- Indirect nuclear spin-spin coupling constants 1J( 17O,11B). First observation and calculation using density functional theory (DFT)
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Coupling constants 1J(17O,11B) of borates, borane adducts and boranes with boron-oxygen bonds have been calculated on the basis of optimised molecular structures using the B3LYP/6-311+G(d,p) level of theory. This indicates that such coupling constants can be of either sign and that their magnitudes can be rather small. Since both 11B and 17O are quadrupole nuclei, it is therefore difficult to measure representative data. In the cases of trimethoxyborane and tetraethyldiboroxanes, it proved possible to obtain experimental data 1J( 17O,11B) (22 and 18 Hz) by measurement of 17O NMR spectra at high temperature (120 °C and 160 °C) respectively. The magnitude of these coupling constants is in reasonable agreement with calculated data. In the case of the diboroxane, this points towards a bond angle B-O-B more close to 180° than to 140°.
- Wrackmeyer, Bernd,Tok, Oleg L.
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Read Online
- Mechanochemical reactions of alkali borohydride with CO2 under ambient temperature
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Many efforts have been made to study the reactions of the borohydride with CO2 in solution. However, it is scarce to achieve the hydrogenation of CO2 using borohydrides as hydrogen source by the solid-gas direct reaction in the condition of ball milling under ambient temperature. Herein, we investigated the solid-gas noncatalytic reaction of ABH4 (A = Li or Na) with CO2 under mechanochemical conditions for the first time. It is found that hydrogen and trimethylborane are formed in the gas phase, as well as borate, formate, and methoxy species are formed in the solid phase.
- Zhu, Wei,Zhao, Juan,Wang, Lu,Teng, Yun-Lei,Dong, Bao-Xia
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p. 828 - 832
(2019/08/07)
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- Nickel-Catalyzed CO2Rearrangement of Enol Metal Carbonates for the Efficient Synthesis of β-Ketocarboxylic Acids
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4-Methylene-1,3-dioxolan-2-ones underwent oxidative addition of a Ni0catalyst in the presence of Me2Al(OMe), followed by a coupling reaction with alkynes, to form δ,?-unsaturated β-ketocarboxylic acids with high regio- and stereoselectivity. The reaction proceeds by [1,3] rearrangement of an enol metal carbonate intermediate and the formal reinsertion of CO2.
- Ninokata, Ryo,Yamahira, Tatsuya,Onodera, Gen,Kimura, Masanari
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supporting information
p. 208 - 211
(2016/12/30)
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- Aluminum Hydride Catalyzed Hydroboration of Alkynes
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An aluminum-catalyzed hydroboration of alkynes using either the commercially available aluminum hydride DIBAL-H or bench-stable Et3Al?DABCO as the catalyst and H-Bpin as both the boron reagent and stoichiometric hydride source has been developed. Mechanistic studies revealed a unique mode of reactivity in which the reaction is proposed to proceed through hydroalumination and σ-bond metathesis between the resultant alkenyl aluminum species and HBpin, which acts to drive turnover of the catalytic cycle.
- Bismuto, Alessandro,Thomas, Stephen P.,Cowley, Michael J.
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supporting information
p. 15356 - 15359
(2016/12/06)
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- Nucleophilicity of Alkyl Zirconocene and Titanocene Precatalysts, and Kinetics of Activation by Carbenium Ions and by B(C6F5)3
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Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6F5)3were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal–carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal–alkyl bond cleavage (M=Zr, Ti) were studied and structure–reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis.
- Berionni, Guillaume,Kurouchi, Hiroaki,Eisenburger, Lucien,Mayr, Herbert
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supporting information
p. 11196 - 11200
(2016/08/03)
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- Nickel-catalyzed multicomponent coupling of alkyne, buta-1,3-diene, and dimethylzinc under carbon dioxide
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A nickel catalyst promoted the coupling of alkynes with buta-1,3-diene and dimethylzinc under carbon dioxide to provide (5E,8Z)-2-vinyldeca-5,8-dienoic acids with high regio- and stereo selectivity. Georg Thieme Verlag Stuttgart. New York.
