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排序方式: 共有163条查询结果,搜索用时 24 毫秒
1.
Nelly A. Kachurovskaya Georgii M. Zhidomirov Rutger A. van Santen 《Research on Chemical Intermediates》2004,30(1):99-103
Periodical calculations of Zn(II) metal cation stabilization in cationic positions with distantly placed aluminium ions has been performed for high-silica ferrierite. It was found that decrease of the stabilization energy at large distances between Al ions (more than 10 Å) is about of 2 eV in comparison with nearest possible position of two Al ions in the zeolite lattice and weekly depended on following increase of the Al-Al distance. Main changes in stabilization energy occured within a 3-Å interval of these distances. Only for the localizations of both Al ions in one zeolite ring zinc cationic form is more stable than hydrogen form. 相似文献
2.
3.
Fedushkin IL Morozov AG Rassadin OV Fukin GK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(19):5749-5757
Compounds [Sr(dpp-bian)(thf)4] (2), [Ba(dpp-bian)(dme)2.5] (3) and [Mg(dtb-bian)(thf)2] (4) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene; dtb-bian = 1,2-bis[(2,5-di-tert-butylphenyl)imino]acenaphthene) were prepared by reduction of dpp-bian and dtb-bian with an excess of metallic Mg, Sr, or Ba in THF or DME. Reactions of [Mg(dpp-bian)(thf)3], 3, and 4 with diphenylacetonitrile gave keteniminates [Mg(dpp-bianH)(NCCPh2)(thf)2] (5), [Mg(dtb-bianH)(NCCPh2)(thf)2] (6), and [Ba(dpp-bianH)(NCCPh2)(dme)2] (7), respectively. The reaction of 2 with CH3C[triple chemical bond]N in THF gave [{Sr(dpp-bianH)[N(H)C(CH3)C(H)CN](thf)}2] (8). The compounds 2, 3, 5-8 were characterized by elemental analysis, and IR and NMR spectroscopy. Molecular structures of 2, 3, 7, and 8 were determined by single-crystal X-ray diffraction. In contrast to reactions of alkali-metal reagents, magnesium amides, or yttriumalkyls with alpha-H acidic nitriles, which are accompanied by an amine or an alkane elimination, the reactions of [Mg(dpp-bian)(thf)3] (1), 2, 3, and 4 with such nitriles proceeded with formation of Mg, Sr, and Ba keteniminates and simultaneous protonation of one nitrogen atom of the bian ligand. The NMR spectroscopic data obtained for complex 5 indicated that in solution the amino hydrogen atom underwent the fast (on the NMR timescale) shuttle transfer between both nitrogen atoms of the dpp-bianH ligand. 相似文献
4.
Molybdenum-95 NMR spectra have been measured for a selection of molybdenum carbonyl compounds and Mo(Σ-C5H5)(η-C5H5)(NO)(S2CNMe2). A chemical shift range of more than 1500 ppm is found. The chemical shifts and linewidths are discussed. 相似文献
5.
Ignatov SK Rees NH Tyrrell BR Dubberley SR Razuvaev AG Mountford P Nikonov GI 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):4991-4999
The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction. 相似文献
6.
