共查询到20条相似文献,搜索用时 31 毫秒
1.
Arnold PL Casely IJ Turner ZR Carmichael CD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(33):10415-10422
A new and modular route to bidentate ligands that combines an alkoxide with a saturated backbone N-heterocyclic carbene (NHC) is presented. The bi(heterocyclic) compounds are formally the addition product of a saturated NHC and the alcohol group of the N-functionalised arm. Using these compounds, the synthesis and structural characterisation of the first electropositive metal complexes of saturated N-heterocyclic carbenes has been achieved, and examples structurally characterised for the yttrium(III) and the uranyl [UO(2)](2+) cations. 相似文献
2.
WANG Jun-Wen XU Fang-Bo LI Qiang-Shan SONG Hai-Bin LIU Yong-Sheng ZHANG Zheng-Zhi 《有机化学》2004,24(Z1):213
Transition metal complexes of stable N-heterocyclic carbenes have recently gained increasing attention as pre-catalysts for a number of important reactions primarily based on the analogy between N-heterocyclic carbenes and strong ó-donating tertiary phosphines,[1] Although a large number of transition-metal carbene complexes have been reported, very few incorporate chelating carbenes were reported.[2,3] Therefore, we have set out to prepare and study transition-metal compounds with chelating di-N-heterocyclic carbenes, and we now report new dicationic tetra(carbine)nickel(Ⅱ) complexes in this class (Scheme 1). Their structures have been determined by single-crystal X-ray diffraction studies (Figure 1). 相似文献
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4.
Galan BR Gembicky M Dominiak PM Keister JB Diver ST 《Journal of the American Chemical Society》2005,127(45):15702-15703
In the presence of carbon monoxide, ruthenium carbenes give a net insertion/ring expansion (Buchner reaction) into one of the aromatic rings of the N-heterocyclic carbene ligand. In alkene metathesis applications, the N-heterocyclic carbene ligand is both robust and typically inert to reactions with the metal-bound carbene. This unique reaction is completely regioselective. The complexes obtained through ring expansion were fully characterized in the solid state using X-ray crystallography and in solution using NMR and IR spectroscopy. 相似文献
5.
A novel electrochemical procedure for the preparation of metal complexes of N-heterocyclic carbenes using imidazolium salts or corresponding silver-NHC complexes as carbene sources and electrolytes, and metal plates as the sacrificial anodes is described. The procedure is simple and good yielding without the use of expensive or air-sensitive reagents. 相似文献
6.
Hahn FE Le Van D Paas M Fröhlich R 《Dalton transactions (Cambridge, England : 2003)》2006,(6):860-864
A versatile synthesis of unsymmetrically N,N'-substituted saturated carbenes is described. The novel racemic imidazolidin-2-ylidenes rac-5 have been synthesized by reductive desulfurization of the corresponding imidazolidin-2-thiones rac-4. The thiones were prepared in two reaction steps from aldimines and secondary amines. Three different substituents at N1, N3 and C4 of the five-membered N-heterocyclic ring can be introduced by choice of suitable aldimines and secondary amines. The dimerization behaviour (diaminocarbene/enetetramine equilibrium) for the unsymmetrically N,N'-substituted imidazolidin-2-ylidenes has been investigated by NMR spectroscopy. Unsymmetrically N-iPr and N-iBu substituted N-heterocyclic carbenes undergo a slow dimerization, whereas N-tBu substituted derivatives are stable as monomeric carbenes indefinitely. The carbene ligand rac-5d has been coordinated to rhodium(I) to give the square-planar rhodium carbene complex [Cl(cod)Rh(rac-5d)]rac-6d which has been characterized by an X-ray diffraction analysis. 相似文献
7.
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
8.
Kremzow D Seidel G Lehmann CW Fürstner A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1833-1853
Oxidative insertion of [Pd(PPh3)4] or [Ni(cod)2]/PPh3 into the C-Cl bond of various 2-chloroimidazolinium- and other -amidinium salts affords metal-diaminocarbene complexes in good to excellent yields. This procedure is complementary to existing methodology in which the central metal does not change its oxidation state, and therefore allows to incorporate carbene fragments that are difficult to access otherwise. The preparation of a variety of achiral as well as enantiomerically pure, chiral metal-NHC complexes (NHC = N-heterocyclic carbene) and metal complexes with acyclic diaminocarbene ligands illustrates this aspect. Furthermore it is shown that oxidative insertion also paves a way to prototype Fischer carbenes of Pd(II). Since the required starting materials are readily available from urea- or thiourea derivatives, this novel approach allows for substantial structural variations of the ligand backbone. The catalytic performance of the resulting library of nickel- and palladium-carbene complexes has been evaluated by applications to prototype Suzuki-, Heck-, and Kumada-Corriu cross-coupling reactions as well as Buchwald-Hartwig aminations. It was found that even Fischer carbenes show appreciable catalytic activity. Moreover, representative examples of all types of neutral and cationic metal-carbene complexes formed in this study have been characterized by X-ray crystallography. 相似文献
9.
