- 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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- 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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- 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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- Boron heterocycles. V. Preparation and characterization of selected heteronuclear diboron ring systems
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Several new heteronuclear diboron ring systems have been prepared from reactions of B2[N(CH3)S]4 and B2Cl4 with selected diols and ethanedithiol. The compounds prepared are crystalline solids, most of
- Welch,Shore
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- Metal-Free Direct Deoxygenative Borylation of Aldehydes and Ketones
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Direct conversion of aldehydes and ketones into alkylboronic esters via deoxygenative borylation represents an unknown yet highly desirable transformation. Herein, we present a one-step and metal-free method for carbonyl deoxy-borylation under mild conditions. A wide range of aromatic aldehydes and ketones are tolerated and successfully converted into the corresponding benzylboronates. By the same deoxygenation manifold with aliphatic aldehydes and ketones, we also enable a concise synthesis of 1,1,2-tris(boronates), a family of compounds that currently lack efficient synthetic methods. Given its simplicity and versatility, we expect that this novel borylation approach could show great promise in organoboron synthesis and inspire more carbonyl deoxygenative transformations in both academic and industrial settings.
- Huang, Chia-Yu,Li, Chao-Jun,Li, Jianbin,Qiu, Zihang,Wang, Haining
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supporting information
p. 13011 - 13020
(2020/09/01)
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- A Versatile NHC-Parent Silyliumylidene Cation for Catalytic Chemo- And Regioselective Hydroboration
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This study describes the first use of a silicon(II) complex, NHC-parent silyliumylidene cation complex [(IMe)2SiH]I (1, IMe =:C{N(Me)C(Me)}2) as a versatile catalyst in organic synthesis. Complex 1 (loading: 10 mol %) was shown to act as an efficient catalyst (reaction time: 0.08 h, yield: 94%, TOF = 113.2 h-1 reaction time: 0.17 h, yield: 98%, TOF = 58.7 h-1) for the selective reduction of CO2 with pinacolborane (HBpin) to form the primarily reduced formoxyborane [pinBOC(-O)H]. The activity is better than the currently available base-metal catalysts used for this reaction. It also catalyzed the chemo- and regioselective hydroboration of carbonyl compounds and pyridine derivatives to form borate esters and N-boryl-1,4-dihydropyridine derivatives with quantitative conversions, respectively. Mechanistic studies show that the silicon(II) center in complex 1 activated the substrates and then mediated the catalytic hydroboration. In addition, complex 1 was slightly converted into the NHC-borylsilyliumylidene complex [(IMe)2SiBpin]I (3) in the catalysis, which was also able to mediate the catalytic hydroboration.
- Leong, Bi-Xiang,Lee, Jiawen,Li, Yan,Yang, Ming-Chung,Siu, Chi-Kit,Su, Ming-Der,So, Cheuk-Wai
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supporting information
p. 17629 - 17636
(2019/11/11)
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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 0057
(2013/03/26)
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- Dehydrocoupling of catecholborane catalyzed by group 4 compounds
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The early transition metal compounds [Cp2TiCl2], [Cp2ZrCl2] and [Cp2HfCl2] were employed as pre-catalysts for the dehydrocoupling of catecholborane. The product of this reaction, bis(catecholato)diborane (B2Cat2), was generated with turnover numbers of up to 90. Heterogeneous catalysis yielded lower turnover numbers, but the metal powders used in these reactions turned out to also display the general ability to promote the dehydrocoupling reaction.
- Braunschweig, Holger,Claes, Christina,Guethlein, Frank
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p. 144 - 145
(2012/06/29)
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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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- Phosphine exchange reactions involving cis-[Pt(PPh3)2(Bcat)2] (cat = 1,2-O2C6H4) and the oxidative addition of 1,2-B2Cl2(NMe2)2 to Pt0
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The reaction between the platinum(II) bis(boryl) complex cis-[Pt(PPh3)2(Bcat)2] (cat = 1,2-O2C6H4) and the tertiary phosphines PMe3, PEt3, PMe2Ph, PMePh2 and dcpe [1,2-bis(dicyclohexylphosphino)ethane] and the phosphite P(OEt)3 afforded the new complexes cis-[Pt(PR3)2(Bcat)2] (PR3 = PMe3, PEt3, PMe2Ph or PMePh2), cis-[Pt(dcpe)-(Bcat)2] and cis-[Pt{P(OEt)3}2(Bcat)2]. With PCy3 the mixed phosphine species cis-[Pt(PCy3)(PPh3)(Bcat)2] is the major product and was characterised by X-ray crystallography. With P(OMe)3 reductive elimination of B2(cat)2 and the formation of platinum(0) products occurs exclusively whereas with dmpe [1,2-bis(dimethylphosphino)ethane] the only identifiable product is the platinum(ii) species [Pt(dmpe)2]Cl2. With dppm [bis(diphenylphosphino)methane] a reaction occurs to give a product assigned the structure cis-[Pt(dppm)(Bcat)2] or [Pt2(dppm)2(Bcat)4] but two binuclear products were isolated as minor products, namely [Pt2(PPh3)(μ-dppm)2(Bcat)(μ-Bcat)] and [Pt2(κ1-dppm)-(μ-dppm) 2(Bcat)(μ-Bcat)]. Both compounds were characterised by X-ray crystallography and shown to contain unusual semi-bridging Bcat groups. The reaction between [Pt(PPh3)2(η-C2H4)] and the diborane(4) compound 1,2-B2Cl2(NMe2)2 is also described which results in B-B bond oxidative addition yielding cis-[Pt(PPh3)2{BCl(NMe2)}2] and a complex to which this bis(boryl) subsequently rearranges, namely trans-[PtCl(PPh3)2{BCl(NMe2)}]. Both of these complexes were characterised by X-ray crystallography and have geometries typical of cis-bis(boryl) and trans-boryl chloride complexes respectively.
- Curtis, David,Lesley, M.J. Gerald,Norman, Nicholas C.,Orpen, A. Guy,Starbuck, Jonathan
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p. 1687 - 1694
(2007/10/03)
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