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1.
Cyclic (Amino)(aryl)carbenes (CAArCs) as Strong σ‐Donating and π‐Accepting Ligands for Transition Metals 下载免费PDF全文
Bin Rao Huarong Tang Prof. Dr. Xiaoming Zeng Liu Liu Dr. Mohand Melaimi Prof. Dr. Guy Bertrand 《Angewandte Chemie (International ed. in English)》2015,54(49):14915-14919
Cyclic (amino)(aryl)carbenes (CAArCs) result from the replacement of the alkyl substituent of cyclic (alkyl)(amino) carbenes (CAACs) by an aryl group. This structural modification leads to enhanced electrophilicity of the carbene center with retention of the high nucleophilicity of CAACs, and therefore CAArCs feature a small singlet–triplet gap. The isoindolium precursors are readily prepared in good yields, and deprotonation at low temperature, in the presence of [RhCl(cod)]2 and [(Me2S)AuCl] lead to air‐stable rhodium and gold CAArC‐supported complexes, respectively. The rhodium complexes promote the [3+2] cycloaddition of diphenylcyclopropenone with ethyl phenylpropiolate, and induce the addition of 2‐vinylpyridine to alkenes by CH activation. The gold complexes allow for the catalytic three‐component preparation of 1,2‐dihydroquinolines from aniline and phenyl acetylene. These preliminary results illustrate the potential of CAArC ligands in transition‐metal catalysis. 相似文献
2.
Yanfeng Jiang Olivier Blacque Dr. Thomas Fox Dr. Christian M. Frech Dr. Heinz Berke Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(7):2240-2249
The five‐coordinated ReI hydride complexes [Re(Br)(H)(NO)(PR3)2] (R=Cy 1 a , iPr 1 b ) were reacted with benzylbromide, thereby affording the 17‐electron mononuclear ReII hydride complexes [Re(Br)2(H)(NO)(PR3)2] (R=Cy 3 a , iPr 3 b ), which were characterized by EPR, cyclic voltammetry, and magnetic susceptibility measurements. In the case of dibromomethane or bromoform, the reaction of 1 afforded ReII hydrides 3 in addition to ReI carbene hydrides [Re(?CHR1)(Br)(H)(NO)(PR3)2] (R1=H 4 , Br 5 ; R=Cy a , iPr b ) in which the hydride ligand is positioned cis to the carbene ligand. For comparison, the dihydrogen ReI dibromide complexes [Re(Br)2(NO)(PR3)2(η2‐H2)] (R=Cy 2 a , iPr 2 b ) were reacted with allyl‐ or benzylbromide, thereby affording the monophosphine ReII complex salts [R3PCH2R′][Re(Br)4(NO)(PR3)] (R′=? CH?CH2 6 , Ph 7 ). The reduction of ReII complexes has also been examined. Complex 3 a or 3 b can be reduced by zinc to afford 1 a or 1 b in high yield. Under catalytic conditions, this reaction enables homocoupling of benzylbromide (turnover frequency (TOF): 3 a 150, 3 b 134 h?1) or allylbromide (TOF: 3 a 575, 3 b 562 h?1). The reaction of 6 a and 6 b with zinc in acetonitrile affords in good yields the monophosphine ReI complexes [Re(Br)2(NO)(MeCN)2(PR3)] (R=Cy 8 a , iPr 8 b ), which showed high catalytic activity toward highly selective dehydrogenative silylation of styrenes (maximum TOF of 61 h?1). Single‐electron transfer (SET) mechanisms were proposed for all these transformations. The molecular structures of 3 a , 6 a , 6 b , 7 a , 7 b , and 8 a were established by single‐crystal X‐ray diffraction studies. 相似文献
3.
Tobias Biberger Raphael J. Zachmann Prof. Alois Fürstner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(42):18581-18587
[(NHC)(cymene)RuCl2] (NHC=N-heterocyclic carbene) complexes instigate a light-driven gem-hydrogenation of internal alkynes with concomitant formation of discrete Grubbs-type ruthenium carbene species. This unorthodox reactivity mode is harnessed in the form of a “hydrogenative metathesis” reaction, which converts an enyne substrate into a cyclic alkene. The intervention of ruthenium carbenes formed in the actual gem-hydrogenation step was proven by the isolation and crystallographic characterization of a rather unusual representative of this series carrying an unconfined alkyl group on a disubstituted carbene center. 相似文献
4.
