共查询到20条相似文献,搜索用时 500 毫秒
1.
Wendian Li Tilong Yang Nan Song Ruihao Li Jiao Long Lin He Xumu Zhang Hui Lv 《Chemical science》2022,13(6):1808
A general and highly efficient method for asymmetric sequential hydrogenation of α,β-unsaturated ketones has been developed by using an iridium/f-Ampha complex as the catalyst, furnishing corresponding chiral alcohols with two contiguous stereocenters in high yields with excellent diastereo- and enantioselectivities (up to 99% yield, >20 : 1 dr and >99% ee). Control experiments indicated that the C C and C O bonds of the enones were hydrogenated sequentially, and the final stereoselectivities were determined by the dynamic kinetic resolution of ketones. Moreover, DFT calculations revealed that an outer sphere pathway was involved in both reduction of C C and C O bonds of enones. The synthetic utility of this method was demonstrated by a gram-scale reaction with very low catalyst loading (S/C = 20 000) and a concise synthetic route to key chiral intermediates of the antiasthmatic drug CP-199,330.A general and efficient method for asymmetric sequential hydrogenation of α,β-unsaturated ketones has been developed. A dynamic kinetic resolution and an outer sphere pathway were involved in this transformation. 相似文献
2.
Isuri U. Jayasooriya Abolghasem Bakhoda Rachel Palmer Kristi Ng Nour L. Khachemoune Jeffery A. Bertke Timothy H. Warren 《Chemical science》2021,12(47):15733
Commercially available benzophenone imine (HN CPh2) reacts with β-diketiminato copper(ii) tert-butoxide complexes [CuII]–OtBu to form isolable copper(ii) ketimides [CuII]–N CPh2. Structural characterization of the three coordinate copper(ii) ketimide [Me3NN]Cu–N CPh2 reveals a short Cu-Nketimide distance (1.700(2) Å) with a nearly linear Cu–N–C linkage (178.9(2)°). Copper(ii) ketimides [CuII]–N CPh2 readily capture alkyl radicals R˙ (PhCH(˙)Me and Cy˙) to form the corresponding R–N CPh2 products in a process that competes with N–N coupling of copper(ii) ketimides [CuII]–N CPh2 to form the azine Ph2C N–N CPh2. Copper(ii) ketimides [CuII]–N CAr2 serve as intermediates in catalytic sp3 C–H amination of substrates R–H with ketimines HN CAr2 and tBuOOtBu as oxidant to form N-alkyl ketimines R–N CAr2. This protocol enables the use of unactivated sp3 C–H bonds to give R–N CAr2 products easily converted to primary amines R–NH2via simple acidic deprotection.Commercially available benzophenone imine (HN CPh2) reacts with β-diketiminato copper(ii) tert-butoxide complexes [CuII]–OtBu to form isolable copper(ii) ketimides [CuII]–N CPh2 that serve as intermediates in catalytic sp3 C−H amination via radical relay. 相似文献
3.
The large amount of waste derived from coupling reagents is a serious drawback of peptide synthesis from a green chemistry viewpoint. To overcome this issue, we report an electrochemical peptide synthesis in a biphasic system. Anodic oxidation of triphenylphosphine (Ph3P) generates a phosphine radical cation, which serves as the coupling reagent to activate carboxylic acids, and produces triphenylphosphine oxide (Ph3P O) as a stoichiometric byproduct. In combination with a soluble tag-assisted liquid-phase peptide synthesis, the selective recovery of desired peptides and Ph3P O was achieved. Given that methods to reduce Ph3P O to Ph3P have been reported, Ph3P O could be a recyclable byproduct unlike byproducts from typical coupling reagents. Moreover, a commercial peptide active pharmaceutical ingredient (API), leuprorelin, was successfully synthesized without the use of traditional coupling reagents.The large amount of waste derived from coupling reagents is a serious drawback of peptide synthesis from a green chemistry viewpoint. 相似文献
4.
