- The complex reactivity of β-diketiminato magnesium(i) dimers towards pinacolborane: Implications for catalysis
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Reactions between the borane, HBpin (pin = pinacolato), and three magnesium(i) dimers, [{(ArNacnac)Mg-}2] (ArNacnac = [(ArNCMe)2CH]-; Ar = xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), have been carried out in 2:1, 5:1 and 20:1 ratios. In all cases, NMR spectroscopic studies have revealed complex mixtures of many known and novel products from these reactions. From extracts of the crude reaction mixtures, low yields of ten compounds, representing six different types of complexes between β-diketiminato magnesium fragments and boron containing ligands, have been isolated and crystallographically characterised. These include unprecedented examples of compounds in which the γ-carbon of the β-diketiminate ligand has been activated by boron hydride fragments. In addition, boryloxide (OBpin), borate ([B(pin)2]- or [(pin)BH2]-), B-O bond ruptured [pinBH2]-, a diborane(5) dianion, or BH3 have been shown to be incorporated into the isolated complexes. The complexity of the products of the reported reactions are discussed in light of recently published patents and papers which report that magnesium(i) dimers act as efficient catalysts, or as pre-catalysts to well defined catalysts, for the hydroboration of a variety of unsaturated substrates by HBpin. Our results strongly suggest that magnesium(i) dimers are not catalysts in these reactions, and that there are many more potential (pre-)catalysts that are generated in these reactions, than have previously been reported.
- Jones, Dafydd D. L.,Matthews, Aidan J. R.,Jones, Cameron
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Read Online
- Hydroborative reduction of amides to amines mediated by La(CH2C6H4NMe2-: O)3
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The deoxygenative reduction of amides to amines is a great challenge for resonance-stabilized carboxamide moieties, although this synthetic strategy is an attractive approach to access the corresponding amines. La(CH2C6H4NMe2-o)3, a simple and easily accessible lanthanide complex, was found to be highly efficient not only for secondary and tertiary amide reduction, but also for the most challenging primary reduction with pinacolborane. This protocol exhibited good tolerance for many functional groups and heteroatoms, and could be applied to gram-scale synthesis. The active species in this catalytic cycle was likely a lanthanide hydride.
- Gong, Mingliang,Guo, Chenjun,Luo, Yunjie,Xie, Hongzhen,Zhang, Fangcao
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p. 779 - 791
(2022/01/22)
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- Selective electrocatalytic hydroboration of aryl alkenes
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Organoboron compounds are powerful precursors of value-added organic compounds in synthetic chemistry, and transition metal-catalysed borylation has always been dominant. To avoid toxic reagents and costs associated with metal catalysts, simpler, more eco
- Zhang, Yahui,Zhao, Xiangyu,Bi, Ce,Lu, Wenqi,Song, Mengyuan,Wang, Dongdong,Qing, Guangyan
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p. 1691 - 1699
(2021/03/09)
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- Hydroboration of terminal olefins with pinacolborane catalyzed by new 2-iminopyrrolyl iron(ii) complexes
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Four paramagnetic 14-electron tetracoordinated Fe(ii) complexes of 5-substituted-2-iminopyrrolyl ligands of the type [Fe{κ2N,N′-5-R-NC4H2-2-C(H)N(2,6-iPr2-C6H3)}(Py)Cl], with R = 2,6-Me2-C6H3 (1a), 2,4,6-iPr3-C6H2 (1b), 2,4,6-Ph3-C6H3 (1c) and CPh3 (1d), were synthesized in moderate yields by reacting the respective 5-substituted-2-iminopyrrolyl potassium salts KLa-d with FeCl2(Py)4 in toluene. Complexes 1a-d were characterized by 1H NMR, FTIR spectroscopies, elemental analysis and by the Evans method, the corresponding effective magnetic moments showing a high-spin electronic nature. X-ray diffraction studies on complexes 1a and 1c showed distorted tetrahedral coordination geometries. Complexes 1a-c, activated with K(HBEt3), were efficient catalyst systems for the hydroboration of several terminal alkenes with pinacolborane in good to high yields (50-90%). This system mainly yielded the respective anti-Markovnikov addition products, except when styrenes were used. A screening of the hydroboration of styrene catalyzed by complexes 1a-c activated with K(HBEt3) showed that the selectivity in the Markovnikov product increased with increasing steric bulkiness of the R group, exhibiting selectivities up to 91%. Additionally, the stoichiometric reaction of complex 1b with K(HBEt3) over 30 minutes yielded the mixture of hydride species 2 and 22 (mixture I). On the other hand, when reacting the same components over 16 h, the Fe(i) complex 3 was also identified in the mixture, in addition to 2 + 22 (mixture II). These mixtures were characterized in solution by the Evans method and in the solid state by elemental analysis, 57Fe M?ssbauer and FTIR spectroscopies, compounds 22 and 3 being also analyzed by X-ray diffraction. These results suggest that the corresponding catalytic cycle follows the borane oxidative addition route to a Fe(i) species.