Maria Inês P. S. Leito Giulia Francescato Clara S. B. Gomes Ana Petronilho 《Molecules (Basel, Switzerland)》2021,26(17)
Organometallic derivatization of nucleosides is a highly promising strategy for the improvement of the therapeutic profile of nucleosides. Herein, a methodology for the synthesis of metalated adenosine with a deprotected ribose moiety is described. Platinum(II) N-heterocyclic carbene complexes based on adenosine were synthesized, namely N-heterocyclic carbenes bearing a protected and unprotected ribose ring. Reaction of the 8-bromo-2′,3′,5′-tri-O-acetyladenosine with Pt(PPh3)4 by C8−Br oxidative addition yielded complex 1, with a PtII centre bonded to C-8 and an unprotonated N7. Complex 1 reacted at N7 with HBF4 or methyl iodide, yielding protic carbene 2 or methyl carbene 3, respectively. Deprotection of 1 to yield 4 was achieved with NH4OH. Deprotected compound 4 reacted at N7 with HCl solutions to yield protic NHC 5 or with methyl iodide yielding methyl carbene 6. Protic N-heterocyclic carbene 5 is not stable in DMSO solutions leading to the formation of compound 7, in which a bromide was replaced by chloride. The cis-influence of complexes 1–7 was examined by 31P{1H} and 195Pt NMR. Complexes 2, 3, 5, 6 and 7 induce a decrease of 1JPt,P of more than 300 Hz, as result of the higher cis-influence of the N-heterocyclic carbene when compared to the azolato ligand in 1 and 4. 相似文献
10.
Alexander Zeller 《Journal of organometallic chemistry》2005,690(13):3292-3299
Via NMR-spectroscopy the relative reactivity of N-heterocyclic silylenes (NHSi) and carbenes (NHC) was studied. Reaction of sterically crowded bis-N-heterocyclic Pd(0) carbene complexes with free N-heterocyclic silylenes led to complete displacement of the N-heterocyclic carbene, which is unexpected knowing that usually a silylene is a weaker bound ligand compared to a carbene. High-level DFT calculations on a small model system and the experimentally used complexes confirm the experimental findings and indicate that steric interactions play an important role in the substitution reaction. 相似文献
11.
Dinuclear N-heterocyclic carbene complexes of silver(I), derived from imidazolium-linked cyclophanes
Baker MV Brown DH Haque RA Skelton BW White AH 《Dalton transactions (Cambridge, England : 2003)》2004,(21):3756-3764
The synthesis of four new silver complexes of bidentate N-heterocyclic carbenes, derived from imidazolium-linked cyclophanes, has been achieved via a simple complexation reaction of the imidazolium-linked cyclophanes with the basic metal source Ag(2)O. The cyclophane structures contain two imidazolyl links between ortho-, meta- and mixed ortho/meta-substituted aromatic rings. The new silver carbene systems are thermally stable and have been characterised by NMR spectroscopy and X-ray crystallography. Three of the complexes have a dimeric structure of the form [L(2)Ag(2)](2+) in the solid state that is rigid on the NMR timescale in solution. The fourth complex has a neutral structure of the form [L(AgBr)(2)], the NMR studies suggesting some lability of the L-Ag bonding in solution. 相似文献
12.
The oxidative kinetic resolution of secondary alcohols has been accomplished using 1:1 complexes of PdCl(2) and N-heterocyclic carbenes. In these reactions, both achiral and chiral carbene ligands are used in conjunction with the chiral base (-)-sparteine. A general synthesis of 1:1 PdCl(2)-carbene complexes has been developed and is amenable to a wide range of carbene ligands. The potential of these complexes in aerobic oxidations is highlighted by the use of a chiral Pd(II) complex and the chiral base (-)-sparteine to enhance the kinetic resolution of a racemic alcohol. [reaction--see text] 相似文献
13.
