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Evidence for Extensive Single‐Electron‐Transfer Chemistry in Boryl Anions: Isolation and Reactivity of a Neutral Borole Radical
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Dr. Rüdiger Bertermann Prof. Dr. Holger Braunschweig Dr. Rian D. Dewhurst Dipl.‐Chem. Christian Hörl Dipl.‐Chem. Thomas Kramer Dr. Ivo Krummenacher 《Angewandte Chemie (International ed. in English)》2014,53(21):5453-5457
Despite the synthesis of a boryl anion by Yamashita et al. in 2006, compounds that show boron‐centered nucleophilicity are still rare and sought‐after synthetic goals. A number of such boryl anions have since been prepared, two of which were reported to react with methyl iodide in apparent nucleophilic substitution reactions. One of these, a borolyl anion based on the borole framework, has now been found to display single‐electron‐transfer (SET) reactivity in its reaction with triorganotetrel halides, which was confirmed by the isolation of the first neutral borole‐based radical. The radical was characterized by elemental analysis, single‐crystal X‐ray crystallography, and EPR spectroscopy, and has implications for the understanding of boron‐based nucleophilic behavior and the emergent role of boron radicals in synthesis. This radical reactivity was also exploited in the synthesis of compounds with rare B? Sn and B? Pb bonds, the latter of which was the first isolated and structurally characterized compound with a “noncluster” B? Pb bond. 相似文献
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Johannes Krebs Martin Haehnel Dr. Ivo Krummenacher Dr. Alexandra Friedrich Prof. Dr. Holger Braunschweig Prof. Dr. Maik Finze Prof. Dr. Lei Ji Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(31):8159-8167
Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC6H4)-closo-1,2-C2B10H10-2-)2(4-MeC6H4)B] ( 1 ), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr2. Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1.− was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1 , 1.− , their calculated geometries, and the S1 excited state of 1 . Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals. 相似文献
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Prof. Holger Braunschweig Dr. Ching‐Wen Chiu Dr. Daniela Gamon Prof. Martin Kaupp Dr. Ivo Krummenacher Dr. Thomas Kupfer Dipl. Chem. Robert Müller Dr. Krzysztof Radacki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(37):11732-11746
Herein, we report on the synthesis of ferrocenylborole [Fc(BC4Ph4)2] featuring two borole moieties in the 1,1′‐positions. The results of NMR and UV/Vis spectroscopy and X‐ray diffraction studies provided conclusive evidence for the enhanced Lewis acidity of the boron centers resulting from the conjugation of two borole fragments. This finding was further validated by the reaction of [Fc(BC4Ph4)2] and the 4‐Me‐NC5H4 adduct of monoborole [Fc(BC4Ph4)], which led to quantitative transfer of the Lewis base. The coordination chemistry of ferrocenylboroles was further studied by examining their reactivity towards several pyridine bases. Accordingly, the strong Lewis acidity of boroles in general was nicely demonstrated by the reaction of [Fc(BC4Ph4)] with 4,4′‐bipyridine. Unlike common borane derivatives such as [FcBMe2], which only forms a 2:1 adduct, we also succeeded in the isolation of a 1:1 Lewis acid/base adduct, with one nitrogen donor of 4,4′‐bipyridine remaining uncoordinated. In addition, the reduction chemistry of ferrocenylboroles [Fc(BC4Ph4)] and [Fc(BC4Ph4)2] has been studied in more detail. Thus, depending on the reducing agent and the reaction stoichiometry, chemical reduction of [Fc(BC4Ph4)] might lead to the migration of the borolediide fragment towards the iron center, affording dianions with either η5‐coordinated C5H4 or η5‐coordinated BC4Ph4 moieties. In contrast, no evidence for borole migration was observed during reduction of bisborole [Fc(BC4Ph4)2], which readily resulted in the formation of the corresponding tetraanion. Finally, our efforts to further enhance the borole ratio in ferrocenylboroles aiming at the synthesis of [Fc(BC4Ph4)4] failed and, instead, generated an uncommon ansa‐ferrocene containing two borole fragments in the 1,1′‐positions and a B2C4 ansa‐bridge. 相似文献
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Hydroboration of Alkynes with Zwitterionic Ruthenium–Borate Complexes: Novel Vinylborane Complexes
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R. S. Anju Bijan Mondal Koushik Saha Subir Panja Babu Varghese Prof. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11393-11400