- Cruz, Tiago F. C.,Pereira, Laura C. J.,Waerenborgh, Jo?o C.,Veiros, Luís F.,Gomes, Pedro T.
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p. 3347 - 3360
(2019/07/10)
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- Deoxygenative Borylation of Secondary and Tertiary Alcohols
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Two different approaches for the deoxygenative radical borylation of secondary and tertiary alcohols are presented. These transformations either proceed through a metal-free silyl-radical-mediated pathway or utilize visible-light photoredox catalysis. Readily available xanthates or methyl oxalates are used as radical precursors. The reactions show broad substrate scope and high functional-group tolerance, and are conducted under mild and practical conditions.
- Friese, Florian W.,Studer, Armido
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supporting information
p. 9561 - 9564
(2019/06/21)
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- Syntheses, Structures, and Reactivity of NHC Copper(I) Boryl Complexes: A Systematic Study
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Five novel NHC copper(I) boryl complexes were synthesized by B-B activation via σ-bond metathesis of symmetrical tetraalkoxy and unsymmetrical dialkoxy diamino diborane(4) derivatives. Despite their low stability, the NHC copper boryl complexes were thoroughly characterized spectroscopically and structurally. Variation of the NHC ligand (ItBu or Me2IiPr) as well as of the boryl ligand (Bpin, Bdmab, or BiPrEn) allowed, for the first time systematically, a study in such complexes of the dependence on steric encumbrance. For sterically more demanding ligand combinations, mononuclear linear complexes were obtained, while with less demanding ligand combinations, dimeric dinuclear complexes with two bridging μ-boryl ligands were obtained, exhibiting extremely short Cu···Cu distances (?). The decomposition of all these complexes was found to proceed via a common pathway, leading ultimately to elemental copper, the free NHC ligand, and the respective symmetrical diborane(4) derivative. The rate of decomposition depended strongly on the steric encumbrance of the individual complex. Two apparently low-valent copper clusters were observed and suggested to be relevant species with respect to the reductive decomposition of the copper(I) boryl complexes.
- Kleeberg, Christian,Borner, Corinna
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p. 4136 - 4146
(2018/11/23)
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- Elusive Phosphine Copper(I) Boryl Complexes: Synthesis, Structures, and Reactivity
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We report the first isolation of phosphine copper boryl complexes - species pivotal to numerous copper-catalyzed borylation reactions. The reaction of diboron(4) derivatives with copper tert-butoxide complexes of phosphine ligands allows the isolation of the dimeric μ-boryl-bridged Cu(I) complexes [(iPr3P)Cu-Bdmab]2 (4) and [(C6H4(Ph2P)2)Cu-Bpin]2 (6) with Cu···Cu distances of 2.24-2.27 ? (dmab = (NMe)2C6H4, pin = (OCMe2)2)). A slightly more sterically demanding boryl ligand furnishes the unprecedented multinuclear copper boryl complex [(iPr3P)2Cu8(B(iPrEn))3(OtBu)3] (5), a potential intermediate of the decomposition of an initial Cu(I) boryl complex (iPrEn = (NiPr)2C2H4). All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and elemental analysis. DFT computations support the nature of these unique complexes and give insight into their electronic structures.
