共查询到20条相似文献,搜索用时 31 毫秒
1.
Flip Holtrop Dr. Andrew R. Jupp Bastiaan J. Kooij Nicolaas P. van Leest Prof. Dr. Bas de Bruin Prof. Dr. J. Chris Slootweg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22394-22400
Frustrated Lewis pairs (FLPs) are well known for their ability to activate small molecules. Recent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride, or tetrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events; that is, being direct SET to B(C6F5)3 or not. The reactions of H2 and Ph3SnH with archetypal P/B FLP systems do not proceed via a radical mechanism. In contrast, reaction with TCQ proceeds via SET, which is only feasible by Lewis acid coordination to the substrate. Furthermore, SET from the Lewis base to the Lewis acid–substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical main-group chemistry. 相似文献
2.
We report the reactivity between the water stable Lewis acidic trioxatriangulenium ion (TOTA+) and a series of Lewis bases such as phosphines and N-heterocyclic carbene (NHC). The nature of the Lewis acid–base interaction was analyzed via variable temperature (VT) NMR spectroscopy, single-crystal X-ray diffraction, UV-visible spectroscopy, and DFT calculations. While small and strongly nucleophilic phosphines, such as PMe3, led to the formation of a Lewis acid–base adduct, frustrated Lewis pairs (FLPs) were observed for sterically hindered bases such as P(tBu)3. The TOTA+–P(tBu)3 FLP was characterized as an encounter complex, and found to promote the heterolytic cleavage of disulfide bonds, formaldehyde fixation, dehydrogenation of 1,4-cyclohexadiene, heterolytic cleavage of the C–Br bonds, and interception of Staudinger reaction intermediates. Moreover, TOTA+ and NHC were found to first undergo single-electron transfer (SET) to form [TOTA]·[NHC]˙+, which was confirmed via electron paramagnetic resonance (EPR) spectroscopy, and subsequently form a [TOTA–NHC]+ adduct or a mixture of products depending the reaction conditions used.Frustration at carbon! Herein, we present a frustrated Lewis pair system derived from a water stable carbon-based Lewis acid, trioxatriangulene (TOTA+), and a variety of Lewis bases, which successfully promotes bond cleavage and molecule fixation. 相似文献
3.
Dr. Damian Pleschka Marten Uebing Dr. Merten Lange Dr. Alexander Hepp Anna-Lena Wübker Prof. Dr. Michael Ryan Hansen Prof. Dr. Ernst-Ulrich Würthwein Prof. Dr. Werner Uhl 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(39):9315-9325
Al/P- and Ga/P-based frustrated Lewis pairs (FLPs) reacted with an azirine under mild conditions under cleavage of the heterocycle on two different positions. Opening of the C−C bond yielded an unusual nitrile–ylide adduct in which a C−N moiety coordinated to the FLP backbone. Cleavage of a C−N bond afforded the thermodynamically favored enamine adduct with the N atom bound to P and Al or Ga atoms. Ring closure was observed upon treatment of an Al/P FLP with electronically unsaturated substrates (4-(1-cyclohexenyl)-1-aza-but-1-en-3-ynes) and yielded by C−N bond formation hexahydroquinoline derivatives, which coordinated to the FLP through P−C and Al−C bonds. Diphenylcyclopropenone showed a diverse reactivity, which depending on steric shielding and the polarizing effect of Al or Ga atoms afforded different products. An AltBu2/P FLP yielded an adduct with the C=O group coordinated to P and Al. The dineopentyl derivative gave an equilibrium mixture consisting of a similar product and a simple adduct with O bound to Al and a three-coordinate P atom. Both compounds co-crystallize. The Ga/P FLP only formed the simple adduct with the same substrate. Rearrangement resulted in all cases in C3-ring cleavage and migration of a mesityl group from P to a former ring C atom by C−C bond formation. Diphenylthiocyclopropenone (evidence for the presence of P=C bonds) and an imine derivative afforded similar products. 相似文献
4.
