- C-H and C-F Bond Activations at a Rhodium(I) Boryl Complex: Reaction Steps for the Catalytic Borylation of Fluorinated Aromatics
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Treatment of the rhodium(I) boryl complex [Rh(Bpin)(PEt3)3] (1, pin = pinacolato = O2C2Me4) with pentafluorobenzene, 1,3,5-trifluorobenzene, 1,3-difluorobenzene, or 3,5-difluoropyridine led to C-H activation reactions to give the aryl complexes [Rh(C6F5)(PEt3)3] (4), [Rh(2,4,6-C6F3H2)(PEt3)3] (5), [Rh(2,6-C6F2H3)(PEt3)3] (6), and [Rh{4-(3,5-C5NF2H2)}(PEt3)3] (8). For 5, 6, and 8 consecutive reactions with in situ generated HBpin occurred to yield [Rh(H)(PEt3)3] (7) and boronic esters. The boryl complex 1 gave with hexafluorobenzene or perfluorotoluene the C-F activation products [Rh(C6F5)(PEt3)3] (4) and [Rh(4-C6F4CF3)(PEt3)3] (9), respectively. The complexes 5, 6, and 9 react with B2pin2 to yield 1 and boronic ester derivatives. On the basis of these stoichiometric reactions catalytic C-H and C-F borylation reactions using 1 or 7 were developed to generate 2-Bpin-1,3,5-C6F3H2, 2-Bpin-1,3-C6F2H3, and 4-Bpin-C6F4CF3 from 1,3,5-trifluorobenzene, 1,3-difluorobenzene, or perfluorotoluene and B2pin2. On treatment of pentafluoropyridine with B2pin2 in the presence of 1 or 7 as catalyst 2-Bpin-C5NF4 was synthesized by C-F borylation at the 2-position. Using 2,3,5,6-tetrafluoropyridine, B2pin2, and catalytic amounts of 7 led to a C-H borylation reaction at the 4-position. 4-Bpin-C5NF4 can also be prepared by the reaction of 2,3,5,6-tetrafluoropyridine with stoichiometric amounts of HBpin or by the reaction of pentafluoropyridine with an excess of HBpin in the presence of 7, whereas the reaction of pentafluoropyridine with stoichiometric amounts of HBpin and 5 mol % 7 resulted in the formation of 2,3,5,6-tetrafluoropyridine via hydrodefluorination reaction at the 4-position. This regioselectivity contrasts the borylation of pentafluoropyridine at the 2-position with 1 as catalyst. Overall, the obtained fluorinated aryl boronic ester derivatives might serve as versatile building blocks. (Chemical Equation Presented).
- Kall?ne, Sabrina I.,Teltewskoi, Michael,Braun, Thomas,Braun, Beatrice
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- Cross-Coupling through Ag(I)/Ag(III) Redox Manifold
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In ample variety of transformations, the presence of silver as an additive or co-catalyst is believed to be innocuous for the efficiency of the operating metal catalyst. Even though Ag additives are required often as coupling partners, oxidants or halide scavengers, its role as a catalytically competent species is widely neglected in cross-coupling reactions. Most likely, this is due to the erroneously assumed incapacity of Ag to undergo 2e? redox steps. Definite proof is herein provided for the required elementary steps to accomplish the oxidative trifluoromethylation of arenes through AgI/AgIII redox catalysis (i. e. CEL coupling), namely: i) easy AgI/AgIII 2e? oxidation mediated by air; ii) bpy/phen ligation to AgIII; iii) boron-to-AgIII aryl transfer; and iv) ulterior reductive elimination of benzotrifluorides from an [aryl-AgIII-CF3] fragment. More precisely, an ultimate entry and full characterization of organosilver(III) compounds [K]+[AgIII(CF3)4]? (K-1), [(bpy)AgIII(CF3)3] (2) and [(phen)AgIII(CF3)3] (3), is described. The utility of 3 in cross-coupling has been showcased unambiguously, and a large variety of arylboron compounds was trifluoromethylated via [AgIII(aryl)(CF3)3]? intermediates. This work breaks with old stereotypes and misconceptions regarding the inability of Ag to undergo cross-coupling by itself.