- Borner, Corinna,Anders, Lisa,Brandhorst, Kai,Kleeberg, Christian
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supporting information
p. 4687 - 4690
(2018/02/07)
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- Cobalt-Catalyzed Regioselective Borylation of Arenes: N-Heterocyclic Silylene as an Electron Donor in the Metal-Mediated Activation of C?H Bonds
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C?H Borylation of arenes has been a subject of great interest recently because of its atom-economy and the wide applicability of borylated products in value-added synthesis. A new bis(silylene)cobalt(II) complex bearing a bis(N-heterocyclic silylene)-pyridine pincer ligand (SiNSi) has been synthesized and structurally characterized. It enabled the regioselective catalytic C?H borylation of pyridines, furans, and fluorinated arenes. Notably, it exhibited complementary regioselectivity for the borylation of fluorinated arenes compared to previously known catalytic systems, demonstrating that N-heterocyclic silylene donors have enormous potential in metal-catalyzed catalytic applications.
- Ren, Hailong,Zhou, Yu-Peng,Bai, Yunping,Cui, Chunming,Driess, Matthias
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supporting information
p. 5663 - 5667
(2017/04/28)
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- A process for preparing a diboron ester (by machine translation)
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The invention discloses a process for preparing a diboron ester. Borane complexes and corresponding diol reaction and produce corresponding mellow borane, the iron then took place in the presence of catalyst to self-coupling forming a diboron ester. Short synthesis steps of the method, high safety, mild reaction conditions, suitable for many kinds of a diboron ester synthesis. (by machine translation)
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Paragraph 0014
(2016/12/16)
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- A method of synthesizing joint boric acidfrequency that ester
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The invention relates to a method for synthesizing bisdiboron. The method comprises the following steps: preparing a tri-substituted boron midbody from raw materials, namely, nafoxidine and boron tribromide which are easy to obtain from the market, in the presence of an acid-binding agent triethylamine; subsequently reacting with boron tribromide to obtain a bromo-boron midbody; coupling the product in the presence of metal sodium to obtain nafoxidine-substituted coupled boron; finally adding pinacol to react, thereby obtaining a target product, namely, the bisdiboron. The method has the advantages that nafoxidine can be directly recycled, and the triethylamine hydrobromide can be also directly recycled after being simply neutralized and dried. The midbodies obtained in the method disclosed by the invention can be directly used after the solvent is simply distilled, except the compound, the midbodies are all solids when being purified, the operation is easy, the solvent and the reagents can be recycled, the damage to the environment is reduced, and the process can be successfully expanded to be the scale greater than 10kg.
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Paragraph 0060-0065
(2017/03/08)
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- Cobalt-Catalyzed C(sp2)-H Borylation: Mechanistic Insights Inspire Catalyst Design
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A comprehensive study into the mechanism of bis(phosphino)pyridine (PNP) cobalt-catalyzed C-H borylation of 2,6-lutidine using B2Pin2 (Pin = pinacolate) has been conducted. The experimentally observed rate law, deuterium kinetic isotope effects, and identification of the catalyst resting state support turnover limiting C-H activation from a fully characterized cobalt(I) boryl intermediate. Monitoring the catalytic reaction as a function of time revealed that borylation of the 4-position of the pincer in the cobalt catalyst was faster than arene borylation. Cyclic voltammetry established the electron withdrawing influence of 4-BPin, which slows the rate of C-H oxidative addition and hence overall catalytic turnover. This mechanistic insight inspired the next generation of 4-substituted PNP cobalt catalysts with electron donating and sterically blocking methyl and pyrrolidinyl substituents that exhibited increased activity for the C-H borylation of unactivated arenes. The rationally designed catalysts promote effective turnover with stoichiometric quantities of arene substrate and B2Pin2. Kinetic studies on the improved catalyst, 4-(H)2BPin, established a change in turnover limiting step from C-H oxidative addition to C-B reductive elimination. The iridium congener of the optimized cobalt catalyst, 6-(H)2BPin, was prepared and crystallographically characterized and proved inactive for C-H borylation, a result of the high kinetic barrier for reductive elimination from octahedral Ir(III) complexes.
