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排序方式: 共有124条查询结果,搜索用时 93 毫秒
101.
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103.
Ding F Valahovic MT Keane JM Anstey MR Sabat M Trindle CO Harman WD 《The Journal of organic chemistry》2004,69(7):2257-2267
Dihapto-coordinated naphthalene complexes of the form TpRe(CO)(L)(eta(2)-naphthalene) (L = PMe(3), pyridine, or 1-methylimidazole) undergo electrophilic addition with dimethoxymethane and with various Michael acceptors to generate 1H-naphthalenium species. These naphthalenium complexes undergo intra- or intermolecular nucleophilic addition reactions with stabilized enolates, silyl ketene acetals, or enols to form the corresponding dihydronaphthalene complexes. Oxidative decomplexation generates the free dihydronaphthalene. When a resolved form of the rhenium dearomatization agent is used, these reactions can be performed enantioselectively. DFT calculations provide a useful guide in explaining the observed stereochemistry. Depending on reaction conditions, a Michael-Michael ring-closure sequence (MIMIRC) or a net [2 + 4] cycloaddition with the bound naphthalene is also observed, and the corresponding tricyclic molecules can be removed from the metal in high yield. 相似文献
104.
The complexes [TpRe(CO)(L)(4,5-eta(2)-furan)], present as diastereomeric mixtures (L = (t)BuNC (1A, 1B), PMe(3) (2A, 2B), pyridine (3A, 3B), or 1-methylimidazole (4A, 4B)), undergo acid-catalyzed methanol addition in CH(2)Cl(2) at -40 degrees C, resulting in the syntheses of dihapto-coordinated 2-methoxy-2,3-dihydrofuran complexes. In all cases, two diastereomers resulted, one in which the oxygen of the dihydrofuran is oriented toward the L ligand (5A, 6A, 7A, and 8A), and one in which the oxygen is oriented away from the L ligand (5B, 6B, 7B, and 8B). In all cases, the methoxy group adds stereoselectively, anti to the metal fragment. In addition, the (t)BuNC complex 1 yields a dihapto-coordinated vinyl ether (5C) that results from ring opening of the protonated furan ligand. In no case does the diastereomeric ratio of products correlate with that of the starting material. 相似文献
105.
Brandau C Kozhuharov C Harman Z Müller A Schippers S Kozhedub YS Bernhardt D Böhm S Jacobi J Schmidt EW Mokler PH Bosch F Kluge HJ Stöhlker T Beckert K Beller P Nolden F Steck M Gumberidze A Reuschl R Spillmann U Currell FJ Tupitsyn II Shabaev VM Jentschura UD Keitel CH Wolf A Stachura Z 《Physical review letters》2008,100(7):073201
Isotope shifts in dielectronic recombination spectra were studied for Li-like (A)Nd(57+) ions with A=142 and A=150. From the displacement of resonance positions energy shifts deltaE(142 150)(2s-2p(1/2))=40.2(3)(6) meV [(stat)(sys)] and deltaE(142 150)(2s-2p(3/2))=42.3(12)(20) meV of 2s-2p(j) transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of (142 150)deltar(2)=-1.36(1)(3) fm(2). The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size. 相似文献
106.
Simon MC López-Urrutia JR Beilmann C Schwarz M Harman Z Epp SW Schmitt BL Baumann TM Behar E Bernitt S Follath R Ginzel R Keitel CH Klawitter R Kubiček K Mäckel V Mokler PH Reichardt G Schwarzkopf O Ullrich J 《Physical review letters》2010,105(18):183001
Photoionization (PI) of Fe14+ in the range from 450 to 1100 eV was measured at the BESSY II storage ring using an electron beam ion trap achieving high target-ion area densities of 10(10) cm(-2). Photoabsorption by this ion is observed in astrophysical spectra and plasmas, but until now cross sections and resonance energies could only be provided by calculations. We reach a resolving power E/ΔE of at least 6500, outstanding in the present energy range, which enables benchmarking and improving the most advanced theories for PI of ions in high charge states. 相似文献
107.
C. Brandau C. Kozhuharov A. Müller D. Bernhardt F. Bosch D. Boutin F. J. Currell C. Dimopoulou B. Franzke S. Fritzsche A. Gumberidze Z. Harman U. D. Jentschura C. H. Keitel Y. S. Kozhedub R. Krücken Yu. A. Litvinov F. Nolden B. O’Rourke R. Reuschl S. Schippers V. M. Shabaev U. Spillmann Z. Stachura M. Steck Th. St?hlker I. I. Tupitsyn D. F. A. Winters A. Wolf 《Hyperfine Interactions》2010,196(1-3):115-127
Sharp resonant structures in the cross section of the atomic electron-ion collision process of dielectronic recombination are exploited to study isotope shifts and hyperfine interaction of heavy highly-charged ions. This novel approach provides a conceptual alternative to existing methods. In this contribution, we present a series of measurements, which we performed at the heavy ion storage ring ESR of the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. In a first experiment the stable isotopes A = 142 and A = 150 of three-electron neodymium ANd57?+? were studied. Isotope shifts of dielectronic resonances associated with 2s???2p j (j?=?1/2, 3/2) transitions were extracted from the measured data. The evaluation of the energy shift was performed within a full QED framework and yielded a change in the mean-square charge radius of $^{142,150}\delta \langle r^2 \rangle = -1.36(1)(3)$ fm2. At GSI, in addition to the investigation of stable isotopes unstable species can be artificially synthesized and studied. Radioisotopes produced in-flight from fragmentation of a 238U primary beam were injected into the ESR and were subsequently separated by their mass-to-charge ratio. This enabled us to perform first DR experiments with the exotic nuclei 237U89?+? (Z = 92 )and 234Pa88?+? (Z = 91). 相似文献
108.
A Hardy type two-weighted inequality is investigated for the multidimensional Hardy operator in the norms of generalized Lebesgue spaces L p(·). Equivalent necessary and sufficient conditions are found for the ${L^{p(\cdot)} \longrightarrow L^{q(\cdot)}}A Hardy type two-weighted inequality is investigated for the multidimensional Hardy operator in the norms of generalized Lebesgue
spaces L
p(·). Equivalent necessary and sufficient conditions are found for the Lp(·) ? Lq(·){L^{p(\cdot)} \longrightarrow L^{q(\cdot)}} boundedness of the Hardy operator when exponents q(0) < p(0), q(∞) < p(∞). It is proved that the condition for such an inequality to hold coincides with the condition for the validity of two-weighted
Hardy inequalities with constant exponents if we require of the exponents to be regular near zero and at infinity. 相似文献
109.
The arene ligand in the complex TpRe(CO)(MeIm)(eta2-benzene) (Tp = hydridotris(pyrazolyl)borate; MeIm = N-methylimidazole) undergoes tandem electrophile/nucleophile 1,4-addition reactions. Subsequent oxidative demetalation affords cis-3,6-disubstituted 1,4-cyclohexadienes (46-84%). Common organic electrophiles such as acetals and Michael acceptors were successfully added to the bound benzene to generate eta3-benzenium complexes, which then were treated with a silyl ketene acetal, silyl vinyl ether, phenyllithium, or malonate ester to afford 1,4-dialkylated dihydrobenzene complexes. The d6 transition metal analogues TpW(NO)(PMe3)(eta2-benzene) and [Os(NH3)5(eta2-benzene)]2+ also undergo 1,4-dialkylation reactions, and the relative ability of all three metals to activate arenes is compared. 相似文献
110.