Building upon previous studies on the synthesis of bis(sigma)borate and agostic complexes of ruthenium, the chemistry of nido‐[(Cp*Ru)2B3H9] ( 1 ) with other ligand systems was explored. In this regard, mild thermolysis of nido‐ 1 with 2‐mercaptobenzothiazole (2‐mbzt), 2‐mercaptobenzoxazole (2‐mbzo) and 2‐mercaptobenzimidazole (2‐mbzi) ligands were performed which led to the isolation of bis(sigma)borate complexes [Cp*RuBH3L] ( 2 a – c ) and β‐agostic complexes [Cp*RuBH2L2] ( 3 a – c ; 2 a , 3 a : L=C7H4NS2; 2 b , 3 b : L=C7H4NSO; 2 c , 3 c : L=C7H5N2S). Further, the chemistry of these novel complexes towards various diphosphine ligands was investigated. Room temperature treatment of 3 a with [PPh2(CH2)nPPh2] (n=1–3) yielded [Cp*Ru(PPh2(CH2)nPPh2)‐BH2(L2)] ( 4 a – c ; 4 a : n=1; 4 b : n=2; 4 c : n=3; L=C7H4NS2). Mild thermolysis of 2 a with [PPh2(CH2)nPPh2] (n=1–3) led to the isolation of [Cp*Ru(PPh2(CH2)nPPh2)(L)] (L=C7H4NS2 5 a – c ; 5 a : n=1; 5 b : n=2; 5 c : n=3). Treatment of 4 a with terminal alkynes causes a hydroboration reaction to generate vinylborane complexes [Cp*Ru(R?C?CH2)BH(L2)] ( 6 and 7 ; 6 : R=Ph; 7 : R=COOCH3; L=C7H4NS2). Complexes 6 and 7 can also be viewed as η‐alkene complexes of ruthenium that feature a dative bond to the ruthenium centre from the vinylinic double bond. In addition, DFT computations were performed to shed light on the bonding and electronic structures of the new compounds. 相似文献
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Inside Back Cover: Evidence for Extensive Single‐Electron‐Transfer Chemistry in Boryl Anions: Isolation and Reactivity of a Neutral Borole Radical (Angew. Chem. Int. Ed. 21/2014)
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Dr. Rüdiger Bertermann Prof. Dr. Holger Braunschweig Dr. Rian D. Dewhurst Dipl.‐Chem. Christian Hörl Dipl.‐Chem. Thomas Kramer Dr. Ivo Krummenacher 《Angewandte Chemie (International ed. in English)》2014,53(21):5473-5473
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Shigeru Sasaki Fumiki Murakami Masaaki Yoshifuji 《Angewandte Chemie (International ed. in English)》1999,38(3):340-343
Significant localization of the unpaired electron on the phosphorus atom of phosphasemiquinone radical anion 1 was revealed by EPR spectroscopy. This species was generated by reduction of 1 , the first stable p‐phosphaquinone. Employment of the 3,5‐di‐tert‐butyl‐4‐oxocyclohexa‐2,5‐dien‐1‐ylidene moiety was essential for the synthesis as well as the effective kinetic protection of 1 . 相似文献
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Prof. Dr. Holger Braunschweig Dr. Ching‐Wen Chiu Johannes Wahler Dr. Krzysztof Radacki Dr. Thomas Kupfer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(40):12229-12233
As neutral isoelectronic analogues of the elusive cyclopentadienyl cation, boroles have been of interest for their prospective applications as strong Lewis acids, chromophores, and electron acceptors. Recently our group discovered a π‐nucleophilic boryl anion based on the borole system. In an effort to extend borole chemistry, we now report the molecular structure of 1‐chloro‐2,3,4,5‐tetraphenylborole ( 1 ) and its corresponding borole dianion resulting from the two‐electron reduction of 1 with KC8. The thermally induced dimerization of 1 yields an unprecedented boracyclohexadiene/borolene spiro‐bicyclic compound and the resulting dimer was fully characterized including a single‐crystal X‐ray analysis. 相似文献
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Hui‐Xian Yeong Dr. Hong‐Wei Xi Dr. Yongxin Li Dr. Sophy Bhasi Kunnappilly Prof. Dr. Bozhen Chen Prof. Dr. Kai‐Chung Lau Prof. Dr. Hajime Hirao Prof. Dr. Kok Hwa Lim Prof. Dr. Cheuk‐Wai So 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14726-14731
The syntheses of a zwitterionic base‐stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene supported by amidinates and low‐valent germanium amidinate substituents are described. The reaction of the amidinate GeI dimer, [LGe:]2 ( 1 , L=PhC(NtBu)2), with two equivalents of the amidinate tin(II) chloride, [LSnCl] ( 2 ), and KC8 in tetrahydrofuran (THF) at room temperature afforded a mixture of the zwitterionic base‐stabilized digermadistannacyclobutadiene, [L2Ge2Sn2L′2] ( 3 ; L′=LGe:), and the bis(amidinate) tin(II) compound, [L2Sn:] ( 4 ). Compound 3 can also be prepared by the reaction of 1 with [LArSnCl] ( 5 , LAr=tBuC(NAr)2, Ar=2,6‐iPr2C6H3) in THF at room temperature. Moreover, the reaction of 1 with the “onio‐substituent transfer” reagent [4‐NMe2‐C5H4NSiMe3]OTf ( 8 ) in THF and 4‐(N,N‐dimethylamino)pyridine (DMAP) at room temperature afforded a mixture of the zwitterionic base‐stabilized tetragermacyclobutadiene, [L4Ge6] ( 9 ), the amidinium triflate, [PhC(NHtBu)2]OTf ( 10 ), and Me3SiSiMe3 ( 11 ). X‐ray structural data and theoretical studies show conclusively that compounds 3 and 9 have a planar and rhombic charge‐separated structure. They are also nonaromatic. 相似文献
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Dr. Akihiro Tsurusaki Prof. Dr. Soichiro Kyushin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):134-137