- Obligacion, Jennifer V.,Semproni, Scott P.,Pappas, Iraklis,Chirik, Paul J.
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supporting information
p. 10645 - 10653
(2016/09/04)
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- Alkali metal catalyzed dehydro-coupling of boranes and amines leading to the formation of a B-N bond
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In this report we describe catalytic B-N bond formation via cross-dehydrocoupling (CDC) of boranes with amines to construct aminoboranes with a high degree conversion (>90%) and chemo-selectivity using alkali metal hexamethyldisilazides [MN(SiMe3)2] (M = Li, and K) as pre-catalysts. It was observed that the lithium and potassium hexamethyldisilazides proved to be an effective pre-catalyst for aliphatic primary, secondary amines, aromatic primary, and substituted amines. The catalyzed cross-dehydrocoupling reaction using [MN(SiMe3)2] (M = Li and K) as a pre-catalyst displayed a broad substrate scope. Pinacolborane smoothly reacted with a number of aliphatic and aromatic amines under ambient conditions whereas a prolonged reaction time of around 8-12 hours was required for 9-BBN to undergo CDC reactions.
- Harinath,Anga, Srinivas,Panda, Tarun K.
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p. 35648 - 35653
(2016/05/19)
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- (N-Heterocyclic Carbene)2-Pd(0)-Catalyzed Silaboration of Internal and Terminal Alkynes: Scope and Mechanistic Studies
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Pd(ITMe)2(PhC≡CPh) acts as a highly reactive precatalyst in the silaboration of terminal and internal alkynes to yield a number of known and novel 1-silyl-2-boryl alkenes. Unprecedented mild reaction temperatures for terminal alkynes, short reaction times, and low catalytic loadings are reported. During mechanistic studies, cis-Pd(ITMe)2(SiMe2Ph)(Bpin) was directly synthesized by oxidative addition of PhMe2SiBpin to Pd(ITMe)2(PhC≡CPh). This represents a very rare example of a (silyl)(boryl)palladium complex. A plausible catalyst decomposition route was also examined.
- Ansell, Melvyn B.,Spencer, John,Navarro, Oscar
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p. 2192 - 2196
(2016/04/26)
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- Application of a nucleophilic boryl complex in the frustrated Lewis pair: Activation of H-H, B-H and CC bonds with B(C6F5)3 and boryl-borate lithium
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The frustrated Lewis pair comprised of B(C6F5)3 and a boryl-borate lithium salt Li[pinBB(Ph)pin] can efficiently activate dihydrogen, pinacolborane and ethylene at ambient temperature. Theoretical studies suggest that the nucleophilic sp2 boryl moiety of Li[pinBB(Ph)pin] plays different roles in these reactions. This journal is
- Zheng, Junhao,Wang, Yuwen,Li, Zhen Hua,Wang, Huadong
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supporting information
p. 5505 - 5508
(2015/03/30)
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- Selective synthesis of unsymmetrical diboryl ptii and diaminoboryl CuI Complexes by B-B activation of unsymmetrical diboranes(4) {pinB-B[(NR)2C6H4]}
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Diaminoboryl ligands are currently intensively investigated because of their unique coordination chemical properties, for example, as part of pincer ligands. Owing to synthetic restrictions, however, access to diaminoboryl complexes is limited. Unsymmetrical diborane(4) derivatives comprising a dialkoxy- and a diaminoboron moiety provide efficient access to diaminoboryl complexes either by oxidative addition or by σ-bond metathesis reactions. Especially, the latter is complementary to existing methods and overcomes the existing limitations. This is illustrated by the modular synthesis of four unsymmetrical diborane(4) derivatives and their application in the selective preparation of unprecedented unsymmetrical diboryl PtII complexes as well as sterically little encumbered diaminoboryl CuI complexes.
