ChemInform Abstract: Dinuclear Manganese, Iron, Chromium, and Cobalt Complexes Derived from Aroylhydrazone Ligands: Synthetic Strategies, Crystal Structures, and Magnetic Properties

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A naturally anti-diffusive compressible two phases Kapila model with boundedness preservation coupled to a high order finite volume solver

International audienceThis paper presents a two phases flow model combined with a high order finite volume solver on unstructured mesh. The solver is highly conservative and preserves the sharpness of the interface without any reconstruction. Special care has been taken for boundedness preservation, as a high order scheme does not guaranty the boundedness of the volume fraction. The efficiency of the method is demonstrated with two numerical experiments: the simple advection test and the interaction between the shock and a bubble. Although experiments have been carried out with fine mesh, it is also demonstrated that the method allows satisfactory results to be obtained with coarse mesh

Unusual Benzyl Migration Reactivity in NHC-Bearing Group 4 Metal Chelates: Synthesis, Characterization, and Mechanistic Investigations

International audienceThe reaction of 1 equiv of [M(CH2Ph)4] (M = Zr, Hf) and 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride [tBu(OCO)H3, 1] cleanly yielded the corresponding M-NHC chloro benzyl derivatives [[tBu(OCO)]M(Cl)(CH2Ph)] (2Zr and 2Hf) along with 3 equiv of toluene. For both metal complexes, the effective formation of a (κ3-OCO) metal chelate and the coordination of a benzyl ligand onto the M(IV) metal center were established by NMR and elemental analysis. In contrast, under identical conditions, the reaction of Ti(CH2Ph)4 with the imidazolinium proligand 1 yielded the unexpected rearranged dimer product 3Ti, arising from the migration of the Ti-Bn group from the metal center to the Ccarbene atom. The molecular structure of 3Ti was established by analogy with the X-ray-determined Zr analogue 3Zr. Compound 3Zr quantitatively formed upon heating a benzene solution of 2Zr at 60 °C. In the solid state, compound 3Zr consists of two seven-coordinate mononuclear Zr fragments that are associated by two bridging μ2-chloride atoms, confirming the migration of the Zr-Bn moiety from the metal center to the Ccarbene atom. Carrying out the reaction of [M(CH2Ph)4] (M = Ti, Zr, Hf) with imidazolinium proligand 1 in THF led to the quantitative formation of the corresponding rearranged monomeric THF adduct [[tBu(OC(Bn)O)]M(Cl)(THF)] (4Ti-THF, 4Zr-THF, and 4Hf-THF), as established by X-ray crystallographic studies in the case of 4Ti-THF. Such a THF-promoted benzyl migration was also observed with the dibenzyl Zr and Hf complexes [[tBu(OCO)]M(CH2Ph)2] (5Zr and 5Hf), leading to the formation of the corresponding THF-rearranged products [[tBu(OC(Bn)O)]M(CH2Ph)(THF)] (6Zr-THF and 6Hf-THF). The addition of 1 equiv of methylmagnesium bromide (CH3MgBr) or phenylmagnesium bromide (PhMgBr) to 1 equiv of the zirconium dichloro NHC complex [[tBu(OCO)]Zr(Cl)2(THF)] (8) in THF yielded the rearranged products [[tBu(OC(Me)O)]M(Cl)(THF)] (9Me) and [[tBu(OC(Ph)O)]M(Cl)(THF)] (9Ph), respectively, as deduced from NMR data. Kinetic studies were carried out on the THF-promoted rearrangement reaction of the benzyl chloro Hf derivative 2Hf in the presence of THF to produce 4Hf-THF. These data are consistent with the reaction rate law being first order both in THF and in the THF adduct 2Hf-THF. DFT calculations on the Ti, Zr, and Hf systems support a benzyl migration reaction occurring at a transient heptacoordinated bis-THF adduct species of the type [[tBu(OCO)]M(Cl)(Bn)(THF)2], which may readily form upon THF coordination to 2Hf-THF. © 2015 American Chemical Society