- Mori, Yasuyuki,Mori, Takamichi,Onodera, Gen,Kimura, Masanari
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supporting information
p. 2287 - 2292
(2014/11/26)
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- Structure, dynamics, and polymerization activity of zirconocenium ion pairs generated with boron-C6F5 compounds and Al 2R6
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Figure Persented: The activation reaction of the olefin polymerization precatalyst Cp*2ZrMe2 with a boron-C 6F5 compound (B(C6F5)3, [Ph3C][B(C6F5)4]) and an aluminum alkyl species (Al2Me6, Al2iBu 6) is studied by NMR spectroscopy in order to determine the nature of the ion pairs that are formed preferentially. We show that a mixture of ion pairs with general formula Cp*2Zr(Me)-μ-Me-E(C 6F5)3-xRx (E = Al, B; x = 0, 1; R = Me, iBu) (1, 2a/b, 4) is generated due to a rapid transfer of pentafluorophenyl groups from boron to aluminum. Therefore, the molecular ratio of the activators determines the final composition of the ion pairs present in solution. When the pentafluorophenyl group transfer is suppressed, the ion pair Cp*2Zr-(μ-Me)2-AlMe2 (5) forms irrespective of the reagent ratio. The high dynamics of these solutions is demonstrated by DNMR studies. Gibbs free energies of activation were determined of 13.6(12) kcal mol-1 at 298 K for the cocatalyst exchange of ion pair Cp*2Zr(Me)-μ-Me-Al(C6F5) 2Me (2a) and 13(2) kcal mol-1 at 298 K for the methyl exchange in Al2(C6F5)xMe 6-x (x = 0, 1). Due to the stability of the ion pairs generated from the Cp*2ZrMe2 precatalyst at temperatures relevant for polymerization, correlations between activities in ethylene polymerization and the nature of the ion pairs can be established. All solutions containing the various ion pairs were found to be catalytically active in ethylene polymerization except that containing the ion pair 2a, which was attributed to the reduced Lewis acidity of the abstractor, as supported by DFT calculations.
- Mathis, Deborah,Couzijn, Erik P. A.,Chen, Peter
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p. 3834 - 3843
(2011/08/09)
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- GASEOUS DIELECTRICS WITH LOW GLOBAL WARMING POTENTIALS
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A dielectric gaseous compound which exhibits the following properties: a boiling point in the range between about ?20° C. to about ?273° C.; non-ozone depleting; a GWP less than about 22,200; chemical stability, as measured by a negative standard enthalpy of formation (dHf0); a toxicity level such that when the dielectric gas leaks, the effective diluted concentration does not exceed its PEL; and a dielectric strength greater than air.
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- Synthesis and structure of cyclic trinuclear zinc disiloxides
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The synthesis and structure of the new disilane-1,2-diol [(Me 3Si)2SiOH]2 (2b) and the trinuclear zinc disiloxides of the formula [Me2Si{(Me3Si)2SiO} 2]2Zn3Me2 (3a), [{(Me 3Si)2Si-O)2]2Zn3Me 2 (3b) and [E-{Me(Me3Si)3SiSiO} 2]2Zn3Me2 (3c) are reported. Compounds 3a-c were prepared by reactions of the corresponding silanedioles 2a-c with ZnMe2. The results of an X-ray structure analysis of 3b reveal an almost perfectly planar spirocyclic Zn3Q4 core with a square-planar geometry of the inner Zn2+ ion, whereas in 3a,c the inner zinc ions are distorted tetrahedral. Upon treatment with B(C 6F5)3, compounds 3b,c have been converted quantitatively into the complexes [{(Me3Si)2SiO} 2]2Zn3(C6F5)2 (4b) and [E-{Me(Me3Si)3SiSiO}2] 2Zn3(C6F5)2 (4c). Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Krempner, Clemens,Reinke, Helmut,Weichert, Katja
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p. 1067 - 1071
(2008/02/09)
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- Trisilane-1,3-diolato complexes of Ti and Zr: Syntheses and X-ray crystal structures
