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61.
Hui‐Xian Yeong Dr. Hong‐Wei Xi Dr. Yongxin Li Prof. Dr. Kok Hwa Lim Dr. Cheuk‐Wai So 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11786-11790
The synthesis and reactivity of a silyliumylidene cation stabilized by an amidinate ligand and 4‐dimethylaminopyridine (DMAP) are described. The reaction of the amidinate silicon(I) dimer [ L Si:]2 ( 1 ; L =PhC(NtBu)2) with one equivalent of N‐trimethylsilyl‐4‐dimethylaminopyridinium triflate [4‐NMe2C5H4NSiMe3]OTf and two equivalents of DMAP in THF afforded [ L Si(DMAP)]OTf ( 2 ). The ambiphilic character of 2 is demonstrated from its reactivity. Treatment of 2 with 1 in THF afforded the disilylenylsilylium triflate [ L′ 2( L )Si]OTf ( 3 ; L′ = L Si:) with the displacement of DMAP. The reaction of 2 with [K{HB(iBu)3}] and elemental sulfur in THF afforded the silylsilylene [ L SiSi(H){(NtBu)2C(H)Ph}] ( 4 ) and the base‐stabilized silanethionium triflate [ L Si(S)DMAP]OTf ( 5 ), respectively. Compounds 2 , 3 , and 5 have been characterized by X‐ray crystallography. 相似文献
62.
Solvent-free reactions were used for the synthesis of a series of imidazolium-based ionic salts: 3,3′-[pyridine-2,6-diylbis(methylene)]bis(1-R-1H-imidazol-3-ium)chloride; (R = methyl, ethyl, butyl, isobutyl, hexyl, and benzyl). A simple and effective filtration process was used to isolate all the products in high purity and with yields ?93% within a 24 h period. The highly pure ionic compounds which are precursors to N-heterocyclic carbene ligands used in catalysis were fully characterized as gray-white hygroscopic salts. 相似文献
63.
Jung Hyun Park Faizan Raza Su-Ji Jeon Hye-In KimTae Woog Kang DaBin YimJong-Ho Kim 《Tetrahedron letters》2014
Graphene oxide (GO) was functionalized with a N-heterocyclic carbene (NHC) precursor, 3-(3-aminopropyl)-1-methylimidazolium bromide ([APMIm][Br]) for the immobilization of palladium catalyst. The GO-supported NHC precursor (IMGO) formed a stable complex with Pd(OAc)2 (GO–NHC–Pd), which showed excellent catalytic activity and fast reaction kinetics in the aqueous-phase Suzuki reaction of aryl bromides and chlorides at relatively mild conditions (1 h at 50 °C). The GO–NHC–Pd catalyst was reused several times without any loss of its catalytic activity in the Suzuki reaction of aryl bromide. 相似文献
64.
Diversity oriented synthesis of conjugate dienes and alkenylcyclopropanes by the sequential reactions using silyl group-substituted titanium carbene complexes was studied. Dienylsilanes were obtained by the olefination of carbonyl compounds with γ-silylvinylcarbene complexes. Cyclopropanation of 1-alkenes with the vinylcarbene complexes produced (E)-(β-silylvinyl)cyclopropanes with high stereoselectivity. The reaction of β-(trialkylsilyl)carbene complexes with zinc alkoxides of homopropargyl alcohols produced 6-silyl-3,5-hexadien-1-ols with high regio- and stereoselectivity. The (E)-alkenylsilanes thus obtained were transformed into a range of unsaturated compounds by the palladium-catalyzed or copper(I)-promoted cross-coupling with organic halides with retention of configuration. 相似文献
65.
A two‐step reaction scheme leading to singlet carbene species that can be detected under matrix conditions for the reaction of Zr(3F) with either CH3F or CH3CN
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Ana E. Torres Guadalupe Castro Ricardo Pablo‐Pedro Fernando Colmenares 《Journal of computational chemistry》2014,35(11):883-890
The results obtained from CASSCF‐MRMP2 calculations are used to rationalize the singlet complexes detected under matrix‐isolation conditions for the reactions of laser‐ablated Zr(3F) atoms with the CH3F and CH3CN molecules, without invoking intersystem crossings between electronic states with different multiplicities. The reaction Zr(3F) + CH3F evolves to the radical products ZrF· + ·CH3. This radical asymptote is degenerate to that emerging from the singlet channel of the reactants Zr(1D) + CH3F because they both exhibit the same electronic configuration in the metal fragment. Hence, the caged radicals obtained under cryogenic‐matrix conditions can recombine through triplet and singlet paths. The recombination of the radical species along the low‐multiplicity channel produces the inserted structures H3C? Zr? F and H2C?ZrHF experimentally detected. For the Zr(3F) + CH3CN reaction, a similar two‐step reaction scheme involving the radical fragments ZrNC· + ·CH3 explains the presence of the singlet complexes H3C? Zr? NC and H2C?Zr(H)NC revealed in the IR‐matrix spectra upon UV irradiation. © 2014 Wiley Periodicals, Inc. 相似文献
66.