Xia Zhong Jiuqi Tan Jianglin Qiao Yuqiao Zhou Cidan Lv Zhishan Su Shunxi Dong Xiaoming Feng 《Chemical science》2021,12(29):9991
Efficient asymmetric synthesis of a collection of small molecules with structural diversity is highly important to drug discovery. Herein, three distinct types of chiral cyclic compounds were accessible by enantioselective catalysis and sequential transformations. Highly regio- and enantioselective [2+2] cycloaddition of (E)-alkenyloxindoles with the internal C C bond of N-allenamides was achieved with N,N′-dioxide/Ni(OTf)2 as the catalyst. Various optically active spirocyclobutyl oxindole derivatives were obtained under mild conditions. Moreover, formal [4+2] cycloaddition products occurring at the terminal C C bond of N-allenamides, dihydropyran-fused indoles, were afforded by a stereospecific sequential transformation with the assistance of a catalytic amount of Cu(OTf)2. In contrast, performing the conversion under air led to the formation of γ-lactones via the water-involved deprotection and rearrangement process. Experimental studies and DFT calculations were performed to probe the reaction mechanism.Three distinct types of chiral cyclic compounds were accessible by catalytic asymmetric synthesis of spirocyclobutyl oxindoles via [2+2] cycloaddition and sequential transformations. 相似文献
5.
Greggory T. Kent Xiaojuan Yu Guang Wu Jochen Autschbach Trevor W. Hayton 《Chemical science》2021,12(43):14383
The reaction of [AnCl(NR2)3] (An = U, Th, R = SiMe3) with in situ generated lithium-3,3-diphenylcyclopropene results in the formation of [{(NR2)3}An(CH C CPh2)] (An = U, 1; Th, 2) in good yields after work-up. Deprotonation of 1 or 2 with LDA/2.2.2-cryptand results in formation of the anionic allenylidenes, [Li(2.2.2-cryptand)][{(NR2)3}An(CCCPh2)] (An = U, 3; Th, 4). The calculated 13C NMR chemical shifts of the Cα, Cβ, and Cγ nuclei in 2 and 4 nicely reproduce the experimentally assigned order, and exhibit a characteristic spin–orbit induced downfield shift at Cα due to involvement of the 5f orbitals in the Th–C bonds. Additionally, the bonding analyses for 3 and 4 show a delocalized multi-center character of the ligand π orbitals involving the actinide. While a single–triple–single-bond resonance structure (e.g., An–C C–CPh2) predominates, the An C C CPh2 resonance form contributes, as well, more so for 3 than for 4.The actinide allenylidenes [{(NR2)3}An(CCCPh2)]− (An = U, Th, R = SiMe3) feature significant ligand-to-metal donation bonding and partial An C double bond character. 相似文献
6.
Satyam Jena Jusaina Eyyathiyil Santosh Kumar Behera Maho Kitahara Yoshitane Imai Pakkirisamy Thilagar 《Chemical science》2022,13(20):5893
We report the design and synthesis of a series of room temperature phosphorescent phosphoramides TPTZPO, TPTZPS, and TPTZPSe with a donor (phenothiazine)–acceptor (P = X, X = O, S, and Se) architecture. All the compounds show structureless fluorescence with a nanosecond lifetime in dilute solutions. However, these compounds show dual fluorescence and room temperature phosphorescence (RTP) in the solid state. Both the intensity and energy of luminescence depend on the heteroatom attached to the phosphorus center. For example, compound TPTZPO with the P O unit exhibits fluorescence at a higher energy region than TPTZPS and TPTZPSe with the P S and P Se groups, respectively. Crystalline samples of TPTZPO, TPTZPS, and TPTZPSe show stronger RTP than the amorphous powder of respective compounds. Detailed steady-state, time-resolved photoluminescence and computational studies established that the 3n–π* state dominated by the phenothiazine moiety is the emissive state of these compounds. Although TPTZPS and TPTZPSe crystallized in the chiral space group, only TPTZPSe showed chiroptical properties in the solid state. The luminescence dissymmetry factor (glum) value of TPTZPS is small and below the detection limit, and a CPL spectrum could not be observed for this compound.The crystallization-induced room temperature phosphorescence and CPL of phosphoramides are reported. The nonplanar phenothiazine and the tetrahedral geometry of phosphorus curbed the non-radiative deactivation pathways, which led to improved RTP. 相似文献
7.
