- Synthesis, characterization, electrochemical properties and catalytic reactivity of N-heterocyclic carbene-containing diiron complexes
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(μ-dmedt)[Fe(CO)3]2 (I, dmedt = 2,3-butanedithiol) was chosen as the parent complex. A series of new model complexes, N-heterocyclic carbene (NHC) substituted (μ-dmedt)[Fe-Fe]-NHC (II, (μ-dmedt)[Fe(CO)2]2[IMe(CH2)2IMe], IMe = 1-methylimidazol-2-ylidene; III, {(μ-dmedt)[Fe2(CO)5]}2[IMe(CH2)2IMe]; IV, (μ-dmedt)[Fe2(CO)5]IMes, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; V, (μ-dmedt)[Fe2(CO)5]IMe, IMe = 1,3-dimethylimidazol-2-ylidene) as mimics of the [Fe-Fe]-H2ase active site were synthesized from I and characterized using solution IR spectroscopy, NMR spectroscopy, elemental analysis and single-crystal X-ray diffraction. The electrochemical properties of complexes I-V, with and without the addition of HOAc, were investigated by cyclic voltammetry in the coordinating solvent CH3CN to evaluate the effects of different NHC ligands on the redox properties of the iron atoms of the series of complexes. It was concluded that all the new complexes are electrochemical catalysts for proton reduction to hydrogen. The symmetrically substituted cisoid basal/basal coordination complex II displays the most negative reduction potential owing to the stronger δ-donating ability of the NHC and the orientation of the NHC donor carbon as a result of the constraints of the bridging bidentate ligands. A new application for the [Fe-Fe]-NHC model complexes in the direct catalytic hydroxylation of benzene to phenol was also studied. Under the optimized experimental conditions (II, 0.01 mmol; benzene, 0.1 mL; CH3CN, 2.0 mL; H2O2, 6.0 mmol; 60 °C, 3 h), the maximal phenol yield was 26.7%.
- Wang, Yanhong,Zhang, Tianyong,Li, Bin,Jiang, Shuang,Sheng, Liao
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- Application of Quantitative 1H and 19F NMR to Organometallics
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Purity assessment of organometallics is particularly important for catalytic applications. While quantitative NMR is a well-known method in pharmaceutic chemistry, the present work illustrates its usefulness for the determination of the ligands and organometallics purities using proton and fluorine NMR. This method is fast, straightforward and provides accuracy results.
- Akhdar, Ayman,Andanson, Jean-Michel,Faure, Sophie,Gautier, Arnaud,Tra?kia, Mounir
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- Steric effect of NHC ligands in Pd(II)–NHC-catalyzed non-directed C–H acetoxylation of simple arenes
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Although there has been a lot of progress in oxidative arene C–H functionalization reactions catalyzed by Pd(II/IV) system, the non-directed, site-selective functionalization of arene molecules is still challenging. It has been established that ligands play a pivotal role in controlling rate- as well as selectivity-determining step in a catalytic cycle involving well-defined metal-ligand bonding. N-heterocyclic carbene (NHC) ligands have had a tremendous contribution in the recent extraordinary success of achieving high reactivity and excellent selectivity in many catalytic processes including cross-coupling and olefin-metathesis reactions. However, the immense potential of these NHC ligands in improving site-selectivity of non-directed catalytic C–H functionalization reactions of simple arenes is yet to be realized, where overriding the electronic bias on deciding selectivity is a burdensome task. The presented work demonstrated an initiative step in this regard. Herein, a series of well-defined discrete [Pd(NHCR′R)(py)I2] complexes with systematically varied degree of spatial congestion at the Pd centre, exerted through the R and R’ substituents on the NHC ligand, were explored in controlling the activity as well as the site-selectivity of non-directed acetoxylation of representative monosubstituted and disubstituted simple arenes (such as toluene, iodobenzene and bromobenzene, naphthalene and 1,2-dichlorobenzene). The resulting best yields were found to be 75% for toluene and 65% for bromobenzene with [Pd(NHCMePh)(py)I2], 75% for iodobenzene and 79% for naphthalene with [Pd(NHCMeMe)(py)I2], and 41% for 1,2-dichlorobenzene with [Pd(NHCCyCy)(py)I2]. Most importantly, with increasing the bulkiness of the NHC ligand in the complexes, the selectivity of the distal C-acetoxylated products in comparison to the proximal ones, was enhanced to a great extent in all cases. Considering the vast library of NHC ligands, this study underscores the future opportunity to develop more strategies to improve the activity and the crucial site-selectivity of C–H functionalization reactions in simple as well as complex organic molecules.
