Auswahl der wissenschaftlichen Literatur zum Thema „Low-Valent zinc“

Low-valent titanium prepared by the reduction of TiCl3 with zinc dust oxidatively adds to α-ketoamides or α-ketoesters with the formation of the corresponding titanium enediolates. These 1,2-difunctional nucleophiles, which have hardly been used in organic synthesis so far, undergo regioselective intramolecular aldol condensation reactions with various electrophiles such as aldehydes, ketones, nitriles, esters and amides. This methodology allows the synthesis of differently substituted coumarin and 2-quinolone derivatives.

The reductive coupling reaction of aldehydes and ketones, including unsymmetrical aliphatic ketones, proceeded smoothly to give the corresponding pinacols in good to high yields under mild conditions by using combination of titanium(II) chloride and zinc or titanium(IV) chloride and zinc in dichloromethane-pivalonitrile. Meso-selective formation of the coupling products was observed in the cases of some aliphatic ketones. The diastereoselectivities of coupling products depend on both difference of bulkiness of 2-, and 2'-substituents of carbonyl group of the reactant, and overall steric effect around the carbonyl groups.Key words: diastereoselective pinacol reaction, dichloromethane-pivalonitrile, titanium(II) chloride, titanium(IV) chloride, zinc.

Zinc plant leach residues (ZPLRs) contain significant amounts of metal compounds of lead (Pb), zinc (Zn), iron (Fe), etc., hence, they are considered as a secondary source of metals. On the other hand, ZPLRs are regarded as hazardous materials because they contain heavy metals that pollute the environment. Resources and environmental concerns of ZPLRs were addressed in this study by removing/recovering Pb and Zn using a concurrent dissolution and cementation technique. To cement the dissolved Pb and Zn in leaching pulp, zero-valent aluminum (ZVAl) was added during ZPLRs leaching in the hydrochloric (HCl)–sodium chloride (NaCl) solution. The resulting cemented metals were agglomerated and separated by sieving. Lead removal increased with increasing both NaCl and HCl concentrations. However, when ZVAl was added, significant Pb removal was achieved at a low concentration. Zinc was not cemented out of the pulp using ZVAl and its recovery from ZPLRs was dependent on the HCl concentration only. By applying a concurrent dissolution and cementation technique, both Pb and Zn were removed using a low concentration of NaCl, and most importantly Pb—the most toxic metal in ZPLRs—was captured and separated before the solid-liquid separation, hence, eliminating the need for extensive washing of the generated residues to remove the inherent residual solution.

N,N,N’,N’-Tetramethyl-formamidinium chloride (2a) reacts with elemental sodium in various solvents to give N,N,N’,N’,N’’,N’’-hexamethyl-guanidinium chloride (4a). The reaction of 2a with potassium affords N,N,N’,N’,N’’,N’’,N’’’,N’’’-octamethyl-oxamidinium dichloride (3a). From the reaction of 2a with magnesium in different solvents in general result mixtures of the salts 4a, 3a and N,N,N’,N’-tetramethyl-formamidinium chloride (10a). The composition of these mixtures depends on the solvent and the reaction temperature. Similar results are obtained, when a zinc/copper couple is used instead of magnesium. Very likely from 2a and magnesium or zinc, respectively, organometallic intermediates 11, 12 are formed which could be trapped by aromatic aldehydes and phenylisocyanate. The salt 2a can be reductively coupled by a low-valent titanium reagent to give the oxamidinium salt 3a.

Two layer system from sputtered indium tin oxide (ITO) and gallium doped zinc oxide (Ga:ZnO, GZO) were studied for transparency in the visible electromagnetic range, reflectivity in the near infrared range, conductivity and valent band for a solar cells with quantum dots. The bi-layer coatings produced at optimized oxygen partial pressure, films thickness and surface roughness exhibit improved optical properties without worsening the electrical parameters, even if additional oxygen introduction during the reactive sputtering of the GZO. With an average optical transmittance of 91.3% in the visible range, average reflection and resistivity lower than 0.4 × 10−2 Ω.cm, these coatings are suitable for top electrode in the solar cells. The obtained results reveal that multilayered stacks of transparent ITO/Ga-doped ZnO coatings possess relatively low surface roughness (7–9 nm) and appropriate refractive index. The additional oxidation of GZO films induces modification of the film thickness and respectively of their optical performances.

