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1.
Establishing the Coordination Chemistry of Antimony(V) Cations: Systematic Assessment of Ph4Sb(OTf) and Ph3Sb(OTf)2 as Lewis Acceptors 下载免费PDF全文
Dr. Alasdair P. M. Robertson Saurabh S. Chitnis Dr. Hilary A. Jenkins Dr. Robert McDonald Dr. Michael J. Ferguson Prof. Neil Burford 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7902-7913
The coordination chemistry of the stiboranes Ph4Sb(OTf) ( 1 a , OTf = OSO2CF3) and Ph3Sb(OTf)2 ( 3 ) with Lewis bases has been investigated. The significant steric encumbrance of the Sb center in 1 a precludes interaction with most ligands, but the relatively low steric demands of 4‐methylpyridine‐N‐oxide (OPyrMe) and OPMe3 enabled the characterization of [Ph4Sb(OPyrMe)][OTf] ( 2 a ) and [Ph4Sb(OPMe3)][OTf] ( 2 b ), rare examples of structurally characterized complexes of stibonium acceptors. In contrast, 3 was found to engage a variety of Lewis bases, forming stable isolable complexes of the form [Ph3Sb(donor)2][OTf]2 [donor=OPMe3 ( 6 a ), OPCy3 ( 6 b , Cy=cyclohexyl), OPPh3 ( 6 c ), OPyrMe ( 6 d )], [Ph3Sb(dmap)2(OTf)][OTf] ( 6 e , dmap=4‐(dimethylamino)pyridine) and [Ph3Sb(donor)(OTf)][OTf] [donor=1,10‐phenanthroline ( 7 a ) or 2,2′‐bipy ( 7 b , bipy=bipyridine)]. These compounds exhibit significant structural diversity in the solid‐state, and undergo ligand exchange reactions in line with their assignment as coordination complexes. Compound 3 did not form stable complexes with phosphine donors, with reactions instead leading to redox processes yielding SbPh3 and products of phosphine oxidation. 相似文献
2.
Metal‐Only Lewis Pairs by Reversible Insertion of Ruthenium and Osmium Fragments into Metal–Boron Double Bonds 下载免费PDF全文
Dipl.‐Chem. Stefanie Bertsch Dr. Rüdiger Bertermann Prof. Dr. Holger Braunschweig Dr. Alexander Damme Dr. Rian D. Dewhurst Dr. Ashwini K. Phukan Christian Saalfrank Dr. Alfredo Vargas Benedikt Wennemann Dr. Qing Ye 《Angewandte Chemie (International ed. in English)》2014,53(16):4240-4243
New metal‐only Lewis pairs (MOLPs: Ru→Cr and Os→Cr) are prepared by the insertion of a zerovalent ruthenium or osmium complex into chromium–boron double bonds of borylene complexes. The reaction creates new borylene complexes (the first ever for osmium), and is crystallization‐controlled; re‐dissolving the complexes results in regeneration of the starting materials. A mechanism is proposed based on DFT calculations, along with a computational study of the unusual MOLPs. 相似文献
3.
Prof. Dr. Douglas W. Stephan Prof. Dr. Gerhard Erker 《Angewandte Chemie (International ed. in English)》2015,54(22):6400-6441
Frustrated Lewis pairs (FLPs) are combinations of Lewis acids and Lewis bases in solution that are deterred from strong adduct formation by steric and/or electronic factors. This opens pathways to novel cooperative reactions with added substrates. Small‐molecule binding and activation by FLPs has led to the discovery of a variety of new reactions through unprecedented pathways. Hydrogen activation and subsequent manipulation in metal‐free catalytic hydrogenations is a frequently observed feature of many FLPs. The current state of this young but rapidly expanding field is outlined in this Review and the future directions for its broadening sphere of impact are considered. 相似文献
4.
Markus Lindqvist Dr. Kirill Axenov Dr. Martin Nieger Dr. Minna Räisänen Prof. Markku Leskelä Prof. Timo Repo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10412-10418
Dimethylamino‐(+)‐camphorenamine reacted with an equimolar amount of Piers’ borane, HB(C6F5)2, to give the corresponding iminium–hydroborate zwitterionic salt. Being in equilibrium with the parent enamine–HB(C6F5)2 N–B pair, this salt was able to split hydrogen heterolytically, hydrogenating the iminium group in the molecule. Detailed studies revealed that the hydrogen splitting in this reaction proceeded through an intermolecular pathway leading to a bornylamine–HB(C6F5)2 adduct. When the starting enamine is present in excess over HB(C6F5)2, the produced bornylamine–HB(C6F5)2 adduct breaks up, eliminating free bornylamine and forming the initial camphorenamine– HB(C6F5)2 pair. This results in hydrogenation of the camphorenamine framework in a catalytic fashion. 相似文献
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Prof. Frédéric‐Georges Fontaine Marc‐André Courtemanche Marc‐André Légaré 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(11):2990-2996
Metal‐free systems, including frustrated Lewis pairs (FLPs) have been shown to bind CO2. By reducing the Lewis acidity and basicity of the ambiphilic system, it is possible to generate active catalysts for the deoxygenative hydroboration of carbon dioxide to methanol derivatives with conversion rates comparable to those of transition‐metal‐based catalysts. 相似文献
7.