- Mandal, Tanmoy,Yadav, Sudha,Choudhury, Joyanta
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- Aluminum nanoparticle preparation: Via catalytic decomposition of alane adducts-influence of reaction parameters on nanoparticle size, morphology and reactivity
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Al nanoparticles represent one of the most challenging classes of metal nanoparticles in synthesis and handling due to their high chemical reactivity and their affinity to oxidation. A promising wet chemical preparation route is the catalytic decomposition of alane adducts. In the current systematic study, we investigated the influence of various reaction parameters, such as precursors, catalysts, solvents, reaction temperatures, capping agents, and concentrations of the reactants on the size and morphology of the resulting Al nanoparticles. One major goal was the optimization of the reaction parameters towards short reaction times. Our studies revealed that Ti alkoxides, such as Ti(OiPr)4, are much more efficient decomposition catalysts compared to other related metal catalysts. Optimized conditions for full conversion times smaller than 15 min are temperatures between 90-100 °C and non-polar solvents such as toluene. Amine alanes containing short alkyl chains, for example H3AlNMe2Et or H3AlNEt3, were the most suitable precursors, leading to the formation of the smallest nanoparticles. The use of weakly coordinating capping agents like amines and phosphines should be preferred over the commonly employed carboxylic acids because they do not accelerate the formation of an amorphous oxide shell upon binding to the particle surface. In conclusion, the best reaction parameters for a fast synthesis of Al nanoparticles via a catalytic decomposition approach are the combination of sterically less hindered amine alanes applying a Ti catalyst in toluene solutions in the presence of amine or phosphine stabilizers at elevated temperatures.
- Kickelbick, Guido,Klein, Thomas
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supporting information
p. 9820 - 9834
(2020/07/30)
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- New expanded-ring NHC platinum(0) complexes: Synthesis, structure and highly efficient diboration of terminal alkenes
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The synthesis and structural characterization of a series of novel platinum(0) complexes were reported. A number of (NHC)Pt(dvtms) (dvtms = 1,3-divinyl-1,1,3,3-tetramethyldisiloxane) complexes were investigated in catalytic addition of B2Pin2 to terminal alkenes. The novel expanded ring N-heterocyclic carbene complex (7-Dipp)Pt(dvtms) showed highest performance, turnover numbers up to 3800 were achieved. The scope of the reaction was illustrated by 20 examples with a variety of alkyl, alkoxy, halogen, ester, ketone and acetal substituents.
- Rzhevskiy, Sergey A.,Topchiy, Maxim A.,Lyssenko, Konstantin A.,Philippova, Anna N.,Belaya, Maria A.,Ageshina, Alexandra A.,Bermeshev, Maxim V.,Nechaev, Mikhail S.,Asachenko, Andrey F.
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supporting information
(2020/02/18)
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- Method for preparing substituted aryl ketone by ketone arylation (by machine translation)
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The invention provides a method, for preparing substituted aryl ketone, by using a nitrogen heterocyclic carbene catalyst, with a saturated nitrogen heterocyclic carbene structure in an oxygen-containing atmosphere at, through α - catalysis of a nitrogen heterocyclic carbene structure, in a nitrogen heterocyclic carbene catalyst with a saturated nitrogen heterocyclic carbene structure under an alkaline condition, in an oxygen-containing atmosphere and can efficiently prepare various substituted, aryl ketones α - under the condition of containing an oxygen. atmosphere. (by machine translation)
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Paragraph 0026; 0029; 0036; 0039
(2020/03/05)
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- Direct intramolecular carbon(sp2)-nitrogen(sp2) reductive elimination from gold(iii)
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The reactivity of bidentate AuIII-Cl species, [(C^N)AuCl2], with a bisphosphine or carbon donor ligands results in reductive elimination. Combined experimental and computational investigations lead to the first evidence of a direct intramolecular C(sp2)-N(sp2) bond formation from a monomeric [(C^N)AuCl2] gold(iii) complex. We show that bidentate ligated Au(iii) systems bypass transmetallation to form C(sp2)-N(sp2) species and NHC-Au-Cl. Mechanistic investigations of the reported transformation reveal a ligand-induced reductive elimination via a key AuIII intermediate. Kinetic studies of the reaction support a second-order rate process.
