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The experimental reaction of [1,2,4-(Me3C)3C5H2]2CeH, Cp′2CeH, and CH3OSO2CH3beginsby α-C–Hactivation of the SCH3group, forming Cp′2CeCH2SO2(OCH3), which evolves intoCp′2CeOCH3with elimination of CH2(and presumably SO2). Prolonged heating of thismixture (days at 60 °C) forms Cp′2CeOSO2CH3and CH3OCH3. The metallacycle[1,2,4-(Me3C)3C5H2][1,2-(Me3C)2-4-(Me2CCH2)C5H2]Ce, when presented with the choice of C–H bondsin CH3S and CH3O groups, deprotonates both withcomparable rates, ultimately forming Cp′2CeOCH3and Cp′2CeOSO2CH3at 20 °C. The experimental studies are illuminated by DFT calculationson the experimental systems, which show that the hydride selects themore acidic CH3S bond, whereas the metallacycle reactswith C–H bonds of both the CH3S and CH3O groups of CH3OSO2CH3. In the metallacyclereaction, the initially formed regioisomers, Cp′2CeCH2SO2(OCH3) and Cp′2CeCH2OSO2CH3, rearrange tothe observed products, Cp′2CeOCH3andCp′2CeOSO2CH3, respectively.Furthermore, C–H activation at the SCH3group formstwo isomers of Cp′2CeCH2SO2(OCH3) in the reaction of CH3OSO2CH3with the metallacycle and only one in the reactionwith the hydride. The lack of selectivity in the reactions of themetallacycle relative to the hydride is due to the metallacycle’sgreater thermodynamic advantage and lower energy barriers, which arelinked to the higher bond energy of Ce–H relative to Ce–Cin the metallacycle. [ABSTRACT FROM AUTHOR]

The orthoC–H bond activation of several pyridine and pyridine N-oxide derivatives mediated by Cp2An(iv)(CH3)2and Cp2An(iii)(CH3) (Cp = C5H5and An = U, Np, Pu) have been investigated at the DFT level. For uranium(iv) complex, an excellent agreement with experimental observations is found, and particularly in the case of 2-picoline where only orthosp2C–H activation is observed without any sp3C–H activation. These differences of reactivity can be explained by the charges distribution at the metathesis transition state level. A predictive study of the reactivity of neptunium and plutonium complexes with pyridine and pyridine N-oxide is reported. This study shows that neptunium and plutonium have almost the same reactivity. The C–H activation mediated by actinide (iii) complexes have found to be more kinetically and thermodynamically favorable than for actinide (iv) complexes. The influence of 5f electrons on organoactinide reactivity is found to be small by comparing implicit and explicit treatment of 5f electrons. [ABSTRACT FROM AUTHOR]

Abstract: A predictive reactivity of Cp2An(IV)Me2 (with An=uranium [U], neptunium [Np] and plutonium [Pu]) with pyridine N-oxide has been studied at the theoretical level. The predictive reaction, which consists in the formation of a formaldehyde complex, begins after the initial formation of a cyclometalated complex produced by a C-H activation of the pyridine N-oxide. A difference of reactivity between U/Pu and Np has been observed and has been attributed to the presence of a more covalent bond between Np and the carbene group in the transition state of formation of a transient carbene intermediate. [ABSTRACT FROM AUTHOR]

Abstract: In the mid 1980s the study of ozone reactivity gained a significant interest with the discoveries of the stratospheric ozone hole () and of the ozone depletion events in the polar boundary layer (). In the stratosphere, the mechanism involves heterogeneous reactions on polar stratospheric clouds that lead to chlorine activation (). In contrast, tropospheric ozone depletion occurring during polar springtime rather involves reactive bromine species. They are released during a series of photochemical and heterogeneous reactions often called the bromine explosion (see the review of ). In this reaction sequence, an essential step is the generation of photolyzable Br2, the precursor of two Br atoms, via the multiphasic reaction (1): The production of reactive HOBr could occur with the oxidation of BrO by HO2. [Copyright &y& Elsevier]

The reaction of one equivalent of carbon monoxide withthe dinucleartetrahydride complex ([NPN]Ta)2(μ-H)4(whereNPN = PhP(CH2SiMe2NPh)2) resultsin the cleavage of the CO triple bond and formation of ([NPN]Ta)(μ-O)(μ-H)(Ta[NPN′])(where NPN′ = PhP(CH2SiMe2NPh)(CH2SiMe2NC6H4)) via extrusionof CH4. The identity of the ditantalum complex was confirmedby single-crystal X-ray analysis, isotopic labeling studies, and GC-MSanalysis of the methane released. DFT calculations were performedto provide information on the initial adduct formed and likely transitionstates for the process. [ABSTRACT FROM AUTHOR]

The reaction of 1 equiv of carbon dioxide with the dinuclear tetrahydride complex ([NPN]Ta)2 (μ-H)4 [where NPN = PhP(CH2SiMe2NPh)2] results in the formation of ([NPN]Ta)2(μ-OCH2O)(μ-H)2 via a combination of migratory insertion and reductive elimi-nation. The identity of the ditantalum complex containing a methylene diolate fragment was confirmed by single-crystal X-ray analysis, NMR analysis, and isotopic labeling studies. Density functional theory calculations were performed to provide information on the structure of the initial adduct formed and likely transition states and intermediates for the process. [ABSTRACT FROM AUTHOR]