- Borner, Corinna,Kleeberg, Christian
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supporting information
p. 2486 - 2489
(2014/06/09)
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- B-H bond cleavage via metal-ligand cooperation by dearomatized ruthenium pincer complexes
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Organic derivatives of boronic acid are widely used reagents useful in various synthetic applications. A fundamental understanding and the exploration of new reaction pathways of boronic reagents with organometallic systems hold promise for useful advancement in chemical catalysis. Herein we present the reactions of simple boranes with dearomatized ruthenium pincer complexes based on PNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) or PNN (2-(di-tert-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine) ligands. NMR studies revealed dehydrogenative addition of the borane B-H bond across the metal center and the ligand. Remarkably, new complexes were observed, which contain the boryl moiety at the benzylic carbon of the pincer ligand arm. X-ray crystal structures of new dearomatized boryl pincer complexes were obtained, and DFT calculations revealed mechanistic details of the adduct formation process through a dehydrogenative pathway. In addition, catalytic aryl-boron coupling reactions were explored. The new boryl pincer systems may possibly be useful in future postmodification techniques for ruthenium pincer complexes, as well as in catalytic B-B and B-C coupling reactions.
- Anaby, Aviel,Butschke, Burkhard,Ben-David, Yehoshoa,Shimon, Linda J. W.,Leitus, Gregory,Feller, Moran,Milstein, David
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p. 3716 - 3726
(2014/08/18)
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- Enantiomerically enriched tris(boronates): Readily accessible conjunctive reagents for asymmetric synthesis
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The catalytic enantioselective diboration of vinyl boronate esters furnishes chiral tris(boronates) in a selective fashion. Subsequent deborylative alkylation occurs in a diastereoselective fashion, both for intermolecular and intramolecular processes.
- Coombs, John R.,Zhang, Liang,Morken, James P.
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p. 16140 - 16143
(2015/01/09)
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- Nanogold-catalyzed cis -silaboration of alkynes with abnormal regioselectivity
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The first example of gold-catalyzed silaboration of alkynes with PhMe 2SiBpin is documented in the presence of supported gold nanoparticles. In the case of terminal alkynes, the reaction proceeds at ambient conditions in very good yields and th
- Gryparis, Charis,Stratakis, Manolis
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supporting information
p. 1430 - 1433
(2014/04/03)
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- Two reversible σ-bond metathesis pathways for boron-palladium bond formation: Selective synthesis of isomeric five-coordinate borylpalladium complexes
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Two reversible σ-bond metathesis pathways for B-B bond activation to give borylpalladium complexes are demonstrated in the reaction of η2-(Si-H)Pd(0) complexes with B2pin2. These two pathways are connected by fluxional beh
- Kirai, Naohiro,Takaya, Jun,Iwasawa, Nobuharu
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supporting information
p. 2493 - 2496
(2013/03/28)
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- Transition-metal catalyzed synthesis of diboranes(4)
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Disclosed is a process for the preparation of a diborane(4) comprising the step of coupling boranes via homogeneous or heterogeneous catalysis in the presence of a catalyst comprising a transition metal selected from Ti, Zr, Hf, Rh, Ir, Ni, Pd and Pt.
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Paragraph 0055; 0056
(2013/03/26)
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- Borylation of organo halides and triflates using tetrakis(dimethylamino) diboron
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We report a new in situ borylation method using tetrakis(dimethylamino) diboron, DMA4B2, in the presence of a diol. Our method uses standard borylation conditions and readily available Pd-catalysts. The scope of this method includes aryl halides and triflates as well as vinyl halides and triflates. The method successfully works with a broad range of diols, enabling the selection of the best boronic ester for subsequent Suzuki coupling.
- Bello, Charles S.,Schmidt-Leithoff, Joachim
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p. 6230 - 6235,6
(2012/12/11)
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- Anomalous efficacy of bimetallic Au/Pd nanoclusters in CCl bond activation and formal metathesis-type CB bond activation at room temperature
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Au/Pd alloy nanoclusters stabilized by poly(N-vinylpyrrolidone) catalyze two different reactions of phenylboronic acid with 4-chlorobenzoic acid at room temperature in a single reaction cycle, cross coupling and metathesis-type homocoupling that is normally inaccessible through conventional catalysis.