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The syntheses and structures of zirconium and titanium complexes containing the novel chelating trisilane-1,3-diolate ligand [Me2Si(R 2SiO)2]2- (R = SiMe3) (5)-H 2 are reported. The chloride complexes [Me2Si(R 2SiO)2]TiCl2 (7a) and [Me2Si(R 2SiO)2]ZrCl2·2THF (7b) were prepared by the reaction of MCl4 (M = Ti, Zr) with [Me2Si(R 2-SiO)2]2Ti (6a) and [Me2Si(R 2SiO)2]2Zr (6b), which are derived from the reaction of 5 with M(NEt2)4, respectively. In the presence of TiCl4, complexes 6a and 7a undergo a ring-opening reaction to produce the dinuclear complex [Me2Si(R2SiO) 2][TiCl3]2 (9). [Me2Si(R 2SiO)2]TiMe2 (10) and [Me2Si(R 2SiO)2]TiBnZ2 (11) were prepared in moderate yields from reactions of 7a with 2 equiv of MeMgBr and BnzMgCl, respectively. According to NMR spectroscopic investigations, the reaction of the dimethyltitanium complex 10 with B(C6F5)3 led to full exchange of both methyl groups by C6F5 groups under quantitative formation of [Me2Si(R2SiO) 2]Ti(C6F5)2 (12) and a mixture of B(C6F5)3-nMen, where n = 1-3. The structure of 12 is further evidenced by the preparation of an identical sample from the reaction of 7a with 2 equiv of C6F5MgBr. Refluxing an ether solution of 12 surprisingly gave [Me2Si(R 2SiO)2]2TiC6F5] 2O (13) as a result of ether cleavage. The structures of the complexes 7a, 7b, 9, 10, and 13 were determined by X-ray crystallography, and structural discussion of the bond parameters will be given.
- Krempner,Koeckerling,Reinke,Weichert
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p. 3203 - 3211
(2008/10/09)
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- PROCESS FOR SYNTHESIS OF DIALKOXYORGANOBORANES
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The invention relates to a process for the synthesis of dialkoxyorganoboranes, in particular to a process for the synthesis of dialkoxyorganoboranes by an ester exchange reaction. Moreover, the invention relates to a process for the synthesis of organo-oxazaborolidine catalysts (organo-CBS) and of trialkylboroxins. Furthermore, the invention relates to methods of using dialkoxyorganoboranes for the preparation of organo-CBS catalysts and in Suzuki-type coupling reactions.
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Page/Page column 9
(2008/06/13)
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- Neutral and cationic aluminum and titanium complexes incorporating sterically demanding organosilicon ligands
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New complexes of aluminum and titanium containing sterically demanding ligands and their reaction with B(C6F5)3 are reported. Treatment of [(Ph2MeSiCH2CH2) 3Si]NCN[Si(CH2CH2SiMePh2) 3] (1) or Si(CH2CH2SiMePh2) 3OH (2) with 1 equiv of AlMe3 results in the formation of the neutral dimethylaluminum complexes {MeC[NSi(CH2CH 2SiMePh2)3]2}AlMe2 (3) and [(Ph2MeSiCH2CH2)3SiOAlMe 2]2 (4). Reaction of 3 with 1 equiv of B(C 6F5)3 forms the neutral complex {MeC[NSi(CH2CH2SiMePh2)3] 2}AlMe(C6F5) (5) and BMe(C6F 5)2. In the case of 4, the analogous reaction produced the dimer [(Ph2MeSiCH2CH2)3SiOAl] 2Me3(C6F5) (6). Treatment of 1 with Ti(C5Me5)Me3 fails to afford the corresponding amidinate complex. However, reaction of 2 with the same titanium half-sandwich complex cleanly gives Ti(C5Me5)[OSi(CH2CH 2SiMePh2)3]Me2 (7). Reaction of 7 with 1 equiv of B(C6F5)3 leads to the formation of the ion pair {Ti(C5Me5)[OSi(CH2CH 2SiMePh2)3]Me}[BMe(C6F 5)3] (8), which is relatively stable at room temperature, slowly decomposing (t1/2 ≈ 48 h) to give a mixture of two neutral titanium complexes, Ti(C5Me5)[OSi(CH2CH 2SiMePh2)3][CH2B(C6F 5)2](C6F5) (9) and TiC 5Me5)[OSi(CH2CH2SiMePh 2)3]Me(C6F5) (10). However, when this reaction is carried out in a 1:0.5 stoichiometry, the decomposition process occurs over the course of 22 h, giving complex 10 selectively. The implications of these results with related Ziegler-Natta catalyst systems are discussed.
