- Gold(0) nanoparticles for selective catalytic diboration
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Going with gold: Gold(0) nanoparticles stabilized with the diphosphine ligand binap mediate the catalytic diboration of styrene, resulting in complete formation of the bis(boronate)ester product. The gold(0) catalytic mechanism can involve base-assisted h
- Ramirez, Jesus,Sanau, Mercedes,Fernandez, Elena
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- Light-Mediated Sulfur-Boron Exchange
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Interaction of sulfides bearing a tetrafluoropyridinyl group with bis(catecholato)diboron followed by treatment with pinacol and triethylamine affording pinacol boronic esters is described. The reaction is promoted by an organic photocatalyst (3DPA2FBN) u
- Panferova, Liubov I.,Dilman, Alexander D.
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supporting information
p. 3919 - 3922
(2021/05/29)
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- Hydroboration of Alkenes Catalysed by a Nickel N-Heterocyclic Carbene Complex: Reaction and Mechanistic Aspects
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The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η5-C5Me5)Cl(IMes)] (IMes=1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in
- Chetcuti, Michael J.,Cornaton, Yann,Djukic, Jean-Pierre,Ritleng, Vincent,Ulm, Franck
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- A General Approach to Deboronative Radical Chain Reactions with Pinacol Alkylboronic Esters
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The generation of carbon-centered radicals from air-sensitive organoboron compounds through nucleohomolytic substitution at boron is a general method to generate non-functionalized and functionalized radicals. Due to their reduced Lewis acidity, alkylboronic pinacol esters are not suitable substrates. We report their in situ conversion into alkylboronic catechol esters by boron-transesterification with a substoichiometric amount of catechol methyl borate combined with an array of radical chain processes. This simple one-pot radical-chain deboronative method enables the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds through C?C bond formation using sulfonyl radical traps. The power of combining radical and classical boron chemistry is illustrated with a modular 5-membered ring formation using a combination of three-component coupling and protodeboronative cyclization.
- André-Joyaux, Emy,Kuzovlev, Andrey,Renaud, Philippe,Tappin, Nicholas D. C.
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p. 13859 - 13864
(2020/06/10)
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- Metal-Free Radical Borylation of Alkyl and Aryl Iodides
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A metal-free radical borylation of alkyl and aryl iodides with bis(catecholato)diboron (B2cat2) as the boron source under mild conditions is introduced. The borylation reaction is operationally easy to conduct and shows high functional group tolerance and broad substrate scope. Radical clock experiments and density functional theory calculations provide insights into the mechanism and rate constants for C-radical borylation with B2cat2 are disclosed.
- Cheng, Ying,Mück-Lichtenfeld, Christian,Studer, Armido
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p. 16832 - 16836
(2018/11/23)
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- Imido-hydrido complexes of Mo(IV): Catalysis and mechanistic aspects of hydroboration reactions
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Imido-hydrido complexes (ArN)Mo(H)(Cl)(PMe3)3 (1) and (ArN)Mo(H)2(PMe3)3 (2) (Ar = 2,6-diisopropylphenyl) catalyse a variety of hydroboration reactions, including the rare examples of addition of HBCat to nitriles to form bis(borylated) amines RCH2N(BCat)2. Stoichiometric reactivity of complexes 1 and 2 with nitriles and HBCat suggest that catalytic reactions proceed via a series of agostic borylamido and borylamino complexes. For complex 1, catalysis starts with addition of nitriles across the Mo-H bond to give (ArN)Mo(Cl)(NCHR)(PMe3)2; whereas for complex 2 stoichiometric reactions suggest initial addition of HBCat to form the agostic complex Mo(H)2(PMe3)3(η3-NAr-HBcat) (16).
- Khalimon, Andrey Y.,Farha, Philip M.,Nikonov, Georgii I.
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supporting information
p. 18945 - 18956
(2015/11/11)
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- Catalytic hydroboration by an imido-hydrido complex of Mo(iv)
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The imido-hydrido complex (ArN)Mo(H)(Cl)(PMe3)3 catalyses a variety of hydroboration reactions, including the first example of catalytic addition of HBCat to nitriles to form the bis(borylated) amines RCH2N(BCat)2/su
- Khalimon, Andrey Y.,Farha, Philip,Kuzmina, Lyudmila G.,Nikonov, Georgii I.
