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51.
Marie-Christine DuclosYuttapong Singjunla Christelle PetitAlain Favre-Réguillon Erwann JeanneauFlorence Popowycz Estelle MétayMarc Lemaire 《Tetrahedron letters》2012,53(45):5984-5986
P-Chirogenic monodentate binaphthyl phosphines were prepared in five steps from enantiomerically pure BINOL. This approach supposes the utilization of two methods previously developed in our group, the formation of secondary phosphine oxide, and the reduction of tertiary phosphine oxide using the association of tetramethyldisiloxane and Ti(OiPr)4. During the last reduction step, only the formation of the more stable diastereoisomer was observed. This product was employed as a ligand for the palladium catalyzed hydrosilylation of styrene to afford the corresponding alcohol with high yield and enantiomeric excess. 相似文献
52.
Raphael Recht Lysiane Omhover-Fougy Valérie Stahl Erwann Hamon 《Magnetic resonance in chemistry : MRC》2022,60(7):719-729
Numerous predictive microbiology models have been proposed to describe bacterial population behaviors in foodstuffs. These models depict the growth kinetics of particular bacterial strains based on key physico-chemical parameters of food matrices and their storage temperature. In this context, there is a prominent issue to accurately characterize these parameters, notably pH, water activity (aw), and NaCl and organic acid concentrations. Usually, all these product features are determined using one destructive analysis per parameter at macroscale (>5 g). Such approach prevents an overall view of these characteristics on a single sample. Besides, it does not take into account the intra-product microlocal variability of these parameters within foods. Nuclear magnetic resonance (NMR) is a versatile non-invasive spectroscopic technique. Experiments can be recorded successively on a same collected sample without damaging it. In this work, we designed a dedicated NMR approach to characterize the microenvironment of foods using 10-mg samples. The multiparametric mesoscopic-scale approach was validated on four food matrices: a smear soft cheese, cooked peeled shrimps, cold-smoked salmon, and smoked ham. Its implementation in situ on salmon fillets enabled to observe the intra-product heterogeneity and to highlight the impact of process on the spatial distribution of pH, NaCl, and organic acids. This analytical development and its successful application can help address the shortcomings of monoparametric methods traditionally used for predictive microbiology purposes. 相似文献
53.
Reduction of exo-2-methyl-3, 4-dichlorobicyclo[3.2.1]oct-2-ene and the exo-2-phenyl-3,4-dibromo analogue with lithium aluminium hydride proceeds mainly with allylic rearrangement. Moreover, hydride enters and bromide leaves synfacially. The stereochemistry of the process is discussed in the light of the favourable energy of a quasi-cyclic transition state in which reagent and halide are complexed. 相似文献
54.
We study the Ricci curvature of a Riemannian metric as a differential operator acting on the space of metrics close (in a
weighted functional spaces topology) to the standard metric of a rank-one noncompact symmetric space. We prove that any symmetric
bilinear field close enough to the standard may be realized as the Ricci curvature of a unique close metric if its decay rate
at infinity (its weight) belongs to some precisely known interval. We also study what happens if the decay rate is too small
or too large. 相似文献
55.
Erwann Aubry Bruno Colbois Patrick Ghanaat Ernst A. Ruh 《Annals of Global Analysis and Geometry》2003,23(3):227-246
For closed n-dimensional Riemannian manifolds M with almostnonnegative Ricci curvature, the Laplacian on one-forms is known toadmit at most n small eigenvalues. If there are n small eigenvalues, or if M is orientable and has n – 1 small eigenvalues, then M isdiffeomorphic to a nilmanifold, and the metric is almost left invariant.We show that our results are optimal for n 4. 相似文献
56.
Low‐Coordinate Barium Boryloxides: Synthesis and Dehydrocoupling Catalysis for the Production of Borasiloxanes 下载免费PDF全文
Erwann Le Coz Dr. Vincent Dorcet Dr. Thierry Roisnel Dr. Sven Tobisch Prof. Dr. Jean‐François Carpentier Dr. Yann Sarazin 《Angewandte Chemie (International ed. in English)》2018,57(36):11747-11751
The first soluble barium boryloxides [Ba]– OB{CH(SiMe3)2} are presented. These mono‐ or dinuclear complexes feature low coordination numbers, as low as two for [Ba(OB{CH(SiMe3)2}2)2], which is further stabilized by intra‐ and intermolecular Ba???H3C agostic interactions. Barium boryloxides and the parent [Ba{N(SiMe3)2}2?(thf)2] catalyze the dehydrocoupling of borinic acids with hydrosilanes, providing borasiloxanes under mild conditions. 相似文献
57.
