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1.
β‐Hydrogen Elimination Reactions of Nickel and Palladium Methoxides Stabilised by PCP Pincer Ligands 下载免费PDF全文
Dr. Luis M. Martínez‐Prieto Elena Ávila Dr. Pilar Palma Dr. Eleuterio Álvarez Prof. Dr. Juan Cámpora 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9833-9849
Nickel and palladium methoxides [(iPrPCP)M‐OMe], which contain the iPrPCP pincer ligand, decompose upon heating to give products of different kinds. The palladium derivative cleanly gives the dimeric Pd0 complex [Pd(μ‐iPrPCHP)]2 (iPrPCHP=2,6‐bis(diisopropylphosphinomethyl)phenyl) and formaldehyde. In contrast, decomposition of [(iPrPCP)Ni‐OMe] affords polynuclear carbonyl phosphine complexes. Both decomposition processes are initiated by β‐hydrogen elimination (BHE), but the resulting [(iPrPCP)M‐H] hydrides undergo divergent reaction sequences that ultimately lead to the irreversible breakdown of the pincer units. Whereas the Pd hydride spontaneously experiences reductive C?H coupling, the decay of its Ni analogue is brought about by its reaction with formaldehyde released in the BHE step. Kinetic measurements showed that the BHE reaction is reversible and less favourable for Ni than for Pd for both kinetic and thermodynamic reasons. DFT calculations confirmed the main conclusions of the kinetic studies and provided further insight into the mechanisms of the decomposition reactions. 相似文献
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Ming‐Hsiu Yang Jordan R. Hunt Dr. Niusha Sharifi Prof. Dr. Ryan A. Altman 《Angewandte Chemie (International ed. in English)》2016,55(31):9080-9083
A palladium‐catalyzed decarboxylative benzylation reaction of α,α‐difluoroketone enolates is reported, in which the key C(α)?C(sp3) bond is generated by reductive elimination from a palladium intermediate. The transformation provides convergent access to α‐benzyl‐α,α‐difluoroketone‐based products, and should be useful for accessing biological probes. 相似文献
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Transfer of Aryl Halide to Alkyl Halide: Reductive Elimination of Alkylhalide from Alkylpalladium Halides Containing syn‐β‐Hydrogen Atoms 下载免费PDF全文
Wei Hao Junnian Wei Weizhi Geng Prof. Dr. Wen‐Xiong Zhang Prof. Dr. Zhenfeng Xi 《Angewandte Chemie (International ed. in English)》2014,53(52):14533-14537
β‐Hydride abstraction is a well‐accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn‐β‐hydrogen atoms will undergo β‐hydride abstraction to afford the Heck‐type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn‐β‐hydrogen atoms may surpass the β‐hydride abstraction or even become exclusive in certain cases. 相似文献
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Enantioselective Palladium‐Catalyzed Oxidative β,β‐Fluoroarylation of α,β‐Unsaturated Carbonyl Derivatives 下载免费PDF全文
Javier Miró Dr. Carlos del Pozo Prof. F. Dean Toste Prof. Santos Fustero 《Angewandte Chemie (International ed. in English)》2016,55(31):9045-9049
The site‐selective palladium‐catalyzed three‐component coupling of deactivated alkenes, arylboronic acids, and N‐fluorobenzenesulfonimide is disclosed herein. The developed methodology establishes a general, modular, and step‐economical approach to the stereoselective β‐fluorination of α,β‐unsaturated systems. 相似文献
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Prof. Dr. Benito Alcaide Dr. Pedro Almendros Dr. Teresa Martínez del Campo Dipl.‐Chem. M. Teresa Quirós Dr. Elena Soriano Prof. Dr. José L. Marco‐Contelles 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(42):14233-14244
Starting from β,γ‐allendiols and α‐allenic acetates, a chemo‐ and regiocontrolled palladium‐catalyzed methodology has provided access to enantiopure 3,6‐dihydropyrans that bear a buta‐1,3‐dienyl moiety. Thus, it has been demonstrated for the first time that the preparation of six‐membered heterocycles through cross‐coupling reactions of two different allenes can be accomplished. These heterocyclization/cross‐coupling reactions have been developed experimentally and their mechanisms have additionally been investigated by a computational study. 相似文献