César Ruiz-Zambrana Rajeev K. Dubey Macarena Poyatos Prof. Aurelio Mateo-Alonso Prof. Eduardo Peris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(44):e202201384
A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies. The rhodium complex was tested in the [3+2] cycloaddition of diphenylcyclopropenone and methylphenylacetylene, where it displayed a redox-switchable behavior. The neutral complex showed moderate activity, which was suppressed when the catalyst was reduced. 相似文献
67.
Substituent effects of fused six, and five‐membered aromatic rings are investigated on the stability, aromaticity, charge distribution, nucleophilic (N), and electrophilic (ω) characters of 20 singlet (s) and triplet (t) Hammick carbenes, at B3LYP/AUG‐cc‐pVTZ and M06‐2X/AUG‐cc‐pVTZ. Results display: (a) The higher thermodynamic and kinetic stability is revealed by carbenes situated between two nitrogen and/or two oxygen heteroatoms of two substituted rings, in a “W” arrangement toward the carbenic center; (b) Regardless of the arrangement, the order of thermodynamical and kinetic stabilization for fused rings is pyrrole > furan > thiophene > phosphole. (c) The substituted Hammick carbenes with two fused heterocyclics, in a given arrangement, show more stability than unsubstituted Hammick carbene; (d) While two five‐membered heterocyclic rings stabilize their corresponding substituted carbenes, two benzene rings destabilize Hammick carbene; (e) In all structures, s species emerges as ground state, exhibiting more stability than its t state; (f) The scrutinized s carbenes show higher N and lower ω than their corresponding t states. 相似文献
68.
Metalation of CH2OH-substituted triazolium salts with CoCl2 under basic conditions affords C,O-bidentate chelating carbene Co(III) complexes ( 3a , 3b ), while analogous phenyl-substituted triazolium salts produce monodentate carbene Co(II) complexes ( 3c , 3d ). The distinct substituent-induced properties of the metal centers were demonstrated by electrochemical measurements and catalytic activities in two specific processes. The complexes showed appreciable activity in the reduction of C=O bonds through hydrosilylation, with methoxybenzene-functionalized triazolylidene Co(III) complex 3a achieving a high selectivity towards aldehydes vs. ketones with turnover frequencies (TOFs) up to 200 h−1. The C,O-chelate systems were also active catalysts in the Biginelli process, a one-step three-component reaction for efficient dihydropyrimidinone synthesis. Optimization of reaction conditions provides high activity with complex 3a , reaching TOFs of 800 h−1, the highest activity known for cobalt NHC complexes to date. 相似文献
69.
Julia Beerhues Maren Neubrand Dr. Sebastian Sobottka Dr. Nicolás I. Neuman Hannes Aberhan Shubhadeep Chandra Prof. Dr. Biprajit Sarkar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(21):6557-6568
Carbene-based radicals are important for both fundamental and applied chemical research. Herein, extensive electrochemical investigations of nine different 1,2,3-triazolylidene selenium adducts are reported. It is found that the half-wave potentials of the first reduction of the selones correlate with their calculated LUMO levels and the LUMO levels of the corresponding triazolylidene-based mesoionic carbenes (MICs). Furthermore, unexpected quasi-reversibility of the reduction of two triazoline selones, exhibiting comparable reduction potentials, was discovered. Through UV/Vis/NIR and EPR spectroelectrochemical investigations supported by DFT calculations, the radical anion was unambiguously assigned to be triazoline centered. This electrochemical behavior was transferred to a triazolylidene-type MIC-gold phenyl complex resulting in a MIC-radical coordinated AuI species. Apart from UV-Vis-NIR and EPR spectroelectrochemical investigations of the reduction, the reduced gold-coordinated MIC radical complex was also formed in situ in the bulk through chemical reduction. This is the first report of a monodentate triazolylidene-based MIC ligand that can be reduced to its anion radical in a metal complex. The results presented here provide design principles for stabilizing radicals based on MICs. 相似文献
70.
Noah Schwarz Xiaofei Sun Dr. Ravi Yadav Dr. Ralf Köppe Dr. Thomas Simler Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12857-12865
Divalent lanthanide and alkaline-earth complexes supported by N-heterocyclic carbene (NHC) ligands have been accessed by redox-transmetalation between air-stable NHC-AgI complexes and the corresponding metals. By using the small ligand 1,3-dimethylimidazol-2-ylidene (IMe), two series of isostructural complexes were obtained: the tetra-NHC complexes [LnI2(IMe)4] (Ln=Eu and Sm) and the bis-NHC complexes [MI2(IMe)2(THF)2] (M=Yb, Ca and Sr). In the former, distortions in the NHC coordination were found to originate from intermolecular repulsions in the solid state. Application of the redox-transmetalation strategy with the bulkier 1,3-dimesitylimidazol-2-ylidene (IMes) ligand yielded [SrI2(IMes)(THF)3], while using a similar procedure with Ca metal led to [CaI2(THF)4] and uncoordinated IMes. DFT calculations were performed to rationalise the selective formation of the bis-NHC adduct in [SrI2(IMe)2(THF)2] and the tetra-NHC adduct in [SmI2(IMe)4]. Since the results in the gas phase point towards preferential formation of the tetra-NHC complexes for both metal centres, the differences between both arrangements are a result of solid-state effects such as slightly different packing forces. 相似文献