首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 484 毫秒
1.
Homobimetallic metallophilic interactions between copper, silver, and gold‐based [(NHC)MX]‐type complexes (NHC=N‐heterocyclic carbene, i.e, 1,3,4‐trimethyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene; X=F, Cl, Br, I) were investigated by means of ab initio interaction energies, Ziegler–Rauk‐type energy‐decomposition analysis, the natural orbital for chemical valence (NOCV) framework, and the noncovalent interaction (NCI) index. It was found that the dimers of these complexes predominantly adopt a head‐to‐tail arrangement with typical M ??? M distance of 3.04–3.64 Å, in good agreement with the experimental X‐ray structure determined for [{(NHC)AuCl}2], which has an Au ??? Au distance of 3.33 Å. The interaction energies between silver‐ and gold‐based monomers are calculated to be about ?25 kcal mol?1, whereas that for the Cu congener is significantly lower (?19.7 kcal mol?1). With the inclusion of thermal and solvent contributions, both of which are destabilizing, by about 15 and 8 kcal mol?1, respectively, an equilibrium process is predicted for the formation of dimer complexes. Energy‐decomposition analysis revealed a dominant electrostatic contribution to the interaction energy, besides significantly stabilizing dispersion and orbital interactions. This electrostatic contribution is rationalized by NHC(δ+) ??? halogen(δ?) interactions between monomers, as demonstrated by electrostatic potentials and derived charges. The dominant NOCV orbital indicates weakening of the π backdonation in the monomers on dimer formation, whereas the second most dominant NOCV represents an electron‐density deformation according to the formation of a very weak M ??? M bond. One of the characteristic signals found in the reduced density gradient versus electron density diagram corresponds to the noncovalent interactions between the metal centers of the monomers in the NCI plots, which is the manifestation of metallophilic interaction.  相似文献   

2.
A total of 35 [Au(NHC)2][MX2] (NHC=N‐heterocyclic carbene; M=Au or Cu; X=halide, cyanide or arylacetylide) complex salts were synthesized by co‐precipitation of [Au(NHC)2]+ cations and [MX2]? anions. These salts contain crystallographically determined polymeric Au???Au or Au???Cu interactions and are highly phosphorescent with quantum yields up to unity and emission color tunable in the entire visible regions. The nature of the emissive excited states is generally assigned to ligand (anion)‐to‐ligand (cation) charge‐transfer transitions assisted by d10???d10 metallophilicity. The emission properties can be further tuned by controlled triple‐component co‐crystallization or by epitaxial growth. Correct recipes for white light‐emitting phosphors with quantum yields higher than 70 % have been achieved by screening the combinatorial pool.  相似文献   

3.
The possible mechanisms and origin of the enantioselectivity of the reaction between 2H‐azirine and an aldehyde catalyzed by an N‐heterocyclic carbene (NHC) were theoretically studied and predicted at the M06‐2X/6‐31G(d,p)/IEF‐PCMMTBE//M06‐2X‐GD3/6‐311++G(2df, 2pd)/IEF‐PCMMTBE level. The most favorable reaction pathway consists of four steps, i.e., complexation of the NHC and the aldehyde, stepwise [1,2]‐proton transfer, C?C bond formation coupled with another proton transfer, and recycling of the NHC. The computational results indicate that the stereoselectivity‐determining step is also the rate‐determining step, which is the third step (i.e., intermolecular addition). The calculated 99 % ee is very close to the experimentally observed value of 96 % ee, demonstrating that the calculations are reliable. Two important roles of the NHC were identified by global reaction index (GRI) analysis and natural population analysis (NPA), that is, realizing the umpolung reactivity of the aldehyde and facilitating the deprotonation of aldehyde. Moreover, the efficiency of different NHC catalysts can be mainly predicted by computing the nucleophilic index of the corresponding Breslow intermediates. Furthermore, distortion/interaction and noncovalent interaction (NCI) analyses revealed that the π???π interactions between the NHC and substrates were the key factor in the reaction enantioselectivity.  相似文献   

4.
A series of monomeric palladacycle complexes bearing n‐butyl‐substituted N‐heterocyclic carbenes, namely [Pd(NHC)X(dmba)] (dmba: dimethylbenzylamine and [Pd(NHC)X(ppy)]; NHC: 1‐n‐butyl‐3‐substituted benzylimidazol‐2‐ylidene; ppy: 2‐phenylpyridine), were prepared either by transmetallation from the corresponding silver carbene complexes or by the reaction of the corresponding acetate‐bridged palladacycle dimer with N‐heterocyclic carbene ligands in high yields. The palladium(II) complexes were characterized using elemental analyses, APCI‐MS, 1H NMR and 13C NMR spectroscopies. These complexes are efficient in the Suzuki–Miyaura coupling reaction between phenylboronic acid and aryl bromides.  相似文献   

