- Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity/Basicity Scale
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A quantitative Lewis acidity/basicity scale toward boron-centered Lewis acids has been developed based on a set of 90 experimental equilibrium constants for the reactions of triarylboranes with various O-, N-, S-, and P-centered Lewis bases in dichloromethane at 20 °C. Analysis with the linear free energy relationship log KB=LAB+LBB allows equilibrium constants, KB, to be calculated for any type of borane/Lewis base combination through the sum of two descriptors, one for Lewis acidity (LAB) and one for Lewis basicity (LBB). The resulting Lewis acidity/basicity scale is independent of fixed reference acids/bases and valid for various types of trivalent boron-centered Lewis acids. It is demonstrated that the newly developed Lewis acidity/basicity scale is easily extendable through linear relationships with quantum-chemically calculated or common physical–organic descriptors and known thermodynamic data (ΔH (Formula presented.)). Furthermore, this experimental platform can be utilized for the rational development of borane-catalyzed reactions.
- Mayer, Robert J.,Hampel, Nathalie,Ofial, Armin R.
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supporting information
p. 4070 - 4080
(2021/01/29)
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- Examining the Effects of Monomer and Catalyst Structure on the Mechanism of Ruthenium-Catalyzed Ring-Opening Metathesis Polymerization
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The mechanism of Ru-catalyzed ring-opening metathesis polymerization (ROMP) is studied in detail using a pair of third generation ruthenium catalysts with varying sterics of the N-heterocyclic carbene (NHC) ligand. Experimental evidence for polymer chelation to the Ru center is presented in support of a monomer-dependent mechanism for polymerization of norbornene monomers using these fast-initiating catalysts. A series of kinetic experiments, including rate measurements for ROMP, rate measurements for initiation, monomer-dependent kinetic isotope effects, and activation parameters were useful for distinguishing chelating and nonchelating monomers and determining the effect of chelation on the polymerization mechanism. The formation of a chelated metallacycle is enforced by both the steric bulk of the NHC and by the geometry of the monomer, leading to a ground-state stabilization that slows the rate of polymerization and also alters the reactivity of the propagating Ru center toward different monomers in copolymerizations. The results presented here add to the body of mechanistic work for olefin metathesis and may inform the continued design of catalysts for ROMP to access new polymer architectures and materials.
- Wolf, William J.,Lin, Tzu-Pin,Grubbs, Robert H.
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supporting information
p. 17796 - 17808
(2019/11/11)
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- Palladium-catalyzed suzuki-miyaura type coupling reaction of aryl halides with triphenylborane-pyridine
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The Suzuki-Miyaura type coupling reaction of aryl halides with triphenylborane-pyridine was described. The reaction can be catalyzed by Pd(OAc)2 (5 mol%) in presence of Cs2CO3 at 50°C or 80°C, and functionalized biaryls were obtained in good to excellent yields. This protocol is general and can tolerate a wide range of functional groups. The Suzuki-Miyaura type coupling reaction of aryl halides with triphenylborane-pyridine was described. The reaction can be catalyzed by Pd(OAc)2 (5 mol%) in the presence of Cs2CO3 at 50°C or 80°C, and functionalized biaryls were obtained in good to excellent yields. This protocol is general and can tolerate a wide range of functional groups. Copyright
- Yang, Minghua,Gu, Yongbing,Wang, Yan,Zhao, Xiyu,Yan, Guobing
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p. 2581 - 2586,6
(2020/09/16)
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- Copper-catalyzed petasis-type reaction: A general route to α-substituted amides from imines, acid chlorides, and organoboron reagents
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A copper-catalyzed Petasis-type reaction of imines, acid chlorides, and organoboranes to form α-substituted amides is described. This reaction does not require the use of activated imines or the transfer of special units from the organoboranes and represent a useful generalization of the Petasis reaction.
- Morin, Marie S. T.,Lu, Yingdong,Black, Daniel A.,Arndtsen, Bruce A.
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experimental part
p. 2013 - 2017
(2012/04/17)
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- Process for making solid triphenylboron-pyridine or its adduct
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A process for producing solid triphenylboron-pyridine (TPBP) spherical particles by separately feeding into a vigorously agitated reaction zone (i) a stream of pyridine and a (ii) stream comprising a solution of sodium hydroxide adduct of triphenylboron (TPBA) whereby the total concentration of TPBA in the combined feed streams is in the range of from 1 wt % to 6 wt %, and simultaneously removing a product stream from said reaction zone and recovering the triphenylboron-pyridine (TPBP) particles.
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Page/Page column 2-3
(2008/06/13)
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- Preparation and reactions of base-free bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium oxide, Cp′2UO
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Reduction of the uranium metallocene [η5-1,2,4-Me 3C)3C5H2]2UCl 2 (1), Cp′2UCl2, in the presence of 2,2′-bipyridyl and sodium naphthalene gives the dark green metallocene complex Cp′2U(bipy) (6), which reacts with p-tolyl azide or pyridine-N-oxide to give Cp′2U=N(p-tolyl) (7) or Cp′ 2U(O)(py) (8), respectively. The Lewis acid BPh3 precipitates Ph3B(py) and gives the base-free oxo Cp′ 2UO (10), which crystallizes from pentane. The oxometallocene 10 behaves as a nucleophile with Me3SiX reagents, but it does not exhibit cycloaddition behavior with acetylenes, suggesting that the polar resonance structure Cp′2U+-O- dominates the double-bond resonance structure Cp′2U=O.
