- Preparation of trialuminum triboron heptakis(dimethylamino)pentahydride
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Treatment of bis(trimethylamine)-alane, [(CH3)3N]2AlH3, with tetrakis(dimethylamino)diborane(4), [(CH3)2N]4B2, results in the formation of the following known compounds: H2, (CH3)3N, [(CH3)2NBH2]2, [(CH3)2N]2BH, and (CH3)3NBH3. In addition, a new species was prepared, Al3B3[N(CH3)2]7H 5, which most likely contains three B-Al bonds. Characterization of this new compound is discussed.
- Hall,Schram
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- Mechanistic insights into dehydrocoupling of amine boranes using dinuclear zirconocene complexes
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Catalytic dehydrocoupling of H3B·NMe2H using the in situ system Cp2Zr(Cl)(μ-Me3SiC3SiMe3)Zr(Cl)Cp2 (1)/MeLi was studied as a model for previously reported dehydropolymerisation of H3B·NMeH2. NMR and UV-vis spectroscopic monitoring of the precatalyst activation sequence as well as a series of stoichiometric experiments showed that formation of a zirconocene dimethyl complex (2) is not relevant for activation of the precatalyst. Instead, deprotonation of H3B·NMe2H and reaction of thus formed Li[NMe2BH3] is proposed to result in the formation of Zr amidoborane and hydride species. DFT analysis using such complexes as active species showed a pathway for formation of H2 and H2BNMe2. 1H NMR spectroscopic monitoring and stoichiometric control experiments revealed the formation of unusual diamagnetic dinuclear complexes Cp2Zr(C2SiMe3)(μ-R)ZrCp2 (R = CH2SiMe3, 7; R = H, 9) formed by activation of the allenediide unit of the precatalyst 1. Such species can be regarded as rare single-component catalysts for the dehydrocoupling of amine boranes. This journal is
- Al Hamwi, Hanan,Beweries, Torsten,Drexler, Hans-Joachim,Heller, Detlef,Jannsen, Nora,Lindenau, Kevin,Neymeyr, Klaus,Rei?, Fabian,Rippke, Mirko,Sawall, Mathias,Selle, Carmen,Spannenberg, Anke
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supporting information
p. 4034 - 4050
(2021/07/06)
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- Dehydropolymerisation of Methylamine Borane and an N-Substituted Primary Amine Borane Using a PNP Fe Catalyst
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Dehydropolymerisation of methylamine borane (H3B?NMeH2) using the well-known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH2CH2PiPr2)2) (1) gives poly(aminoborane)s by a chain-growth mechanism. In toluene, rapid dehydrogenation of H3B?NMeH2 following first-order behaviour as a limiting case of a more general underlying Michaelis–Menten kinetics is observed, forming aminoborane H2B=NMeH, which selectively couples to give high-molecular-weight poly(aminoborane)s (H2BNMeH)n and only traces of borazine (HBNMe)3 by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H3B?NMe2H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally. A silyl functionalised primary borane H3B?N(CH2SiMe3)H2 was studied in homo- and co-dehydropolymerisation reactions to give the first examples for Si containing poly(aminoborane)s.
- Anke, Felix,Boye, Susanne,Spannenberg, Anke,Lederer, Albena,Heller, Detlef,Beweries, Torsten
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supporting information
p. 7889 - 7899
(2020/06/02)
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- Stable BH3adducts to rhodium amide bonds
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Rh(I) diolefin amides, [Rh(trop2N)(L)] (trop2N?=?bis(5H-dibenzo[a,d]cyclohepten-5-yl)amide), form the corresponding hydrido amine species, [RhH(trop2NH)(L)], by reaction with Me2HN-BH3(DMAB). Both amide and amine complexes are active dehydrocoupling catalysts, forming the monomer [Me2N?=?BH2], the linear [Me2NHBH2NMe2BH3] and the cyclic dimer [Me2BNH2]2. Good catalytic activity was observed especially for complexes which contain a metal hydride unit, Rh–H, in a co-planar cis-arrangement with respect to the N-H unit and for those bearing an N-heterocyclic carbene ligand (IMe) in trans-position to the active basic site of the ligand. Four-membered Rh–N–B–H metallacycles [Rh{(μ-H)BH2}(Ntrop2)(L)] (L?=?PPh3, IMe) were isolated by direct reaction of the amide complex with BH3(THF). These stable species are not active in the dehydrogenation of DMAB. Their isolation and lack of reactivity gives some indication for a possible catalyst deactivation. This observation is consistent with a mechanism in which the unprotected amine or amide ligand is essential for N–H and B–H bond cleavage.