- Kim, Jong Hyun,Mertens, R. Tyler,Agarwal, Amal,Parkin, Sean,Berger, Gilles,Awuah, Samuel G.
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supporting information
p. 6273 - 6282
(2019/05/17)
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- Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High-Molar-Mass Polyethers
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A dual catalytic setup based on N-heterocyclic olefins (NHOs) and magnesium bis(hexamethyldisilazide) (Mg(HMDS)2) was used to prepare poly(propylene oxide) with a molar mass (Mn) >500 000 g mol?1, in some cases even >106 g mol?1, as determined by GPC/light scattering. This is achieved by combining the rapid polymerization characteristics of a zwitterionic, Lewis pair type mechanism with the efficient epoxide activation by the MgII species. Transfer-to-monomer, traditionally frustrating attempts at synthesizing polyethers with a high degree of polymerization, is practically removed as a limiting factor by this approach. NMR and MALDI-ToF MS experiments reveal key aspects of the proposed mechanism, whereby the polymerization is initiated via nucleophilic attack by the NHO on the activated monomer, generating a zwitterionic species. This strategy can also be extended to other epoxides, including functionalized monomers.
- Walther, Patrick,Krau?, Annabelle,Naumann, Stefan
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supporting information
p. 10737 - 10741
(2019/07/04)
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- A more sustainable and efficient access to IMes·HCl and IPr·HCl by ball-milling
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Herein is described a mechanochemical one-pot two-step procedure giving access to various NHC (N-heterocyclic carbene) precursors. This original approach enabled the production of the widely used IPr·HCl, IMes·HCl, Io-Tol·HCl and ICy·HCl in much better yields than conventional solvent-based procedures, while the environmental impact was drastically reduced.
- Beillard, Audrey,Bantreil, Xavier,Métro, Thomas-Xavier,Martinez, Jean,Lamaty, Frédéric
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supporting information
p. 964 - 968
(2018/03/13)
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- Tuning the Catalyst Reactivity of Imidazolylidene Catalysts through Substituent Effects on the N-Aryl Groups
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A series of imidazolium salts with various N-aryl groups were synthesized, and their catalytic activities were evaluated to investigate the contribution of the N-aryl groups to the catalytic activity in the synthesis of γ-butyrolactone through an a3
- Kyan, Ryuji,Sato, Kohei,Mase, Nobuyuki,Watanabe, Naoharu,Narumi, Tetsuo
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supporting information
p. 2750 - 2753
(2017/05/24)
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- A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki-Heck Reaction
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Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal-ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal-NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki-Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to "cocktail"-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal clusters and nanoparticles can be readily formed from M-NHC complexes after formation of new M-C or M-H bonds followed by C-NHC or H-NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems.
- Astakhov, Alexander V.,Khazipov, Oleg V.,Chernenko, Andrey Yu.,Pasyukov, Dmitry V.,Kashin, Alexey S.,Gordeev, Evgeniy G.,Khrustalev, Victor N.,Chernyshev, Victor M.,Ananikov, Valentine P.
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p. 1981 - 1992
(2017/06/14)
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- Unraveling the synthesis of homoleptic [Ag(N, N -diaryl-NHC)2]Y (Y = BF4, PF6) complexes by ball-milling
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A user-friendly and general mechanochemical method was developed to access rarely described NHC (N-heterocyclic carbene) silver(i) complexes featuring N,N-diarylimidazol(idin)ene ligands and non-coordinating tetrafluoroborate or hexafluorophosphate counter anions. Comparison with syntheses in solution clearly demonstrated the superiority of the ball-milling conditions.