5.
This study discusses the synthesis of two new 2‐hydroxyethyl substituted N‐heterocyclic carbene (NHC) precursors. The NHC precursors were prepared from 1‐(alkyl/aryl)benzimidazole and alkyl halides. They were characterized using 1H NMR, 13C NMR, FT‐IR, UV–Vis spectroscopy, and elemental analysis techniques. Molecular and crystal structures of 1 and 2 were determined using the single‐crystal X‐ray diffraction method. Crystal structure of the compounds features NHC precursors and chloride anions. Additionally in 2 , the asymmetric unit has a water molecule, which forms a tetrameric chloride‐hydrate assembly with the chloride anion. The chloride anions play an important role in the stabilization of crystal structures to form a two‐dimensional supramolecular architecture. The 3D Hirshfeld surface and the associated 2D fingerprint plots were also drawn to gain insights into the behavior of the interactions in the compounds.  相似文献   

6.
Based on 1‐amino‐4‐hydroxy‐triptycene, new saturated and unsaturated triptycene‐NHC (N‐heterocyclic carbene) ligands were synthesized from glyoxal‐derived diimines. The respective carbenes were converted into metal complexes [(NHC)MX] (M=Cu, Ag, Au; X=Cl, Br) and [(NHC)MCl(cod)] (M=Rh, Ir; cod=1,5‐cyclooctadiene) in good yields. The new azolium salts and metal complexes suffer from limited solubility in common organic solvents. Consequently, the introduction of solubilizing groups (such as 2‐ethylhexyl or 1‐hexyl by O‐alkylation) is essential to render the complexes soluble. The triptycene unit infers special steric properties onto the metal complexes that enable the steric shielding of selected areas close to the metal center. Next, chiral and meso‐triptycene based N‐heterocyclic carbene ligands were prepared. The key step in the synthesis of the chiral ligand is the Buchwald–Hartwig amination of 1‐bromo‐4‐butoxy‐triptycene with (1S,2S)‐1,2‐diphenyl‐1,2‐diaminoethane, followed by cyclization to the azolinium salt with HC(OEt)3. The analogous reaction with meso‐1,2‐diphenyl‐1,2‐diaminoethane provides the respective meso‐azolinium salt. Both the chiral and meso‐azolinium salts were converted into metal complexes including [(NHC)AuCl], [(NHC)RhCl(cod)], [(NHC)IrCl(cod)], and [(NHC)PdCl(allyl)]. An in situ prepared chiral copper complex was tested in the enantioselective borylation of α,β‐unsaturated esters and found to give an excellent enantiomeric ratio (er close to 90:10).  相似文献   

7.
The base‐controlled mechanisms for N‐heterocyclic carbene (NHC)‐catalyzed divergent [3+3] and [3+2] annulation reactions were examined by using the DFT method. The reaction initiates with the complexation of NHC and enal to give the Breslow intermediate, which diverges afterward. Then, the azomethine imine can either react with the Breslow intermediate to give the six‐membered ring product or the β‐carbon protonation occurs for forming the enolate intermediate controlled by different bases. The formed enolate intermediate reacts with azomethine imine to afford the five‐membered ring product. The calculated results show that only the base K2CO3 can facilitate the structural transformation between homoenolate and enolate to switch the chemoselectivity; therefore, the [3+3] annulation happens preferentially in the presence of base DBU while the other situation occurs with K2CO3 as base. The NCI analysis results reveal that the stereoselectivity is predominately determined by the π???π, C?H???O, and C?H???N interactions. The obtained mechanistic insights should provide valuable clues for the rational design of these kinds of divergent reactions.  相似文献   

8.
MP2 and DFT calculations with correlation consistent basis sets indicate that isolated linear anionic dialkylgold(I) complexes form moderately strong (ca. 10 kcal mol?1) Au???H hydrogen bonds with single H2O molecules as donors in the absence of sterically demanding substituents. Relativistic effects are critically important in the attraction. Such bonds are significantly weaker in neutral, strong σ‐donor N‐heterocyclic carbene (NHC) complexes (ca. 5 kcal mol?1). The overall association (>11 kcal mol?1), however, is strengthened by co‐operative, synergistic classical hydrogen bonding when the NHC ligands bear NH units. Further manipulation of the interaction by ligands positioned trans to the carbene, is possible.  相似文献   