- Müller, Fabian,Trincado, Monica,Pribanic, Bruno,Vogt, Matthias,Grützmacher, Hansj?rg
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p. 154 - 162
(2016/11/01)
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- Catalytic Dehydrocoupling of Amine-Boranes using Cationic Zirconium(IV)-Phosphine Frustrated Lewis Pairs
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A series of novel, intramolecular Zr(IV)/P frustrated Lewis pairs (FLPs) based on cationic zirconocene fragments with a variety of ancillary cyclopentadienyl and 2-phosphinoaryloxide (-O(C6H4)PR2, R = tBu and 3,5-CF3-(C6H3)) ligands are reported and their activity as catalysts for the dehydrocoupling of dimethylamine-borane (Me2NH·BH3) assessed. The FLP system [(C9H7)2ZrO(C6H4)PtBu2][B(C6F5)4] is shown to give unprecedented turnover frequencies (TOF) for a catalyst based on a group 4 metal (TOF ≥ 600 h-1), while also proving to be the most efficient FLP catalyst reported to date. The mechanism of this reaction has been probed using analogous intermolecular Zr(IV)/P FLPs, permitting deconvolution of the reactions taking place at both the Lewis acidic and basic sites. Elucidation of this mechanism revealed an interesting cooperative two-cycle process where one cycle is FLP mediated and the other, a redistribution of a linear diborazane intermediate, relies solely on the presence of a Zr(IV) Lewis acid.
- Metters, Owen J.,Flynn, Stephanie R.,Dowds, Christiana K.,Sparkes, Hazel A.,Manners, Ian,Wass, Duncan F.
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p. 6601 - 6611
(2016/10/14)
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- Titanocene(iii) complexes with 2-phosphinoaryloxide ligands for the catalytic dehydrogenation of dimethylamine borane
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A study of the dehydrogenation of dimethylamine borane using different titanocene(iii) complexes with 2-phosphinoaryloxide ligands is presented. Complexes Cp2Ti(κ2-O, P-O-C6H4-PR2) (3a: R = i-Pr, 3b: R = Ph) (Cp = η5-cyclopentadienyl) and Cp?2Ti(κ1-O-O-C6H4-PR2) (5a: R = i-Pr, 5b: R = Ph) (Cp? = η5-pentamethylcyclopentadienyl) were prepared by reactions of the 2-phosphinophenol ligand with different titanocene sources and fully characterised. Their catalytic activity depends on the steric influence of the cyclopentadienyl ligand, the coordination mode of the 2-phosphinoaryloxide ligand and on the used solvent. Complex 3a showed a turnover number of 43.2 in the neat substrate after 24 hours. EPR investigations were used to elucidate the fate of the Ti(iii) catalyst.
- Klahn, Marcus,Hollmann, Dirk,Spannenberg, Anke,Brückner, Angelika,Beweries, Torsten
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p. 12103 - 12111
(2016/01/15)
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- P-C-Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine-Boranes
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{Rh(xantphos)}-based phosphido dimers form by P-C activation of xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in the presence of amine-boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B·NMeH2 and dimeric [H2BNMe2]2 from H3B·NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine-borane dehydropolymerization.
- Johnson, Heather C.,Weller, Andrew S.