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Imidazolin‐2‐ylidenaminophosphines as Highly Electron‐Rich Ligands for Transition‐Metal Catalysts 下载免费PDF全文
Marius A. Wünsche Paul Mehlmann Tim Witteler Florenz Buß Patrick Rathmann Dr. Fabian Dielmann 《Angewandte Chemie (International ed. in English)》2015,54(40):11857-11860
A variety of chemical transformations benefit from the use of strong electron‐donating ancillary ligands, such as alkylphosphines or N‐heterocyclic carbenes when electron‐rich metal centers are required. Herein, we describe a facile and highly modular access to monodentate and bidentate imidazolin‐2‐ylidenamino‐substituted phosphines. Evaluation of the phosphine’s electronic properties substantiate that the formal replacement of alkyl or aryl groups by imidazolin‐2‐ylidenamino groups dramatically enhance their donor ability beyond that of alkylphosphines and even N‐heterocyclic carbenes. The new phosphines have been coordinated onto palladium(II) centers, and the beneficial effect of the novel substitution patterns has been explored by using the corresponding complexes in the palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction of non‐activated aryl chloride substrates. 相似文献
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Amadeu Bonet Henrik Gulyás Dr. Igor O. Koshevoy Dr. Francisco Estevan Dr. Mercedes Sanaú Dr. M. Angeles Úbeda Dr. Elena Fernández Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(21):6382-6390
Diphenyl(3‐methyl‐2‐indolyl)phosphine (C9H8NPPh2, 1 ) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N‐bridging coordination mode. On treating 1 with [Pd(O2CCH3)2], the new complexes [Pd(μ‐C9H7NPPh2)(NCCH3)]2 ( 2 ) or [Pd(μ‐C9H7NPPh2)(μ‐O2CCH3)]2 ( 3 ) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(μ‐C9H7NPPh2)3(μ‐O2CCH3)] ( 4 ), in which the bimetallic unit is bonded by three C9H7NPPh2? moieties and one carboxylate group. Using this methodology, [Pd2(μ‐C6H4PPh2)2(μ‐C9H7NPPh2)(μ‐O2CCX3)] (X=H ( 7 ); X=F ( 8 )) were synthesised from the ortho‐metalated compounds [Pd(C6H4PPh2)(μ‐O2CCX3)]2 (X=H ( 5 ); X=F ( 6 )). Complexes 3 , 4 , 7 , and 8 have been found to be active in the catalytic β‐boration of α,β‐unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive β‐boration/cross‐coupling reaction with dimethyl acrylamide as the substrate (99 % conversion, 89 % isolated yield). 相似文献
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Benito Alcaide Prof. Dr. Pedro Almendros Dr. Teresa Martínez del Campo Dr. Elena Soriano Dr. José L. Marco‐Contelles Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(36):9127-9138
Regiocontrolled metal‐catalyzed preparations of enantiopure dihydropyrans and tetrahydrooxepines have been synthesized starting from β‐ and γ‐allenols derived from D ‐glyceraldehyde. The PdII‐catalyzed cyclizative coupling reactions of β‐allenols 1 a and 1 b with allyl bromide effectively afforded enantiopure tetrafunctionalized dihydropyrans through a 6‐endo oxycyclization protocol, whereas the gold‐, platinum‐, and palladium‐mediated heterocyclization of γ‐allenol 2 furnished tetrahydrooxepines 13 – 16 through regioselective 7‐endo‐trig oxycyclization reactions. Moreover, density functional calculations were performed to predict the regioselectivity of the γ‐allenol cycloetherification to tetrahydrooxepines on the basis of both the tether nature and characteristics of the metals, and to gain an insight into the mechanism of the oxycyclization reactions. 相似文献