- Amo, Virginia,Andres, Roman,De Jesus, Ernesto,De La Mata, F. Javier,Flores, Juan C.,Gomez, Rafael,Gomez-Sal, M. Pilar,Turner, John F. C.
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p. 2331 - 2338
(2008/10/09)
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- Polymorphism in the crystal structures of the group 13 trimethyls
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Crystal structure have been determined for trimethylboron, BMe3, and for a new polymorph of trimethylgallium, GaMe3; in addition, the crystal structure of trimethylthallium, TlMe3, has been redetermined. The BMe3 crystal structure represents a new structural type for the group 13 trimethyl derivatives in the solid state. In contrast to its heavier analogues, it consists of layer containing only very weakly interacting BMe3 molecules. GaMe3 forms a ladder-like pseudo-polymer via long gallium-to-methyl intermolecular interactions with Ga...C distances in the range 3.096(3)-3.226(4) A. This is compared with a recently reported crystal structure of a polymorph, which, like InMe3 and TlMe3, is characterized by the formation of pseudo-tetramers. The effects of crystallization and secondary interactions have been analyzed by comparison with related crystallographic, gas-phase electron diffraction, and spectroscopic studies of these and other trimethyl derivatives of the group 13 elements. The energetic differences between polymorphs of BMe3, GaMe3, and InMe3 have been explored by plane wave DFT calculations. The energy differences between the BMe3-like layered structure and the InMe3-like pseudo-tetrameric structure are calculated to be -1.7, +3.6, and +10.4 kJ mol-1 for BMe3, GaMe3, and InMe3, respectively.
- Boese, Roland,Downs, Anthony J.,Greene, Timothy M.,Hall, Alexander W.,Morrison, Carole A.,Parsons, Simon
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p. 2450 - 2457
(2008/10/08)
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- Reactions of zinc dialkyls with (perfluorophenyl)boron compounds: Alkylzinc cation formation vs C6F5 transfer
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Reaction between ZnR2 and [H(OEt2)2] [B(C6F5)4] in ether leads to the salts [RZn(OEt2)3]-[B(C6F5)4], while mixtures of ZnR2 (R = Me, Et) and B(C6F5)3 in toluene-d8 undergo facile alkyl/C6F5 group exchange to give Zn(C6F5)2·(toluene). Mixtures of ZnR2 and B(C6F5)3 in hydrocarbon/diethyl ether solvent mixtures react with alkyl transfer to afford the ion pairs [RZn(OEt2)3][RB(C6 F5)3], whereas the reaction of ZnEt2 with [Ph3C][B(C6F5)4] in toluene-d8 proceeds with β-H abstraction to give ethene and Ph3CH, with the subsequent rapid formation of Zn(C6F5)2.
- Walker, Dennis A.,Woodman, Timothy J.,Hughes, David L.,Bochmann, Manfred
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p. 3772 - 3776
(2008/10/08)
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- Synthesis and Reactivity of New Aminopentaboranes
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of 2-XB5H8 (X = Br or Cl) with secondary or tertiary silylamines proceed with elimination of hydrogen halides and/or halosilanes and attachment of amino groups to the clusters. Reaction of 2-BrB5H8 with (Me3-Si)2NH produces 2-[(Me3Si)2N]B5H8 in 57% yield. Other bis(silyl)amines react analogously. With (t-Bu)(Me3-Si)NH, 2-BrB5H8 produces 2-[(Me3Si)(t-Bu)N]B5H8 and hypho-2,3-μ-(t-BuNH)B5H10. (t-Bu)(Et3Si)NH reacts analogously. Low temperature analysis of the (t-Bu)(Me3Si)NH reaction in dichloromethane solution via 11B NMR spectroscopy discloses a dual reaction pathway producing a 2-aminopentaborane and a proposed arachno-2,3-μ-(t-BuNH)B5H8 intermediate which subsequently reacts with boranes to form hypho-2,3-μ-(t-BuNH)B5H8. When the above reaction is carried out in B5D9 solution, normal nido-[(t-Bu)(Me3Si)N]B5H8 and partially deuterated hypho-2,3-μ-(t-BuNH)B5H10 is formed. Reaction of 2-[(Me3Si)2N]B5H8 with BCl3 produces 2-[(Me3Si)2N·BCl3]B5H 8, and with (t-Bu)CN produces 2,3-μ-(t-BuCH=N)-2-[(Me3Si)2N]B5H 7.