Thayalaraj Christopher Jeyakumar Masilamani Deepa Sambath Baskaran Chinnappan Sivasankar 《应用有机金属化学》2020,34(10):e5811
Activation and cleavage of molecular hydrogen (H2) to proton and hydride is an important task for several reasons, especially as a reagent in hydrogenation. In this scenario, with the support of density-functional theory methods, a novel strategy has been devised for the conversion of coordinated nitride into ammonia using molecular hydrogen in the presence of tri-tert-butylphosphine (PtBu3). The proposed methodology is based on the formation of frustrated Lewis pair (FLP) from [OsVI(tpy)(Cl)2(N)]+ (tpy = 2,2′:6′,2′′-terpyridine ) and PtBu3 followed by reaction with molecular hydrogen to form an FLP–H2 adduct. The FLP–H2 adduct can further undergo H–H bond cleavage heterolytically to produce proton and hydride which can be eventually used for the functionalization of coordinated nitride to ammonia. The calculated energy profile comprising all possible intermediates and transition-state molecules suggests that the proposed reaction pathway is energetically viable at elevated temperatures. 相似文献
5.
Accessing Frustrated Lewis Pair Chemistry from a Spectroscopically Stable and Classical Lewis Acid‐Base Adduct 下载免费PDF全文
Dr. Timothy C. Johnstone Gabriel N. J. H. Wee Prof. Dr. Douglas W. Stephan 《Angewandte Chemie (International ed. in English)》2018,57(20):5881-5884
B(C6F5)3 and P(MeNCH2CH2)3N form a classical Lewis adduct, (C6F5)3BP(MeNCH2CH2)3N. Although (C6F5)3BP(MeNCH2CH2)3N does not exhibit spectroscopic evidence of dissociation into its constituent acid and base, products of frustrated Lewis pair (FLP) addition reactions are seen with PhNCO, PhCH2N3, PhNSO, and CO2. Computational studies show that thermal access to the dissociated acid and base permits FLP reactivity to proceed. These results demonstrate that FLP reactivity extends across the entire continuum of equilibria governing Lewis acid‐base adducts. 相似文献
6.
Devin H. A. Boom Ewoud J. J. de Boed Emmanuel Nicolas Martin Nieger Andreas W. Ehlers Andrew R. Jupp J. Chris Slootweg 《无机化学与普通化学杂志》2020,646(13):586-592
The reaction of the intramolecular frustrated Lewis pair (FLP) tBu2PCH2BPh2 with the amine-boranes NH3 · BH3 and Me2NH · BH3 leads to the formation of the corresponding FLP-H2 adducts as well as novel five-membered heterocycles that result from capturing the in situ formed amino-borane by a second equivalent of FLP. The sterically more demanding tBu2PCH2BMes2 does not form such a five-membered heterocycle when reacted with Me2NH · BH3 and its H2 adduct liberates dihydrogen at elevated temperatures, promoting the metal-free catalytic dehydrogenation of amine-boranes. 相似文献
7.
Elucidating the Reactivity of Vicinal Dicarbenoids: From Lewis Adduct Formation to B−C Bond Activation 下载免费PDF全文
Hauke Kelch Stephanie Kachel Dr. Mehmet Ali Celik Dr. Marius Schäfer Dr. Benedikt Wennemann Dr. Krzysztof Radacki Dr. Alex R. Petrov Prof. Dr. Matthias Tamm Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13815-13818
The reactivity of the diaminoacetylene Pip‐C≡C‐Pip (Pip=piperidyl=NC5H10) towards phenyldichloro‐ and triphenylborane is presented. In the case of the less Lewis acidic PhBCl2, the first example of a double Lewis adduct of a vicinal dicarbenoid is reported. For the more Lewis acidic triphenylborane, coordination to the bifunctional carbene leads to a mild B?C bond activation, resulting in a syn‐1,2‐carboboration. Ensuing cis/trans isomerization yields a novel ethylene‐bridged frustrated Lewis pair (FLP). The compounds were characterized using multinuclear NMR spectroscopy, structural analysis, and mass spectrometry. Reactivity studies of both isomers with the N‐heterocyclic carbene 1,3‐dimethylimidazol‐2‐ylidene (IMe) aided in elucidating the proposed isomerization pathway. DFT calculations were carried out to elucidate the reaction mechanism. The rather low free energy of activation is consistent with the observation that the reaction proceeds smoothly at room temperature. 相似文献
8.