Julian Böhnke Prof. Dr. Holger Braunschweig Dr. William C. Ewing Dr. Christian Hörl Thomas Kramer Dr. Ivo Krummenacher Dr. Jan Mies Dr. Alfredo Vargas 《Angewandte Chemie (International ed. in English)》2014,53(34):9082-9085
The complexation of two equivalents of a cyclic (alkyl)(amino)carbene (CAAC) to tetrabromodiborane, followed by reduction with four equivalents of sodium naphthalide, led to the formation of the CAAC‐stabilized linear diboracumulene (CAAC)2B2. The capacity of the CAAC ligand to facilitate B2→CAAC donation of π‐electron density resulted in important differences between this species and a previously reported complex featuring a B?B triple bond stabilized by cyclic di(amino)carbenes, including a longer B? B bond and shorter B? C bonds. Frontier orbital analysis indicated sharing of valence electrons across the entire linear C‐B‐B‐C unit in (CAAC)2B2, which is supported by natural population analysis and cyclic voltammetry. 相似文献
5.
Fatme Dahcheh Prof. Dr. Douglas W. Stephan Prof. Dr. Guy Bertrand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):199-204
The reaction of a cyclic (alkyl)(amino)carbene (CAAC) with dichloro‐ and dibromobis(trimethylsilyl)aminoborane results in the formation of haloiminoborane–CAAC adducts. When the iodo analogue is used, an oxidative addition at the carbene center affords a cationic iminoboryl–CAAC adduct, featuring a boron–nitrogen triple bond. Similar salts are also obtained by halide abstraction from the chloro‐ and bromoiminoborane–CAAC adducts. The reactivity of all of these compounds towards CO2 is discussed. 相似文献
6.
Janis V. Musso Mathis J. Benedikter Dr. Dongren Wang Dr. Wolfgang Frey Hagen J. Altmann Prof. Dr. Michael R. Buchmeiser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(40):8709-8713
The first reversible N-heterocyclic carbene (NHC) induced α-H abstraction in tungsten(VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH2Ph)2(OtBu)2 (Ar=2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert-butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by 1H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium-labeled complex in comparison to its non-deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α-H abstraction is the rate-determining step (RDS) of the reaction. 相似文献
7.
Facile Syntheses of N‐Heterocyclic Carbene Precursors through I2‐ or NIS‐Promoted Amidiniumation of N‐Alkenyl Formamidines 下载免费PDF全文
We have developed I2‐ or N‐iodosuccinimide (NIS)‐mediated amidiniumation of N‐alkenyl formamidines for the syntheses of cyclic formamidinium salts, some of which could be directly used as N‐heterocyclic carbene (NHC) precursors. Treatment of iodine‐containing formamidinium salts with Al2O3 led to the formation of cyclic formamidinium salts with an unsaturated backbone. A rhodium(I) complex ligated by a representative NHC was prepared by the reaction of [Rh(cod)Cl]2 (cod=1,5‐cyclooctadiene) with the free carbene obtained in situ from deprotonation of the corresponding formamidinium salts. The NHCs prepared in situ can also react with S8 to afford the corresponding thiones. 相似文献
8.
Ana Pereira Dr. Yohan Champouret Dr. Carmen Martín Dr. Eleuterio Álvarez Prof. Dr. Michel Etienne Prof. Dr. Tomás R. Belderraín Prof. Dr. Pedro J. Pérez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9769-9775
Copper–carbene [TpxCu?C(Ph)(CO2Et)] and copper–diazo adducts [TpxCu{η1‐N2C(Ph)(CO2Et)}] have been detected and characterized in the context of the catalytic functionalization of O?H bonds through carbene insertion by using N2?C(Ph)(CO2Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N‐bound diazo adduct is a dormant species and is not en route to the formation of the copper–carbene intermediate. 相似文献
9.