- McGaff, Robert W.,Gaines, Donald F.
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p. 7850 - 7856
(2008/10/09)
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- Methylzinc tetrahydroborate: Physical and chemical properties and crystal structure at low temperature
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Methylzinc tetrahydroborate, MeZnBH4, has been prepared by two routes and initially characterized by elemental analysis and its spectroscopic properties. The structure has been determined by X-ray crystallography at 150 K [trigonal, space group R3c, a = b = 15.831(10), c = 8.36(2) A, Z = 18, R = 0.072] to reveal helical polymers in which MeZn+ and BH4- units alternate, with the latter functioning as a bidentate ligand with respect to both of the adjacent metal atoms. It thus resembles the structure of solid Be(BH4)2 with the difference that the zinc is five-co-ordinated, the Me and H ligands adopting a distorted square-pyramidal geometry. Chemical properties of methylzinc tetrahydroborate investigated include its thermal decomposition and its reactions with ammonia, dimethyl sulfide, triphenylphosphine and CO; disproportionation into Me2Zn and Zn(BH4)2 appears to be a common feature of its chemistry.
- Aldridge, Simon,Blake, Alexander J.,Downs, Anthony J.,Parsons, Simon,Pulham, Colin R.
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p. 853 - 859
(2007/10/03)
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- Reactions of the diboron tetrahalides B2Cl4 and B2Br4 with B5H9: Preparation and properties of the (dihaloboryl)pentaborane derivatives 1-BX2B5H8, (X = Br, Cl, F, OCH3, t-Bu, H) and synthesis of (BCl2)3B5H6
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The reactions of B2Cl4 with excess B5H9 yield 1-BCl2B5H8 (73%) while those of B2Br4 generate 1-BBr2B5H8 (80%). Ligand exchange of 1-BCl2B5H8 with excess BBr3 forms 1-BBr2B5H8 (86%), that with Hg(CF3)2 results in 1-BF2B5H8 (96%), that with CH3OH generates 1-B(OCH3)2B5H8 (46%), and that with Li(t-Bu) prepares B(t-Bu)(Cl)B5H8 (23%) and B(t-Bu)2B5H8 (20%). The relative thermal stabilities of these products are BF2B5H8 > BCl2B5H8 > BBr2B5H8 > B(OCH3)2B5H8 > B(t-Bu)2B5H8. All of these BX2B5H8 compounds (X = F, Cl, OCH3, t-Bu) decompose to form BX3 and B5H9 as the volatile products. Reactions of BCl2B5H8 with excess B2Cl4 yield (BCl2)3B5H6, a compound of limited thermal stability, but no evidence for further BCl2 substitution on the pentaborane cage was obtained. Reductions of BCl2B5H8 with LiBH4 in C6H5Cl or C6H4Cl2 form apparent equilibrium mixtures of 1:1′,2′-[B5H8][B2H5] and 1:1′-[B5H8][B2H5]. One or both of these compounds decompose with the evolution of B2H6, B5H9, and coupled pentaborane cages (B5H7)n, where n can be at least as large as 8. The 11B NMR and mass spectrometric evidence from the last reaction is consistent with the initial dimerization of the hexaborane 1-BH2B5H8, which is rapidly followed by the formation of 1:1′-[B5H8][B2H5], the cross product arising from the interaction of B2H6 with (BH2B5H8)2, and then isomerization of this heptaborane to 1:1′,2′-[B5H8][B2H5].
