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1.
The synthesis of the first four-membered N-heterocyclic carbene is described. Depending on the substituents on the nitrogen atoms, it is possible to characterize at room temperature the carbene dimer or the free carbene. Crystallographic analyses are provided for these carbene species. 相似文献
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Pyrimidinium beta?nes (1), readily accessible via a straightforward modular synthesis from a formamidine and a monosubstituted malonic acid, are readily deprotonated by nBuLi (or KHMDS) to give the stable carbene species [2]Li+ (abbreviated as maloNHC). The latter represents the archetype of a subgroup of N-heterocyclic carbenes incorporating a malonate as remote anionic functional group within their heterocyclic backbone. While playing the dual role of monodentate 2 e- L type donor and noncoordinating charge carrier X, such ligands are seen to provide a rational route to zwitterionic complexes, as illustrated here by three examples (Rh, Fe, Ag). In particular, the reaction of [2]Li+ with [RhCl(1,5-COD)]2 produces the neutral 14 e- complex Rh(maloNHC)(COD) (3) in which coordinative unsaturation at the metal is relieved in the solid state by an uncommon labile bonding interaction between the Cipso of one of the mesityl arms and the Rh center. 相似文献
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A new N-heterocyclic carbene (NHC) containing a fused bithiophene backbone has been synthesized along with its silver(I) and BPh(3) complexes. The donor strength of this unique NHC has been determined from the IR stretching frequencies of the isolated NHC-Rh(CO)(2)Cl complex. The photophysical properties of all of the novel compounds have been investigated and are presented. 相似文献
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Olefin metathesis catalyst: stabilization effect of backbone substitutions of N-heterocyclic carbene
Ruthenium olefin metathesis catalysts bearing an N-phenyl-substituted N-heterocyclic carbene (NHC) ligand that are resistant to decomposition through C-H activation have been prepared and tested in ring closing metathesis (RCM), cross metathesis (CM), and ROMP reactions. The N, N'-diphenyl-substituted NHC complex proved to be one of the most efficient catalysts in RCM to form tetrasubstituted olefins. 相似文献
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Frey GD Song M Bourg JB Donnadieu B Soleilhavoup M Bertrand G 《Chemical communications (Cambridge, England)》2008,(39):4711-4713
Conjugate acids of cyclic (amino)(phosphino)carbenes (P-NHCs) have been prepared, and several different processes have been observed during their deprotonation, which include the formation of a metastable P-NHC, an azomethine ylide, and a bicyclic phosphirane. 相似文献
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N-Heterocyclic carbenes (NHCs) can bind as two-electron sigma-donor ligands to lanthanide and actinide metal cations. In this review we summarise how the incorporation of an anionic group (alkoxide or amido), to form heterobidentate NHC ligands, allows the synthesis of a range of f-block NHC adducts. The tethering group also allows the lability of the NHC group, and its subsequent reactivity, to be studied. We include a brief survey of the known, structurally characterised f-element-NHC bond distances, and a range of substrates that react to displace the metal-bound NHC group. 相似文献
9.
Friederike Tewes 《Journal of organometallic chemistry》2007,692(21):4593-4602
Novel carbohydrate bearing imidazolium salts have been synthesized and used for the in situ generation of the corresponding N-heterocyclic carbenes. These compounds were successfully used as catalysts of the conjugate umpolung of cinnamaldehyde to form γ-butyrolactones. In addition, silver and palladium complexes of these N-heterocyclic carbenes were synthesized and structurally characterized. 相似文献
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The alkylation of a chelating bis(carbene) complex of CrCl(2) yields an unusual bimetallic complex featuring a short Cr-Cr distance, novel ligand coordination, and CH(3) ligand exchange. 相似文献
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Nitron: a stable N-heterocyclic carbene that has been commercially available for more than a century
Färber C Leibold M Bruhn C Maurer M Siemeling U 《Chemical communications (Cambridge, England)》2012,48(2):227-229
The analytical reagent Nitron is a mesoionic compound whose structure consists of a cationic triazolium unit with an anionic PhN substituent. We provide clear evidence for the existence of a singlet diaminocarbene tautomer whose structure is composed of a 1,2,4-triazol-5-ylidene unit bearing an NHPh substituent. 相似文献
12.
Milosevic S Brenner E Ritleng V Chetcuti MJ 《Dalton transactions (Cambridge, England : 2003)》2008,(15):1973-1975
The first examples of mixed metal trinuclear clusters carrying N-heterocyclic carbene (NHC) ligands were isolated from reactions of the complexes [Ni(NHC)ClCp] [NHC = bis-(2,6-diisopropylphenyl)- or bis-(2,4,6-trimethylphenyl)-imidazol-2-ylidene] with [Mo(CO)(3)Cp](-); the unsaturated 46-electron clusters have triangular MoNi(2) cores and the reaction pathway activates usually inert Ni-Cp and Ni-NHC bonds. 相似文献
13.