Nereida Hidalgo Dr. Juan José Moreno Marina Pérez-Jiménez Dr. Celia Maya Dr. Joaquín López-Serrano Dr. Jesús Campos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(27):5982-5993
A joint experimental/computational effort to elucidate the mechanism of dihydrogen activation by a gold(I)/platinum(0) metal-only frustrated Lewis pair (FLP) is described herein. The drastic effects on H2 activation derived from subtle ligand modifications have also been investigated. The importance of the balance between bimetallic adduct formation and complete frustration has been interrogated, providing for the first time evidence for genuine metal-only FLP reactivity in solution. The origin of a strong inverse kinetic isotopic effect has also been clarified, offering further support for the proposed bimetallic FLP-type cleavage of dihydrogen. 相似文献
9.
Dr. Alison C. McQuilken Quang Minh Dao Dr. Allan Jay P. Cardenas Dr. Jeffery A. Bertke Prof. Dr. Stefan Grimme Prof. Dr. Timothy H. Warren 《Angewandte Chemie (International ed. in English)》2016,55(46):14335-14339
We report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates iPr2ArNCO (iPr2Ar=2,6‐iPr2C6H3) and Ph2tBuArNCO (Ph2tBuAr=2,6‐Ph2‐4‐tBuC6H2) with Piers’ borane (HB(C6F5)2). While hydroboration of smaller isocyanates such as iPr2ArNCO leads to isocyanate—N/B FLP adducts, hydroboration of the bulkier Ph2tBuArNCO allows isolation of the substrate‐free aminoborane with a short, covalent N?B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a “normal” FLP along the reaction pathway, supported by high‐level DFT studies and variable‐temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid–base interaction. 相似文献
10.
B(C6F5)3‐Catalyzed Transfer Hydrogenation of Imines and Related Heteroarenes Using Cyclohexa‐1,4‐dienes as a Dihydrogen Source 下载免费PDF全文
Dr. Indranil Chatterjee Prof. Dr. Martin Oestreich 《Angewandte Chemie (International ed. in English)》2015,54(6):1965-1968
The strong boron Lewis acid tris(pentafluorophenyl)borane, B(C6F5)3, is shown to abstract a hydride from suitably donor‐substituted cyclohexa‐1,4‐dienes, eventually releasing dihydrogen. This process is coupled with the FLP‐type (FLP=frustrated Lewis pair) hydrogenation of imines and nitrogen‐containing heteroarenes that are catalyzed by the same Lewis acid. The net reaction is a B(C6F5)3‐catalyzed, i.e., transition‐metal‐free, transfer hydrogenation using easy‐to‐access cyclohexa‐1,4‐dienes as reducing agents. Competing reaction pathways with or without the involvement of free dihydrogen are discussed. 相似文献
11.
《Angewandte Chemie (International ed. in English)》2017,56(8):2198-2202
A bulky substituted stannane Ar*SnH3 (Ar*=2,6‐(2′,4′,6′‐triisopropylphenyl)phenyl) was treated with the well‐known frustrated Lewis pair (FLP) Pt Bu3/B(C6F5)3 in varying stoichiometries. To some degree, hydride abstraction and adduct formation is observed, leading to [Ar*SnH2(Pt Bu3)]+ which is rather unreactive toward further dehydrogenation. In a competing process, the FLP proved to be capable of completely striping‐off hydrogen and hydrides to generate the first cationic phosphonio‐stannylene [Ar*Sn(Pt Bu3)]+. This behavior provides insight into the activation/abstraction mechanism processes involved in these Group 14 hydride derivatives. 相似文献
12.
Daniel J. Scott Dr. Nicholas A. Phillips Joshua S. Sapsford Arron C. Deacy Dr. Matthew J. Fuchter Dr. Andrew E. Ashley 《Angewandte Chemie (International ed. in English)》2016,55(47):14738-14742
Despite the rapid development of frustrated Lewis pair (FLP) chemistry over the last ten years, its application in catalytic hydrogenations remains dependent on a narrow family of structurally similar early main‐group Lewis acids (LAs), inevitably placing limitations on reactivity, sensitivity and substrate scope. Herein we describe the FLP‐mediated H2 activation and catalytic hydrogenation activity of the alternative LA iPr3SnOTf, which acts as a surrogate for the trialkylstannylium ion iPr3Sn+, and is rapidly and easily prepared from simple, inexpensive starting materials. This highly thermally robust LA is found to be competent in the hydrogenation of a number of different unsaturated functional groups (which is unique to date for main‐group FLP LAs not based on boron), and also displays a remarkable tolerance to moisture. 相似文献
13.