9.
10.
An unexpected cationic bis‐N‐heterocyclic carbene (NHC) benzylidene ether based ruthenium complex ( 2 a ) was prepared through the double incorporation of an unsymmetrical unsaturated N‐heterocyclic carbene (U2‐NHC) ligand that bore an N‐substituted cyclododecyl side chain. The isolation and full characterization (including X‐ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring‐closing metathesis, which could be “switched on” under acidic conditions.  相似文献   

11.
The role of CH–π and CF–π interactions in determining the structure of N‐heterocyclic carbene (NHC) palladium complexes were studied using 1H NMR spectroscopy, X‐ray crystallography, and DFT calculations. The CH–π interactions led to the formation of the cisanti isomers in 1‐aryl‐3‐isopropylimidazol‐2‐ylidene‐based [(NHC)2PdX2] complexes, while CF–π interactions led to the exclusive formation of the cis‐syn isomer of diiodobis(3‐isopropyl‐1‐pentafluorophenylimidazol‐2‐ylidene) palladium(II).  相似文献   

12.
A 1‐phosphonium‐8‐borane‐decorated naphthalene molecule 2 has been found to react with N,N′‐dimethylimidazol‐2‐ylidene (IMe), a popular member of the N‐heterocyclic carbene (NHC) family, which converts it into two vinyl‐amine fragments one of which is trapped between the phosphonium and borane unit by the formation of a C?C and a B?N bond. The same reactivity was not observed for larger NHC molecules. Control experiments and mechanistic studies have established the involvement of an ylide–borane molecule and an imidazolium salt in addition to IMe carbene in this new transformation of an NHC.  相似文献   

13.
The oxidative coupling of anionic imidazol‐4‐ylidenes protected at the C2 position with [MnCp(CO)2] or BH3 led to the corresponding 4,4′‐bis(2H‐imidazol‐2‐ylidene) complexes or adducts, in which the two carbene moieties are connected through a single C?C bond. Subsequent acidic treatment of the later species led to the corresponding 4,4′‐bis(imidazolium) salts in good yields. The overall procedure offers practical access to a novel class of Janus‐type bis(NHC)s. Strikingly, the coplanarity of the two NHC rings within the mesityl derivative 4,4′‐bis(IMes), favored by steric hindrance along with stabilizing intramolecular C?H???π aryl interactions, allows the alignment of the π‐systems and, as a direct consequence, significant electron communication through the bis(carbene) scaffold.  相似文献   

14.
From the reaction of 1H‐imidazole ( 1a ), 4,5‐dichloro‐1H‐imidazole ( 1b ) and 1H‐benzimidazole ( 1c ) with p‐cyanobenzyl bromide ( 2 ), symmetrically substituted N‐heterocyclic carbene (NHC) [( 3a–c )] precursors, 1‐methylimidazole ( 5a ), 4,5‐dichloro‐1‐methylimidazole ( 5b ) and 1‐methylbenzimidazole ( 5c ) with benzyl bromide ( 6 ), non‐symmetrically substituted N‐heterocyclic carbene (NHC) [( 7a–c )] precursors were synthesized. These NHC? precursors were then reacted with silver(I) acetate to yield the NHC‐silver complexes [1,3‐bis(4‐cyanobenzyl)imidazole‐2‐ylidene] silver(I) acetate ( 4a ), [4,5‐dichloro‐1,3‐bis(4‐cyanobenzyl)imidazole‐2‐ylidene] silver(I) acetate ( 4b ), [1,3‐bis(4‐cyanobenzyl)benzimidazole‐2‐ylidene] silver(I) acetate ( 4c ), (1‐methyl‐3‐benzylimidazole‐2‐ylidene) silver(I) acetate ( 8a ), (4,5‐dichloro‐1‐methyl‐3‐benzylimidazole‐2‐ylidene) silver(I) acetate ( 8b ) and (1‐methyl‐3‐benzylbenzimidazole‐2‐ylidene) silver(I) acetate ( 8c ) respectively. The four NHC‐precursors 3a–c, 7c and four NHC–silver complexes 4a–c and 8c were characterized by single crystal X‐ray diffraction. The preliminary antibacterial activity of all the compounds was studied against Gram‐negative bacteria Escherichia coli, and Gram‐positive bacteria Staphylococcus aureus using the qualitative Kirby‐Bauer disc‐diffusion method. All NHC–silver complexes exhibited medium to high antibacterial activity with areas of clearance ranging from 4 to 12 mm at the highest amount used, while the NHC‐precursors showed significantly lower activity. In addition, all NHC–silver complexes underwent preliminary cytotoxicity tests on the human renal‐cancer cell line Caki‐1 and showed medium to high cytotoxicity with IC50 values ranging from 53 ( ± 8) to 3.2 ( ± 0.6) µM. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
The remarkable resilience of N‐heterocyclic carbene (NHC) gold bonds has quickly made NHCs the ligand of choice when functionalizing gold surfaces. Despite rapid progress using deposition from free or CO2‐protected NHCs, synthetic challenges hinder the functionalization of NHC surfaces with protic functional groups, such as alcohols and amines, particularly on larger nanoparticles. Here, we synthesize NHC‐functionalized gold surfaces from gold(I) NHC complexes and aqueous nanoparticles without the need for additional reagents, enabling otherwise difficult functional groups to be appended to the carbene. The resilience of the NHC?Au bond allows for multi‐step post‐synthetic modification. Beginning with the nitro‐NHC, we form an amine‐NHC terminated surface, which further undergoes amide coupling with carboxylic acids. The simplicity of this approach, its compatibility with aqueous nanoparticle solutions, and its ability to yield protic functionality, greatly expands the potential of NHC‐functionalized noble metal surfaces.  相似文献   

