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1.
Conor Pranckevicius Christoph Herok Felipe Fantuzzi Bernd Engels Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2019,58(37):12893-12897
Singly NHC‐coordinated (aminoboryl)aminoborenium salts react with Na2[Fe(CO)4] to yield stable coordination complexes of aminoborylene‐stabilized aminoborylenes, which exhibit exceptional σ‐donor properties. Upon photolytic CO extrusion from the metal center, the diboron ligand adopts a novel η3‐BBN coordination mode, where bond‐strengthening backdonation from the metal center into the vacant B?B π‐orbital is observed. This bonding situation can be alternatively described as a Fe‐diaminodiborene complex. In a related reduction of CAAC‐stabilized (aminoboryl)aminoborenium with KC8, the reduced species can be captured with nucleophiles to form three‐coordinate (diaminoboryl)borylenes, where both amino groups have migrated to the distal boron atom. Collectively, these reactions illustrate the isomeric flexibility imparted by amino groups on this reduced diboron system, thus opening multiple avenues of novel reactivity. 相似文献
2.
Low‐Temperature N2 Binding to Two‐Coordinate L2Fe0 Enables Reductive Trapping of L2FeN2− and NH3 Generation
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Dr. Gaël Ung Prof. Jonas C. Peters 《Angewandte Chemie (International ed. in English)》2015,54(2):532-535
The two‐coordinate [(CAAC)2Fe] complex [CAAC=cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T80 °C). The resulting putative three‐coordinate N2 complex, [(CAAC)2Fe(N2)], was trapped by one‐electron reduction to its corresponding anion [(CAAC)2FeN2]? at low temperature. This complex was structurally characterized and features an activated dinitrogen unit which can be silylated at the β‐nitrogen atom. The redox‐linked complexes [(CAAC)2FeI][BArF4], [(CAAC)2Fe0], and [(CAAC)2Fe?IN2]? were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC8 and HBArF4?2 Et2O at ?95 °C [up to (3.4±1.0) equivalents of ammonia per Fe center]. The N2 reduction activity is highly temperature dependent, with significant N2 reduction to NH3 only occurring below ?78 °C. This reactivity profile tracks with the low temperatures needed for N2 binding and an otherwise unavailable electron‐transfer step to generate reactive [(CAAC)2FeN2]?. 相似文献
3.
The Synthesis of B2(SIDip)2 and its Reactivity Between the Diboracumulenic and Diborynic Extremes
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Julian Bhnke Holger Braunschweig Theresa Dellermann William C. Ewing Kai Hammond J. Oscar C. Jimenez‐Halla Thomas Kramer Jan Mies 《Angewandte Chemie (International ed. in English)》2015,54(46):13801-13805
A new compound with the formula L‐B2‐L wherein the stabilizing ligand (L) is 1,3‐bis[diisopropylphenyl]‐4,5‐dihydroimidazol‐2‐ylidene (SIDip) has been synthesized, isolated, and characterized. The π‐acidity of the SIDip ligand, intermediate between the relatively non‐acidic IDip (1,3‐bis[diisopropylphenyl]imidazol‐2‐ylidene) ligand and the much more highly acidic CAAC (1‐[2,6‐diisopropylphenyl]‐3,3,5,5‐tetramethylpyrrolidin‐2‐ylidene) ligand, gives rise to a compound with spectroscopic, electrochemical, and structural properties between those of L‐B2‐L compounds stabilized by CAAC and IDip. Reactions of all three L‐B2‐L compounds with CO demonstrate the differences caused by their respective ligands, as the π‐acidities of the CAAC and SIDip carbenes enabled the isolation of bis(boraketene) compounds (L(OC)B‐B(CO)L), which could not be isolated from reactions with B2(IDip)2. However, only B2(IDip)2 and B2(SIDip)2 could be converted into bicyclic bis(boralactone) compounds. 相似文献
4.
Wenlong Yang Kelsie E. Krantz Diane A. Dickie Andrew Molino David J. D. Wilson Robert J. Gilliard 《Angewandte Chemie (International ed. in English)》2020,59(10):3971-3975
The synthesis and reactivity study of the first isolable boraphosphaketene, cyclic(alkyl)(amino) carbene (CAAC)‐borafluorene‐P=C=O ( 2 ), is described. Photolysis of compound 2 results in the formation of CAAC‐stabilized BP‐doped phenanthryne ( 3 ) through tandem decarbonylation, monoatomic phosphide insertion, and ring‐expansion. Notably, while BN‐doped phenanthryne was previously discussed as a reactive intermediate which could not be isolated, the heavier BP‐doped analogue exhibits remarkable solution and solid‐state stability. The reactivity of 2 with stable carbenes was also explored. Addition of CAAC to 2 led to migration of the original CAAC ligand from boron to phosphorus and coordination of the added CAAC to carbon, affording compound 4 . Reaction of 1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene (NHC) with 2 resulted in N?C bond activation to give the unusual spiro‐heterocyclic compound ( 5 ). 相似文献
5.