Bakhmutova EV Bakhmutov VI Belkova NV Besora M Epstein LM Lledós A Nikonov GI Shubina ES Tomàs J Vorontsov EV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(3):661-671
The interaction of [NbCp(2)H(3)] with fluorinated alcohols to give dihydrogen-bonded complexes was studied by a combination of IR, NMR and DFT methods. IR spectra were examined in the range from 200-295 K, affording a clear picture of dihydrogen-bond formation when [NbCp(2)H(3)]/HOR(f) mixtures (HOR(f) = hexafluoroisopropanol (HFIP) or perfluoro-tert-butanol (PFTB)) were quickly cooled to 200 K. Through examination of the OH region, the dihydrogen-bond energetics were determined to be 4.5+/-0.3 kcal mol(-1) for TFE (TFE = trifluoroethanol) and 5.7+/-0.3 kcal mol(-1) for HFIP. (1)H NMR studies of solutions of [NbCp(2)H(2)(B)H(A)] and HFIP in [D(8)]toluene revealed high-field shifts of the hydrides H(A) and H(B), characteristic of dihydrogen-bond formation, upon addition of alcohol. The magnitude of signal shifts and T(1) relaxation time measurements show preferential coordination of the alcohol to the central hydride H(A), but are also consistent with a bifurcated character of the dihydrogen bonding. Estimations of hydride-proton distances based on T(1) data are in good accord with the results of DFT calculations. DFT calculations for the interaction of [NbCp(2)H(3)] with a series of non-fluorinated (MeOH, CH(3)COOH) and fluorinated (CF(3)OH, TFE, HFIP, PFTB and CF(3)COOH) proton donors of different strengths showed dihydrogen-bond formation, with binding energies ranging from -5.7 to -12.3 kcal mol(-1), depending on the proton donor strength. Coordination of proton donors occurs both to the central and to the lateral hydrides of [NbCp(2)H(3)], the former interaction being of bifurcated type and energetically slightly more favourable. In the case of the strong acid H(3)O(+), the proton transfer occurs without any barrier, and no dihydrogen-bonded intermediates are found. Proton transfer to [NbCp(2)H(3)] gives bis(dihydrogen) [NbCp(2)(eta(2)-H(2))(2)](+) and dihydride(dihydrogen) complexes [NbCp(2)(H)(2)(eta(2)-H(2))](+) (with lateral hydrides and central dihydrogen), the former product being slightly more stable. When two molecules of TFA were included in the calculations, in addition to the dihydrogen-bonded adduct, an ionic pair formed by the cationic bis(dihydrogen) complex [NbCp(2)(eta(2)-H(2))(2)](+) and the homoconjugated anion pair (CF(3)COO...H...OOCCF(3))(-) was found as a minimum. It is very likely that these ionic pairs may be intermediates in the H/D exchange between the hydride ligands and the OD group observed with the more acidic alcohols in the NMR studies. 相似文献
7.
The attempted preparation of bis(trifluoromethylsulphanyl)thioketene is described. Mono-and di-(trifluoromethylsulphanyl)-substituted orthothioesters may be prepared fromCH3C(SC2H5)3 and CF3SCl in the presence of anhydrous ZnCl2. The unstable compoundshave been isolated and characterized. The corresponding CF3Se and CF3SO2 derivativesare only formed as intermediates which decompose to ketene diethylmercaptal. Suchmono- and di-substituted products are obtained in good yield from H2C=C(SC2H5)2 andCF3ECl (E=S, Se). The reaction of H2C=C(SC2H5)2 with CF3SO2F gave only poor yieldsof (CF3SO2)nCH2−n=C(SC2H5)2 (n=1, 2) which were only capable of characterizationin etheral solution by spectral means. Attempts to prepare (CF3S)2C=C=S by refluxing(CF3S)2CHC(O)Cl, (CF3S)2CHC(O)OH or (CF3S)2C=C=O with P4S10 in toluene yieldedonly the cyclic dimer and the corresponding 1,3,4-trithiolan. 相似文献
8.
9.
Anton Dmitrienko Prof. Melanie Pilkington Prof. Georgii I. Nikonov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(18):5730-5736
The AlI compound NacNacAl ( 1 , NacNac = [ArNC(Me)CHC(Me)NAr]−, Ar = 2,6-iPr2C6H3) serves as a template for the chemoselective coupling between carbonyls (benzophenone, fenchone, isophorone, p-tolyl benzoate, N,N-dimethylbenzamide, (1-phenylethylidene)aniline) and pyridine. With the CH-acidic ketone (1R)-(+) camphor, the reaction affords a hydrido alkoxide compound of Al, formed as the result of enolization, whereas an enolizable imine, (1-phenylethylidene)aniline, and the bulky ketone isophorone, still chemoselectively couple with pyridine. In contrast, reaction with the ester p-tolyl benzoate results in cleavage of the ester bond together with replacement of the alkoxy group by a hydrogen atom of the pyridine moiety. This study demonstrates that for carbonyl substrates featuring phenyl substituents, the reaction proceeds via intermediate formation of η2(C,X)-coordinated (X = O, N) carbonyl adducts, whereas the reaction of 1 with (R)-(−)-fenchone in the absence of pyridine leads to CH activation in the pendant isopropyl group of the Ar substituent of the NacNac ligand. 相似文献