共查询到14条相似文献,搜索用时 8 毫秒
1.
Dr. Burgert Blom Miriam Stoelzel Prof. Matthias Driess 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):40-62
This account is a review on the synthesis and transition‐metal coordination chemistry of N‐heterocyclic silylenes (NHSi’s) over the last 20 years till the present time (2012). Recently, fascinating and novel synthetic methods have been developed to access transition‐metal–NHSi complexes as an emerging class of compounds with a wealth of intriguing reactivity patterns. The striking influence of coordinating NHSi’s to transition‐metal complex fragments affording different reactivities to the “free” NHSi is a connecting theme (“leitmotif”) throughout the review, and highlights the potential of these compounds which lie at the interface of contemporary main‐group and classical organometallic chemistry towards new molecular catalysts for small‐molecule activation. 相似文献
2.
A Systematic Study of Structure and E−H Bond Activation Chemistry by Sterically Encumbered Germylene Complexes
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Matthew Usher Dr. Andrey V. Protchenko Dr. Arnab Rit Dr. Jesús Campos Dr. Eugene L. Kolychev Dr. Rémi Tirfoin Prof. Dr. Simon Aldridge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11685-11698
A series of new germylene compounds has been synthesized offering systematic variation in the σ‐ and π‐capabilities of the α‐substituent and differing levels of reactivity towards E?H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn)] ( 1 – 6 : ERn=NHDipp, CH(SiMe3)2, P(SiMe3)2, Si(SiMe3)3 or B(NDippCH)2; terphenyl=C6H3Mes2‐2,6=ArMes or C6H3Dipp2‐2,6=ArDipp; Dipp=C6H3iPr2‐2,6, Mes=C6H2Me3‐2,4,6), while the related complex [{(Me3Si)2N}Ge{B(NDippCH)2}] ( 8 ) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X‐ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ‐donating boryl or silyl ancillary donors. HOMO–LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)‐germylene system [ArMesGe{B(NDippCH)2}] ( 6 ‐Mes), which features a wide C‐Ge‐B angle (110.4(1)°) and (albeit relatively weak) ancillary π‐acceptor capabilities, has the smallest HOMO–LUMO gap (119 kJ mol?1). These features result in 6 ‐Mes being remarkably reactive, undergoing facile intramolecular C?H activation involving one of the mesityl ortho‐methyl groups. The related aryl(silyl)‐germylene system, [ArMesGe{Si(SiMe3)3}] ( 5 ‐Mes) has a marginally wider HOMO–LUMO gap (134 kJ mol?1), rendering it less labile towards decomposition, yet reactive enough to oxidatively cleave H2 and NH3 to give the corresponding dihydride and (amido)hydride. Mixed aryl/alkyl, aryl/amido and aryl/phosphido complexes are unreactive, but amido/boryl complex 8 is competent for the activation of E?H bonds (E=H, B, Si) to give hydrido, boryl and silyl products. The results of these reactivity studies imply that the use of the very strongly σ‐donating boryl or silyl substituents is an effective strategy for rendering metallylene complexes competent for E?H bond activation. 相似文献
3.