The use of galvanic interactions between zero-valent aluminum (ZVAl) and activated carbon (AC) to recover gold (Au) ions is a promising technique to overcome the challenges due to the poor recovery in ammonium thiosulfate systems, but the applicability to practical Au ore processing remains elusive so far. The present study describes (1) the recovery of Au ions from low Au concentrations, which are typical concentrations used in Au ore processing; and (2) an investigation into the effects of various coexisting base metal ions that can be present in pregnant ore-leached solutions. The results showed that high Au recovery (i.e., over 85%) was obtained even at low Au concentrations under the following conditions: 1:1 of 0.15 g of ZVAl and AC with 10 mL of ammonium thiosulfate solution containing 5 mg/L of Au ions at 25 °C for 1 h in an anoxic atmosphere. Selected coexisting metal ions (i.e., copper, iron, cobalt, nickel, and zinc) were studied to establish their effects on Au recovery, and the results showed that the Au recovery was enhanced (about 90%) when copper ions coexist in the solution with minimal effects from other competing base metal ions.

Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted much attention recently due to the high abundance, low cost, high theoretical capacity up to 820 mAh g-1 with multi-valent charge carrier, and compatibility with aqueous electrolyte of the zinc anode.[1] Especially, the introduction of neutral or mild acidic electrolyte greatly improves the reversibility of zinc anode compared to conventional alkaline ZIBs.[2] Among all the cathode candidates, MnO2 is most attractive due to its relatively high energy density, low toxicity and low cost.[3] However, MnO2 electrode suffers from capacity fading during cycling mainly due to Mn dissolution and structural change. The addition of Mn2+ into the mild acidic electrolyte is a common method to suppress Mn dissolution.[4] Other strategies like structural design and surface coatings are also developed to suppress Mn dissolution.[5, 6] Though the cycle performance still cannot meet the demand of application, as the irreversible formation of inactive ZnMn2O4 during cycles still requires to be tackled. Here, we proposed Bi2O3 as a facile electrode additive in the electrode to suppress ZnMn2O4 formation and improve the cyclability of commercial electrolytic manganese dioxide (EMD). XRD, in-situ pH measurements and ICP tests suggest that inactive ZnMn2O4 is formed upon cycling due to the interaction between MnO2 and zincate ions in the electrolyte from localized increase in pH, and Bi2O3 dissolves into the electrolyte in the presence of zincate ions and forms a complex with the zincate ions to suppress the reaction pathway. A high capacity of 269 mAh g-1 is maintained at 100 mA g-1 after 50 cycles with a capacity retention of 91.5% when EMD with 10 wt% of Bi2O3 is tested in ZnSO4 electrolyte without Mn2+ additive. Combining both Bi2O3 electrode additive and Mn2+ electrolyte additive, EMD can maintain a stable capacity of 190 mAh g-1 for 1000 cycles at 1000 mA g-1 (about 3.3C). More characterizations are underway to further understand the role of Bi2O3 and the results will be shown during the meeting. Reference: [1] B. Tang, L. Shan, S. Liang, J. Zhou, Issues and opportunities facing aqueous zinc-ion batteries, Energy & Environmental Science, 12 (2019) 3288-3304. [2] J. Hao, X. Li, X. Zeng, D. Li, J. Mao, Z. Guo, Deeply understanding the Zn anode behaviour and corresponding improvement strategies in different aqueous Zn-based batteries, Energy & Environmental Science, 13 (2020) 3917-3949. [3] N. Zhang, X. Chen, M. Yu, Z. Niu, F. Cheng, J. Chen, Materials chemistry for rechargeable zinc-ion batteries, Chemical Society Reviews, 49 (2020) 4203-4219. [4] H. Pan, Y. Shao, P. Yan, Y. Cheng, K.S. Han, Z. Nie, C. Wang, J. Yang, X. Li, P. Bhattacharya, Reversible aqueous zinc/manganese oxide energy storage from conversion reactions, Nature Energy, 1 (2016) 1-7. [5] J. Huang, Z. Wang, M. Hou, X. Dong, Y. Liu, Y. Wang, Y. Xia, Polyaniline-intercalated manganese dioxide nanolayers as a high-performance cathode material for an aqueous zinc-ion battery, Nature communications, 9 (2018) 1-8. [6] B. Wu, G. Zhang, M. Yan, T. Xiong, P. He, L. He, X. Xu, L. Mai, Graphene scroll‐coated α‐MnO2 nanowires as high‐performance cathode materials for aqueous Zn‐ion battery, Small, 14 (2018) 1703850. Figure 1