16.
A number of saturated abnormal N‐heterocyclic carbene (NHC) complexes of gold, in combination with KBArF4 as activator, were successfully applied in the chemoselective addition of hydrazine to alkynes. The reaction proceeds even at room temperature, which was not possible to date with gold catalysts. The reaction can be applied to a number of substituted arylalkynes. With alkylalkynes the yields are low. The saturated abnormal NHC ligands are resistant to isomerization to the saturated normal NHC coordination mode under basic reaction conditions. Under acidic conditions, a simple protonation at the nitrogen atom not neighboring the carbene center was observed and unambiguously characterized by an X‐ray crystal‐structure analysis. Computational studies confirm that such an isomerization would be highly exothermic, the observed kinetic stability probably results from the need to shift two protons in such a process.  相似文献   

17.
Novel acyclic Pd(II)‐N‐heterocyclic carbene (NHC) metallacrown ethers 5a , 5b have been synthesized. Reaction of the imidazolium salts bearing a long polyether chain with Ag2O afforded Ag‐NHC complexes, which then reacted as carbene transfer agent with PdCl2(MeCN)2 to give the desired acyclic Pd(II)‐NHC metallacrown ether complexes 5a and 5b . The 1H NMR and 13C NMR spectra show 5a and 5b exist as mixtures of cis and trans isomers in solution. The trans isomer of 5a was characterized by X‐ray diffraction, which clearly demonstrated two pseudo‐crown ether cavities in trans‐ 5a . Pd(II)‐NHC complexes 5a and 5b have been shown to be highly effective in the Suzuki‐Miyaura reactions of a variety of aryl bromides in neat water without the need of inert gas protection.  相似文献   

18.
Syntheses of the first heteroleptic N‐heterocyclic carbene (NHC)–phosphane platinum(0) complexes and formation of the corresponding Lewis acid–base adducts with aluminum chloride is reported. The influence of N‐heterocyclic carbenes on tuning the Lewis basic properties of the metal complexes was judged from spectroscopic, structural, and computational data. Conclusive experimental evidence for the enhanced Lewis basicity of NHC‐containing complexes was provided by a transfer reaction.  相似文献   

19.
A mononuclear bis(NHC)/AuI (NHC=N‐heterocyclic carbene) cationic complex with a rigid bis(phosphane)‐functionalized NHC ligand (PCNHCP) was used to construct linear Au3 and Ag2Au arrays, a Au5 cluster with two intersecting crosslike Au3 arrays, and an unprecedented Cu6 complex with two parallel Cu3 arrays. The impact of metallophilic interactions on photoluminescence was studied experimentally.  相似文献   

20.
Discovered by Hawthorne in 1965, dicarbollide ions are an intriguing class of nido ‐carboranes that mimic the behavior of the cyclopentadienyl anion. Herein, we show that it is possible to directly link the dicarbollide ion to an N‐heterocyclic carbene (NHC) to form an isolable N‐dicarbollide‐substituted NHC dianion. This molecule can be accessed by the sequential double deprotonation of a mono‐nido ‐carboranyl imidazolium zwitterion. As revealed by a single‐crystal X‐ray diffraction study, the first deprotonation leads to a monoanionic dicarbollide ion that adopts a bis(dicarbollide) structure in the solid state. Subsequent deprotonation of this monoanion leads to the first N‐dicarbollide NHC, which was fully characterized by multinuclear NMR spectroscopy as well as single‐crystal X‐ray diffraction.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号