Molecular nitrogen (N2) is abundant in the atmosphere and, found in many biomolecules, an essential element of life. The Haber–Bosch process, developed over 100 years ago, requires relatively harsh conditions to activate N2 on the iron surface and generate ammonia for use as fertilizer or to produce other chemicals, leading to consumption of more than 2 % of the world's annual energy supply. Thus, developing “green” approaches for N2 activation under mild conditions is particularly important and urgent. Here we demonstrate that a metal‐free N2 activation could be favorable both thermodynamically and kinetically (with an activation energy as low as 9.1 kcal mol?1) by using a carbon‐boron formal frustrated Lewis pair, which is supported by high‐level coupled cluster calculations. Mechanistic studies reveal that aromaticity plays a crucial role in stabilizing both the transition state and the product. Our findings highlight the importance of a combination of an N‐heterocyclic carbene with a methyleneborane unit in metal‐free N2 activation, providing conceptual guidance for experimental realization. 相似文献
8.
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
9.
Masato Hirai Prof. Dr. François P. Gabbaï 《Angewandte Chemie (International ed. in English)》2015,54(4):1205-1209
Because of hydration, fluoride ions in water typically elude complexation by neutral Lewis acids. Here, we show how this limitation can be overcome with a bidentate Lewis acid containing two antimony(V) centers. This derivative ( 2 ) is obtained by the simple reaction of 4,5‐bis(diphenylstibino)‐9,9‐dimethylxanthene ( 1 ) with two equivalents of 3,4,5,6‐tetrachlorobenzoquinone (o‐chloranil). It features two square‐pyramidal stiborane units oriented in a face‐to‐face fashion. Titration experiments show that this new bidentate Lewis acid binds fluoride in aqueous solutions containing 95 % water with a binding constant (K) of 700±30 M ?1. The structure of the fluoride adduct confirms fluoride anion chelation between the two antimony centers. 相似文献
10.
Alexander E. Waked Rouzbeh Ostadsharif Memar Prof. Dr. Douglas W. Stephan 《Angewandte Chemie (International ed. in English)》2018,57(37):11934-11938
Reaction of PPh3 and [(p‐ClC6H4)N2][BF4] affords [(p‐ClC6H4)N(PPh3)N(PPh3)][BF4] 1 , while reaction with (Ph2PCH2)2 gave [(p‐ClC6H4)(NPh2PCH2)2)][BF4] 2 . These species confirm the Lewis acidity of [(p‐ClC6H4)N2(PR3)][BF4] cations at N. In contrast, use of bulky phosphines afford the species [ArN2(PR3)][BF4] (R=tBu 3 , Mes 4 ). Compound 3 undergoes one electron reduction to give the stable radical [(p‐ClC6H4)N2(PtBu3)]. 5 . Combination of 3 and PtBu3 acts as an FLP to effect (SPh)2 cleavage, generating [PhSPtBu3]+ and the radical [ArN2(PR3)].. Collectively, these data affirm the ability of the cations [ArN2(PR3)]+ to behave as one or two electron acceptors. 相似文献
11.
Metal‐Free Dihydrogen Oxidation by a Borenium Cation: A Combined Electrochemical/Frustrated Lewis Pair Approach 下载免费PDF全文
Elliot J. Lawrence Thomas J. Herrington Dr. Andrew E. Ashley Dr. Gregory G. Wildgoose 《Angewandte Chemie (International ed. in English)》2014,53(37):9922-9925
In order to use H2 as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H2 into 2 H+ and 2 e?. Herein, we report a metal‐free approach to catalyze the oxidation of H2 by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H2 with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC‐stabilized borenium cation [(IiPr2)(BC8H14)]+ (IiPr2=C3H2(NiPr)2, NHC=N‐heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H2 oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol?1. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C6F5)3, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach. 相似文献
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Alvaro A. Omaa Rachel K. Green Ryo Kobayashi Yingjie He Evan R. Antoniuk Michael J. Ferguson Yuqiao Zhou Jonathan G. C. Veinot Takeaki Iwamoto Alex Brown Eric Rivard 《Angewandte Chemie (International ed. in English)》2021,60(1):228-231
The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB , iPr2P(C6H4)BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2}] and [PB{GeH2}] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine‐borane ligand ( PB ) after element deposition, and 2) the single‐source precursor [PB{SiH2}] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2}] was also prepared, and shown to release poly(dimethylsilane) [SiMe2]n upon heating. Overall, this study introduces a “closed loop” deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures. 相似文献
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Michael Weger Raphael K. Grtsch Maximilian G. Knaus Marco M. Giuman David C. Mayer Philipp J. Altmann Estelle Mossou Birger Dittrich Alexander Pthig Bernhard Rieger 《Angewandte Chemie (International ed. in English)》2019,58(29):9797-9801
Deprotonation usually occurs as an unwanted side reaction in the Lewis pair polymerization of Michael acceptors, for which the conjugated addition of the Lewis base to the acid‐activated monomer is the commonly accepted initiation mechanism. This has also been reported for B?P‐based bridged Lewis pairs (BLPs) that form macrocyclic addition products. We now show that the formerly unwanted deprotonation is the likely initiation pathway in the case of Al?P‐based BLPs. In a detailed study of a series of Al?P‐based BLPs, using a combination of single‐crystal diffraction experiments (X‐ray and neutron) and mechanistic investigations (experimental and computational), an active role of the methylene bridge was revealed, acting as a base towards the α‐acidic monomers. Additionally, the polymerization studies proved a living behavior combined with significantly high activities, narrow molecular mass distributions, and the possibility of copolymerization. 相似文献
16.