Isabelle Georg Markus Bursch Burkhard Endeward Michael Bolte Hans-Wolfram Lerner Stefan Grimme Matthias Wagner 《Chemical science》2021,12(37):12419
Treatment of hexachloropropene (Cl2C C(Cl)–CCl3) with Si2Cl6 and [nBu4N]Cl (1 : 4 : 1) in CH2Cl2 results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [nBu4N][Cl2C C(SiCl3)–C(SiCl3)2] ([nBu4N][1]). Tetrachloroallene Cl2C C CCl2 was identified as the first intermediate of the reaction cascade. In the solid state, [1]− adopts approximate Cs symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [1]− of C C–Si//Si–C–Si = 78.3(1)°. One-electron oxidation of [nBu4N][1] with SbCl5 furnishes the distillable blue radical 1˙. The neutral propene Cl2C C(SiCl3)–C(SiCl3)2H (2) was obtained by (i) protonation of [1]− with HOSO2CF3 (HOTf) or (ii) H-atom transfer to 1˙ from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl3 substituents in 2 to Si(OMe)3 (2OMe) or SiMe3 (2Me) substituents was achieved by using MeOH/NMe2Et or MeMgBr in CH2Cl2 or THF, respectively. Upon addition of 2 equiv. of tBuLi, 2Me underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe3 migration and Cl/Li exchange to afford the allenyl lithium compound Me3Si(Li)C C C(SiMe3)2 (Li[4]), which is an efficient building block for the introduction of Me, SiMe3, or SnMe3 (5) groups. The trisilylated, monochlorinated allene Cl3Si(Cl)C C C(SiCl3)2 (6), was obtained from [nBu4N][1] through Cl−-ion abstraction with AlCl3 and rearrangement in CH2Cl2 (1˙ forms as a minor side product, likely because the system AlCl3/CH2Cl2 can also act as a one-electron oxidant).Treatment of hexachloropropene (Cl2C C(Cl)–CCl3) with Si2Cl6 and [nBu4N]Cl (1 : 4 : 1) in CH2Cl2 results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [nBu4N][Cl2C C(SiCl3)–C(SiCl3)2] ([nBu4N][1]). 相似文献
8.
Christian Cerezo-Navarrete Arthur H. G. David Adrin García-Zaragoza Marcos D. Codesal Pascual Oa-Burgos Iker del Rosal Romuald Poteau Araceli G. Campaa Luis M. Martínez-Prieto 《Chemical science》2022,13(44):13046
The search for new ligands capable of modifying the metal nanoparticle (MNP) catalytic behavior is of increasing interest. Herein we present the first example of RuNPs stabilized with non-planar heptagon-containing saddle-shaped nanographenes (Ru@1 and Ru@2). The resemblance to graphene-supported MNPs makes these non-planar nanographene-stabilized RuNPs very attractive systems to further investigate graphene–metal interactions. A combined theoretical/experimental study allowed us to explore the coordination modes and dynamics of these nanographenes at the Ru surface. The curvature of these saddle-shaped nanographenes makes them efficient MNP stabilizers. The resulting RuNPs were found to be highly active catalysts for the hydrogenation of aromatics, including platform molecules derived from biomass (i.e. HMF) or liquid organic hydrogen carriers (i.e. N-indole). A significant ligand effect was observed since a minor modification on the hept-HBC structure (C CH2 instead of C O) was reflected in a substantial increase in the MNP activity. Finally, the stability of these canopied RuNPs was investigated by multiple addition experiments, proving to be stable catalysts for at least 96 h.Ruthenium nanoparticles stabilized with non-planar polycyclic aromatic hydrocarbons (PAHs) are active catalysts in the hydrogenation of aromatic substrates under mild conditions. 相似文献
9.