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p. 455 - 457
(2012/01/13)
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- Synthesis of group 9 metal-olefin complexes with identical ligand frameworks and comparison of their catalytic activity in [2+2+2] cycloaddition and other addition reactions
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The preparation and catalytic evaluation of the three group 9 (cyclopentadienyl)metal(trimethylvinylsilane) complexes of the type C 5H5M(H2C=CHSiMe3)2 (M=cobalt, rhodium and iridium) are reported. The complexes were investigated in [2+2+2] cycloaddition as well as in hydrogenation, hydroformylation and hydroboration reactions. Despite the identical organic frameworks and structural parameters, the complexes display remarkable reactivity and stability differences. Copyright
- Weding, Nico,Jackstell, Ralf,Jiao, Haijun,Spannenberg, Anke,Hapke, Marko
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experimental part
p. 3423 - 3433
(2012/03/09)
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- Electronic tuning of a carbene center via remote chemical induction, and relevant effects in catalysis
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The present report develops the idea that an N-heterocyclic carbene incorporating a remote anionic functionality-here, a malonate group-as a backbone component of its heterocy- clic framework, can be post-function- alized directly from its transition- metal complexes, upon simple addition of a variety of electrophiles interacting directly with the malonate group in the outer coordination sphere. From a palette of selected electrophilic reagents, it was thus possible to modulate the electronic donor properties of the car- bene center over a rather broad range. Both the zwitterionic complex [Rh{malo-NHCj(cod)] and the cationic derivatives [Rh{malo-NHCE}(cod)] + (where ma/o-NHCE represents the ligand modified by a selected electro- phile E ) were used as pre-catalysts in two types of catalytic reactions, namely, the polymerization of phenyl- acetylene and the hydroboration of styrene. The results indicate that, in both cases, the zwitterionic species is by far the best catalyst, whereas a decrease in the ligand donicity induced by the added electrophile results in a concomitant reduction of catalytic activity. Apparent deviations to such a trend in the case of the hydroboration of styrene were rationalized in terms of an interaction between the reactive catechol- borane substrate and the remote functionality of the N-heterocyclic carbene leading to an in situ modification of the nature of the active species. These observations serve as a useful basis to define the scope and limitations of the present conceptual approach in catalysis.
- Cesar, Vincent,Lugan, Noel,Lavigne, Guy
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experimental part
p. 11432 - 11442
(2010/11/24)
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- Chemoselective hydroboration of alkynes vs. alkenes over gold catalysts
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Alkynes are preferentially hydroborated in the presence of alkenes when using gold catalysts; the active species involves a borane-gold interaction.
- Leyva, Antonio,Zhang, Xin,Corma, Avelino
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experimental part
p. 4947 - 4949
(2010/01/06)
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- Rh(I)-catalyzed asymmetric hydrosilylation and hydroboration/oxidation reactions using berens ligand
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The Berens ligand 2 was used in a number of Rh(I)-catalyzed asymmetric hydrosilylations of acetophenones under standard conditions, affording the corresponding 1-arylalcohols in ees up to 65%. Some novel Rh catalysts were generated in situ from the neutral precatalyst [Rh(μ-Cl)(COD)]2 and screened in the catalytic asymmetric hydroboration/oxidation of styrenes, gave enantioselectivities of up to 62%. Copyright Taylor & Francis Group, LLC.
- Marques, Carolina S.,Burke, Anthony J.
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experimental part
p. 4207 - 4214
(2009/04/06)
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- Iterative stereospecific reagent-controlled homologation of pinacol boronates by enantioenriched α-chloroalkyllithium reagents
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Reaction of pinacol boronates with putative enantioenriched α-chloroalkyllithium species, generated in situ from homochiral α-chloroalkylsulfoxides by sulfoxide ligand exchange with t-BuLi in PhMe at -78 °C, gave chain-extended boronic ester products with generally excellent stereochemical fidelity. Iteration of this stereospecific reagent-controlled homologation (StReCH) process enabled the programmed synthesis of all four stereoisomers of a stereodiad-containing model system (4-benzyl-1,6-diphenylhexan-2-ol) with er ≥ 97:3 in all cases. Copyright
- Blakemore, Paul R.,Burge, Matthew S.
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p. 3068 - 3069
(2008/02/05)
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- Metal catalysed hydroboration of vinyl sulfides, sulfoxides, sulfones, and sulfonates
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The hydroboration of phenyl vinyl sulfide with catecholborane (HBcat) and pinacolborane (HBpin) has been examined with a number of rhodium complexes, all of which proceed with excellent regiocontrol in favour of the branched product PhSCH(B(OR)2)CH3. The corresponding linear product can be obtained exclusively in reactions employing [Cp*IrCl2]2 and HBcat. Catalysed hydroborations of (E)-2-(p-toluenethio)styrene with HBcat using Rh(acac)(dppp) gave predominant formation of one product while reactions using HBpin afforded several products arising from a competing C-S bond cleavage (acac = acetylacetonato, dppp = 1,3-bis(diphenylphosphino)propane). Although reactions of phenyl vinyl sulfoxide were complicated by a competing deoxygenation reaction, hydroborations of phenyl vinyl sulfone using HBcat once again gave regioselective formation of either the branched or linear products, depending on the choice of catalyst used to effect this transformation. Catalysed hydroborations of phenyl vinyl sulfonate were less chemo- and regioselective, yielding hydrogenation and diboration products in addition to the two hydroboration product isomers.