The object of research is kaolin from the Hlukhovetsky deposit (Ukraine). On its basis, granulated sorbent materials were obtained with the addition of various amounts of cellulose as a pore former. After forming the samples, they were dried and fired at a temperature of 800 °C. The obtained granules with a size of 8–9 mm were modified with zero-valent iron. The physicochemical, including sorption properties of granular composites were studied. Using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), the morphology of the obtained samples was investigated and the presence of zero-valent iron particles on the surface and in the pores of the sorbents was confirmed. Based on desorption experiments, it was determined by chemical analysis that the Fe0 content in modified samples with increased pore former content increases from 0.01 g/g of granules for a sample containing 1% cellulose to 0.016 g/g for a carrier with 3 % pore former. The specific surface area and pore volume of the samples were determined by the method of low-temperature adsorption-desorption of nitrogen. Thus, with an increase in the content of the pore former in the ceramic mass, the specific surface of both unmodified and modified samples slightly decreases. Thus, with a cellulose content of 1 %, it is 20 m2/g and 17 m2/g, respectively. When the pore former is increased to 3%, these values are 15 m2/g and 12 m2/g. After applying a layer of zero-valent iron on porous granules, the volume of pores decreases, which is due to the formation of agglomerates of iron particles during synthesis. The study of the sorption capacity of the obtained sorbents with respect to Cr(VI) from model solutions containing a mixture of metal cations (copper, cadmium, cobalt, zinc) showed that granular materials exhibit sorption capacity for metal anions, even in the presence of cations. The amount of chromium sorption naturally increases for modified samples with an increase in the cellulose content in them. However, for model solutions that do not additionally contain metal cations, the sorption value is somewhat higher. Thus, for a sample with a 3 % pore former content, the sorption value is 0.7 mg/g and 0.9 mg/g, respectively, at an initial chromium(VI) concentration of 10 mg/g. The obtained experimental data indicate that the obtained porous granular sorbents based on kaolin can be used in the further treatment of wastewater from electroplating enterprises, which contain a mixture of pollutants in both anionic and cationic forms.