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Hua‐Jie Jiang Xiu‐Mei Zhong Zi‐Ye Liu Rui‐Long Geng Yang‐Yang Li Yun‐Dong Wu Xinhao Zhang Liu‐Zhu Gong 《Angewandte Chemie (International ed. in English)》2020,59(31):12774-12778
A hybrid palladium catalyst assembled from a chiral phosphoric acid (CPA) and thioamide enables a highly efficient and enantioselective β‐C(sp3)?H functionalization of thioamides (up to 99 % yield, 97 % ee). A kinetic resolution of unsymmetrical thioamides by intermolecular C(sp3)?H arylation can be achieved with high s‐factors. Mechanistic investigations have revealed that stereocontrol is achieved by embedding the substrate in a robust chiral cavity defined by the bulky CPA and a neutral thioamide ligand. 相似文献
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Antje Meltzer Carsten Präsang Dr. Carsten Milsmann Matthias Driess Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(17):3170-3173
The right mix does the trick : Elusive {Ni0(η6‐arene)} moieties can be dramatically stabilized by the N‐heterocyclic silylene ligand 1 , which has a zwitterionic mesomeric structure. The σ, π‐acid–base synergism between nickel and 1 explains the unexpectedly high stability of the new silylene complexes 2 , which enables arene exchange studies at a Ni0 center. Addition of B(C6F5)3 to 2 affords the zwitterionic silylene complex 3 (see scheme, R=2,6‐iPr2C6H3).
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Ming Chen Feipeng Liu Prof.Dr. Guangbin Dong 《Angewandte Chemie (International ed. in English)》2018,57(14):3815-3819
A direct and catalytic method is reported here for β‐arylation of N‐protected lactams with simple aryl iodides. The transformation is enabled by merging soft enolization of lactams, palladium‐catalyzed desaturation, Ar?X bond activation, and aryl conjugate addition. The reaction is operated under mild reaction conditions, is scalable, and is chemoselective. Application of this method to concise syntheses of pharmaceutically relevant compounds is demonstrated. 相似文献
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Selective Reductive Elimination at Alkyl Palladium(IV) by Dissociative Ligand Ionization: Catalytic C(sp3)−H Amination to Azetidines 下载免费PDF全文
Manuel Nappi Chuan He William G. Whitehurst Ben G. N. Chappell Prof. Dr. Matthew J. Gaunt 《Angewandte Chemie (International ed. in English)》2018,57(12):3178-3182
A palladium(II)‐catalyzed γ‐C?H amination of cyclic alkyl amines to deliver highly substituted azetidines is reported. The use of a benziodoxole tosylate oxidant in combination with AgOAc was found to be crucial for controlling a selective reductive elimination pathway to the azetidines. The process is tolerant of a range of functional groups, including structural features derived from chiral α‐amino alcohols, and leads to the diastereoselective formation of enantiopure azetidines. 相似文献
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Localized Mixed‐Valence and Redox Activity within a Triazole‐Bridged Dinucleating Ligand upon Coordination to Palladium 下载免费PDF全文
Daniël L. J. Broere Raoul Plessius Dr. Joanne Tory Dr. Serhiy Demeshko Prof. Dr. Bas de Bruin Dr. Maxime A. Siegler Prof. Dr. Frantisek Hartl Dr. Jarl Ivar van der Vlugt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13965-13975
The new dinucleating redox‐active ligand ( LH4 ), bearing two redox‐active NNO‐binding pockets linked by a 1,2,3‐triazole unit, is synthetically readily accessible. Coordination to two equivalents of PdII resulted in the formation of paramagnetic (S= ) dinuclear Pd complexes with a κ2‐N,N′‐bridging triazole and a single bridging chlorido or azido ligand. A combined spectroscopic, spectroelectrochemical, and computational study confirmed Robin–Day Class II mixed‐valence within the redox‐active ligand, with little influence of the secondary bridging anionic ligand. Intervalence charge transfer was observed between the two ligand binding pockets. Selective one‐electron oxidation allowed for isolation of the corresponding cationic ligand‐based diradical species. SQUID (super‐conducting quantum interference device) measurements of these compounds revealed weak anti‐ferromagnetic spin coupling between the two ligand‐centered radicals and an overall singlet ground state in the solid state, which is supported by DFT calculations. The rigid and conjugated dinucleating redox‐active ligand framework thus allows for efficient electronic communication between the two binding pockets. 相似文献