Dr. Niklas Zwettler Prof. Dr. Nadia C. Mösch-Zanetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(24):6064-6076
Lewis acid–base pair chemistry has been placed on a new level with the discovery that adduct formation between an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introduction of steric demand, thus preserving the reactivity of both Lewis centers, resulting in highly unusual chemistry. Some of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting a variety of small molecules, such as dihydrogen, in a heterolytic and even catalytic manner. This is in sharp contrast to classical reactions where the inert substrate must be activated by a metal-based catalyst. Very recently, research has emerged combining the two concepts, namely the formation of FLPs in which a metal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being a Lewis acid or base, also ancillary ligands can be used as part of the Lewis pair, still with the benefit of the redox-active metal center nearby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition-metal or rare-earth-metal compounds with the Lewis acid B(C6F5)3. It covers a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Future goals of this young and exciting area are briefly discussed. 相似文献
14.
Dr. Devin H. A. Boom Dr. Andrew R. Jupp Dr. Martin Nieger Dr. Andreas W. Ehlers Prof. Dr. J. Chris Slootweg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13299-13308
The geminal frustrated Lewis pair (FLP) tBu2PCH2BPh2 ( 1 ) reacts with phenyl-, mesityl-, and tert-butyl azide affording, respectively, six, five, and four-membered rings as isolable products. DFT calculations revealed that the formation of all products proceeds via the six-membered ring structure, which is thermally stable with an N-phenyl group, but rearranges when sterically more encumbered Mes−N3 and tBu−N3 are used. The reaction of 1 with Me3Si−N3 is believed to follow the same course, yet subsequent N2 elimination occurs to afford a four-membered heterocycle ( 5 ), which can be considered as a formal FLP-trimethylsilylnitrene adduct. Compound 5 reacts with hydrochloric acid or tetramethylammonium fluoride and showed frustrated Lewis pair reactivity towards phenylisocyanate. 相似文献
15.
N‐Methylacridinium Salts: Carbon Lewis Acids in Frustrated Lewis Pairs for σ‐Bond Activation and Catalytic Reductions 下载免费PDF全文
Dr. Ewan R. Clark Dr. Michael J. Ingleson 《Angewandte Chemie (International ed. in English)》2014,53(42):11306-11309
N‐methylacridinium salts are Lewis acids with high hydride ion affinity but low oxophilicity. The cation forms a Lewis adduct with 4‐(N,N‐dimethylamino)pyridine but a frustrated Lewis pair (FLP) with the weaker base 2,6‐lutidine which activates H2, even in the presence of H2O. Anion effects dominate reactivity, with both solubility and rate of H2 cleavage showing marked anion dependency. With the optimal anion, a N‐methylacridinium salt catalyzes the reductive transfer hydrogenation and hydrosilylation of aldimines through amine–boranes and silanes, respectively. Furthermore, the same salt is active for the catalytic dehydrosilylation of alcohols (primary, secondary, tertiary, and ArOH) by silanes with no observable over‐reduction to the alkanes. 相似文献
16.
Autoinduced Catalysis and Inverse Equilibrium Isotope Effect in the Frustrated Lewis Pair Catalyzed Hydrogenation of Imines 下载免费PDF全文
Dipl.‐Chem. Sebastian Tussing Dr. Lutz Greb Dipl.‐Chem. Sergej Tamke Dr. Birgitta Schirmer Priv.‐Doz. Claudia Muhle‐Goll Prof. Dr. Burkhard Luy Prof. Dr. Jan Paradies 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8056-8059
The frustrated Lewis pair (FLP)‐catalyzed hydrogenation and deuteration of N‐benzylidene‐tert‐butylamine ( 2 ) was kinetically investigated by using the three boranes B(C6F5)3 ( 1 ), B(2,4,6‐F3‐C6H2)3 ( 4 ), and B(2,6‐F2‐C6H3)3 ( 5 ) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol?1) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect. 相似文献
17.