In recent years, hybrid supercapacitors with greater potential and improved energy density have been completed by combining some battery and supercapacitor type electrodes. According to some researchers’ research, “hybrid” supercapacitor systems are technically “asymmetric” supercapacitor systems since they are built on two separate supercapacitor type electrodes. The primary aim behind the development of a hybrid capacitor (HC) is to improve the energy density or specific energy of the device, which will significantly boost the storage property. Moreover, the use of an electrical double layer capacitor type electrode provides a large surface area, improving the electrode/electrolyte interaction region, and helps in the fast ion-adsorption process, which prevents the degradation of the battery-type electrode due to repeated charge-discharge cycles. A suitable combination of specific power (due to the EDLC electrode) and specific energy (due to the faradic electrode) could drastically enhance the stability and longevity of the hybrid supercapacitor device. The di/tri-valent metal ion (Mg2+, Zn2+, Ca2+, Al3+, etc.) hybrid capacitors have garnered considerable attention in recent years owing to their potential cost benefit and application in stationary storage systems, whose development is crucial for the mass-scale penetration of renewable energy technologies. Zinc‐ion hybrid supercapacitors (ZIHSs) may be the most promising energy storage device alternatives for portable and large‐scale electronic devices, as they combine the benefits of both supercapacitors and zinc‐ion batteries. ZIHSs are mostly based on battery-type Zn metal as an anode and physical adsorption-based carbon materials as the cathode. Porous carbon materials with high surface area, good electrochemical stability, low cost, high electronic conductivity and tuneable surface structure are deemed as promising cathode materials for ZIHSs. It is generally recognized that the micropores facilitate electrochemical energy storage, and mesopores can effectively reduce the ion diffusion distance and transport resistance. Therefore, the adjustment and optimization of porous carbons electrodes are of great significance to ZIHSs. This work provides some insight into the strategy for designing effective non-aqueous and aqueous Zn-ion hybrid supercapacitors. Electrochemical characteristics of Zn-ion hybrid supercapacitor cells based on non-aqueous 1 M acetonitrile (AN) or propylene carbonate (PC) electrolytes with addition Zn(BF4)2, zinc di[bis(trifluoromethylsulfonyl)imide] (Zn(TFSI)2) and zinc trifluoromethanesulfonate (Zn(OTf)2) have been studied. Very high energy and power densities (80 Wh kg−1 and 21.2 kW kg−1) have been measured for 1 M Zn(BF4)2/AN based Zn-ion based hybrid supercapacitors (Fig. 1a). Very good stability during 3,000 cycles of cells has been achieved demonstrating reasonably high energy efficiency value (66.8%) for Zn(TFSI)2/AN based ZIHS cell, decreasing in the order of electrolytes: Zn(TFSI)2/AN > Zn(BF4)2/PC > Zn(TFSI)2/PC > Zn(OTf)2/AN > Zn(BF4)2/AN. Some assembled ZIHSs had shown excellent cycling and energy stability over 20,000 cycles [1]. Electrochemical behaviour of Zn cation based salts in various aqueous electrolytes (ZnSO4, Zn(BF4)2, Zn(TFSI)2, and Zn(OTf)2) has been studied in thin ZIHS cell and compared with Zn(ClO4)2 aqueous electrolyte based cell electrochemical characteristics. At moderate specific power value (10 kW kg− 1) noticeable decrease of specific energy has been established in the order of aqueous electrolytes: Zn(ClO4)2 ⩾ Zn(BF4)2 > Zn(OTf)2 > Zn(TFSI)2 > ZnSO4 (Fig. 1b). The stability of Zn-ion hybrid supercapacitor cells under study in aqueous electrolyte solutions has been tested using the long lasting (up to 10,000 cycles) constant current charge/discharge method and very good stability for Zn(OTf)2, Zn(ClO4)2 and ZnSO4 has been observed [2,3]. Taking into account the cheap and environmental friendliness electrodes and electrolyte used, the results can be applied for assembling of the cheap high energy density hybrid supercapacitors for sustainable energy storage/recuperation complexes, combined with photovoltaic fields and/or wind electricity generating systems. Acknowledgements This work was supported by the Estonian Ministry of Education and Research (TK210, Centre of Excellence in Sustainable Green Hydrogen and Energy Technologies), Personal Research Grant PRG676 and R&D project EAG228. The experimental part of the research was partially co-funded by the Feasibility Fund of the University of Tartu Development Fund. References [1] K.