Hahn FE Paas M Le Van D Fröhlich R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(17):5080-5085
Nonaromatic, "saturated", spirocyclic N-heterocyclic diaminocarbenes 11 can be obtained from spirocyclic imidazolidin-2-thiones 10 by reductive desulfurization with potassium. The unsymmetrically N,N'-substituted spirocyclic imidazolidin-2-thiones were obtained by reaction of ketimines 9 with lithium N-butyl-N-lithiomethyldithiocarbamate (6). 13C NMR spectroscopy revealed that the unsymmetrically N,N'-substituted spirocyclic imidazolidin-2-ylidene 11 a undergoes a slow, acid-catalyzed dimerization to give the enetetramine 11 a=11 a, which exists in two isomeric forms (syn and anti). This reaction is reversible under special circumstances. Carbenes of type 11 react with [W(CO)6] to yield air-stable carbene complexes of type [W11(CO)5] (14). The molecular structures of two derivatives 14 a and 14 b were established by X-ray crystallography and show clear distortion of the five-membered N-heterocyclic ring, caused by the spirocyclic molecular structure of the carbene ligands of type 11. 相似文献
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N杂环卡宾的反应性能较高,与周期表中几乎所有的金属都能发生反应形成稳定的配合物.主要阐述了N杂环卡宾的结构与类型,其金属配合物的合成方法及在化学反应中的催化作用和应用前景. 相似文献
16.
由于N-杂环卡宾结构的多样性,以及它们的金属络合物良好的稳定性和催化活性,近年来受到了人们的广泛关注。本文对N-杂环卡宾及其金属络合物的性质和合成方法进行了综述。参考文献30篇。 相似文献
17.
自从1991年Arduengo第一次分离得到稳定的游离N-杂环卡宾以后,N-杂环卡宾金属络合物的研究在近几年来得到了迅速的发展。N-杂环卡宾的反应性能较高,它们与周期表中几乎所有的元素都能发生反应。N-杂环卡宾金属络合物对许多反应有催化作用,它们是一类有潜在应用价值的催化剂。本文对近年来相关的研究成果进行了综述。 相似文献
18.
Marc C.B. Legault Craig S. McKay Joseph MoranMatthew A. Lafreniere John Paul Pezacki 《Tetrahedron letters》2012,53(42):5663-5666
Alkyne-tethered imidazole and 1,2,4-triazole-based N-heterocyclic carbene precursors have been prepared and studies of the intramolecular reactions of carbenes are performed. Products consistent with intramolecular cyclizations and subsequent rearrangements were observed. Mechanistic studies using crossover experiments showed that the products did arise from intramolecular carbene additions. The reactions are proposed to go through vinylogous diaminocarbene intermediates similar to vinylogous dialkoxycarbenes formed during Boger cycloaddition reactions. Imidazole substituted dienes were observed to be the major products of tandem cyclization and elimination reactions that were observed for imidazole-based N-heterocyclic carbenes. 相似文献
19.
Dr. Mohand Melaimi Dr. Michèle Soleilhavoup Prof. Guy Bertrand 《Angewandte Chemie (International ed. in English)》2010,49(47):8810-8849
The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong σ‐donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus‐based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon‐based ligands (which are not NHCs), and which feature even stronger σ‐donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made. 相似文献
20.
The potential energy surfaces for the chemical reactions of group 14 carbenes have been studied using density functional theory (B3LYP/LANL2DZ). Five saturated five-membered-ring N-heterocyclic carbene Dipp[upper bond 1 start]N(CH(2))(2)N(Dipp)E[upper bond 1 end]: (five-ring-E:) species, where E = C, Si, Ge, Sn and Pb, have been chosen as model reactants in this work. Also, four kinds of chemical reactions; addition of water, methane insertion, alkene cycloaddition and dimerization, have been used to study the chemical reactivities of these group 14 carbenes. The present theoretical investigations suggest that the relative carbenic reactivity decreases in the order: C > Si > Ge > Sn > Pb. That is, the heavier the group 14 atom (E), the more stable is the carbene towards chemical reactions. This may be the reason that there have been many instances reported of the synthesis and characterization of stable group 14 five-membered-ring N-heterocyclic carbene species with various alkyl protecting substituents at room temperature. Furthermore, the singlet-triplet energy splitting of the five-ring-E:, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their reactivities. The results obtained allow a number of predictions to be made. 相似文献