Jing Xiang Min Peng Yi Pan Li-Juan Luo Shun-Cheung Cheng Xin-Xin Jin Shek-Man Yiu Wai-Lun Man Chi-Chiu Ko Kai-Chung Lau Tai-Chu Lau 《Chemical science》2021,12(43):14494
N-Dealkylation of amines by metal oxo intermediates (M O) is related to drug detoxification and DNA repair in biological systems. In this study, we report the first example of N-dealkylation of various alkylamines by a luminescent osmium(vi) nitrido complex induced by visible light.The visible light-induced N-dealkylation of various alkylamines by a luminescent osmium(vi) nitrido complex has been investigated. We provide definitive evidence that these reactions occur via an ET/PT mechanism.High-valent metal oxo (M O) species play key roles in many chemical and biological oxidation processes.1 They are versatile oxidants that can perform oxidation of substrates via a variety of pathways, including electron transfer, H-atom transfer, hydride transfer and O-atom transfer. In principle, high-valent metal nitrido (M N) complexes should also function as versatile oxidants similar to M O. Although there have been significant advances in M N oxidation chemistry in recent years, the reactivity of M N is still rather limited in scope compared to M O.2 M N is intrinsically less oxidizing than M O due to the stronger electron donating property of the N3− ligand than the O2− ligand. Attempts to increase the oxidizing power of M N by increasing the oxidation state or by using less electron-donating ancillary ligands often led to decomposition of the complexes, mainly due to facile coupling of the nitrido ligands to yield N2 (2M N → 2M + N2).3 One appealing strategy to enhance the reactivity of M N is photochemical excitation. We have recently designed an osmium(vi) nitrido complex [OsVI(N)(L)(CN)3]− (NO2-OsN, HL = 2-(2-hydroxy-5-nitrophenyl)benzoxazole) that is strongly luminescent in the solid state and in fluid solutions.4 It readily absorbs visible light to generate a long-lived and highly oxidizing excited state with a redox potential of ca. 1.4 V. The excited state of this complex also possesses [Os N˙] nitridyl characteristics that enable it to readily abstract H-atoms from inert organic substrates.5We report herein the visible-light induced N-dealkylation of various alkylamines by NO2-OsN. Iron oxo species have been used by heme and nonheme enzymes to carry out N-dealkylation reactions of tertiary amines, which are important processes involved in detoxification and DNA repair.6 A number of synthetic iron(iv) oxo complexes are also able to carry out such N-dealkylation reactions.7 Mechanistic studies using cytochrome P450 and synthetic iron oxo complexes indicate that there are two possible mechanisms for N-dealkylation of amines, namely hydrogen-atom transfer (HAT) and electron transfer–proton transfer (ET–PT) (Fig. 1).8 In this work we report the first example of N-dealkylation of various aromatic as well as aliphatic tertiary amines by a nitrido complex upon visible light excitation. We also provide unambiguous evidence that these reactions occur via an ET/PT mechanism.Open in a separate windowFig. 1Two possible mechanisms for N-demethylation of tertiary amines by cytochrome P450 and synthetic Fe(iv) oxo complexes (P = porphyrin). 相似文献
10.
1,3-Phosphaazaallenes are heteroallenes of the type RP C NR′ and little is known about their reactivity. In here we describe the straightforward synthesis of ArPCNR (Ar = Mes*, 2,4,6-tBu-C6H2; MesTer, 2.6-(2,4,6-Me3C6H2)–C6H3; DipTer, 2.6-(2,6-iPr2C6H2)–C6H3; R = tBu; Xyl, 2,6-Me2C6H3) starting from phospha-Wittig reagents ArPPMe3 and isonitriles CNR. It is further shown that ArPCNtBu are thermally labile with respect to the loss of iso-butene and it is shown that the cyanophosphines ArP(H)CN are synthetically feasible and form the corresponding phosphanitrilium borates with B(C6F5)3, whereas deprotonation of DipTerP(H)CN was shown to give an isolable cyanidophosphide. Lastly, the reactivity of ArPCNR towards Pier''s borane was investigated, showing hydroboration of the C N bond in Mes*PCNtBu to give a hetero-butadiene, while with DipTerPCNXyl the formation of the Lewis acid–base adduct with a B–P linkage was observed.The combination of phospha-Wittig reagents with isonitriles affords 1,3-phosphaazaallenes and their diverse reactivity has been studied in detail. 相似文献
11.
12.
The discovery of new reactions enables chemists to attain a better understanding of fundamental chemical reactivity and push the boundaries of organic synthesis. Our understanding and manipulation of high-energy states such as reactive conformations, intermediates, and transition structures contribute to this field. Herein we interrogate epoxide ring-closure by inserting the C N functionality into a well-known precursor to nucleophilic epoxide ring-closure. The synthesis of tetrasubstituted, nitrile-tethered epoxides takes place via activation of iminologous diols followed by fragmentation. Mechanistic study reveals the transformation to be stereospecific, which is consistent with the concerted nature of the epoxide ring-closure.The discovery of new reactions enables chemists to attain a better understanding of fundamental chemical reactivity and push the boundaries of organic synthesis. 相似文献
13.