Copper‐Catalyzed Vicinal Diphosphination of Styrenes: Access to 1,2‐Bis(diphenylphosphino)ethane‐Type Bidentate Ligands from Olefins 下载免费PDF全文
Yuto Okugawa Prof. Dr. Koji Hirano Prof. Dr. Masahiro Miura 《Angewandte Chemie (International ed. in English)》2016,55(43):13558-13561
A copper/N‐heterocyclic carbene (NHC) catalyzed oxidative vicinal diphosphination of styrenes with diphenyl(trimethylsilyl)phosphine proceeds in the presence of LiOtBu and a pyridine N‐oxide/MnO2 combined oxidant to deliver the corresponding 1,2‐bis(diphenylphosphino)ethanes (DPPEs) in good yields. The present copper catalysis can provide access to the DPPE‐type ligands directly from the relatively simple alkenes. 相似文献
10.
Dr. Ulrich F. J. Mayer Elliot Murphy Dr. Mairi F. Haddow Prof. Michael Green Prof. Roger W. Alder Prof. Duncan F. Wass 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4287-4299
We make the case for benzo[c]quinolin‐6‐ylidene ( 1 ) as a strongly electron‐donating carbene ligand. The facile synthesis of 6‐trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate ( 2 ) gives straightforward access to a useful precursor for oxidative addition to low‐valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin‐6‐ylidene)(CO)5]+ ( 15 ) and [Pd(benzo[c]quinolin‐6‐ylidene)(PPh3)2(L)]2+ L=THF ( 21 ), OTf ( 22 ) or pyridine ( 23 ). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR‐stretching‐frequency data for the manganese compound suggests benzo[c]quinolin‐6‐ylidene is at least as strong a donor as any heteroatom‐stabilised carbene ligand reported. 相似文献
11.
A Cyclization–Rearrangement Cascade for the Synthesis of Structurally Complex Chiral Gold(I)–Aminocarbene Complexes 下载免费PDF全文
Dr. Filip Kolundžić Dr. Annamalai Murali Dr. Patricia Pérez‐Galán Dipl.‐Chem. Jonathan O. Bauer Prof. Dr. Carsten Strohmann Dr. Kamal Kumar Prof. Dr. Herbert Waldmann 《Angewandte Chemie (International ed. in English)》2014,53(31):8122-8126
A facile synthesis of chiral cyclic alkyl aminocarbene–gold(I) complexes from gold‐free 1,7‐enyne substrates was developed. The novel cyclization–rearrangement reaction sequence is triggered by the addition of (Me2S)AuCl to different 1,7‐enynes and leads to structurally unique carbene–gold(I) complexes in high yields. These novel complexes are catalytically active and inhibit the proliferation of different human cancer cell lines. 相似文献
12.
Nikolaos V. Tzouras Marina Saab Wim Janssens Thibault Cauwenbergh Prof. Dr. Kristof Van Hecke Dr. Fady Nahra Prof. Dr. Steven P. Nolan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(24):5541-5551
The discovery of sustainable and scalable synthetic protocols leading to gold–aryl compounds bearing N-heterocyclic carbene (NHC) ligands sparked an investigation of their reactivity and potential utility as organometallic synthons. The use of a mild base and green solvents provide access to these compounds, starting from widely available boronic acids and various [Au(NHC)Cl] complexes, with reactions taking place under air, at room temperature and leading to high yields with unprecedented ease. One compound, (N,N′-bis[2,6-(di-isopropyl)phenyl]imidazol-2-ylidene)(4-methoxyphenyl)gold, ([Au(IPr)(4-MeOC6H4)]), was synthesized on a multigram scale and used to gauge the reactivity of this class of compounds towards C−H/N−H bonds and with various acids, revealing simple pathways to gold–based species that possess attractive properties as materials, reagents and/or catalysts. 相似文献
13.