A Sterically Constrained Tricyclic PC3 Phosphine: Coordination Behavior and Insertion of Chalcogen Atoms into P−C Bonds
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Dr. Anne Hentschel M. Sc. Alexander Brand Dr. Philipp Wegener Prof. Dr. Werner Uhl 《Angewandte Chemie (International ed. in English)》2018,57(3):832-835
A tricyclic phosphine has been generated that has a rigid molecular backbone with the P atoms exclusively bound to C(sp2) atoms as well as a very large Tolman angle and buried volume. It is an interesting new ligand in coordination chemistry (Au, Pd complexes) and shows unusual insertion reactions into its endocyclic P?C bonds facilitated by its inherent molecular strain. 相似文献
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Bartole-Scott A Braunschweig H Kupfer T Lutz M Manners I Nguyen TL Radacki K Seeler F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(4):1266-1273
Reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with a variety of dialkyl(dichloro)silanes in aliphatic solvents afforded the corresponding [1]silatrochrocenophanes. Structural characterization by X-ray diffraction analysis of the [1]silatrochrocenophanes bearing Me2Si, (iPr)2Si, and silacyclobutane bridges revealed tilt angles alpha of 15.56(12) degrees , 15.8(1) degrees , and 16.33(17) degrees , respectively. Analogously, a [2]silatrochrocenophane (6) was prepared in excellent yield by reaction of [(eta5-C5H4Li)(eta7-C7H6Li)Cr]tmeda with 1,2-dichloro-1,1,2,2-tetramethyldisilane. This complex also was characterized structurally and exhibited a tilt angle alpha of 2.60(15) degrees. The [1]silatrochrocenophane bearing the Me2Si bridge underwent facile and regioselective carbon-silicon bond cleavage with [Pt(PEt3)4] to give a very high yield of an oxidative addition product. The ring-opening polymerization of these novel [1]silatrochrocenophanes afforded ring-opened chromium-based polymers. 相似文献
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A PCP Pincer Ligand for Coordination Polymers with Versatile Chemical Reactivity: Selective Activation of CO2 Gas over CO Gas in the Solid State
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Junpeng He Nolan W. Waggoner Samuel G. Dunning Dr. Alexander Steiner Dr. Vincent M. Lynch Prof. Simon M. Humphrey 《Angewandte Chemie (International ed. in English)》2016,55(40):12351-12355
A tetra(carboxylated) PCP pincer ligand has been synthesized as a building block for porous coordination polymers (PCPs). The air‐ and moisture‐stable PCP metalloligands are rigid tetratopic linkers that are geometrically akin to ligands used in the synthesis of robust metal–organic frameworks (MOFs). Here, the design principle is demonstrated by cyclometalation with PdIICl and subsequent use of the metalloligand to prepare a crystalline 3D MOF by direct reaction with CoII ions and structural resolution by single crystal X‐ray diffraction. The Pd?Cl groups inside the pores are accessible to post‐synthetic modifications that facilitate chemical reactions previously unobserved in MOFs: a Pd?CH3 activated material undergoes rapid insertion of CO2 gas to give Pd?OC(O)CH3 at 1 atm and 298 K. However, since the material is highly selective for the adsorption of CO2 over CO, a Pd?N3 modified version resists CO insertion under the same conditions. 相似文献
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RhV‐Nitrenoid as a Key Intermediate in RhIII‐Catalyzed Heterocyclization by CH Activation: A Computational Perspective on the Cycloaddition of Benzamide and Diazo Compounds
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Tao Zhou Wei Guo Dr. Yuanzhi Xia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9209-9218
A mechanistic study of the substituent‐dependent ring formations in RhIII‐catalyzed C?H activation/cycloaddition of benzamide and diazo compounds was carried out by using DFT calculations. The results indicated that the decomposition of the diazo is facilitated upon the formation of the five‐membered rhodacycle, in which the RhIII center is more electrophilic. The insertion of carbenoid into Rh?C(phenyl) bond occurs readily and forms a 6‐membered rhodacycle, however, the following C?N bond formation is difficult both kinetically and thermodynamically by reductive elimination from the RhIII species. Instead, the RhV‐nitrenoid intermediate could be formed by migration of the pivalate from N to Rh, which undergoes the heterocyclization much more easily and complementary ring‐formations could be modulated by the nature of the substituent at the α‐carbon. When a vinyl is attached, the stepwise 1,3‐allylic migration occurs prior to the pivalate migration and the 8‐membered ring product will be formed. On the other hand, the pivalate migration becomes more favorable for the phenyl‐contained intermediate because of the difficult 1,3‐allylic migration accompanied by dearomatization, thus the 5‐membered ring product was formed selectively. 相似文献
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Back Cover: A Planar‐Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones (Angew. Chem. Int. Ed. 26/2018)
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Dr. Evgeniya A. Trifonova Nikita M. Ankudinov Dr. Andrey A. Mikhaylov Dr. Denis A. Chusov Dr. Yulia V. Nelyubina Prof. Dr. Dmitry S. Perekalin 《Angewandte Chemie (International ed. in English)》2018,57(26):7904-7904
11.