Tornatzky J Kannenberg A Blechert S 《Dalton transactions (Cambridge, England : 2003)》2012,41(27):8215-8225
The importance of unsymmetrical N-heterocyclic carbenes (uNHCs) as ligands in metal-catalyzed reactions is undeniable. While uNHCs show similar properties as compared with symmetrical NHCs, dissymmetrization allows for further fine-tuning. The introduction of chelatization, hemilability, bifunctionality, shielding effects, and chirality-transfer influences the catalyst's stability, reactivity, and selectivity, thus offering access to tailor-made systems including mono- and multidentate uNHC ligands. Based on selected examples, the structure-reactivity relationship of uNHCs employed in metal catalysts is presented. The focus is on catalytically active complexes, which either offer access to new applications or lead to significantly improved results in metal-catalyzed reactions. 相似文献
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While organocatalyzed domino reactions or "organocascade catalysis" developed into an important tool in synthetic chemistry during the past decade, the utility of N-heterocyclic carbenes (NHCs) as catalysts in domino reactions has only received growing attention in the past three years. Taking into account the unique activation modes of the substrates by NHC catalysts, it is often difficult to distinguish between a single chemical transformation and a sequential one-pot transformation. Therefore, herein we present a critical consideration of domino, cascade, and tandem catalysis in the case of NHC catalysts and highlight recent publications in this area. 相似文献
15.
Abernethy CD Codd GM Spicer MD Taylor MK 《Journal of the American Chemical Society》2003,125(5):1128-1129
Reaction of 1,3-dimesitylimidazol-2-ylidene and trichloro-oxo-vanadium(V) yields an air stable 1:1 adduct, which demonstrates the utility of N-heterocyclic carbenes to stabilize metal complexes in high oxidation states. The molecular structure of this compound reveals that the chloride ligands cis to the carbene are oriented toward the Ccarbene atom. Density functional theory calculations show that a bonding interaction occurs between lone pairs of these chlorides and the formally unoccupied p-orbital of the carbene. Previous studies indicated that this orbital was not involved in the bonding of N-heterocyclic carbenes to transition metals. The observed interaction therefore represents a new bonding mode for these widely used ligands. 相似文献
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The first N-Heterocyclic Carbene (NHC) mediated activation of stable carboxylate esters to generate enolate intermediates is disclosed. The catalytically generated arylacetic ester enolates undergo enantioselective reactions with α,β-unsaturated imines. 相似文献
18.
Arnold PL Edworthy IS Carmichael CD Blake AJ Wilson C 《Dalton transactions (Cambridge, England : 2003)》2008,(28):3739-3746
Magnesium dications bind strongly to a tridentate anionic dicarbene ligand L = [N{CH(2)CH(2)(CNCHCHNMes)}(2)] forming dinuclear and trinuclear Mg complexes with some particularly short Mg-C bonds. Treatment of the proligand H(4)LCl(3) with three equivalents of methyl magnesium chloride or benzyl magnesium chloride affords Mg(3)(HL)Cl(6) in high yield. A suspension of in thf was heated to 80 degrees C for 2 h to afford Mg(2)(L)Cl(3), consistent with the loss of one equivalent of MgCl(2), and the deprotonation of the remaining acidic NH, lost as HCl gas. Treatment of Mg(3)(HL)Cl(6) with one equivalent of KC(8) results in deprotonation of the ligand amine NH to afford Mg(3)(L)Cl(5); treatment with a second equivalent forms the radical anion of the complex, K[Mg(3)(L)Cl(5)], which decomposes upon storage, precluding its structural characterisation. The acidic NH proton of the ligand in Mg(3)(HL)Cl(6) can also be removed by deprotonation with Li{N(SiMe(3))(2)}; additional equivalents of which also exchange the magnesium-bound chlorides for silylamido ligands, affording Mg(2)(L)Cl(2)N' and Mg(2)(L)Cl(N')(2), which have both been characterised by single-crystal X-ray diffraction studies. 相似文献
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The truly hemilabile nature of a novel thioether-functionalized N-heterocyclic carbene ligand is demonstrated in a range of Pd(II) complexes. 相似文献
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[reaction: see text] A catalytically active palladium-complexed tetracyclic N-heterocyclic carbene (NHC) was prepared in three steps from commercially available 1,10-phenanthroline by using a reduction-cyclization-deprotonation sequence. The new carbene framework is a prototype for the development of a series of chiral N-heterocyclic carbenes. 相似文献