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As part of our effort to improve our understanding of aziridination mechanism, we used tetra substitution of a diphenol ligand to modify the redox properties of corresponding Fe complexes. This allowed us to confirm that aziridination catalysis by Fe‐based complexes is governed by electron affinity of the active species and further show that it correlates with the FeIII/FeII redox potential. [ABSTRACT FROM AUTHOR]

A combined experimental and theoretical investigation on the cerium(IV) oxo complex [(LOEt)2Ce(=O)(H2O)]⋅MeC(O)NH2 (1; LOEt−=[Co(η5‐C5H5){P(O)(OEt)2}3]−) demonstrates that the intermediate spin‐state nature of the ground state of the cerium complex is responsible for the versatility of its reactivity towards small molecules such as CO, CO2, SO2, and NO. CASSCF calculations together with magnetic susceptibility measurements indicate that the ground state of the cerium complex is of multiconfigurational character and comprised of 74 % of CeIV and 26 % of CeIII. The latter is found to be responsible for its reductive addition behavior towards CO, SO2, and NO. This is the first report to date on the influence of the multiconfigurational ground state on the reactivity of a metal–oxo complex. [ABSTRACT FROM AUTHOR]

Abstract: The first three insertion steps of propylene for isoselective metallocenes from the one‐carbon‐bridged cyclopentadienyl–fluorenyl {Cp/Flu} and silicon‐bridged ansa‐bis(indenyl) {SBI} families were computed by using a theoretical method implementing the B3PW91 functional in combination with solvent corrections incorporated with the Solvation Model based on Density (SMD) continuum model. For C1‐symmetric {Cp/Flu}‐type metallocenes, two mechanisms of stereocontrol were validated theoretically: more facile and more stereoselective chain “stationary” insertion (or site epimerization backskip) and less stereoselective alternating mechanisms. For the C2‐symmetric {SBI}‐type system, the computation results were in complete agreement with the sole operating chain migratory insertion mechanism. The thermochemical data obtained through the study were used to predict microstructures of polypropylenes by using three‐parameter and one‐parameter statistical models for the two metallocene systems, respectively. The calculated meso/rac pentad distributions were found to be in good agreement with those determined experimentally for isotactic polypropylene samples obtained at different polymerization temperatures. [ABSTRACT FROM AUTHOR]

The reaction of carbon disulfide (CS2) with the side-on end-on dinitrogen complex ([NPNSi]Ta)2(μ–η1:η2-N2)(μ-H)2 (1) (where [NPNSi] = [PhP(CH2SiMe2NPh)2]) has been studied and shown to generate two products, the ratio of which depends on the concentration of added carbon disulfide. At high concentrations of CS2, N–N bond cleavage and functionalization occur to generate a ditantalum complex with an isothiocyanato ligand N-bound to Ta along with bridging sulfido and nitrido moieties. At lower concentrations of CS2, less dinitrogen functionalization is observed; instead, N2 is displaced and the CS2 molecule is completely disassembled to generate a ditantalum derivative with bridging methylene and two sulfide moieties. Kinetic and DFT studies have been performed and provide clues about the product ratio and mechanistic information and shed light on why N2 functionalization is challenging. [ABSTRACT FROM AUTHOR]

The reaction of (C5Me5)2Th(CH3)2 with the phosphonium salts [CH3PPh3]X (X=Cl, Br, I) was investigated. When X=Br and I, two equivalents of methane are liberated to afford (C5Me5)2Th[CHPPh3]X, rare terminal phosphorano-stabilized carbenes with thorium. These complexes feature the shortest thorium-carbon bonds (≈2.30 Å) reported to date, and electronic structure calculations show some degree of multiple bonding. However, when X=Cl, only one equivalent of methane is lost with concomitant formation of benzene from an unstable phosphorus(V) intermediate, yielding (C5Me5)2Th[κ2-(C,C′)-(CH2)(CH2)PPh2]Cl. Density functional theory (DFT) investigations of the reaction energy profiles for [CH3PPh3]X, X=Cl and I showed that in the case of iodide, thermodynamics prevents the production of benzene and favors formation of the carbene. [ABSTRACT FROM AUTHOR]