Nandu Bala Sharma Jayshree Shahai Rajendra Singh Ghadwal Erwann Jeanneau 《Journal of Coordination Chemistry》2016,69(1):135-148
Reaction of Ti(OPri)4 with 2-methyl-2,4-pentanediol [HOGOH, where G = CMe2CH2CH(Me)] in 1?:?3 M ratio under reflux afforded the monomeric [Ti(OGO)(OGOH)2] (1), which on further reactions with [Al(OPri)3] or [Nb(OPri)5] in 1?:?1 and 1?:?2 M ratios afforded heterometallic derivatives, [Ti(OGO)3{M(OPri)n?2}] and [Ti(OGO)3{M(OPri)n?1}2] [where M = Al (n = 3), Nb (n = 5)], respectively. Similar reactions of Zr(OPri)4?PriOH with a number of glycols [HOGOH, where G = CH(Me)CH(Me), CMe2CMe2, CMe2CH2CH(Me)] yielded dimeric [Zr2(OGO)2(OGOH)4]. [Zr2(OGO)6{M(OPri)n?2}2] and [Zr2(OGO)4(OGOH)2M(OPri)n?2] [M = Al (n = 3), Ti (n = 4), Nb (n = 5)] were prepared by 1?:?2 and 1?:?1 reactions, respectively, of [Zr2(OGO)2(OGOH)4] with Al(OPri)3, Ti(OPri)4, or Nb(OPri)5. Surprisingly, a 1?:?2 reaction of [VO(OPri)3] with 2,2-diethyl-1,3-propanediol in benzene followed a different reaction and produced a neutral tetranuclear derivative [V4(O)4(μ-OCH2CEt2CH2O)2(OCH2CEt2CH2O)4] (18). All of these derivatives were characterized by elemental analysis, molecular weight measurements, FT-IR, and 1H NMR (and wherever possible, by 27Al or 51V NMR) spectroscopic studies. The derivatives [Zr2(OCMe2CH2CH(Me)O)2(OCMe2CH2CH(Me)OH)4] (9 and 18) were additionally characterized by single-crystal X-ray structure analysis. 相似文献
58.
Kevin Grollier Emmanuel Chefdeville Dr. Erwann Jeanneau Dr. Thierry Billard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12910-12916
The synthesis of trifluoromethylselenolated aromatic molecules via an auxiliary-assisted, palladium catalyzed, C−H bonds functionalization with trifluoromethyl tolueneselenosulfonate as reagent is described. The mono- or bis-products can be preferentially formed. Some mechanistic investigations were realized to better understand the reaction. This methodology was also extended to fluoroalkylselenyl groups. 相似文献
59.
Erwann Le Coz Dr. Samia Kahlal Prof. Dr. Jean-Yves Saillard Dr. Thierry Roisnel Dr. Vincent Dorcet Prof. Dr. Jean-François Carpentier Dr. Yann Sarazin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(59):13509-13513
The first unsupported barium siloxide, the homoleptic dimer [Ba2{μ2-OSi(SiMe3)3}3{OSi(SiMe3)3}], is presented, and its structural features are discussed in the light of DFT computations. This complex, together with the related [Ba{μ2-OSi(SiMe3)3}{N(SiMe3)2}]2 and their parent [Ba{N(SiMe3)2}2]2, mediates the formation of asymmetric siloxanes R3Si−O−SiR′3 through the first case of main group metal-mediated dehydrocoupling of silanols and hydrosilanes. Early kinetic analysis highlights an unusual catalytic manifold. 相似文献
60.
Bhagyesh Purohit Erwann Jeanneau Thibault Cornier Gilles Ledoux Shashank Mishra 《印度化学会志》2022,99(2):100322
With an objective to have easy access to high quality BaYF5 matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF5 NCs co-doped with Yb3+/Tm3+ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed. 相似文献