- Dhital, Raghu Nath,Sakurai, Hidehiro
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supporting information; experimental part
p. 630 - 632
(2012/07/30)
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- Transition-metal-catalyzed synthesis of diboranes(4)
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The diboranes(4) bis(catecholato)diborane (B2Cat2) and bis(pinacolato)diborane (B2Pin2) are important precursors for organoboronic esters, which are versatile reagents for the formation of carbon-carbon bonds. A new catalytic synthesis for these compounds starts from catecholborane or pinacolborane and gives the dehydrocoupling products B2Cat2 and B2Pin2 with turnover numbers of up to 11 600 (see scheme). Copyright
- Braunschweig, Holger,Guethlein, Frank
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scheme or table
p. 12613 - 12616
(2012/02/04)
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- Mechanism of the mild functionalization of arenes by diboron reagents catalyzed by iridium complexes. Intermediacy and chemistry of bipyridine-ligated iridium trisboryl complexes
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This paper describes mechanistic studies on the functionalization of arenes with the diboron reagent B2pin2 (bis-pinacolato diborane(4)) catalyzed by the combination of 4,4′-di-tert-butylbipyridine (dtbpy) and olefin-ligated iridium halide or olefin-ligated iridium alkoxide complexes. This work identifies the catalyst resting state as [Ir(dtbpy)(COE)(Bpin)3] (COE = cyclooctene, Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolanyl). [Ir(dtbpy)(COE)(Bpin)3] was prepared by independent synthesis in high yield from [Ir(COD)(OMe)] 2, dtbpy, COE, and HBpin. This complex is formed in low yield from [Ir(COD)(OMe)]2, dtbpy, COE, and B2pin2. Kinetic studies show that this complex reacts with arenes after reversible dissociation of COE. An alternative mechanism in which the arene reacts with the Ir(I) complex [Ir(dtbpy)Bpin] after dissociation of COE and reductive elimination of B2pin2 does not occur to a measurable extent. The reaction of [Ir(dtbpy)(COE)(Bpin)3] with arenes and the catalytic reaction of B2pin2 with arenes catalyzed by [Ir(COD)(OMe)]2 and dtbpy occur faster with electron-poor arenes than with electron-rich arenes. However, both the stoichiometric and catalytic reactions also occur faster with the electron-rich heteroarenes thiophene and furan than with arenes, perhaps because η2-heteroarene complexes are more stable than the η2-arene complexes and the η2-heteroarene or arene complexes are intermediates that precede oxidative addition. Kinetic studies on the catalytic reaction show that [Ir(dtbpy)(COE)(Bpin)3] enters the catalytic cycle by dissociation of COE, and a comparison of the kinetic isotope effects of the catalytic and stoichiometric reactions shows that the reactive intermediate [Ir(dtbpy)(Bpin)3] cleaves the arene C-H bond. The barriers for ligand exchange and C-H activation allow an experimental assessment of several conclusions drawn from computational work. Most generally, our results corroborate the conclusion that C-H bond cleavage is turnover-limiting, but the experimental barrier for this bond cleavage is much lower than the calculated barrier.
- Boller, Timothy M.,Murphy, Jaclyn M.,Hapke, Marko,Ishiyama, Tatsuo,Miyaura, Norio,Hartwig, John F.
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p. 14263 - 14278
(2007/10/03)
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- PREPARATION OF DIBORONIC ESTERS
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This invention relates to a process for the preparation of an ester of diboronic acid comprising reacting a tetrakis(dialkylamino)diboron with an alcohol to form the ester and a volatile dialkylamine, wherein the volatile dialkylamine is liberated from the reaction mixture in gaseous form.
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- A short synthesis of tetraalkoxydiborane(4) reagents
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The synthesis of a series of bis(catecholato)diborane(4) compounds, B2(1,2-O2C6H4)2, B2-(1,2-O2C6H3Me-4)2, B2(1,2-O2C6H2Me2-3,5) 2, B2[1,2-O2C6H3But-4)] 2, and B2[1,2-O2C6H2But2 -3,5]2, is reported. The compounds have been synthesized by reaction of 1% sodium/mercury amalgam with the corresponding halocatecholboranes, which are cleanly formed from the reaction of BCl3 or BBr3 and catechol. Combining these two steps in one pot, B2[1,2-O2C6H3But-4)] 2 was prepared from BCl3 and 4-tert-butylcatechol, and B2[1,2-O2C6H2But2 -3,5]2 was prepared from 3,5-di-tert-butylcatechol and BBr3 on a multigram scale. Bis-(pinacolato)diborane(4) was not formed from reaction of chloropinacolborane and Na/Hg, but it was formed by in situ addition of pinacol to either B2[1,2-O2C6H3But-4)] 2 or B2[1,2-O2C6H2But2 -3,5]2. Cyclic voltammetry indicated that the reduction potentials of the chloro-catecholborane reactant and of the bis(catecholato)diborane(4) product are similar. These similar potentials make selective reduction of haloborane difficult and thus far unique to sodium-mercury amalgam.