Gang Wang Wenqi Li Tianxiang Liu Yonghong Zhang Bin Wang Fei Xue Weiwei Jin Caiyan Ma Yu Xia Chenjiang Liu 《Chemical science》2022,13(39):11594
A palladium-catalyzed dearomative reaction of indoles has been developed through a domino Heck/gem-difluorovinylation sequence. By taking advantage of a difluorocarbene precursor (ClCF2COONa), the palladium difluorocarbene ([Pd] CF2) species was formed smoothly. Then, a migratory insertion/β-H elimination process enabled access to polycyclic indolines containing 1,1-difluoroethylene units in acceptable yields with a broad substrate scope, which also showed dearomative gem-difluorovinylation for the first time. Remarkably, the superb diversified transformations allowed the product to install various functional groups.Dearomative gem-difluorovinylation was reported for the first time and provided a new way to construct complex organofluorine compounds rapidly. 相似文献
14.
Bing-Yu Li Lauren Voets Ruben Van Lommel Fien Hoppenbrouwers Mercedes Alonso Steven H. L. Verhelst Wim M. De Borggraeve Joachim Demaerel 《Chemical science》2022,13(8):2270
Sulfur(vi) Fluoride Exchange (SuFEx) chemistry has emerged as a next-generation click reaction, designed to assemble functional molecules quickly and modularly. Here, we report the ex situ generation of trifluoromethanesulfonyl fluoride (CF3SO2F) gas in a two chamber system, and its use as a new SuFEx handle to efficiently synthesize triflates and triflamides. This broadly tolerated protocol lends itself to peptide modification or to telescoping into coupling reactions. Moreover, redesigning the SVI–F connector with a S O → S NR replacement furnished the analogous triflimidoyl fluorides as SuFEx electrophiles, which were engaged in the synthesis of rarely reported triflimidate esters. Notably, experiments showed H2O to be the key towards achieving chemoselective trifluoromethanesulfonation of phenols vs. amine groups, a phenomenon best explained—using ab initio metadynamics simulations—by a hydrogen bonded termolecular transition state for the CF3SO2F triflylation of amines.Triflyl fluoride gas (CF3SO2F) and its aza analogues are reported as new SuFEx activators. These SVI–F reagents react efficiently with a variety of nucleophiles, yet the presence of water grants complete chemoselectivity to phenols. 相似文献
15.
The construction of chiral quaternary carbon stereocenters has been a long-standing challenge in organic chemistry. Particularly, α-quaternary amino acids that are of high importance in biochemistry still lack a straightforward synthetic method. We here reported a hydroformylation approach to access chiral quaternary stereogenic centers, which has been a long-standing challenge in transition metal catalysis. α,β-Unsaturated carboxylic acid derivatives undergo hydroformylation with a rhodium catalyst to generate an α-quaternary stereocenter under mild conditions. By using this method, a variety of chiral α-quaternary amino acids could be synthesized with satisfactory enantioselectivity. In-depth investigation revealed that the regioselectivity is dramatically influenced by the electronic properties of the substituents attached to the target C C bond. By applying NMR and DFT analyses, the chiral environment of a rhodium/Yanphos complex was depicted, based on which a substrate-catalyst interaction model was proposed.A rhodium-catalyzed asymmetric hydroformylation reaction was reported to construct chiral α-quaternary amino acid derivatives. High chemo-, regio- and enantioselectivity were realized in one step. 相似文献
16.