Prof. Dr. José Enrique Barquera-Lozada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4633-4639
Allenes (carbodicarbenes) and [3]cumulenes are linear carbon chains that can be bent when the terminal group has a strong carbene nature. This bending can be quite pronounced in allenes but not in [3]cumulenes. In this study, how N-heterocyclic or cyclic (alkyl)(amino) carbene (NHC and CAAC, respectively) terminal groups can modify the linear structure of [n]cumulenes has been analyzed. A low π acidity of the terminal carbene affects the linearity of [2n]cumulenes. Indeed, it has been found that the NHC [4]cumulene is extremely bent, contrary to classical [4]cumulenes. The predicted NHC [4]cumulene or tricarbodicarbene has two lone pairs and the π electrons are delocalized over the whole molecule. More significantly, DFT calculations have shown that this bent [4]cumulene is very stable, considerably more so than the corresponding [3]cumulene, which has been elusive to synthesize. Remarkably, calculations have shown that all the NHC [2n]cumulenes are more than 25 kcal mol−1 more stable than the [2n−1]cumulenes. 相似文献
14.
Dr. Dominik Munz Dr. Jiaxiang Chu Dr. Mohand Melaimi Prof. Dr. Guy Bertrand 《Angewandte Chemie (International ed. in English)》2016,55(41):12886-12890
The synthesis of N‐heterocyclic carbene (NHC)–cyclic (alkyl)(amino) carbene (CAAC) heterodimers is presented. As the free carbenes do not react together in solution, the synthetic approach involves the addition of a free NHC to a cyclic iminium salt, which results in the formation of the protonated heterodimer. Subsequent deprotonation leads to the isolation of the corresponding mixed Wanzlick dimers. One‐ and two‐electron oxidations of these triazaolefins result in the formation of stable cationic radicals and bis(cations), respectively, which have been isolated and fully characterized. Cyclic voltammetry, UV/Vis spectroscopy, spin density, and DFT calculations suggest that these heterodimers feature complementary electronic properties to tetrathiafulvalenes (TTFs). 相似文献
15.
Control of N‐Heterocyclic Carbene Catalyzed Reactions of Enals: Asymmetric Synthesis of Oxindole‐γ‐Amino Acid Derivatives 下载免费PDF全文
Dr. Xiang‐Yu Chen Jia‐Wen Xiong Qiang Liu Sun Li He Sheng Dr. Carolina von Essen Prof. Dr. Kari Rissanen Prof. Dr. Dieter Enders 《Angewandte Chemie (International ed. in English)》2018,57(1):300-304
A strategy to control the switch between a non‐cycloaddition reaction and a cycloaddition reaction of enals, using N‐heterocyclic carbene (NHC) catalyisis, has been developed. The new scalable protocol leads to γ‐amino‐acid esters bearing a tetrasubstituted stereocenter in good yields and high stereoselectivities by homo‐Mannich reactions of enals and isatin‐derived ketimines. By simply changing the N‐ketimine substituent to an ortho‐hydroxy phenyl group, the corresponding spirocyclic oxindolo‐γ‐lactams are obtained. 相似文献
16.
《Angewandte Chemie (International ed. in English)》2017,56(1):397-400
The neutral radical (Me2‐cAAC)2AlCl2 ( 2 ) is stabilized by cyclic (alkyl)(amino)carbenes (cAACs). Complex 2 was synthesized by reduction of the Me2‐cAAC:→AlCl3 ( 1 ) adduct with KC8 in the presence of another equivalent of Me2‐cAAC. The crystal structure of 2 shows that the Al−C bond lengths of the two carbenes bound to the Al center are considerably different, which is likely the result of intermolecular interactions. Quantum‐chemical calculations from the gas phase give an equilibrium structure with identical Al−C bond lengths. Compound 2 exhibits monoradical character, which was confirmed by EPR measurements. A bonding analysis indicates that the unpaired electron resides mainly at the carbene carbon atoms. Compound 2 is an example for an unusual neutral Al radical. 相似文献
17.
