共查询到20条相似文献,搜索用时 15 毫秒
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Dr. John Popp Dr. Schirin Hanf Prof. Dr. Evamarie Hey-Hawkins 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(26):5765-5769
Tertiary phosphines are generally known to withstand inversion under moderate conditions. In this work, a remarkable racemization process of three P-chiral ferrocenyl phosphines is reported. Subjected to conventional column chromatography as highly enantioenriched compounds, they greatly experienced racemization when collected at the column outlet within minutes. Initially, attention was drawn to this unusual inversion behavior after observing that the superb enantiomeric excess of these ligands (>95 % ee in all cases) was almost lost in their corresponding ruthenium(II) complexes. Successively excluding possible racemization causes, these P-chiral ferrocenyl phosphines were found to undergo a significant, acid-catalyzed racemization process at room temperature within a few minutes. This process is mainly observed during standard column chromatography by using conventional silica or alumina, but can also be triggered deliberately by addition of certain acids. Therefore, the stereochemical preservation of P-chiral phosphines during their purification may per se not always be guaranteed, since column chromatography is the most frequently used technique for purifying such types of compounds. 相似文献
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Yuchao Deng Xiao-Jing Wei Prof. Xiao Wang Prof. Dr. Yuhan Sun Prof. Dr. Timothy Noël 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(64):14532-14535
Transition-metal-catalyzed cross-coupling chemistry can be regarded as one of the most powerful protocols to construct carbon–carbon bonds. While the field is still dominated by palladium catalysis, there is an increasing interest to develop protocols that utilize cheaper and more sustainable metal sources. Herein, we report a selective, practical, and fast iron-based cross-coupling reaction that enables the formation of Csp−Csp3 and Csp2−Csp3 bonds. In a telescoped flow process, the reaction can be combined with the Grignard reagent synthesis. Moreover, flow allows the use of a supporting ligand to be avoided without eroding the reaction selectivity. 相似文献
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Exploiting the Brønsted Acidity of Phosphinecarboxamides for the Synthesis of New Phosphides and Phosphines 下载免费PDF全文
Andrew R. Jupp Gemma Trott Éléonore Payen de la Garanderie James D. G. Holl Dr. Duncan Carmichael Prof. Dr. Jose M. Goicoechea 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8015-8018
We demonstrate that the synthesis of new N‐functionalized phosphinecarboxamides is possible by reaction of primary and secondary amines with PCO? in the presence of a proton source. These reactions proceed with varying degrees of success, and although primary amines generally afford the corresponding phosphinecarboxamides in good yields, secondary amines react more sluggishly and often give rise to significant decomposition of the 2‐phosphaethynolate precursor. Of the new N‐derivatized phosphinecarboxamides available, PH2C(O)NHCy (Cy=cyclohexyl) can be obtained in sufficiently high yields to allow for the exploration of its Brønsted acidity. Thus, deprotonating PH2C(O)NHCy with one equivalent of potassium bis(trimethylsilyl)amide (KHMDS) gave the new phosphide [PHC(O)NHCy]?. In contrast, deprotonation with half of an equivalent gives rise to [P{C(O)NHCy}2]? and PH3. These phosphides can be employed to give new phosphines by reactions with electrophiles, thus demonstrating their enormous potential as chemical building blocks. 相似文献
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Iron‐catalyzed Cross‐Coupling of Propargyl Carboxylates and Grignard Reagents: Synthesis of Substituted Allenes 下载免费PDF全文
Dr. Simon N. Kessler Prof. Dr. Jan‐E. Bäckvall 《Angewandte Chemie (International ed. in English)》2016,55(11):3734-3738
Presented herein is a mild, facile, and efficient iron‐catalyzed synthesis of substituted allenes from propargyl carboxylates and Grignard reagents. Only 1–5 mol % of the inexpensive and environmentally benign [Fe(acac)3] at ?20 °C was sufficient to afford a broad range of substituted allenes in excellent yields. The method tolerates a variety of functional groups. 相似文献
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Simon Sengupta Philipp Schüler Dr. Helmar Görls Dr. Phil Liebing Dr. Sven Krieck Prof. Matthias Westerhausen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(50):e202201359