- Zi, Guofu,Jia, Li,Werkema, Evan L.,Walter, Marc D.,Gottfriedsen, Jochen P.,Andersen, Richard A.
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p. 4251 - 4264
(2008/10/09)
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- Bis(tetramethylpiperidino)aluminum Halide Adducts tmp2AlX·Do and Tetrahaloaluminates of Tricoordinated Aluminum Cations [tmp2Al(Do)]AlX4
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Upon treatment with Lewis bases Do (Do = pyridine bases or THF), the Lewis acids tmp2AlX (X = Cl, Br, I) are converted exclusively to the monoadducts tmp2AlX·Do (2-4). The AlX bonds of these addition compounds are considerably elongated, indicating a tendency towards the formation of ionic species [tmp2Al(Do)]X. Due to the steric requirements of the bulky tmp ligands, addition of an excess of the Lewis base does not force these compounds to form tetracoordinated aluminum cations [tmp2Al(Do)2]+ or pentacoordinated adducts tmp2AlX·Do2. Attempts to prepare ionic representatives by reaction of tmp2AlX·Do with "ate" complexes of comparatively low nucleophilicity [MY = NaBPh4, AgBPh4, LiB(C6F5)4, AgBF4, AgOtos] result in phenylation products [e.g. tmp2AlPh (5a) and BPh3·py (5b)] or tetracoordinated addition compounds tmp2AlY·Do (Y = anion). However, addition of one equivalent of AlX3 (X = Br, I) initiates halide abstraction with formation of the ionic [tmp2Al(Do)]AlX4 species 6a-f, as indicated by 27Al-NMR data and conductivity measurements. Solid [tmp2Al(Py)]AlI4 (6b) decomposes readily into tmpAlI2 and tmpAlI2·py (7c) Addition of non-polar aliphatic solvents to solutions of [tmp2Al(Do)]AlX4 (6) leads to slow decomposition into tmp2AlX and AlX3·Do (7a-b, d). This also occurs in polar donor solvents, where compounds AlX3·Do are favoured due to the formation of penta- or hexacoordinated species AlX3·Do·Solvn (n = 1, 2). Semiempirical AM1 calculations reveal the gas-phase stability of the tricoordinated bis(tmp)aluminum cation in the salt [tmP2AlPy]AlCl4 as the only representative in a series of calculated aluminum cations [(R2N)2AlPy]AlCl4 (R2N = Me2N, Et2N, iPr2N, tmp). According to these calculations, the stability of a given cation increases when tetrachloroalummate is replaced by tetraiodoaluminate. Ab initio calculations have been performed on two cations [(H2N)2Al(Do)]+ (Do = NH3, py) and indicate very short Al-N bond lengths owing to ionic bonding contributions.
- Krossing, Ingo,No?th, Heinrich,Schwenk-Kircher, Holger
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p. 927 - 939
(2007/10/03)
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- Skeletal rearrangements of arylborane complexes mediated by redox reactions: thermal and photochemical oxidation by metal ions
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A variety of metal salts have been found to undergo reduction by thermal and photochemical interaction with tetraarylborate salts and with neutral alkyl- and aryl-borane complexes.In the cases of Cu2+, Cu+, Ni2+, Co2+, Pd2+, Pt2+, Ag+, Zn2+, Hg2+, Sn2+, Pb2+ and Rh3+ salts, such photochemical reductions with NaBPh4 led to the deposition of the free metal, while a number of binary mixtures of metal salts led to the codeposition of both metals, sometimes as true alloys, under such photoreduction.In the course of these reductions the arylboratereductants underwent oxidative coupling of the aryl groups to form biaryls in a strictly intra-ionic (for BAr4-) or intramolecular (Ar3B) manner respectively.Individual studies of the photochemistry of the tetraarylborate anion itself, of cuprous tetraphenylborate and of the triphenylborane-pyridine complex have adduced evidence for a gamut of reactive intermediates capable of serving as the photoreductant for metal ions, such as triarylborane radical anions, diarylborate(I) anions or arylborenes, 7-borabicycloheptadiene anions or neutral complexes and finally arylborohydride anions or arylboron hydrides.The role of these intermediates both in the photoinduced skeletal rearrangements of arylboranes and in the concomitant reduction of metal ions is discussed in critical detail.Key words: Boron; Aryl; Oxidation; Copper; Nickel; Zinc
- Eisch, John J.,Shah, Jamshed H.,Boleslawski, Marek P.
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- THE REACTIONS OF DIBORANE WITH ARYL-ORGANOTIN COMPOUNDS
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A number of tetraaryltin compounds, Ar4Sn (where Ar = phenyl, o- and p-tolyl, and p-chlorophenyl) and tryphenyltin compounds, PH3SnX (where X = Cl, H, OH, OCOCH3 and OCOCF3) have been treated with diborane in tetrahydrofuran.Transmetallation occurs in which one or more aryl groups are transferred to boron.The organoboron intermediates give phenols upon oxidation and boronic and borinic acids upon hydrolysis.Pyridine complexes of organoboranes have also been isolated.
- Pickles, G. M.,Spencer, T.,Thorpe, F. G.,Chopa, A. B.,Podesta, J. C.
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