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81.
Jade I. Fostvedt Lauren N. Grant Benjamin M. Kriegel Andreas H. Obenhuber Trevor D. Lohrey Robert G. Bergman John Arnold 《Chemical science》2020,11(42):11613
The bis(imido) complexes (BDI)Nb(NtBu)2 and (BDI)Nb(NtBu)(NAr) (BDI = N,N′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate; Ar = 2,6-diisopropylphenyl) were shown to engage in 1,2-addition and [2 + 2] cycloaddition reactions with a wide variety of substrates. Reaction of the bis(imido) complexes with dihydrogen, silanes, and boranes yielded hydrido-amido-imido complexes via 1,2-addition across Nb-imido π-bonds; some of these complexes were shown to further react via insertion of carbon dioxide to give formate-amido-imido products. Similarly, reaction of (BDI)Nb(NtBu)2 with tert-butylacetylene yielded an acetylide-amido-imido complex. In contrast to these results, many related mono(imido) Nb BDI complexes do not exhibit 1,2-addition reactivity, suggesting that π-loading plays an important role in activating the Nb–N π-bonds toward addition. The same bis(imido) complexes were also shown to engage in [2 + 2] cycloaddition reactions with oxygen- and sulfur-containing heteroallenes to give carbamate- and thiocarbamate-imido complexes: some of these complexes readily dimerized to give bis-μ-sulfido, bis-μ-iminodicarboxylate, and bis-μ-carbonate complexes. The mononuclear carbamate imido complex (BDI)Nb(NAr)(N(tBu)CO2) (12) could be induced to eject tert-butylisocyanate to generate a four-coordinate terminal oxo imido intermediate, which could be trapped as the five-coordinate pyridine or DMAP adduct. The DMAP adducted oxo imido complex (BDI)NbO(NAr)(DMAP) (16) was shown to engage in 1,2-addition of silanes across the Nb-oxo π-bond; this represents a new reaction pathway in group 5 chemistry.Another slice of pi: the addition of a second π-donor ligand engenders 1,2-addition and [2 + 2] cycloaddition reactivity across Nb-imido and Nb-oxo bonds. 相似文献
82.
Copper Salt‐Controlled Divergent Reactivity of [Cu]CF2PO(OEt)2 with α‐Diazocarbonyl Derivatives
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Dr. Tatiana Besset Prof. Dr. Xavier Pannecoucke Dr. Thomas Poisson 《Angewandte Chemie (International ed. in English)》2016,55(45):14141-14145
Herein, we report a copper salt‐controlled divergent reactivity toward α‐diazocarbonyl compounds. By a simple change of the copper counteranion under identical reaction conditions, the reported method allowed an easy access to either (Z)‐α‐fluorovinylphosphonate or alkyl‐SCF2PO(OEt)2 derivatives in good yields. Mechanistic studies were performed and suggested two different pathways to explain the formation of these products. 相似文献
83.
Dr. Alex T. O'Neil Jade Pope Prof. John A. Harrison Prof. Jonathan A. Kitchen 《欧洲无机化学杂志》2023,26(30):e202300358
We report the synthesis of a new pyrene, dipicolinic acid-based ligand ( L1H ) and its corresponding multi-emissive and multifunctional europium complex [Eu( L1 )3] that is capable of single component color switchable emission from red to blue and also white. At high concentration (10 mM) the single component system results in near pure white emission (CIE coordinates x,y=0.329, 0.324). Furthermore, the system showed ratiometric oxygen sensing with oxygen significantly quenching the pyrene centered emission but not the Eu3+ emission, resulting in an overall emission color change from blue to red on increasing oxygen content. 相似文献
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87.
Single-pass and approximate dynamic-programming algorithms for order acceptance and capacity planning 总被引:2,自引:0,他引:2
This paper investigates dynamic order acceptance and capacity planning under limited regular and non-regular resources. Our
goal is to maximize the profits of the accepted projects within a finite planning horizon. The way in which the projects are
planned affects their payout time and, as a consequence, the reinvestment revenues as well as the available capacity for future
arriving projects. In general, project proposals arise dynamically to the organization, and their actual characteristics are
only revealed upon arrival. Dynamic solution approaches are therefore most likely to obtain good results. Although the problem
can theoretically be solved to optimality as a stochastic dynamic program, real-life problem instances are too difficult to
be solved exactly within a reasonable amount of time. Efficient and effective heuristics are thus required that supply a response
without delay. For this reason, this paper considers both ‘single-pass’ algorithms as well as approximate dynamic-programming
algorithms and investigates their suitability to solve the problem. Simulation experiments compare the performance of our
procedures to a first-come, first-served policy that is commonly used in practice. 相似文献
88.