- Beillard, Audrey,Bantreil, Xavier,Métro, Thomas-Xavier,Martinez, Jean,Lamaty, Frédéric
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supporting information
p. 17859 - 17866
(2016/11/18)
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- Electrochemical flow-reactor for expedient synthesis of copper-N-heterocyclic carbene complexes
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An electrochemical flow-cell for highly efficient and selective generation of CuI-N-heterocyclic carbene complexes under neutral and ambient conditions is reported. The feasibility of the flow-cell is demonstrated through the electrochemical sy
- Chapman, Michael R.,Shafi, Yarseen M.,Kapur, Nikil,Nguyen, Bao N.,Willans, Charlotte E.
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supporting information
p. 1282 - 1284
(2015/02/19)
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- Oxygen-atom insertion of NHCecopper complex: The source of oxygen from N, N-dimethylformamide
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An unprecedented protocol for oxygen-atom insertion reaction of NHCecopper complexes has been developed by employing N,N-dimethylformamide as the oxygen source, which allows the preparation of imidazolinones from carbene complexes and decodes one of the m
- Zeng, Wei,Wang, Enyu,Qiu, Rui,Sohail, Muhammad,Wu, Shaoxiang,Chen, Fu-Xue
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supporting information
p. 44 - 48
(2013/10/08)
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- A direct and practical approach for the synthesis of Au(I)-NHC complexes from commercially available imidazolium salts and Au(III) salts
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A direct and practical approach for the synthesis of Au(I)-NHC complexes from imidazolium salts and commercially available aurate salt (MAuCl 4·2H2O) is described. The reaction proceeded without sacrificing carbene transfer agent (Ag
- Zhu, Shifa,Liang, Renxiao,Chen, Lijuan,Wang, Chao,Ren, Yanwei,Jiang, Huanfeng
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supporting information; experimental part
p. 815 - 818
(2012/03/10)
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- A direct and practical approach for the synthesis of N-heterocyclic carbene coinage metal complexes
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A novel direct and practical synthetic route leading to N-heterocyclic carbene coinage metal complexes has been developed by using air stable, commercial available Au(III) salt [MAuCl4·2H2O], CuCln (n=1,2) or AgCl, and imidazolium salts as starting materials. The reaction proceeded without sacrificing carbene transfer agent (Ag 2O) or using highly sensitive free NHC.
- Zhu, Shifa,Liang, Renxiao,Jiang, Huanfeng
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supporting information; experimental part
p. 7949 - 7955
(2012/09/22)
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- PKas of the conjugate acids of N-heterocyclic carbenes in water
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pKa values of 19.8-28.2 are reported for the conjugate acids of a large series of NHCs in water. The effects of ring size, N-substituent and C(4)-C(5) saturation on pKa are discussed.
- Higgins, Eleanor M.,Sherwood, Jennifer A.,Lindsay, Anita G.,Armstrong, James,Massey, Richard S.,Alder, Roger W.,O'Donoghue, Annmarie C.
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supporting information; experimental part
p. 1559 - 1561
(2011/03/22)
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- Facile synthesis of dichlorosilane by metathesis reaction and dehydrogenation of dihydrogermane by a frustrated Lewis pair
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The reaction of GeCl2·dioxane with 1,4-diazabutadiene compounds [(HCNAr)2, Ar = 2,6-iPr2C6H 3, (1); Ar = 2,4,6-Me3C6H2, (2)] leads to the formation of dichlorogermane derivatives [{N(2,6-iPr 2C6H3)CH}2]GeCl2 (3) and [{N(2,4,6-Me3C6H2)CH}2]GeCl 2 (4) respectively. The reaction of compound 2 with SiCl 2·NHC (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) (5) results in the formation of dichlorosilane [{N(2,4,6-Me3C 6H2)CH}2]SiCl2 (6) which is the precursor for the synthesis of N-heterocyclic silylene. Furthermore the reaction of dichlorogermane 3 with two equivalents of AlH3·NMe 3 in toluene leads to the dihydrogermane [{N(2,6-iPr 2C6H3)CH}2]GeH2 (7). Interestingly this dihydrogermane (7) is dehydrogenated by the frustrated Lewis pair, N-heterocyclic carbene (1,3-di-tert-butylimidazol-2-ylidene) and tris(pentafluorophenyl)borane, to form the N-heterocyclic germylene [{N(2,6-iPr2C6H3)CH}2]Ge (8).