The radical anion of cyclopentasilane‐fused hexasilabenzvalene was synthesized by the reduction of the corresponding neutral compound. X‐ray crystallographic analysis showed a more trans‐bent structure of the disilene moiety than the neutral compound. Theoretical calculations showed that the highly trans‐bent structure is attributed to the hexasilabenzvalene structure. The EPR spectrum showed that an unpaired electron exists mainly at the disilene moiety. In the UV/Vis spectrum, a large bathochromic shift was observed compared with the neutral compound. 相似文献
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Marcel Schorpp Tim Heizmann Maximillian Schmucker Stephan Rein Stefan Weber Ingo Krossing 《Angewandte Chemie (International ed. in English)》2020,59(24):9453-9459
The perfluorinated dihydrophenazine derivative (perfluoro‐5,10‐bis(perfluorophenyl)‐5,10‐dihydrophenazine) (“phenazineF”) can be easily transformed to a stable and weighable radical cation salt by deelectronation (i.e. oxidation) with Ag[Al(ORF)4]/ Br2 mixtures (RF=C(CF3)3). As an innocent deelectronator it has a strong and fully reversible half‐wave potential versus Fc+/Fc in the coordinating solvent MeCN (E°′=1.21 V), but also in almost non‐coordinating oDFB (=1,2‐F2C6H4; E°′=1.29 V). It allows for the deelectronation of [FeIIICp*2]+ to [FeIV(CO)Cp*2]2+ and [FeIV(CN‐tBu)Cp*2]2+ in common laboratory solvents and is compatible with good σ‐donor ligands, such as L=trispyrazolylmethane, to generate novel [M(L)x]n+ complex salts from the respective elemental metals. 相似文献
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Subrata Bhattacharjee Anjali Raju Rahul N. Gaykar Rajesh G. Gonnade Tony Roy Akkattu T. Biju 《化学:亚洲杂志》2020,15(14):2203-2207
A mild and easy to perform multicomponent coupling involving phosphines, arynes generated from 2‐(trimethylsilyl)aryl triflates, and CO2 allowing the transition‐metal‐free synthesis of zwitterionic phosphonium benzoates has been developed. The reaction proceeds via the generation of 1 : 1 zwitterionic intermediates from phosphines and arynes followed by the interception with CO2 to deliver the carboxylates in moderate to good yields instead of the anticipated benzooxaphosphol‐3(1H)‐ones. 相似文献
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Michael Lesslie Dr. Justin Kai‐Chi Lau John T. Lawler Dr. K. W. Michael Siu Dr. Jos Oomens Dr. Giel Berden Dr. Alan C. Hopkinson Dr. Victor Ryzhov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(7):2243-2246
Intramolecular hydrogen atom transfer (HAT) was examined in homocysteine (Hcy) thiyl radical/alkali metal ion complexes in the gas phase by combination of experimental techniques (ion‐molecule reactions and infrared multiple photon dissociation spectroscopy) and theoretical calculations. The experimental results unequivocally show that metal ion complexation (as opposed to protonation) of the regiospecifically generated Hcy thiyl radical promotes its rapid isomerisation into an α‐carbon radical via HAT. Theoretical calculations were employed to calculate the most probable HAT pathway and found that in alkali metal ion complexes the activation barrier is significantly lower, in full agreement with the experimental data. This is, to our knowledge, the first example of a gas‐phase thiyl radical thermal rearrangement into an α‐carbon species within the same amino acid residue and is consistent with the solution phase behaviour of Hcy radical. 相似文献
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Muhammad O. Ali John C. Lasseter Dr. Remigiusz Żurawiński Dr. Anna Pietrzak Dr. Jacek Pecyna Dr. Jakub Wojciechowski Prof. Andrienne C. Friedli Dr. Damian Pociecha Prof. Piotr Kaszyński 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2616-2630
Two series of 1,12-bis-zwitterionic derivatives of the [closo-B12H12]2− anion ( B ), containing either two 4-alkoxypyridinium groups ( 1B[n]-p ) or one 4-alkoxypyridinium and one 4-pentylthianium groups ( 2B[n]-p ), were prepared and their structural (XRD, DFT), thermal, and photophysical properties were compared with those of the analogous derivatives of the [closo-B10H10]2− anion ( 1A[n]-p and 2A[n]-p ). Some 1,7-derivatives of B were isolated and investigated. Both series 1[n] and 2[n] exhibit nematic and crystalline polymorphism; the 12-vertex derivatives ( B ) have higher transition temperatures than those of the 10-vertex analogues ( A ). All compounds fluoresce with quantum yields higher for 1B (ΦF=0.37 for 1B[7]-p and ΦF=0.27 for 2B[7]-p ) than those for the 10-vertex analogues (ΦF=0.04 for 2A[5]-p ). DFT calculations demonstrate an order of magnitude lower first hyperpolarizability, β(−ω,ω,0), for 2B[7]-p than that for the 10-vertex analogue 2A[7]-p (1.7×10−30 vs. 18.9×10−30 esu at ω=0). 相似文献