-S. Põder, J. Eskusson, E. Lust, and A. Jänes, J. Electrochem. Soc. 170, 060501, 2023. [2] J. Eskusson, T. Thomberg, E. Lust, and A. Jänes, J. Electrochem. Soc. 169,020512, 2022. [3] J. Eskusson, T. Thomberg, T. Romann, K. Lust, E. Lust, and A. Jänes, J. Solid State Electrochem. 25, 2869, 2021. Figure 1

Les travaux de cette thèse portent sur la synthèse, le mécanisme de formation et la réactivité de composés bimétalliques de zinc (I). Ces complexes, qui présentent une liaison zinc-zinc interne, sont particulièrement sensibles à l'oxygène et à l'humidité, nécessitant ainsi des conditions de synthèse rigoureusement contrôlées. Souvent, leur mécanisme de formation est rarement élucidé. Bien que des exemples de composés bimétalliques d'aluminium ou de magnésium aient été utilisés pour réduire des alcynes en vinylbimétalliques-1,2, menant à la formation d'alcènes tetrasubstitués en un seul pot, aucun exemple de formation de vinyldizinc-1,2 par cette méthode n'a été rapporté. Pourtant, la richesse des transformations impliquant des liaisons C-Zn, connues pour leur grande tolérance fonctionnelle en raison de leur faible caractère ionique, suggère que les composés bimétalliques de zinc pourraient offrir des perspectives prometteuses en synthèse. Ce projet vise à comprendre la nature d'un complexe bimétallique de zinc biradicalaire et à explorer sa réactivité, notamment dans le cadre de la réduction de triples liaisons pour former des vinyls dizinc-1,2. Ces travaux ont été menés en symbiose entre chimie expérimentale et computationnelle. La synergie entre ces deux disciplines a permis une compréhension plus approfondie des mécanismes, des influences électroniques des espèces impliquées, ainsi que de l'origine des produits obtenus expérimentalement, souvent issus d'intermédiaires difficiles à caractériser. Dans la première partie, la synthèse et la réactivité de ce complexe sont étudiées, avec une proposition de mécanisme appuyée par des calculs DFT. Ensuite, une méthode de dizincation d'alcyne est présentée, permettant l'obtention de vinyl dizinc-1,2. Enfin, une méthode de synthèse alternative est proposée dans la dernière partie
This thesis focuses on the synthesis, formation mechanism, and reactivity of zinc(I) bimetallic compounds. These complexes, which feature an internal zinc-zinc bond, are particularly sensitive to oxygen and moisture, requiring strictly controlled synthesis conditions. The formation mechanism of such complexes is often not well understood. While there are examples of aluminum or magnesium bimetallic compounds being used to reduce alkynes into 1,2-vinylbimetallics—resulting in the formation of tetrasubstituted alkenes in a one-pot process—no examples of 1,2-vinyldizinc formation using this method have been reported. However, the broad range of transformations involving C-Zn bonds, known for their high functional group tolerance due to their low ionic character, suggests that zinc bimetallic compounds could offer promising avenues in synthesis. This project aims to understand the nature of a biradical zinc bimetallic complex and explore its reactivity, particularly in the reduction of triple bonds to form 1,2-vinyldizinc compounds. The work was conducted through a synergy between experimental and computational chemistry. This interdisciplinary approach enabled a deeper understanding of the mechanisms, electronic influences of the involved species, and the origin of the experimentally obtained products, which often arise from intermediates that are difficult to characterize. The first section of this thesis examines the synthesis and reactivity of this complex, with a proposed mechanism supported by DFT calculations. Next, a method for the dizincation of alkynes is presented, allowing for the production of 1,2-vinyldizinc compounds. Finally, an alternative synthesis method is proposed in the last section

