(4):1870-1874
The functionalization of C-H bonds has yet to achieve widespread use in synthetic chemistry in part because of the lack of synthetic reagents that function in the presence of other functional groups. These problems have been overcome in enzymes, which have metal-oxo active sites that efficiently and selectively cleave C-H bonds. How high-energy metal-oxo transient species can perform such difficult transformations with high fidelity is discussed in this tutorial review. Highlighted are the relationships between redox potentials and metal-oxo basicity on C-H bond activation, as seen in a series of bioinspired manganese-oxo complexes. 相似文献
18.
Efficient rhodium(I)-catalyzed regioselective functionalization of aromatic C-H bonds has been realized with acid chlorides as the coupling partners via decarbonylation and C-H activation under phosphine-free conditions. 相似文献
19.
The origin of the high levels of reactivity and diastereoselectivity (>99:1 dr) observed in the oxazoline-directed, Pd(II)-catalyzed sp(3) C-H bond iodination and acetoxylation reactions as reported in previous publications has been studied and explained on the basis of experimental and computational investigations. The characterization of a trinuclear chiral C-H insertion intermediate by X-ray paved the way for further investigations into C-H insertion step through the lens of stereochemistry. Computational investigations on reactivities and diastereoselectivities of C-H activation of t-Bu- and i-Pr-substituted oxazolines provided good agreement with the experimental results. Theoretical predictions with DFT calculations revealed that C-H activation occurs at the monomeric Pd center and that the most preferred transition state for C-H activation contains two sterically bulky t-Bu substituents in anti-positions due to steric repulsion and that this transition state leads to the major diastereomer, which is consistent with the structure of the newly characterized C-H insertion intermediate. The structural information about the transition state also suggests that a minimum dihedral angle between C-H bonds and Pd-OAc bonds is crucial for C-H bond cleavage. We have also utilized density functional theory (DFT) to calculate the energies of various potential intermediates and transition states with t-Bu- and i-Pr-substituted oxazolines and suggested a possible explanation for the substantial difference in reactivity between the t-Bu- and i-Pr-substituted oxazolines. 相似文献
20.
Latifi R Tahsini L Kumar D Sastry GN Nam W de Visser SP 《Chemical communications (Cambridge, England)》2011,47(38):10674-10676
Density functional theory calculations on the reactivity of a Ni(II)-superoxo complex in C-H bond activation, aromatic hydroxylation and heteroatom oxidation reactions have been explored; the Ni(II)-superoxo complex is able to react with substrates with weak C-H bonds and PPh(3). 相似文献