The reaction of (C5Me5)2Th(CH3)2 with the phosphonium salts [CH3PPh3]X (X=Cl, Br, I) was investigated. When X=Br and I, two equivalents of methane are liberated to afford (C5Me5)2Th[CHPPh3]X, rare terminal phosphorano-stabilized carbenes with thorium. These complexes feature the shortest thorium-carbon bonds (≈2.30 Å) reported to date, and electronic structure calculations show some degree of multiple bonding. However, when X=Cl, only one equivalent of methane is lost with concomitant formation of benzene from an unstable phosphorus(V) intermediate, yielding (C5Me5)2Th[κ2-(C,C′)-(CH2)(CH2)PPh2]Cl. Density functional theory (DFT) investigations of the reaction energy profiles for [CH3PPh3]X, X=Cl and I showed that in the case of iodide, thermodynamics prevents the production of benzene and favors formation of the carbene. [ABSTRACT FROM AUTHOR]

Improving our comprehension of diverse CO2 activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. CO2 activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO2 is readily reduced to CO, but isolated thorium(III) CO2 activation is unprecedented. We show that the thorium(III) complex, [Th(Cp′′)3] ( 1, Cp′′={C5H3(SiMe3)2-1,3}), reacts with CO2 to give the mixed oxalate-carboxylate thorium(IV) complex [{Th(Cp′′)2[κ2-O2C{C5H3-3,3′-(SiMe3)2}]}2(μ-κ2:κ2-C2O4)] ( 3). The concomitant formation of oxalate and carboxylate is unique for CO2 activation, as in previous examples either reduction or insertion is favored to yield a single product. Therefore, thorium(III) CO2 activation can differ from better understood uranium(III) chemistry. [ABSTRACT FROM AUTHOR]

A fifteen year contribution of computational studies carried out in close synergy with experiments is summarized. This interplay has allowed some important breakthroughs in the field of organolanthanide chemistry. The variety of different reaction mechanisms in lanthanide chemistry appear to be broader than the simple bond metathesis. [ABSTRACT FROM AUTHOR]

A joint experimental/theoretical (DFT) study of the activation of heteroallenes CO xS2- x ( x = 0-2) by [Sm(Giso)2] {Giso- = [(ArN)2CNCy2]-, Cy = cyclohexyl, Ar = 2,6-diisopropylphenyl} is reported. All heteroallenes are reduced in a different manner. Indeed, while activation of CS2 yields a bimetallic CS2 coupled product through C-S bond formation, CO2 forms an oxalate complex through C-C bond formation. This subsequently undergoes CO2 insertion into one of its Sm-N bonds. Finally, COS activation is predicted to yield a dithiocarbonate complex, through the formation of an intermediate sulfido complex [(Giso)2Sm(µ-S)Sm(Giso)2]. Therefore, [Sm(Giso)2] is a very versatile reagent, since it is a rare example of a complex that allows formation of several activation products involving valence isoelectronic substrates. This is rationalized by DFT calculations, and the latter emphasizes both the lack of kinetic stability of CS vs. CO and the high thermodynamic stability of the oxalate. [ABSTRACT FROM AUTHOR]

The theoretical treatment of single electron transfer (SET) of the redox chemistry mediated by f-element complexes is reviewed and summarized. The different computational strategies to account for the SET energy are presented and commented on the basis of the subsequent mechanistic investigation. Moreover, the mechanistic investigation of the subsequent reactivity, mainly in the field of heteroallene activation, using DFT-based approaches is also summarized. All reported reactivities are found to involve formation of bimetallic species and share in common the formation of the same key intermediate in which the substrate is doubly reduced and stabilized by two oxidized metal centers. Modern computational methods are found to efficiently account for such reactivity. [ABSTRACT FROM AUTHOR]