- Demonti, Luca,Mézailles, Nicolas,Nebra, Noel,Saffon-Merceron, Nathalie
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supporting information
p. 15396 - 15405
(2021/10/12)
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- Protodeboronation of (Hetero)Arylboronic Esters: Direct versus Prehydrolytic Pathways and Self-/Auto-Catalysis
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The kinetics and mechanism of the base-catalyzed hydrolysis (ArB(OR)2→ ArB(OH)2) and protodeboronation (ArB(OR)2→ ArH) of a series of boronic esters, encompassing eight different polyols and 10 polyfluoroaryl and heteroaryl moieties, have been investigated by in situ and stopped-flow NMR spectroscopy (19F,1H, and11B), pH-rate dependence, isotope entrainment,2H KIEs, and KS-DFT computations. The study reveals the phenomenological stability of boronic esters under basic aqueous-organic conditions to be highly nuanced. In contrast to common assumption, esterification does not necessarily impart greater stability compared to the corresponding boronic acid. Moreover, hydrolysis of the ester to the boronic acid can be a dominant component of the overall protodeboronation process, augmented by self-, auto-, and oxidative (phenolic) catalysis when the pH is close to the pKaof the boronic acid/ester.
- Hayes, Hannah L. D.,Wei, Ran,Assante, Michele,Geogheghan, Katherine J.,Jin, Na,Tomasi, Simone,Noonan, Gary,Leach, Andrew G.,Lloyd-Jones, Guy C.
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supporting information
p. 14814 - 14826
(2021/09/13)
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- Transition Metal Catalyst-Free, Base-Promoted 1,2-Additions of Polyfluorophenylboronates to Aldehydes and Ketones
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A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K+ in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O?H???O and O?H???N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.
- Budiman, Yudha P.,Friedrich, Alexandra,Kole, Goutam Kumar,Liu, Zhiqiang,Luo, Xiaoling,Marder, Todd B.,Radius, Udo,Tian, Ya-Ming,Westcott, Stephen A.
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supporting information
p. 16529 - 16538
(2021/06/23)
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- Base-Free Pd-Catalyzed C?Cl Borylation of Fluorinated Aryl Chlorides
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Catalytic C?X borylation of aryl halides containing two ortho-fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accele
- Budiman, Yudha P.,Lorenzen, Sabine,Liu, Zhiqiang,Radius, Udo,Marder, Todd B.
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supporting information
p. 3869 - 3874
(2021/02/03)
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- Copper-Catalyzed Oxidative Cross-Coupling of Electron-Deficient Polyfluorophenylboronate Esters with Terminal Alkynes
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We report herein a mild procedure for the copper-catalyzed oxidative cross-coupling of electron-deficient polyfluorophenylboronate esters with terminal alkynes. This method displays good functional group tolerance and broad substrate scope, generating cro
- Liu, Zhiqiang,Budiman, Yudha P.,Tian, Ya-Ming,Friedrich, Alexandra,Huang, Mingming,Westcott, Stephen A.,Radius, Udo,Marder, Todd B.
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supporting information
p. 17267 - 17274
(2020/12/01)
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- C-H Functionalization at Sterically Congested Positions by the Platinum-Catalyzed Borylation of Arenes
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Despite significant progress in the area of C-H bond functionalization of arenes, no general method has been reported for the functionalization of C-H bonds at the sterically encumbered positions of simple arenes, such as mesitylene. Herein, we report the development of the first platinum-based catalyst for C-H borylation of arenes and heteroarenes. Notably, this method exhibited high tolerance toward steric hindrance and provided rapid access to a series of 2,6-disubstituted phenylboronic esters, valuable building blocks for further elaborations.
- Furukawa, Takayuki,Tobisu, Mamoru,Chatani, Naoto
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supporting information
p. 12211 - 12214
(2015/10/12)
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- Fluorine-controlled C-H borylation of arenes catalyzed by a PSiN-pincer platinum complex
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An efficient, regioselective synthesis of fluorine-substituted arylboronic esters was achieved through fluorine-controlled C-H borylation of arenes with diboron catalyzed by a PSiN-platinum complex. The promising utility of the PSiN-platinum catalyst and its unique regioselectivity were demonstrated for the first time, which would complement the well-developed Ir-catalyzed C-H borylation.
- Takaya, Jun,Ito, Shisei,Nomoto, Hironori,Saito, Narumasa,Kirai, Naohiro,Iwasawa, Nobuharu
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supporting information
p. 17662 - 17665
(2015/12/18)
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- Nano-Fe2O3-catalyzed direct borylation of arenes
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Nano-Fe2O3-catalyzed borylation of arenes with diboron pinacol ester B2pin2 has been found to give borylation products with selectivity controlled by electronic effects of substituents. The Royal Society of Chem
- Yan, Guobing,Jiang, Yubo,Kuang, Chunxiang,Wang, Shuai,Liu, Haichao,Zhang, Yan,Wang, Jianbo
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p. 3170 - 3172
(2010/08/06)
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