Liane M. Moreau Ekaterina Lapsheva Jorge I. Amaro-Estrada Michael R. Gau Patrick J. Carroll Brian C. Manor Yusen Qiao Qiaomu Yang Wayne W. Lukens Dimosthenis Sokaras Eric J. Schelter Laurent Maron Corwin H. Booth 《Chemical science》2022,13(6):1759
This study presents the role of 5d orbitals in the bonding, and electronic and magnetic structure of Ce imido and oxo complexes synthesized with a tris(hydroxylaminato) [((2-tBuNO)C6H4CH2)3N]3− (TriNOx3−) ligand framework, including the reported synthesis and characterization of two new alkali metal-capped Ce oxo species. X-ray spectroscopy measurements reveal that the imido and oxo materials exhibit an intermediate valent ground state of the Ce, displaying hallmark features in the Ce LIII absorption of partial f-orbital occupancy that are relatively constant for all measured compounds. These spectra feature a double peak consistent with other formal Ce(iv) compounds. Magnetic susceptibility measurements reveal enhanced levels of temperature-independent paramagnetism (TIP). In contrast to systems with direct bonding to an aromatic ligand, no clear correlation between the level of TIP and f-orbital occupancy is observed. CASSCF calculations defy a conventional van Vleck explanation of the TIP, indicating a single-reference ground state with no low-lying triplet excited state, despite accurately predicting the measured values of f-orbital occupancy. The calculations do, however, predict strong 4f/5d hybridization. In fact, within these complexes, despite having similar f-orbital occupancies and therefore levels of 4f/5d hybridization, the d-state distributions vary depending on the bonding motif (Ce O vs. Ce N) of the complex, and can also be fine-tuned based on varying alkali metal cation capping species. This system therefore provides a platform for understanding the characteristic nature of Ce multiple bonds and potential impact that the associated d-state distribution may have on resulting reactivity.Ce(iv) complexes with multiple bonds display similar f0 fractions, but different f/d hybridization, 5d-orbital energies, and TIP levels. 相似文献
17.
Miao Yang Fenglei Qiu El-Sayed M. El-Sayed Wenjing Wang Shunfu Du Kongzhao Su Daqiang Yuan 《Chemical science》2021,12(40):13307
Although porous organic cages (POCs), particularly imine-linked (C N) ones, have advanced significantly over the last few decades, the reversible nature of imine linkages makes them prone to hydrolysis and structural collapse, severely limiting their applications under moist or water conditions. Herein, seven water-stable hydrazone-linked (C N–N) POCs are prepared through a simple coupling of the same supramolecular tetraformylresorcin[4]arene cavitand with different dihydrazide linkers. Their structures are all determined by single-crystal X-ray crystallography, demonstrating rich structural diversity from the [2 + 4] lantern, [3 + 6] triangular prism, and unprecedented [4 + 8] square prism to the extra-large [6 + 12] octahedron. In addition, they respectively exhibit tunable window diameters and cavity volumes ranging from about 5.4 to 11.1 nm and 580 to 6800 Å3. Moreover, their application in the water environment for pollutant removal was explored, indicating that they can effectively eliminate various types of contaminants from water, including radionuclide waste, toxic heavy metal ions, and organic micropollutants. This work demonstrates a convenient method for rationally constructing versatile robust POCs and presents their great application potentialities in water medium.A convenient method for constructing water-stable hydrazone-linked porous organic cages (POCs) with tunable structures has been reported, and such POCs can be used as robust adsorbents for effective removal of various pollutants from water. 相似文献
18.
Debabrata Dhara Arumugam Jayaraman Marcel Hrterich Rian D. Dewhurst Holger Braunschweig 《Chemical science》2022,13(19):5631
While a stable base-free arylalumylene bearing a sterically encumbered terphenyl substituent has been reported previously, we herein report that our attempts to form a base-stabilised arylalumylene bearing a relatively small terphenyl substituent and an N-heterocyclic carbene base led instead to a “masked” dialumene (LRAl AlRL), self-stabilised by one peripheral aromatic group. Intriguingly, examining the behavior of this species or its transient dialumene formed from reducing the diiodoarylalane in aromatic solvents under different conditions reveals that they both decouple into the desired base-stabilised arylalumylene. This transient acyclic, dicoordinate alumylene is highly reactive, deconstructing benzene and toluene to furnish dialuminium derivatives of pentalene, providing the first example of a neutral AlI compound able to deconstruct these less reactive arenes. Computational insights were also gained on the dialumene dissociation and on the mechanism of arene deconstruction by alumylene.Attempts to form a base-stabilised arylalumylene by reducing an NHC-coordinated diiodoterphenylalane led to a masked dialumene. Reactivity studies showed it decouples to initially aimed arylalumylene, which easily deconstructs less reactive arenes. 相似文献
19.