- Anastasi, Natia R.,Waltz, Karen M.,Weerakoon, Wimali L.,Hartwig, John F.
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p. 365 - 369
(2008/10/08)
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- Mild iridium-catalyzed borylation of arenes. High turnover numbers, room temperature reactions, and isolation of a potential intermediate
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The borylation of arenes leads to the formation of synthetically versatile products from unactivated arene reagents. We report that Ir(I) precursors in conjunction with bipyridine ligands catalyze in high yields the borylation of arenes under mild conditions. These reactions encompase arenes bearing both electron-withdrawing and electron-donating substituents. The temperatures required for the transformation are much lower than those previously reported for direct arene borylation. The combination of [Ir(COE)2Cl]2 and (4,4-di-t-butyl)bipyridine even allows for reaction at room temperature. The same catalyst system at 100 °C provides remarkably high turnover numbers for a hydrocarbon functionalization process. Mechanistic studies show that the reactions involve uncommon, Ir(II) tris-boryl complexes. An example of this type of complex ligated by di-t-butylbipyridine was isolated and structurally characterized. It reacted rapidly at room temperature to produce aryl boronate esters in high yields. Copyright
- Ishiyama, Tatsuo,Takagi, Jun,Ishida, Kousaku,Miyaura, Norio,Anastasi, Natia R.,Hartwig, John F.
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p. 390 - 391
(2007/10/03)
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- Tetra(pyrrolidino)diborane(4), [(C4H8N)2B]2, as a New Improved Alternative Synthetic Route to Bis(pinacolato)diborane(4) - Crystal Structures of the Intermediates
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The compound tetra(pyrrolidino)diborane(4) (3) is an important new and alternative precursor for the preparation and synthesis of bis(pinacolato)diborane(4). The latter is the major intermediate among the diborane derivatives used for many addition and insertion reactions into multiple bonds. The crystal structure of 3 and its precursor, tris(pyrrolidino)borane, 1, were determined. In addition the solvolysis reactions and solution behavior of 3 with alcohols were examined.
- Ali, Hijazi Abu,Goldberg, Israel,Srebnik, Morris
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- Synthetic routes to cyclic and unsymmetric diborane(4) compounds
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The reaction between 1,2-B2Cl2(NMe2)2 and disodium catecholate Na2[1,2-O2C6H4] affords the cyclic diborane(4) compound 1,2- B2(NMe2)2(cat) (cat = 1,2-O2C6H4), whereas a similar reaction using dilithium thiocatecholate Li2[1,2-S2C6H4] affords the 1,1-isomer 1,1- B2(NMe2)2(thiocat) (thiocat = 1,2-S2C6H4). Both compounds can be used to prepare unsymmetric diborane(4) species.
- Lesley, M.J. Gerald,Norman, Nicholas C.,Orpen, A. Guy,Starbuck, Jonathan
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p. 115 - 117
(2007/10/03)
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- Transition metal complexes incorporating the BF2 ligand formed by oxidative addition of the B-B bond in B2F4
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The reactions between B2F4 and the platinum and iridium complexes [Pt(PPh3)2(η-C2H4)], [Pt(dppb)(r)-C2H4)] [dppb = l,4-bis(diphenylphosphino)butane] and trans-[IrCl(CO)(PPh3)2] afforded the difluoroboryl complexes cis-[Pt(BF2)2(PPh3)2], cis-[Pt(BF2)2(dppb)] and fac-[Ir(BF2)3(CO)(PPh3)2] respectively all of which have been characterised by X-ray crystallography. The isoelectronic platinum dppb nitrito complex cw-[Pt(NO2)2(dppb)] has also been prepared and structurally characterised. The Royal Society of Chemistry 2000.