Dr. Philipp Bissinger Prof. Dr. Holger Braunschweig Dr. Alexander Damme Dr. Thomas Kupfer Dr. Ivo Krummenacher Dr. Alfredo Vargas 《Angewandte Chemie (International ed. in English)》2014,53(22):5689-5693
The realization of a phosphine‐stabilized diborene, Et3P?(Mes)B?B(Mes)?PEt3 ( 4 ), by KC8 reduction of Et3P?B2Mes2Br2 in benzene enabled the evaluation and comparison of its electronic structure to the previously described NHC‐stabilized diborene IMe?(Dur)B?B(Dur)?IMe ( 1 ). Importantly, both species feature unusual electron‐rich boron centers. However, cyclic voltammetry, UV/Vis spectroscopy, and DFT calculations revealed a significant influence of the Lewis base on the reduction potential and absorption behavior of the B? B double bond system. Thus, the stronger σ‐donor strength and larger electronegativity of the NHC ligand results in an energetically higher‐lying HOMO, making 1 a stronger neutral reductant as 4 ( 1 : E1/2=?1.55 V; 4 : ?1.05 V), and a smaller HOMO–LUMO gap of 1 accompanied by a noticeable red‐shift of its lowest‐energy absorption band with respect to 4 . Owing to the highly negative reduction potentials, 1 and 4 were easily oxidized to afford rare boron‐centered radical cations ( 5 and 6 ). 相似文献
6.
Audrey Cassen Yann Gloaguen Laure Vendier Carine Duhayon Amalia Poblador‐Bahamonde Christophe Raynaud Eric Clot Gilles Alcaraz Sylviane Sabo‐Etienne 《Angewandte Chemie (International ed. in English)》2014,53(29):7569-7573
Tuning the nature of the linker in a L~BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C? H and ε‐Bsp2? H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH2P2” fragment through connected σ‐bonds of different polarity, and affords selective B? H, C? H, and B? C bond activation as illustrated by reactivity studies with H2 and boranes. 相似文献
7.
L3C3P3: Tricarbontriphosphide Tricyclic Radicals and Cations Stabilized by Cyclic (alkyl)(amino)carbenes
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Dr. Zhongshu Li Yuanfeng Hou Yaqi Li Dr. Alexander Hinz Prof. Dr. Jeffrey R. Harmer Prof. Dr. Cheng‐Yong Su Prof. Dr. Guy Bertrand Prof. Dr. Hansjörg Grützmacher 《Angewandte Chemie (International ed. in English)》2018,57(1):198-202
Alkynes usually oligomerize to give rings with a conjugated π‐electron system. In contrast, phosphaalkynes, R?C≡P, frequently give compounds with polycyclic structures, which are thermodynamically more stable than the corresponding π‐conjugated isomers. The syntheses of the first C3P3 tricyclic compounds are reported with either radical or cationic ground states stabilized by cyclic (alkyl)(amino)carbenes (CAACs). These compounds may be considered as examples of tricarbontriphosphide coordinated by carbenes and are likely formed via trimerization of the corresponding mono‐radicals CAAC‐CP.. The mechanism for the formation of these tricarbontriphosphide radicals has been rationalized by a combination of experiments and DFT calculations. 相似文献
8.
Bottleable Neutral Analogues of [B2H5]− as Versatile and Strongly Binding η2 Donor Ligands
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Dr. Sunewang R. Wang Dominic Prieschl James D. Mattock Dr. Merle Arrowsmith Dr. Conor Pranckevicius Dr. Tom E. Stennett Dr. Rian D. Dewhurst Dr. Alfredo Vargas Prof. Dr. Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2018,57(21):6347-6351
Herein we report the discovery that two bottleable, neutral, base‐stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B?B bond. The resulting complexes represent the first known complexes containing unsupported, neutral σB?B diborane ligands. Single‐crystal X‐ray analyses of these complexes show that the X?Cu moiety (X=Cl, OTf, C6F5) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B?B bond, interacting almost equally with both boron atoms and causing a B?B bond elongation. DFT studies show that σ donation from and π backdonation to the pseudo‐π‐like B?B bond account for their formation. Astoundingly, these copper σB?B complexes are inert to ligand exchange with pyridine under either heating or photoirradiation. 相似文献
9.