The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R2N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R2N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR2)2 and MgBr2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state. 相似文献
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Continuous‐Flow Synthesis of Functionalized Phenols by Aerobic Oxidation of Grignard Reagents 下载免费PDF全文
Dr. Zhi He Prof. Dr. Timothy F. Jamison 《Angewandte Chemie (International ed. in English)》2014,53(13):3353-3357
Phenols are important compounds in chemical industry. An economical and green approach to phenol preparation by the direct oxidation of aryl Grignard reagents using compressed air in continuous gas‐liquid segmented flow systems is described. The process tolerates a broad range of functional groups, including oxidation‐sensitive functionalities such as alkenes, amines, and thioethers. By integrating a benzyne‐mediated in‐line generation of arylmagnesium intermediates with the aerobic oxidation, a facile three‐step, one‐flow process, capable of preparing 2‐functionalized phenols in a modular fashion, is established. 相似文献
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Mario Marín Juan J. Moreno Carlos Navarro-Gilabert Dr. Eleuterio Álvarez Dr. Celia Maya Dr. Riccardo Peloso Prof. Dr. M. Carmen Nicasio Prof. Dr. Ernesto Carmona 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):260-272
The experimental and computational characterization of a series of dialkylterphenyl phosphines, PR2Ar′ is described. The new P-donors comprise five compounds of general formula PR2Ar (R=Me, Et, iPr, c-C5H9 and c-C6H11); Ar = 2,6-C6H3-(3,5-C6H3-(CMe3)2)2), and another five PR2Ar′ phosphines containing the bulky alkyl groups iPr, c-C5H9 or c-C6H11, in combination with Ar′=Ar , Ar , or Ar ( L1 – L10 ). Steric and electronic parameters have been determined computationally and from IR and X-ray data obtained for the phosphines and for some derivatives, including tricarbonyl and dicarbonyl nickel complexes, Ni(CO)3(PR2Ar′) and Ni(CO)2(PR2Ar′). In the solid state, the free phosphines PR2Ar′ adopt one of the three possible structures formally related by rotation around the Cipso−P bond. Details on their relative energies and on the influence of the free phosphine structure on its coordination chemistry towards Ni(CO)n (n = 2, 3) fragments has been obtained by experimental and computational methods. 相似文献
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近30年来,Pd催化交叉偶联形成P-C键的反应在药物、催化剂配体、阻燃剂和高分子材料等领域受到普遍重视。本文介绍了Pd催化交叉偶联反应形成P-C键的方法,以及利用该法制备有机膦化合物的研究进展。作为反应底物的磷亲核试剂包括亚磷酸二烷基酯、亚膦酸酯、次膦酸酯、氧化膦、伯或仲膦、三芳基膦、亚磷酸三烷基酯、膦-硅(锡)化合物和膦-硼烷复合物等,参与偶联反应的亲电试剂包括卤代烯烃、卤代芳烃、三氟甲磺酸烯基酯、三氟甲磺酸芳基酯、乙烯基硼酸酯等,并对反应机理、反应条件和反应的影响因素进行了探讨。 相似文献
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Westerhausen M Gärtner M Fischer R Langer J Yu L Reiher M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(22):6292-6306
Compounds of the type aryl--M--X, with M=Ca, Sr, Ba and X as any kind of ligand (such as halide, phosphanide, amide, aryl), are presented. The low reactivity of the heavy alkaline earth metals calcium, strontium, and barium enforces an activation prior to use for the direct synthesis. The insertion of these metals into C--I bonds of aryl iodides (direct synthesis) yields aryl metal iodides and has to be performed at low temperatures and in THF. Aryl alkaline-earth-metal compounds show some characteristics: 1) the ease of ether cleavage enforces low reaction temperatures, 2) for Sr and Ba the Schlenk equilibrium is shifted towards homoleptic MI2 and MPh2, 3) high solubility of diaryl alkaline-earth-metal derivatives in THF even at low temperatures initiated quantum chemical investigations on the aggregation behavior, and 4) a strong low field shift of the 13C resonances of the ipso carbon atoms in NMR spectra was observed. First results from quantum chemical calculations on diaryl dicalcium(I) suggest a long Ca--Ca bond with a considerable Ca--Ca bond dissociation energy. Initial results on a selection of applications such as metallation, metathesis, and addition reactions of aryl calcium compounds are presented as well. 相似文献
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T Kruczyński N Pushkarevsky P Henke R Köppe E Baum S Konchenko J Pikies H Schnöckel 《Angewandte Chemie (International ed. in English)》2012,51(36):9025-9029
Magnesium bromide radicals have to be prepared as high-temperature molecules and trapped as a metastable solution because a seemingly simple reduction of donor-free Grignard compounds failed. However, the essential role of magnesium(I) species during the formation of Grignard compounds could be demonstrated experimentally. 相似文献