- Saulys,Morrison
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p. 4174 - 4179
(2008/10/08)
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- Contributions to the Chemistry of Boron. Part 194. Synthesis and Characterization of Mono, Bi-, and Tri-cyclic Boron-Nitrogen-Sulphur Ring Systems. Crystal Structure of 2,7,9,14-Tetrakis(diethylamino)-3,5,6,10,12,13-hexathia-1,8-diaza-2,4,7,9,11,14-hexaboratricyclo4,8> tetra...
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Reactions of the triborylamines N(BX2)3 (X = Cl or Br) with bis(dimethylboryl)disulphane (2) proceed via 4-dihalogenoboryl-3,5-dihalogeno-1,2,4,3,5-dithiazadiborolidines (3) to 2,8-dihalogeno-3,4,6,7-tetrathia-1-aza-2,5,8-triborabicyclo1,5> octanes (4a) and (4b).The bromo derivative (4b) reacts with additional (2) (1:1 molar ratio) to procedure impure NB3S6, but with an excess of (2) to yield a tricyclic system NB4S6(CH3).The halogen atoms in (4a) and (4b) can be substituted by methyl groups from Sn(CH3)4 as the methylating agent.Amination of compound (4a) with Sn(CH3)3 seems to proceed via the bis(diethylamino)derivative, but a new triclinic system (8) is the final product the structure of which has been determined by X-ray crystallography.U.v. and He I photoelectron spectra support n.m.r. evidence that the bicyclic rings (4) are planar 10?-electron systems.This conclusion is supported by MNDO and PPP calculations.
- Kendrick, Aidan,Noeth, Heinrich,Stalla, Beate,Storch, Wolfgang
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p. 1311 - 1320
(2007/10/02)
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- Sodium hydridotrimethylboronate and its ether solvate. Study of hydridotrialkylboronates as reagents for the preparation of beryllium hydrides
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Sodium hydridotrimethylborate is tetrameric in benzene solution and its etherate, (NaBMe3H)4OEt2 probably also retains its solid state cubane arrangement in benzene solution.Reactions of NaBR3H (R = Me, Et) in a variety of ratios with halo and organoberyllium compounds have been studied.Exchange between Et2Be and NaBEt3H does not occur to any appreciable extent beyond the EtBH stage and reaction of equimolar EtBeCl and NaBEt3H resulted in the formation of EtBeH, isolated as its trimethylamine complex.NaBR3H and BeCl2 in 1/1, 2/1 and 4/1 ratios did not yield pure beryllium hydrides.
- Bell, Norman A.,Coates, Geoffrey E.,Heslop, J. Alan
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p. 287 - 292
(2007/10/02)
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- Contributions to the Chemistry of Boron, 152. 1,3,2,4-Diazaphosphaboretidines and 1,3,2,4-Diazasilaboretidines Prepared via Intra- and Intermolecular Cyclocondensation
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1,3,2,4-Diazaphospha(sila)boretidines 5 and 9 are accessible via thermal decomposition of compounds of type E(NR'-BR2)2 (8) or from organoboron dihalides or boron trihalides and E(NR'Li)2 .The formation of 1,3-di-tert-butyl-4-methyl(or ethyl)-1,3,2,4-diazaphospha(sila)boretidines from the precursor E(NR'-BR2)2 proceeds by an intramolecular cyclocondensation.NMR data reveal less shielded B and P atoms in the new heterocycles as compared with noncyclic compounds; this is attributed to a strained ring system.A tetracoordinated as well as a tricoordinated boron atom is observed in CH3(O)P(NR'BR2)2 compounds resulting from intramolecular BO coordination.