Gamal A. El-Hiti 《Monatshefte für Chemie / Chemical Monthly》2004,135(3):323-331
Summary. 6-Methyl-3H-quinazolin-4-one reacted with alkyllithium reagents at –78°C in THF to give 2-alkyl-1,2-dihydro-6-methyl-3H-quinazolin-4-ones in high yields. However, no reaction took place when LDA was used as the lithium reagent. 6-Bromo-3H-quinazolin-4-one reacted with excessive butyllithium to give 2-butyl-1,2-dihydro-3H-quinazolin-4-ones in very good yields. However, the lithiation of 6-bromo-3H-quinazolin-4-one was achieved by the use of a combination of methyllithium (1.1 equivalents) and tert-butyllithium (2.2 equivalents) at –78°C in THF. The dilithio reagent thus obtained reacted with a variety of electrophiles (H2O, iodoethane, benzaldehyde, anisaldehyde, cyclohexanone, 2-hexanone, benzophenone, phenyl isothiocyanate, TITD) to give the corresponding 6-substituted 3H-quinazolin-4-ones in excellent yields. Reaction of the dilithio reagent with 1,3-dibromopropane gave 6,6-(propanediyl)bis(3H-quinazolin-4-one).Present address: Centre for Clean Chemistry, Department of Chemistry, University of Wales Swansea, Swansea SA2 8PP, UK 相似文献
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《Journal of separation science》2017,40(23):4503-4510
We present a validated liquid chromatography with tandem mass spectrometry method for simultaneous determination of 20‐(S )‐protopanaxatriol and its two oxidative stereoisomeric metabolites (20S ,24S )‐epoxy‐dammarane‐3,6,12,25‐tetraol (M1) and (20S ,24R )‐epoxy‐dammarane‐3,6,12,25‐tetraol (M2) in rat plasma. 20‐(S )‐Protopanaxatriol, M1, and M2 were extracted with methanol and separated on an ACQUITY HSS T3 column. The mass spectrometry detection was accomplished in selected reaction monitoring mode with precursor‐to‐product ion transitions of m/z 493.4→143.1 for M1 and M2, m/z 475.4→391.3 for 20‐(S )‐protopanaxatriol, and m/z 459.4→375.3 for 20‐(S )‐protopanaxadiol (internal standard). The method showed good linearity over the concentration ranges of 1–1000 ng/mL for 20‐(S )‐protopanaxatriol and 0.5–200 ng/mL for M1 and M2, with correlation coefficients of more than 0.995. The lower limits of quantification for 20‐(S )‐protopanaxatriol, M1, and M2 were 1, 0.5, 0.5 ng/mL, respectively. The intra‐ and interday precisions (RSD, %) were less than 10.41% while the accuracy (relative error, %) ranged from –3.14 to 8.73%. Under the current conditions, M1 and M2 were completely separated within 3 min. The validated assay was successfully applied to evaluating pharmacokinetic profiles of 20‐(S )‐protopanaxatriol, M1, and M2 in rat. 相似文献
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Sourav Biswas Christopher S. Qiu Louise N. Dawe Yuming Zhao Graham J. Bodwell 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(27):9264-9268
A new synthetic strategy (contractive annulation) for the synthesis of highly strained cyclophanes has been conceived and its viability has been demonstrated through a nine‐step synthesis of [2](6,1)naphthaleno[1]paracyclophane from [2.2]paracyclophane. 相似文献
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Sourav Biswas Christopher S. Qiu Louise N. Dawe Yuming Zhao Graham J. Bodwell 《Angewandte Chemie (International ed. in English)》2019,58(27):9166-9170
A new synthetic strategy (contractive annulation) for the synthesis of highly strained cyclophanes has been conceived and its viability has been demonstrated through a nine‐step synthesis of [2](6,1)naphthaleno[1]paracyclophane from [2.2]paracyclophane. 相似文献