Wenlong Yang Kelsie E. Krantz Lucas A. Freeman Diane A. Dickie Andrew Molino Gernot Frenking Sudip Pan David J. D. Wilson Robert J. Gilliard 《Angewandte Chemie (International ed. in English)》2020,59(10):3850-3854
N‐Heterocyclic carbene (NHC)‐ and cyclic (alkyl)(amino)carbene (CAAC)‐stabilized borafluorene radicals have been isolated and characterized by elemental analysis, single‐crystal X‐ray diffraction, UV/Vis absorption, cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and theoretical studies. Both the CAAC–borafluorene radical ( 2 ) and the NHC–borafluorene radical ( 4 ) have a considerable amount of spin density localized on the boron atoms (0.322 for 2 and 0.369 for 4 ). In compound 2 , the unpaired electron is also partly delocalized over the CAAC ligand carbeneC and N atoms. However, the unpaired electron in compound 4 mainly resides throughout the borafluorene π‐system, with significantly less delocalization over the NHC ligand. These results highlight the Lewis base dependent electrostructural tuning of materials‐relevant radicals. Notably, this is the first report of crystalline borafluorene radicals, and these species exhibit remarkable solid‐state and solution stability. 相似文献
10.
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
11.
Takao Kikuchi Jun Takagi Dr. Hironori Isou Tatsuo Ishiyama Prof. Dr. Norio Miyaura Dr. 《化学:亚洲杂志》2008,3(12):2082-2090
Borylation of the vinylic C? H bond of 1,4‐dioxene, 2,3‐dihydrofuran, 3,4‐dihydro‐2H‐pyran and their γ‐substituted analogs was carried out in the presence of bis(pinacolato)diboron (B2pin2) and a catalytic amount of IrI‐dtbpy (dtbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine) complex. The two boron atoms in B2pin2 participated in the coupling, thus giving two equivalents of the coupling product from one equivalent of B2pin2. The borylation of 1,4‐dioxene in hexane resulted in 81 % yield at room temperature. The borylation of 2,3‐dihydrofurans at 80 °C in octane suffered from low regioselectivity, and gave a mixture of α‐ and β‐coupling products even for hindered γ‐disubstituted analogs, but γ‐substituted analogs of 3,4‐dihydro‐2H‐pyran achieved high α‐selectivity, giving single coupling products. This protocol was applied to the syntheses of a key precursor of vineomycinone B2 methyl ester and other C‐substituted D ‐glucals by borylation of protected D ‐glucals with B2pin2 to give α‐boryl glucal followed by cross‐coupling with haloarenes, benzyl bromide, and allyl bromide. A catalytic cycle that involves the oxidative addition of sp2 C? H bond to iridium(III)‐trisboryl intermediate as the rate‐determining step has been proposed. 相似文献
12.
Dr. Huaiyu Zhang Dr. Rui Yuan Prof. Dr. Wei Wu Prof. Dr. Yirong Mo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(12):2619-2625
Recently, Braunschweig et al. found that borylene (CAAC)DurB, in which CAAC is a cyclic alkyl(amino) carbene and Dur refers to 2,3,5,6-tetramethylphenyl, can bind and activate N2, and the resulting [(CAAC)DurB]2N2 is of a bent BNNB core. The N2 ligand in transition metal complexes is generally linear, so herein, the bonding nature of both terminal end-on and end-on bridging borylene-N2 complexes is investigated with valence bond (VB) theory. In the terminal end-on (CAAC)HBN2 the bonding follows the mechanism in transition metals with a σ donation and a π back-donation, but in the end-on bridging borylene-N2 complex, the σ donation comes from the π orbitals of N2, and thus, there are two opposite and perpendicular push–pull channels. It is the push–pull interaction that governs the enhanced activation of N2 and the BNNB bent geometry. It is expected that the substituents bonded to B can modulate the bent angle and the strength of the push–pull interaction. Indeed, (CAAC)FB exhibits enhanced catalytic capacity for the activation of N2. 相似文献
13.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(33):9961-9964
A zwitterionic boraalkenyl boronium 3 was synthesized by reduction of cyclic (alkyl)(amino)carbene (cAAC) and trimethylphosphine (PMe3)‐coordinated tetrabromodiborane 2 with KC8 in the presence of PMe3. Further reduction of 3 led to the formation of neutral allenic diborene 4 . X‐ray diffraction and computational studies revealed that 4 features the cumulated C=B and B=B double bonds. The reaction of 4 with four isonitrile molecules afforded a heterocycle 5 with the B2C3 five‐membered ring, via a complete scission of the B=B bond of 4 . 相似文献
14.