Sophie Bourcier Clémentine Poisson Yasmine Souissi Said Kinani Stéphane Bouchonnet Michel Sablier 《Rapid communications in mass spectrometry : RCM》2010,24(20):2999-3010
With the future aim of elucidating the unknown structures of estrogen degradation products, we characterized the dissociation pathways of protonated estrone (E1) under collisional activation in liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments employing a quadrupole time‐of‐flight mass spectrometer. Positive ion and negative ion modes give information on the protonated and deprotonated molecules and their product ions. The mass spectra of estrone methyl ether (CH3‐E1) and estrone‐d4 (E1‐d4) were compared with that of E1 in order (i) to elucidate the dissociation mechanisms of protonated and deprotonated molecules and (ii) to propose likely structures for each product ions. The positive ion acquisition mode yielded more fragmentation. The mass spectra of E1 were compared with those of estradiol (E2), estriol (E3) and 17‐ethynylestradiol (EE2). This comparison allowed the identification of marker ions for each ring of the estrogenic structure. Accurate mass measurements have been carried out for all the identified ions. The resulting ions revealed to be useful for the characterization of structural modifications induced by photolysis on each ring of the estrone molecule. These results are very promising for the determination of new metabolites in the environment. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
89.
A Mahjoub M Hochlaf GA Garcia L Nahon L Poisson 《The journal of physical chemistry. A》2012,116(34):8706-8712
The near threshold photofragmentation pattern of δ-valerolactam(+) and δ-valerolactam(2)(+) has been recorded combining electron/ion coincidence techniques and vacuum ultraviolet synchrotron radiation. The experimental method yields the fragment intensity as a function of the internal energy deposited into the parent cation, up to 3.1 eV above the first ionization threshold. In parallel, ab initio studies on the δ-valerolactam(+) and δ-valerolactam(2)(+) cations and their ionic and neutral fragmentation products have been performed with the aim of determining the isomers of the ionic products observed experimentally as well as of their neutral counterparts. These computations were performed using the PBE0 exchange-correlation functional and the aug-cc-pVDZ basis set. We found good agreement between the calculated reaction enthalpies and experimental appearance energies of the ions. More generally, our experimental and theoretical results reveal that the fragmentation of the ionic species of interest leads to a multitude of neutral and ionic fragments, which may be formed after intramolecular isomerization and complex decomposition processes. Multistep reaction pathways are expected. 相似文献
90.
Vacuum ultraviolet photoionization of C3 总被引:1,自引:0,他引:1
Nicolas C Shu J Peterka DS Hochlaf M Poisson L Leone SR Ahmed M 《Journal of the American Chemical Society》2006,128(1):220-226
Photoionization efficiency (PIE) curves for C(3) molecules produced by laser ablation are measured from 11.0 to 13.5 eV with tunable vacuum ultraviolet undulator radiation. A step in the PIE curve versus photon energy, obtained with N(2) as the carrier gas, supports the conclusion of very effective cooling of C(3) to its linear (1)Sigma(g)(+) ground state. The second step observed in the PIE curve versus photon energy could be the first experimental evidence of the C(3)(+)((2)Sigma(g)(+)) excited state. The experimental results, complemented by ab initio calculations, suggest a state-to-state vertical ionization energy of 11.70 +/- 0.05 eV between the C(3)(X(1)Sigma(g)(+)) and the C(3)(+)(X(2)Sigma(u)(+)) states. An ionization energy of 11.61 +/- 0.07 eV between the neutral and ionic ground states of C(3) is deduced using the data together with our calculations. Accurate ab initio calculations are performed for both linear and bent geometries on the lowest doublet electronic states of C(3)(+) using Configuration Interaction (CI) approaches and large basis sets. These calculations confirm that C(3)(+) is bent in its electronic ground state, which is separated by a small potential barrier from the (2)Sigma(u)(+) minimum. The gradual increase at the onset of the PIE curve suggests a geometry change between the ground neutral and cationic states. The energies between several doublet states of the ion are theoretically determined to be 0.81, 1.49, and 1.98 eV between the (2)Sigma(u)(+) and the (2)Sigma(g)(+),( 2)Pi(u), (2)Pi(g) excited states of C(3)(+), respectively. 相似文献