博士
國立清華大學
化學系
100
The reaction between diamido ligand, Li4[Me2Si(NDipp)2]2 (Dipp = 2,6-iPrC6H3), and MCl2 (M = Mn and Cd) yields Mn2{??-Me2Si(NDipp)2}2 (3) and Cd2{????-Me2Si(NDipp)2}2 (4). After stepwise reduction of Complex 3, we could separate [(THF)2K⊂18-crown-6][Mn2{????-Me2Si(NDipp)2]2 (18-crwon-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane; THF = tetrahydrofuran ([(THF)2K⊂18-crown-6][5]), [K⊂222-crptand]2[Mn2{??-Me2Si(NDipp)2]2 (222-cryptand = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) ([K⊂222-cryptand]2[6]) and [K2⊂6]. Both Complex [K⊂222-cryptand]2[6] and [K2⊂6] possess [Mn22+] core with Mn-Mn single bond. The addition of KH to Complex 4 leads the isolation of tetranuclear cadmium complex, [(THF)2K⊂18-crown-6]2[{??-Me2Si(NDipp)2}Cd{??Me2Si(NDipp)2}Cd]2 ([(THF)2K⊂18-crown-6]2[7]), with Cd-Cd single bond. The isolation of these compounds corroborate the existence of the intermediates anticipated in structural transformations between Zn2{????-Me2Si(NDipp)2}2 (1) and [{??-Me2Si(NDipp)2}Zn-Zn{??-Me2Si(NDipp)2}]2- (2) by theoretical calculations. A series of stable molecules containing unprecedented three-center, two-electron M-A-M bonds (M = Zn, Cd; A = K, Rb) were prepared. Reduction of dinuclear Zn(II) and Cd(II) compounds, [Zn(THF)(????-N2N)]2 (N2N = 2,6-(DippN)2-4-MeC5H4N) (8) and [Cd(????-N2N)]2 (9), by potassium graphite or elemental rubidium with the presence of 18-crown-6 ether afforded thermally stable compounds [K(THF)n(18-crown-6)][(MKM)(N2N)2] (10: M = Zn, n = 0; 11: M = Cd, n = 1) and [Rb(THF)(18-crown-6)][(ZnRbZn)(N2N)2] (12). The A-M bond lengths are surprisingly short (Zn-Kavg = 2.474 Å, Cd-Kavg = 2.606 Å, and Zn-Rbavg = 2.532 Å). The M-Rb-M three-center, two-electron covalent bonding is also supported by the fact that the bridging alkali metals cannot be replaced by other Group 1 metal ions via ion exchange reactions. Complex 10 shows highly reducting potential in view of the reaction between 10 and MgI2. Treatment of pyridyl diamido ligand, Li2[N2N](OEt2), with CrCl3 and subsequently reduced by 2.5 equiv of potassium graphite gives a novel quintuply-bonded dichromium complex, {(OEt2)KCr(??:??-N2N)}2 (26). We also found the arene-philic and substitution effect on the formation of Cr-Cr quintuple bond. In addition, the reaction of NbCl3(DME) and different type of ligands, such as amidinates, pyridyl diamido ligand, and ??dimine ligand, leads to the isolation of (??Cl)3[Li(THF)2(??Cl)2][Nb(??-HC(N-2,6-iPr2C6H3)]2 (30), Cl3Nb(??-o,o’-iPr2C6H3-DAB) (o,o’-iPr2C6H3-DAB = 2,3-dimethyl-1,4-bis-(2,6-iPr2C6H3)-1,4-diaza-1,3-butadiene)) (31), and [ClNb (????-N2N)]2 (32). Complex 30 and 32 have Nb=Nb doble bond. Redution of Complex 31 with zinc powder gives dinioubium complex, [ClNb(??Cl)2Nb(THF)](??-o,o’-iPr2C6H3-DAB)2 (33), with Nb-Nb single bond. However, addition of 0.25 equiv of amidinates ligand to the precursor, reduced by potassium graphite from NbCl3(DME), leads to the isolation of tetranuclear niobium(II) complex, [{(THF)Nb}(??Cl) 2{Nb(THF)Cl}]2[????-HC(N-2,6-iPr2C6H3)2]2 (29). It’s an unprecedented butter-fly conformation. We also present N-N coupling reactions mediated by univalent Zn–Zn and Mn–Mn bonds. Treatment of the Zn–Zn bonded complex K2[{??-Me2Si(NDipp)2}Zn-Zn{??-Me2Si(NDipp)2}]¬¬ (17) with 2 equiv of p-tolylazide or azidotrimethylsilane in presence of 18-crwon-6 ether gives [K(18-crown-6)(THF)]2{[??-Me2Si(NDipp)2]Zn(????-RNN2NR)Zn[??-Me2Si(NDipp)2]} (R = p-tolyl) (19a) with a bridging trans-tetrazene ligand [(p-tolyl)NN2N(p-tolyl)] and [K(18-crown-6)(THF)2]2 {[??-Me2Si(NDipp)2]Zn(??NSiMe3)Zn[??-Me2Si(NDipp)2]} (20), respectively. However, addition of 2 equiv of organic azides RN3 (R = 1-adamantyl, p-tolyl) to the Mn–Mn bonded complex [Mn(Nacnac)]2 (Nacnac = HC[C(Me)N(2,6-iPr2C6H3)]2 (18) also induces N-N coupling to give (????:??-RN6R)[Mn(Nacnac)]2 (20: R = adamantyl; 21: R = p-tolyl). Both 20 and 21 feature essentially the same core with a bridging hexazene ligand (RNN4NR). Interestingly, a trinuclear manganese complex [(Nacnac)Mn(μ-N3)]3 (22), where three manganese atoms are linked together via three bridging azido ligands, is obtained if 18 is treated with 2 equiv of azidotrimethylsilane. Furthermore, the reaction of Silyl-linked bis(amidinate) ligand, [Li(THF)4][Li3{??-??-Me2Si[NC(C6H5)N(2,6-iPr2C6H3)]2}2] and CuI leads to the isolation of Cu4{????-Me2Si[NC(C6H5)N(2,6-iPr2C6H3)]2}2 (34) with the d10-d10 interactions between four copper atoms. Finally, addition of the same ligand to CrCl3 gives [Cl(??Cl)(THF)Cr]2{????-Me2Si[NC(C6H5)N(2,6-iPr2C6H3)]2} (35). [Cl(THF) Cr]2{????-Me2Si[NC(C6H5)N(2,6-iPr2C6H3)]2} (36) is prepared by further reduced by 2 equiv of potassium graphite from complex 35. There is no bonding interactions between two dichormium atoms of Comples 34 and 35. All the synthesized products are characterized by NMR spectroscopy and elemental analysis and their molecular structures are determined by single crystal X-ray crystallography.

Abstract In a general sense, the Reformatsky reaction can be taken as subsuming all enolate formations by oxidative addition of a metal or a low-valent metal salt into a carbon-halogen bond activated by a vicinal carbonyl group, followed by reaction of the enolates thus formed with an appropriate electrophile (Scheme 14.1).1-3 The insertion of metallic zinc into a.-haloesters is the historically first and still most widely used form of this process, to which this chapter is confined. It is the mode of enolate formation that distinguishes the Reformatsky reaction from other fields of metal enolate chemistry.