Dr. James T. Goettel Haopeng Gao Simon Dotzauer Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(5):1136-1143
A cyclic (alkyl)(amino)carbene (CAAC) has been shown to react with a covalent azide similar to the Staudinger reaction. The reaction of MeCAAC with trimethylsilyl azide afforded the N-silylated 2-iminopyrrolidine (MeCAAC=NSiMe3), which was fully characterized. This compound undergoes hydrolysis to afford the 2-iminopyrrolidine and trimethylsiloxane which co-crystallize as a hydrogen-bonded adduct. The N-silylated 2-iminopyrrolidine was used to transfer the novel pyrrolidine-2-iminato ligand onto both main-group and transition-metal centers. The reaction of the tetrabromodiborane bis(dimethyl sulfide) adduct with two equivalents of MeCAAC=NSiMe3 afforded the disubstituted diborane. The reaction of MeCAAC=NSiMe3 with TiCl4 and CpTiCl3 afforded MeCAAC=NTiCl3 and MeCAAC=NTiCl2Cp, respectively. 相似文献
18.
Phosphine exchange of [RuIIBr(MeCOO)(PPh3)2(3‐RBzTh)] (3‐RBzTh=3‐benzylbenzothiazol‐2‐ylidene) with a series of diphosphines (bis(diphenylphosphino)methane (dppm), 1,2‐bis(diphenylphosphino)ethylene (dppv), 1,1′‐bis(diphenylphosphino)ferrocene (dppf), 1,4‐bis(diphenylphosphino)butane (dppb), and 1,3‐(diphenylphosphino)propane (dppp)) gave mononuclear and neutral octahedral complexes [RuBr(MeCOO)(η2‐P2)(3‐RBzTh)] (P2=dppm ( 2 ), dppv ( 3 ), dppf ( 4 ), dppb ( 5 ), or dppp ( 6 )), the coordination spheres of which contained four different ligands, namely, a chelating diphosphine, carboxylate, N,S‐heterocyclic carbene (NSHC), and a bromide. Two geometric isomers of 6 ( 6a and 6 b ) have been isolated. The structures of these products, which have been elucidated by single‐crystal X‐ray crystallography, show two structural types, I and II, depending on the relative dispositions of the ligands. Type I structures contain a carbenic carbon atom trans to the oxygen atom, whereas two phosphorus atoms are trans to bromine and oxygen atoms. The type II system comprises a carbene carbon atom trans to one of the phosphorus atoms, whereas the other phosphorus is trans to the oxygen atom, with the bromine trans to the remaining oxygen atom. Complexes 2 , 3 , 4 , and 6a belong to type I, whereas 5 and 6 b are of type II. The kinetic product 6 b eventually converts into 6a upon standing. These complexes are active towards catalytic reduction of para‐methyl acetophenone by 2‐propanol at 82 °C under 1 % catalyst load giving the corresponding alcohols. The dppm complex 2 shows the good yields (91–97 %) towards selected ketones. 相似文献
19.
Steffen Styra Dr. Mohand Melaimi Dr. Curtis E. Moore Prof. Arnold. L. Rheingold Timo Augenstein Prof. Dr. Frank Breher Prof. Guy Bertrand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(23):8441-8446
A stable cyclic (alkyl)(amino)carbene (CAAC) 1 inserts into the para‐CF bond of pentafluoropyridine, and after fluoride abstraction, the iminium‐pyridyl adduct [ 3 ]+ was isolated. A cyclic voltammetry study shows a reversible three‐state redox system involving [ 3 ]+, [ 3 ] ? , and [ 3 ] ? . The CAAC‐pyridyl radical [ 3 ] ? , obtained by reduction of [ 3 ]+ with magnesium, has been spectroscopically and crystallographically characterized. In contrast to the lack of π communication between the CAAC and the pyridine units in cation [ 3 ]+, the unpaired electron of [ 3 ] ? is delocalized over an extended π system involving both heterocycles. 相似文献
20.
Dr. Lingbing Kong Dr. Rakesh Ganguly Dr. Yongxin Li Prof. Dr. Rei Kinjo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):1922-1925
Oxidative addition of the C?O bond in L2PhB: (L=oxazol‐2‐ylidene) to an AlI center induced ring expansion of an oxazol‐2‐ylidene ring, affording a unique organoboron species formally involving either an Al, N, O mixed heterocyclic carbene or anionic (amino)(boryl)carbene fragment. 相似文献