Dr. Kartik Chandra Mondal Dr. Sudipta Roy Dr. Susmita De Dr. Pattiyil Parameswaran Dr. Birger Dittrich Dr. Fabian Ehret Prof. Dr. Wolfgang Kaim Prof. Dr. Herbert W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11646-11649
Compound (Me2‐cAAC:)2Co0 ( 2 ; Me2‐cAAC:=cyclic (alkyl) amino carbene; :C(CH2)(CMe2)2N‐2,6‐iPr2C6H3) was synthesized by the reduction of the precursor (Me2‐cAAC:)2CoICl ( 1 ) with KC8 in THF. The cyclic voltammogram of 1 exhibited one‐electron reduction, which suggests that synthesis of a bent 2‐metallaallene ( 2 ) from 1 should be possible. Compound 2 contains one cobalt atom in the formal oxidation state zero, which is stabilized by two Me2‐cAAC: ligands. Bond lengths from X‐ray diffraction are 1.871(2) and 1.877(2) Å with a C‐Co‐C bond angle of 170.12(8)°. The EPR spectrum of 2 exhibited a broad resonance attributed to the unique quasi‐linear structure, which favors near degeneracy and gives rise to very rapid relaxation conditions. The cAAC?Co bond in 2 can be considered as a typical Dewar–Chatt–Duncanson type of bonding, which in turn retains 2.5 electron pairs on the Co atom as nonbonding electrons. 相似文献
15.
Triamidoamine–Uranium(IV)‐Stabilized Terminal Parent Phosphide and Phosphinidene Complexes
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Dr. Benedict M. Gardner Dr. Gábor Balázs Prof. Dr. Manfred Scheer Dr. Floriana Tuna Prof. Eric J. L. McInnes Dr. Jonathan McMaster Dr. William Lewis Prof. Alexander J. Blake Prof. Stephen T. Liddle 《Angewandte Chemie (International ed. in English)》2014,53(17):4484-4488
Reaction of [U(TrenTIPS)(THF)][BPh4] ( 1 ; TrenTIPS=N{CH2CH2NSi(iPr)3}3) with NaPH2 afforded the novel f‐block terminal parent phosphide complex [U(TrenTIPS)(PH2)] ( 2 ; U–P=2.883(2) Å). Treatment of 2 with one equivalent of KCH2C6H5 and two equivalents of benzo‐15‐crown‐5 ether (B15C5) afforded the unprecedented metal‐stabilized terminal parent phosphinidene complex [U(TrenTIPS)(PH)][K(B15C5)2] ( 4 ; U?P=2.613(2) Å). DFT calculations reveal a polarized‐covalent U?P bond with a Mayer bond order of 1.92. 相似文献
16.
Room Temperature Ring Expansion of N‐Heterocyclic Carbenes and BB Bond Cleavage of Diboron(4) Compounds
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Sabrina Pietsch Ursula Paul Dr. Ian A. Cade Dr. Michael J. Ingleson Prof. Dr. Udo Radius Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9018-9021
We report the isolation and detailed structural characterization, by solid‐state and solution NMR spectroscopy, of the neutral mono‐ and bis‐NHC adducts of bis(catecholato)diboron (B2cat2). The bis‐NHC adduct undergoes thermally induced rearrangement, forming a six‐membered ‐B?C?N?C?C‐N‐heterocyclic ring via C?N bond cleavage and ring expansion of the NHC, whereas the mono‐NHC adduct is stable. Bis(neopentylglycolato)diboron (B2neop2) is much more reactive than B2cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis. 相似文献
17.
Liu Leo Liu Levy L. Cao Jiliang Zhou Douglas W. Stephan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(1):279-283
The reactions of the cyclic alkyl amino carbene (CAAC) 1 with phosphaalkynes generate the kinetically unstable CAAC‐derived phosphirenes 4 and 5 , which undergo rearrangement/dimerization reactions to give the vinyl‐substituted diphosphenes 2 , 3 , and 6 . The P=P double bond scission of 2 or 3 is unprecedentedly effected by S8, [AuCl(tht)], or MeOTf at room temperature, which affords a dithiophosphorane 7 , a phosphepine Au complex 8 , or phosphepinium cations 9 and 10 , respectively. The cationic species feature little homoaromaticity while representing the first examples of the phosphorus‐containing analogue of the tropylium ion. 相似文献
18.
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
19.
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
20.
Uwe Schmidt Luis Werner Merle Arrowsmith Andrea Deissenberger Alexander Hermann Alexander Hofmann Stefan Ullrich James D. Mattock Alfredo Vargas Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2020,59(1):325-329
The reaction of aryl‐ and amino(dihydro)boranes with dibora[2]ferrocenophane 1 leads to the formation 1,3‐trans‐dihydrotriboranes by formal hydrogenation and insertion of a borylene unit into the B=B bond. The aryltriborane derivatives undergo reversible photoisomerization to the cis‐1,2‐μ‐H‐3‐hydrotriboranes, while hydride abstraction affords cationic triboranes, which represent the first doubly base‐stabilized B3H4+ analogues. 相似文献