The first nickel bis-boryl complexes cis-[Ni(iPr2ImMe)2(Bcat)2], cis-[Ni(iPr2ImMe)2(Bpin)2] and cis-[Ni(iPr2ImMe)2(Beg)2] are reported, which were prepared via the reaction of a source of [Ni(iPr2ImMe)2] with the diboron(4) compounds B2cat2, B2pin2 and B2eg2 (iPr2ImMe = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; B2cat2 = bis(catecholato)diboron; B2pin2 = bis(pinacolato)diboron; B2eg2 = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB2 moiety in these square planar complexes, reminiscent of the bonding situation of “non-classical” H2 complexes. [Ni(iPr2ImMe)2] also efficiently catalyzes the diboration of alkynes using B2cat2 as the boron source under mild conditions. In contrast to the known platinum-catalyzed diboration, the nickel system follows a different mechanistic pathway, which not only provides the 1,2-borylation product in excellent yields, but also provides an efficient approach to other products such as C–C coupled borylation products or rare tetra-borylated compounds. The mechanism of the nickel-catalyzed alkyne borylation was examined by means of stoichiometric reactions and DFT calculations. Oxidative addition of the diboron reagent to nickel is not dominant; the first steps of the catalytic cycle are coordination of the alkyne to [Ni(iPr2ImMe)2] and subsequent borylation at the coordinated and, thus, activated alkyne to yield complexes of the type [Ni(NHC)2(η2-cis-(Bcat)(R)C C(R)(Bcat))], exemplified by the isolation and structural characterization of [Ni(iPr2ImMe)2(η2-cis-(Bcat)(Me)C C(Me)(Bcat))] and [Ni(iPr2ImMe)2(η2-cis-(Bcat)(H7C3)C C(C3H7)(Bcat))].Nickel bis-boryl complexes cis-[Ni(NHC)2(Bcat)2], cis-[Ni(NHC)2(Bpin)2] and cis-[Ni(NHC)2(Beg)2] are presented and the nickel-catalyzed alkyne borylation is reported. 相似文献
20.
Po-Chun Yang Kuan-Po Yu Chi-Tien Hsieh Junjie Zou Chia-Te Fang Hsin-Kuan Liu Chih-Wen Pao Liang Deng Mu-Jeng Cheng Chun-Yi Lin 《Chemical science》2022,13(33):9637
High-spin, late transition metal imido complexes have attracted significant interest due to their group transfer reactivity and catalytic C–H activation of organic substrates. Reaction of a new two-coordinate iron complex, Fe{N(tBu)Dipp}2 (1, Dipp = 2,6-diisopropylphenyl), with mesitylazide (MesN3) afforded a three-coordinate Fe–imidyl complex, Fe{N(tBu)Dipp}2( NMes) (2). X-ray crystallographic characterization of single crystals of 2 showed a long Fe–N distance of 1.761(1) Å. Combined magnetic and spectroscopic (Mössbauer and X-ray absorption near edge structure spectroscopy, XANES) characterization of 2 suggests that it has an S = 2 ground state comprising an S = 5/2 Fe(iii) center antiferromagnetically coupled to an S = 1/2 imidyl ligand. Reaction of 1 and 1-azidoadamantane (AdN3) generated a putative, transient Fe{N(tBu)Dipp}2( NAd) (3′) complex that yielded an intramolecular C–H amination product, Fe{N(tBu)Dipp}{κ2-N,N′-_N(CMe2CH2̲NHAd)Dipp} (3). Quantum mechanical calculations further confirmed the spectroscopic assignment of 2 and 3′, as well as the differences in their stability and reactivity. Importantly, imidyl radical delocalization onto the mesityl ring significantly increased the stability of 2 and reduced its reactivity toward potential hydrogen atom transfer (HAT) reagents. In contrast, quantum mechanical calculations of 3′ revealed that the radical was solely localized on the imidyl N, leading to a high reactivity toward the proximal C–H bond of the N(tBu)Dipp− ligand.A stable three-coordinate Fe imido radical (i.e. imidyl) complex can be stabilized via N radical delocalization onto the aryl imido substituent. 相似文献