- Jana, Anukul,Tavcar, Gasper,Roesky, Herbert W.,Schulzke, Carola
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experimental part
p. 6217 - 6220
(2010/09/06)
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- SYNTHESIS OF 1,3 DISUBSTITUTED IMIDAZOLIUM SALTS
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Imidazolium salts are the immediate precursors to N-heterocyclic carbenes (NHC) yet a simple, general synthetic route to a wide variety of imidazolium salts is not yet available. Such a straightforward route is described for two specific members of this family of ligand precursor: l,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride (IMes-HCl) and l,3-Bis(2,6-diispropylphenyl)imidazolium chloride (IPrHCl). The procedure appears general and similar protocols can be used to isolate various imidazolium salts.
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Page/Page column 4; 6; 7-8
(2008/06/13)
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- Probing the efficiency of N-heterocyclic carbene promoted O- to C-carboxyl transfer of oxazolyl carbonates
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(Chemical Equation Presented) Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
- Thomson, Jennifer E.,Campbell, Craig D.,Concellon, Carmen,Duguet, Nicolas,Rix, Kathryn,Slawin, Alexandra M. Z.,Smith, Andrew D.
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p. 2784 - 2791
(2008/09/20)
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- Synthesis of chromium N-heterocyclic carbene complexes using chromium Fischer carbenes as a source of chromium carbonyls
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Chromium Fischer carbene complexes, [Cr{{double bond, long}OMe(R)}(CO)5] have been utilized as a source of chromium carbonyls in the synthesis of chromium NHC complexes. Using the synthetic method, chromium complexes of various NHC ligands were isolated in reasonable yields. Moreover, the method can be employed for the synthesis of molybdenum and tungsten NHC compounds.
- Kim, Seongjin,Choi, Soo Young,Lee, Young Tak,Park, Kang Hyun,Sitzmann, Helmut,Chung, Young Keun
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p. 5390 - 5394
(2008/03/12)
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- Tuning the electronic properties of N-heterocyclic carbenes
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The electron-donating properties of N-heterocyclic carbenes ([N,N′-bis(2,6-dimethylphenyl)imidazol]-2-ylidene and the respective dihydro ligands) with 4,4′-R-substituted aryl rings (4,4′-R = NEt2, OC12H25, Me, H, Br, S(4-t
- Leuthaeusser, Steffen,Schwarz, Daniela,Plenio, Herbert
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p. 7195 - 7203
(2008/03/12)
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- Synthesis of 1,3 distributed imidazolium salts
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Imidazolium salts are the immediate precursors to N-heterocyclic carbenes (NHC) yet a simple, general synthetic route to a wide variety of imidazolium salts is not yet available. Such a straightforward route is described for two specific members of this family of ligand precursor: 1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride (IMes.HCl) and 1,3-Bis(2,6-diispropylphenyl)imidazolium chloride (IPr.HCl). The procedure appears general and similar protocols can be used to isolate various imidazolium salts.
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Page/Page column 3; 5-7
(2008/06/13)
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- Imidazolylidenes, imidazolinylidenes and imidazolidines
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Starting from glyoxal, 1,3-diarylimidazolinium chlorides 3 were obtained in a three-step sequence via the diimines (1) and ethylene diamine dihydrochlorides (2). Reduction of 1,3-diarylimidazolinium chlorides (3) with lithium alumnium hydride furnished the 1,3- diarylimidazolidines (4) while their deprotonation with potassium hydride in thf gave access to stable carbenes (1,3-diarylimidazolin-2-ylidenes, 5). Similarly substituted imidazol-2-ylidenes are described for comparison.
- Arduengo III, Anthony J.,Krafczyk, Roland,Schmutzler, Reinhard,Craig, Hugh A.,Goerlich, Jens R.,Marshall, William J.,Unverzagt, Markus
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p. 14523 - 14534
(2007/10/03)
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