- Lu, Norman,Norman, Nicholas C.,Guy Orpen,Quayle, Michael J.,Timms, Peter L.,Whittell, George R.
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p. 4032 - 4037
(2007/10/03)
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- Bis-Catecholate, Bis-Dithiocatecholate, and Tetraalkoxy Diborane(4) Compounds: Aspects of Synthesis and Electronic Structure
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The synthesis and characterization of a series of bis-catecholate diborane(4) compounds, B2(1,2-O2C6H4)2 (3), B2(1,2-O2-4-MeC6H3)2 (7), B2(1,2-O2-4-MeC6H3)2 (7), B3(1,2-O2-4-ButC6H3) 2 (8), B2(1,2-O2-3,5-Bu2tC 6H2)2 (9), B2(1,2-O2-3-MeOC6H3)2 (10), bis-dithiocatecholate diborane(4) compounds, B2(1,2-S2C6H4)2 (13), B2(1,2-S2-4-MeC6H3)2 (14), and tetraalkoxy diborane(4) compounds, B2(OCH2CMe2CH2O)2 (11) and B2(OCMe2CMe2O)2 (12) from B2(NMe2)4 (1) is described, as are the bis(NHMe2) adducts of 3 and 9, namely [B2(1,2-O2C6H4) 2-(NHMe2)2] (4) and [B2(1,2-O2-3,5-Bu2tC 6H2)2(NHMe2)2] (5). The latter two compounds are intermediates in the formation of 3 and 9 from 1. Compound 1 is synthesized by reductive coupling of BCl(NMe2)2, which in turn is prepared from reaction of BCl3 with B(NMe2)3 in a 1:2 stoichiometry. We have also characterized [B2Cl4-(NHMe2)2] (15) formed from addition of HCl to 1 prior to complete reaction with diols, and the salt, [NH2Me2]-[B(1,2-O2C6H 4)2] (16), which arises from addition of cacechol to B(NMe2)3. Thus, any B(NMe2)3 impurity present after the preparation of 1 needs to be removed by distillation prior to reaction with alcohols. The dimer, [BCl2-(μ-NMe2)]2 (17) has also been characterized. This is formed from reaction of BCl3 with B(NMe2)3 if a 2:1 rather than 1:2 sloichiometry is used. Photoelectron spectra of 1, 3, 8, 11, and 12 are reported along with those of the corresponding diols, catechol, 4-But-catechol, 2,2-dimethyl-1,3-propanediol, and pinacol. The ionization energies of the B2(OR)4 compounds follow the series 8 2N4 framework increases the IE by ca. 1.65 eV, whereas the presence of an aromatic ring rather than an aliphatic chain decreases the IE by ca. 1.50 eV. The presence of electron donating But-groups also decreases the IE.
- Lawlor, Fiona J.,Norman, Nicholas C.,Pickett, Nigel L.,Robins, Edward G.,Nguyen, Paul,Lesley, Gerry,Marder, Todd B.,Ashmore, Jennifer A.,Green, Jennifer C.
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p. 5282 - 5288
(2008/10/08)
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- Contributions to the Chemistry of Boron, 153. The Crystal and Molecular Structure of a 1.3.2-Dioxaborolan-2-yl-1'.3'.2'-dioxaborolane
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The structure of the title compounds 5 has been investigated by X-ray crystallography in order to discern between two structural alternatives. 5 crystallizes in the monoclinic space group P21/c, and almost planar B-B bonded dioxaborolane rings are present in the molecule. 5 possesses a crystallographically imposed center of inversion, and approaches the point group symmetry D2h. - Key words: X-Ray Structure, 4.4.5.5-Tetramethyl-1.3.2-dioxaborolane-2-yl-4'.4'.5'.5'-tetramethyl-1'.3'.2'-dioxaborolane
- Noeth, H.
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p. 1463 - 1466
(2007/10/02)
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