Cyclic(Alkyl)(Amino)Carbene (CAAC)-Supported Zn Alkyls: Synthesis, Structure and Reactivity in Hydrosilylation Catalysis

The reactivity of ZnII dialkyl species ZnMe2 with a cyclic(alkyl)(amino)carbene, 1-[2,6-bis(1-methylethyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene (CAAC, 1), was studied and extended to the preparation of robust CAAC-supported ZnII Lewis acidic organocations. CAAC adduct of ZnMe2 (2), formed from a 1:1 mixture of 1 and ZnMe2, is unstable at room temperature and readily undergoes a CAAC carbene insertion into the Zn−Me bond to produce the ZnX2-type species (CAAC-Me)ZnMe (3), a reactivity further supported by DFT calculations. Despite its limited stability, adduct 2 was cleanly ionized to robust two-coordinate (CAAC)ZnMe+ cation (5+) and derived into (CAAC)ZnC6F5+ (7+), both isolated as B(C6F5)4− salts, showing the ability of CAAC for the stabilization of reactive [ZnMe]+ and [ZnC6F5]+ moieties. Due to the lability of the CAAC−ZnMe2 bond, the formation of bis(CAAC) adduct (CAAC)2ZnMe+ cation (6+) was also observed and the corresponding salt [6][B(C6F5)4] was structurally characterized. As estimated from experimental and calculations data, cations 5+ and 7+ are highly Lewis acidic species and the stronger Lewis acid 7+ effectively mediates alkene, alkyne and CO2 hydrosilylation catalysis. All supporting data hints at Lewis acid type activation–functionalization processes. Despite a lower energy LUMO in 5+ and 7+, their observed reactivity is comparable to those of N-heterocyclic carbene (NHC) analogues, in line with charge-controlled reactions for carbene-stabilized ZnII organocations

Direct Arylation of Sydnones with Aryl Chlorides toward Highly Substituted Pyrazoles

The direct arylation of the C4 position of both N-alkyl- and N-arylsydnones with aryl/heteroaryl chlorides has been realized. The reaction is quite general and allows access to a wide range of 4-substituted sydnones. Yields of more challenging substrates can be improved through the use of aryl bromides

Iridium-Catalyzed Homogeneous Hydrogenation and Hydrosilylation of Carbon Dioxide

The knowledge of the potential of transition metal-based complexes as catalysts for the reduction of CO2 has grown significantly over the last few decades. This chapter focuses on the progress made during recent years in the field of homogeneous iridium-catalyzed reduction of CO2 by using hydrogen and/or silicon hydrides as reducing agents, comparing them with homogeneous catalysts based on other transition metals. The reported studies on iridium-catalyzed CO2 reduction processes show that an important point to keep in mind when designing a catalyst is the nature of the reducing agent (hydrogen, hydrosilanes, and/or hydrosiloxanes). Thus, iridium(III) half-sandwich complexes with 4,4′-dihydroxy-bipyridine (DHBP) or 4,7-dihydroxy-1,10-phenanthroline (DHPT) ligands, and iridium(III)-PNP pincer complexes have proven to be excellent catalysts for the hydrogenation of CO2 to formic acid. However, Ir(III)-NSiNMe (NSiN = fac-bis-(4-methylpyridine-2-yloxy)methylsilyl) and Ir(III)-NSiMe (NSiMe = 4-methylpyridine-2-yloxydimethylsilyl) species are not stable under hydrogen atmosphere but are effective catalysts for the reduction of CO2 with hydrosiloxanes to silylformate under solvent-free conditions and moderate CO2 pressures and temperatures. Moreover, while using iridium(III)-DHBP half-sandwich complexes, high CO2 and H2 pressures are required to achieve the catalytic CO2 hydrogenation to methanol; Ir-NSiMe species catalyze the reduction of CO2 to methoxysilane with hydrosiloxanes under low CO2 pressure.Peer reviewe