- Webb, Jonathan D.,Harrison, Daniel J.,Norman, David W.,Blacquiere, Johanna M.,Vogels, Christopher M.,Decken, Andreas,Bates, Craig G.,Venkataraman,Baker, R. Thomas,Westcott, Stephen A.
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- A valuable, inexpensive CuIN-heterocyclic carbene catalyst for the selective diboration of styrene
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The complexes [Cu(NHC)(NCMe)]BF4 (NHC = N-heterocyclic ligand), with bis(catecholato)diboron (B2(cat)2) as the boron source, efficiently catalyze the diboration of styrene with very high degrees of conversion. With the appropriate NHC ligand, the reaction proceeds quantitatively toward the diborated derivative PhCH(Bcat)-CH2(Bcat). The [styrene]/[B2(cat)2] ratio also has a strong effect on the selectivity: the use of an excess of styrene allows modification of the selectivity toward the formation solely of the monoborated derivative. PhCH 2-CH2(Bcat). DFT calculations suggest that no oxidative addition processes take place at copper, hut that intermediates containing coordinated σ-bonds are involved in the catalytic cycle.
- Lillo, Vanesa,Fructos, Manuel R.,Ramirez, Jesus,Braga, Ataualpa A. C.,Maseras, Feliu,Diaz-Requejo, M. Mar,Perez, Pedro J.,Fernandez, Elena
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p. 2614 - 2621
(2008/04/01)
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- Reagent-controlled asymmetric homologation of boronic esters by enantioenriched main-group chiral carbenoids
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Putative enantioenriched carbenoid species, (R)-1-chloro-2- phenylethylmagnesium chloride (9) and (S)-1-chloro-2-phenylethyllithium (26), generated in situ by sulfoxide ligand exchange from (-)-(Rs,R)-1- chloro-2-phenylethyl p-tolyl sulfoxide (8), effected the stereocontrolled homologation of boronic esters. sec-Alcohols derived from the product boronates by oxidation with basic hydrogen peroxide exhibited % ee closely approaching that of sulfoxide 8 in examples employing Li-carbenoid 26.
- Blakemore, Paul R.,Marsden, Stephen P.,Vater, Huw D.
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p. 773 - 776
(2007/10/03)
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- Metal promoted asymmetry in the 1,2-diboroethylarene synthesis: Diboration versus dihydroboration
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Metal catalysed addition of diboranes to vinylarenes produces the desired 1,2-bis(boronate)ester and mono(boronate)esters as by-products. Their relative rate is a sensitive function between the nature of the catalytic system and the electronic effects of the substrate, that influences the mechanistic steps of the catalytic cycle. However, asymmetry is only induced as moderate enantiomeric excess values, providing an enantioface differentiation, between the bis- and mono(boronate)esters. Alternatively, the method based on the catalytic asymmetric dihydroboration/oxidation of alkynes as diphenylacetylene can provide 1,2-diphenyl-1,2-ethanediol (hydrobenzoin) with a selectivity of 68% mainly as the erythro isomer.
- Ramirez, Jesus,Segarra, Anna M.,Fernandez, Elena
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p. 1289 - 1294
(2007/10/03)
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- Preparation of alcohols from alkenes via the homologation of boronates with (trimethylsilyl)diazomethane
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(Matrix presented) Alkylcatecholboranes obtained from alkenes were converted to the corresponding alkylmethanols by reaction with (trimethylsilyl)diazomethane followed by oxidation and treatment with fluoride.
- Goddard, Jean-Philippe,Le Gall, Thierry,Mioskowski, Charles
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p. 1455 - 1456
(2007/10/03)
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- On titanium-promoted hydroborations of alkenes by borohydride and by catecholborane
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Some literature reports of catalyzed hydroborations of alkenes by the borohydride anion and by catecholborane were investigated to probe the actual mode of hydroboration. Reactions involving both TiCl3 and Ti(OiPr)4 seems to involve predominantly formation of BH3 in situ, although there is some evidence that the metal may be directly involved in a few cases. Ambiguity arises because it is shown that alkyl boronate esters can be formed by exchange between catecholborane and alkylboranes, so formation of these esters is not firm evidence of catalysis.
- Burgess, Kevin,Van Der Donk, Wilfred A.
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p. 3616 - 3620
(2008/10/08)
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