A Combined “Electrochemical–Frustrated Lewis Pair” Approach to Hydrogen Activation: Surface Catalytic Effects at Platinum Electrodes 下载免费PDF全文
Elliot J. Lawrence Dr. Robin J. Blagg Dr. David L. Hughes Dr. Andrew E. Ashley Dr. Gregory G. Wildgoose 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):900-906
Herein, we extend our “combined electrochemical–frustrated Lewis pair” approach to include Pt electrode surfaces for the first time. We found that the voltammetric response of an electrochemical–frustrated Lewis pair (FLP) system involving the B(C6F5)3/[HB(C6F5)3]? redox couple exhibits a strong surface electrocatalytic effect at Pt electrodes. Using a combination of kinetic competition studies in the presence of a H atom scavenger, 6‐bromohexene, and by changing the steric bulk of the Lewis acid borane catalyst from B(C6F5)3 to B(C6Cl5)3, the mechanism of electrochemical–FLP reactions on Pt surfaces was shown to be dominated by hydrogen‐atom transfer (HAT) between Pt, [Pt?H] adatoms and transient [HB(C6F5)3] ? electrooxidation intermediates. These findings provide further insight into this new area of combining electrochemical and FLP reactions, and proffers additional avenues for exploration beyond energy generation, such as in electrosynthesis. 相似文献
18.
Timo A. Kinder René Pior Dr. Sebastian Blomeyer Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Norbert W. Mitzel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(23):5899-5903
Chlorogermane (C2F5)3GeCl with very electronegative pentafluoroethyl groups was converted with LiCH2P(tBu)2 to obtain the intramolecular frustrated Lewis pair (FLP) (C2F5)3GeCH2P(tBu)2, a neutral, germanium-based FLP. Its reactivity was compared to its silicon homologue (C2F5)3SiCH2P(tBu)2. Both FLPs cleave NO but give cyclic (Si) and open-chain oxides (Ge). In reactions with HCl both FLPs gave the same adduct type in the solid state, while the proton seems more mobile in solution in the germanium case. Reactions with PhCNO and Me3SiCHN2 result in ring-type adducts. The structures of (C2F5)3GeCH2P(tBu)2 and of five adducts with substrates were elucidated by X-ray diffraction. The study clearly showed the germanium compound to have a more moderate Lewis acidity compared to the silicon analogue. 相似文献
19.
Idan Avigdori Dr. Alla Pogoreltsev Dr. Alexander Kaushanski Dr. Natalia Fridman Prof. Dr. Mark Gandelman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):23682-23685
N-heterocyclic nitrogen Lewis acids are a recent addition to the field of organic chemistry. Based on nitrenium cations, these acids where previously shown to generate Lewis adducts when combined with the appropriate Lewis bases. Herein, a triazinium-based Lewis acid was combined with tBu3P to generate a frustrated Lewis pair (FLP) capable of cleaving, for the first time, Si−H bonds in silanes. Whereas low yields were initially encountered owing to insufficient Lewis acidity, a new nitrenium-based Lewis acid was synthesized, and its superior Lewis acidity was experimentally and computationally confirmed. A FLP based on this acid cleaved the Si−H bond in PhSiH3, generating the triazane product in a quantitative yield. This unprecedented N−H triazane was fully characterized by multinuclear NMR techniques and single-crystal X-ray crystallography. A new class of compounds, N-H triazanes display the potential capacity to participate in hydride transfer reactions. 相似文献
20.
Philipp Holtkamp Felix Friedrich Erik Stratmann Andreas Mix Beate Neumann Hans‐Georg Stammler Norbert W. Mitzel 《Angewandte Chemie (International ed. in English)》2019,58(15):5114-5118
The geminal frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 ( 2 ) was prepared by reacting (F5C2)3SnCl with LiCH2P(tBu)2. It is neutral and contains an extremely electronegatively substituted, but relatively soft (hard–soft acid–base, HSAB) acidic tin function. Its FLP‐type reactivity was proven by reaction with a variety of small molecules (CO2, SO2, CS2, PhNCO, HCl, (Ph3P)AuCl). However, it shows no reaction in H/D scrambling experiments with H2/D2 mixtures and binds CO2 reversibly, as was observed by VT‐NMR spectroscopy. Compound 2 and all its adducts were completely characterized by means of multinuclear NMR spectroscopy, elemental analysis, and X‐ray diffraction experiments. 相似文献