The reaction at 20 °C of the metallocenelanthanide hydride, [1,2,4-(Me3C)3C5H2]2CeH, UGRAPHIC DISPLAY="INLINE" ID="UGT1" SRC="UGT1"/, and excess methyltrifluoromethanesulfonate, CH3OSO2CF3, results in formation of UGRAPHIC DISPLAY="INLINE" ID="UGT2" SRC="UGT2"/, UGRAPHIC DISPLAY="INLINE" ID="UGT3" SRC="UGT3"/, UGRAPHIC DISPLAY="INLINE" ID="UGT4" SRC="UGT4"/ and the bimetallic complex UGRAPHIC DISPLAY="INLINE" ID="UGT5" SRC="UGT5"/. The metallocenes UGRAPHIC DISPLAY="INLINE" ID="UGT6" SRC="UGT6"/, UGRAPHIC DISPLAY="INLINE" ID="UGT7" SRC="UGT7"/, and UGRAPHIC DISPLAY="INLINE" ID="UGT8" SRC="UGT8"/ react with excess CH3OSO2CF3 to form UGRAPHIC DISPLAY="INLINE" ID="UGT9" SRC="UGT9"/, CH3OCH3, CH3F, and (CH3O)2SO, respectively, at 20 °C. Thus, the net reaction is UGRAPHIC DISPLAY="INLINE" ID="UGT10" SRC="UGT10"/ but the pathway is not a direct methyl transfer. Comparison of the reactivity of CH3OSO2CF3 and CH3OSO2CH3 (Werkema et al., Organometallics, 2012, 31, 870) is revealing since both form a similar set of products but the rates of reaction of CH3OSO2CF3 are faster. The bimetallic complex, in which the SO32− anion bridges two UGRAPHIC DISPLAY="INLINE" ID="UGT11" SRC="UGT11"/ fragments, is unique in organometallic chemistry. The 1H NMR spectrum is fluxional at 20 °C and the low temperature spectrum is consistent with the geometry observed in the solid state. Density Functional Theory (DFT) calculations of the Gibbs energy profiles for the reaction of CH3OSO2CF3 with UGRAPHIC DISPLAY="INLINE" ID="UGT12" SRC="UGT12"/ show that the CH-bond activation and direct CH3 group transfer have similar activation energy barriers. This contrasts with what is observed in the reaction of UGRAPHIC DISPLAY="INLINE" ID="UGT13" SRC="UGT13"/ with CH3OSO2CH3, where CH-bond activation at the SCH3 group is preferred. Remarkably, the activation energy barriers for C–O-bond cleavage are similar in CH3OSO2CH3 and CH3OSO2CF3, which is traced to the calculated small exoergicity of −1.7 kcal mol−1 for the reaction of UGRAPHIC DISPLAY="INLINE" ID="UGT14" SRC="UGT14"/. This contrasts, perhaps, with conventional wisdom that overemphasizes the effect of the electron-withdrawing ability of the CF3 group on the chemical and physical properties of sulfonate esters. [ABSTRACT FROM AUTHOR]

Reaction mechanisms for the oxidative reactions of CO2 and COS with [(C5Me5)2Sm] have been investigated by means of DFT methods. The experimental formation of oxalate and dithiocarbonate complexes is explained. Their formation involve the samarium(III) bimetallic complexes [(C5Me5)2Sm-CO2-Sm(C5Me5)2] and [(C5Me5)2Sm-COS-Sm(C5Me5)2] as intermediates, respectively, ruling out radical coupling for the formation of the oxalate complex. [ABSTRACT FROM AUTHOR]

The determination of the solvation shell of Hg(ii)-containing molecules and especially the interaction between Hg(ii) and water molecules is the first requirement to understand the transmembrane passage of Hg into the cell. We report a systematic DFT study by stepwise solvation of HgCl2including up to 24 water molecules. In order to include pH and salinity effects, the solvation patterns of HgClOH, Hg(OH)2and HgCl3−were also studied using 24 water molecules. In all cases the hydrogen bond network is crucial to allow orbital-driven interactions between Hg(ii) and the water molecules. DFT Born–Oppenheimer molecular dynamics simulations starting from the stable HgCl2–(H2O)24structure revealed that an HgCl2–(H2O)3trigonal bipyramid effective solute appears and then the remaining 21 water molecules build a complete first solvation shell, in the form of a water-clathrate. In the HgCl2, HgClOH, Hg(OH)2–(H2O)24optimized structures Hg also directly interacts with 3 water molecules from an orbital point of view (three Hg–O donor–acceptor type bonds). All the other interactions are through hydrogen bonding. The cluster-derived solvation energies of HgCl2, HgClOH and Hg(OH)2are estimated to be −34.4, −40.1 and −47.2 kcal mol−1, respectively. [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]