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
17.
Marina Uzelac Dr. David R. Armstrong Dr. Alan R. Kennedy Prof. Eva Hevia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15826-15833
This study reports the use of the trisalkylgallium GaR3 (R=CH2SiMe3), containing sterically demanding monosilyl groups, as an effective Lewis‐acid component for frustrated Lewis pair activation of carbonyl compounds, when combined with the bulky N‐heterocyclic carbene 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (ItBu) or 1,3‐bis(tert‐butyl)imidazolin‐2‐ylidene (SItBu). The reduction of aldehydes can be achieved by insertion into the C=O functionality at the C2 (so‐called normal) position of the carbene affording zwitterionic products [ItBuCH2OGaR3] ( 1 ) or [ItBuCH(p‐Br‐C6H4)OGaR3] ( 2 ), or alternatively, at its abnormal (C4) site yielding [aItBuCH(p‐Br‐C6H4)OGaR3] ( 3 ). As evidence of the cooperative behaviour of both components, ItBu and GaR3, neither of them alone are able to activate any of the carbonyl‐containing substrates included in this study NMR spectroscopic studies of the new compounds point to complex equilibria involving the formation of kinetic and thermodynamic species as implicated through DFT calculations. Extension to ketones proved successful for electrophilic α,α,α‐trifluoroacetophenone, yielding [aItBuC(Ph)(CF3)OGaR3] ( 7 ). However, in the case of ketones and nitriles bearing acidic hydrogen atoms, C?H bond activation takes place preferentially, affording novel imidazolium gallate salts such as [{ItBuH}+{(p‐I‐C6H4)C(CH2)OGaR3}?] ( 8 ) or [{ItBuH}+{Ph2C=C=NGaR3}?] ( 12 ). 相似文献
18.
Dr. Bao‐Hua Xu Raul Alfonso Adler Yanez Hiroshi Nakatsuka Prof. Dr. Masato Kitamura Dr. Gerald Kehr Prof. Dr. Gerhard Erker 《化学:亚洲杂志》2012,7(6):1347-1356
The frustrated Lewis pair (FLP) Mes2PCH2CH2B(C6F5)2 ( 1 ) reacts with an enolizable conjugated ynone by 1,4‐addition involving enolate tautomerization to give an eight‐membered zwitterionic heterocycle. The conjugated endione PhCO‐CH?CH‐COPh reacts with the intermolecular FLP tBu3P/B(C6F5)3 by a simple 1,4‐addition to an enone subunit. The same substrate undergoes a more complex reaction with the FLP 1 that involves internal acetal formation to give a heterobicyclic zwitterionic product. FLP 1 reacts with dimethyl maleate by selective overall addition to the C?C double bond to give a six‐membered heterocycle. It adds analogously to the triple bond of an acetylenic ester to give a similarly structured six‐membered heterocycle. The intermolecular FLP P(o‐tolyl)3/B(C6F5)3 reacts analogously with acetylenic ester by trans‐addition to the carbon–carbon triple bond. An excess of the intermolecular FLP tBu3P/B(C6F5)3, which contains a more nucleophilic phosphane, reacts differently with acetylenic ester examples, namely by O? C(alkyl) bond cleavage to give the {R‐CO2[B(C6F5)3]2?}[alkyl‐PtBu3+] salts. Simple aryl or alkyl esters react analogously by using the borane‐stabilized carboxylates as good leaving groups. All essential products were characterized by X‐ray diffraction. 相似文献
19.
Xiong Sun Qin Zhu Zhuoyi Xie Dr. Wei Su Prof. Dr. Jun Zhu Prof. Dr. Congqing Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14295-14299
Frustrated Lewis pairs (FLPs) represent a new paradigm of main-group chemistry. The Lewis acidic centers in FLP chemistry are typically B and Al atoms in the studies reported over the past decade, and most of them are tri-coordinated with strong electron-withdrawing groups. Herein, a Ga/P system is reported which contains an unprecedented four-coordinated Lewis acidic Ga center. This Ga/P species performs classical addition reactions toward heterocumulenes, alkyne, diazomethane, and transition metal complex. Regioselective formation of the products can be rationalized by DFT calculations. The penta-coordinated gallium atom center in these products is rare in the FLP chemistry. This study enriches the diversity of FLPs and demonstrates that a four-coordinated Lewis acidic site with a donor-acceptor bond can also be FLP active. 相似文献