- Jacksties, Wolfgang,Noeth, Heinrich,Storch, Wolfgang
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p. 2030 - 2043
(2007/10/02)
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- Organoboranes. 40. A simple preparation of borinic esters from organolithium reagents and selected boronic esters
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Monoorganyldiisopropoxyboranes, RB(O-i-Pr)2, react cleanly at -78 °C with 1 equiv of organolithium compounds, R′Li, to form the corresponding complexes of the borinic acid esters, LiRR′B(O-i-Pr)2. Treatment of these complexes with an equivalent of anhydrous hydrogen chloride in ethyl ether liberates the borinic esters, RR′BO-i-Pr, and isopropyl alcohol, usually readily separated by distillation. Alternatively, treatment of the complexes with 1 mol of an appropriate acid chloride liberates the borinic esters, RR′BO-i-Pr, and an isopropyl ester, RCO2-i-Pr. By careful selection of the acid chloride, these two products can be easily separated by distillation. A careful examination of the reaction of other boronic esters in this reaction revealed that the boronic esters of 1,3-propanediol forms the 1:1 complex cleanly on reaction with organolithium compounds at -78 °C. (Formula Presented) Treatment of these ate complexes either with hydrogen chloride in ether or with an appropriate acid chloride provides the pure borinic ester. Consequently, simple rational procedures are now available for the synthesis in high purities and yields of either boronic or borinic acids and esters, either through hydroboration or through the use of organolithium compounds.
- Brown, Herbert C.,Cole, Thomas E.,Srebnik, Morris
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p. 1788 - 1792
(2008/10/08)
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- Organoboranes. 31. A simple preparation of boronic esters from organolithium reagents and selected trialkoxyboranes
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The reaction of methyllithium with trimethoxyborane at -78°C in ethyl ether yields a mixture of methylated boranes and their corresponding ate complexes. We have found that under the same conditions triisopropoxyborane reacts cleanly with methyllithium to form the lithium methyltriisopropoxyborate complex. Protonation of this complex with anhydrous hydrogen chloride quantitatively yields methyl diisopropoxyborane. This reaction of organolithium reagent with triisopropoxyborane appears to provide a general, valuable route to boronic esters. Other alkoxyboranes were examined for their selectivity for monomethylation by methyllithium. In addition to triisopropoxyborane, triisobutoxyborane and tri-sec-butoxyborane also give the methylboronic esters quantitatively. This development provides the first general preparation of boronic esters from organolithium reagents.
- Brown, Herbert C.,Cole, Thomas E.
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p. 1316 - 1319
(2008/10/08)
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- Syntheses and crystal structures of the tetrakis(methyltrihydroborato) compounds of zirconium(IV), thorium(IV), uranium(IV), and neptunium(IV)
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Zr(BH3CH3)4, Th(BH3CH3)4, U(BH3CH3)4, and Np(BH3CH3)4 have been synthesized and their molecular structures determined by single-crystal X-ray diffraction. Infrared spectroscopy and nuclear magnetic resonance data are presented for the Zr, Th, and U compounds. The space groups, unit cell parameters, and R factors are as follows: Zr(BH3CH3)4, tetragonal, P42/n, a = 10.311 (6) ?, c = 5.851 (3) ?, Z = 2, dx = 1.103 g/cm3, R = 0.013 (F2 > 3σ(F2)); Th(BH3CH3)4, triclinic, P1, a = 18.408 (6) ?, b = 16.910 (6) ?, c = 8.834 (3) ?, α = 88.06 (4)°, β = 90.83 (4)°, γ = 88.08 (4)°, Z = 8, dx = 1.681 g/cm3, R = 0.068 (F2 > 3σ(F2)); U(BH3CH3)4, monoclinic, P21n, a = 18.228 (6) ?, b = 16.749 (6) ?, c = 8.765 (2) ?, β = 90.69 (4)°, Z = 8, dx = 1.755 g/cm3, R = 0.041 (F2 > 3σ(F2)); Np(BH3CH3)4, tetragonal, P42/n, a = 10.552 (6) ?, c = 5.950 (3) ?, Z = 2, dx = 1.767 g/cm3, R = 0.016 (F2 > 3σ(F2)). All compounds are monomolecular in the crystalline state. The metal atoms are tetrahedrally coordinated to the four BH3CH3 groups through tridentate hydrogen bridges. The M-B distances are 2.335 ± 0.003 ? for Zr, 2.56 ± 0.05 ? for Th, 2.49 ± 0.02 ? for U, and 2.487 ± 0.006 ? for Np.
- Shinomoto, Ron,Gamp, Eduard,Edelstein, Norman M.,Templeton, David H.,Zalkin, Allan
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p. 2351 - 2355
(2008/10/08)
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