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Dr. Kai E. O. Ylijoki Prof. Dr. Peter H. M. Budzelaar Prof. Dr. Jeffrey M. Stryker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(32):9894-9900
Alkyl‐substituted η5‐pentadienyl half‐sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η2,η3‐cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η5‐cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, C? C bond formation, olefin arm capture, and a second C? C bond formation; the initial decoordination/capture step is rate‐limiting. Once the η2,η3‐cycloheptadienyl complex has been formed, isomerization to η5‐cycloheptadienyl again involves several steps: olefin decoordination, β‐hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1‐ and 5‐positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3‐position have a strongly retarding effect on the same step. Substituents at the alkyne (2‐butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive. 相似文献
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Formal Gold‐to‐Gold Transmetalation of an Alkynyl Group Mediated by Palladium: A Bisalkynyl Gold Complex as a Ligand to Palladium 下载免费PDF全文
Alberto Toledo Dr. Isabel Meana Prof. Dr. Ana C. Albéniz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(38):13216-13220
The reaction of [Au(C?C?n‐Bu)]n with [Pd(η3‐allyl)Cl(PPh3)] results in a ligand and alkynyl rearrangement, and leads to the heterometallic complex [Pd(η3‐allyl){Au(C?C?n‐Bu)2}]2 ( 3 ) with an unprecedented bridging bisalkynyl–gold ligand coordinated to palladium. This is a formal gold‐to‐gold transmetalation that occurs through reversible alkynyl transmetalations between gold and palladium. 相似文献
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Santhosh Kumar K. S. Dr. Yugang Li Dr. Yves Gnanou Dr. Ulrich Baisch Dr. Yohan Champouret Dr. Rinaldo Poli Prof. Kiyoshi C. D. Robson W. Stephen McNeil Prof. 《化学:亚洲杂志》2009,4(8):1257-1265
Complexes Co[OC(Ph)CHC(Me)NAr]2 [Ar=Ph, 1 ; o,o′‐C6H3Me2 (Xyl), 2 ; p‐C6H4CF3, 3 ] are tested in the polymerization of vinyl acetate (VAc) initiated by V‐70 (0.8 equiv) at 30 °C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected Mn values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2 > 1 > 3 . Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V‐70/ 1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(β‐diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization. 相似文献
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Modulation of Benzene or Naphthalene Binding to Palladium Cluster Sites by the Backside‐Ligand Effect 下载免费PDF全文
Yuki Ishikawa Seita Kimura Kohei Takase Koji Yamamoto Dr. Yuki Kurashige Prof. Takeshi Yanai Prof. Tetsuro Murahashi 《Angewandte Chemie (International ed. in English)》2015,54(8):2482-2486
The backside‐ligand modulation strategy to enhance the substrate binding property of Pd clusters is reported. The benzene or naphthalene binding ability of Pd3 or Pd4 clusters is enhanced significantly by the backside cyclooctatetraene ligand, leading to the formation of the first solution‐stable benzene‐ or naphthalene Pd clusters. The present results imply that the ligand design of the metal clusters, especially for the backside ligand of the metal cluster site, is crucial to acquire a desired reactivity of metal clusters. 相似文献