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supporting information
p. 10173 - 10177
(2015/09/01)
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- Synthesis and the thermal and catalytic dehydrogenation reactions of amine-thioboranes
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A series of trimethylamine-thioborane adducts, Me3N· BH2SR (R = tBu [2a], nBu [2b], iPr [2c], Ph [2d], C6F 5 [2e]) have been prepared and characterized. Attempts to access secondary and primary amine adducts of thioboranes via amine-exchange reactions involving these species proved unsuccessful, with the thiolate moiety shown to be vulnerable to displacement by free amine. However, treatment of the arylthioboranes, [BH2-SPh]3 (9) and C6F 5SBH2·SMe2 (10) with Me2NH and iPr2NH successfully yielded the adducts Me2NH· BH2SR (R = Ph [11a], C6F5 [12a]) and iPr 2NH·BH2SR (R = Ph [11b], C6F5 [12b]) in high yield. These adducts were also shown to be accessible via thermally induced hydrothiolation of the aminoboranes Me2N=BH 2, derived from the cyclic dimer [Me2N-BH 2]2 (13), and iPr2N=BH2 (14), respectively. Attempts to prepare the aliphatic thiolate substituted adducts R2NH·BH2SR′ (R = Me, iPr; R′ = tBu, nBu, iPr) via this method, however, proved unsuccessful, with the temperatures required to facilitate hydrothiolation also inducing thermal dehydrogenation of the amine-thioborane products to form aminothioboranes, R2N= BH(SR′). Thermal and catalytic dehydrogenation of the targeted amine-thioboranes, 11a/11b and 12a/12b were also investigated. Adducts 11b and 12b were cleanly dehydrogenated to yield iPr2N=BH(SPh) (22) and iPr2N=BH(SC6F5) (23), respectively, at 100 °C (18 h, toluene), with dehydrogenation also possible at 20 °C (42 h, toluene) with a 2 mol % loading of [Rh(μ-Cl)cod]2 in the case of the former species. Similar studies with adduct 11a evidenced a competitive elimination of H2 and HSPh upon thermolysis, and other complex reactivity under catalytic conditions, whereas the fluorinated analogue 12a was found to be resistant to dehydrogenation.
- Robertson, Alasdair P. M.,Haddow, Mairi F.,Manners, Ian
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p. 8254 - 8264
(2012/09/22)
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- Catalytic dehydrogenation of dimethylamine borane by group 4 metallocene alkyne complexes and homoleptic amido compounds
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Dehydrogenation of Me2NH·BH3 (1) by group 4 metallocene alkyne complexes of the type Cp2M(L)(η2- Me3SiC2SiMe3) [Cp = η5- cyclopentadienyl; M = Ti, no L (2Ti); M = Zr, L = pyridine (2Zr)] and group 4 metal amido complexes of the type M(NMe2)4 [M = Ti (8Ti), Zr (8Zr)] is presented.
- Beweries, Torsten,Hansen, Sven,Kessler, Monty,Klahn, Marcus,Rosenthal, Uwe
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supporting information; experimental part
p. 7689 - 7692
(2011/09/20)
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- Heterogeneous dehydrocoupling of amine-borane adducts by skeletal nickel catalysts
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Skeletal Ni, produced by the selective leaching of Al from a Ni/Al alloy, has been successfully employed in the catalytic dehydrogenation of various amineborane adducts. The combination of low cost and facile single-step synthesis make this system a potentially attractive alternative to the previously described precious metal and other first-row metal catalysts. The heterogeneous nature of the catalyst facilitates convenient product purification, and this is the first such system to be based on a first-row transition metal. Catalytic dehydrocoupling of Me2NH·BH3 (1) and Et2NH3 BH3 (5) was demonstrated using 5 mol % skeletal Ni catalyst at 20 °C and produced [Me2N·BH2]2 (2) and [Et2N-BH2]2/Et2NdBH2 (6), respectively. The related adduct iPr2NH3 BH 3 (7) was also dehydrogenated to afford iPr2NdBH2 (8) but with significant catalyst deactivation. Catalytic dehydrocoupling of MeNH2 3 BH3 (9) was found to yield the cyclic triborazane [MeNH-BH 2]3 (10) as the major product, whereas high molecular weight poly- (methylaminoborane) [MeNH-BH2]n (11) (Mw = 78 000 Da, PDI = 1.52) was formed when stoichiometric quantities of Ni were used. Similar reactivity was also observed with NH3 3 BH3 (12), which produced cyclic oligomers and insoluble polymers, [NH2-BH2] xx (14), under catalytic and stoichiometric Ni loadings, respectively. Catalyst recycling was hindered by gradual poisoning. A study of possible catalyst poisons suggested that BH3 was the most likely surface poison, in line with previous work on colloidal Rh catalysts. Catalytic borane adducts using skeletal Cu and Fe was also explored. Skeletal Cu was found to be a less active dehydrogenation catalyst for amine-borane adducts but also yielded poly(methylaminoborane) under stoichiometric conditions on reaction with MeNH2 · BH3 (9). Skeletal Fe was found to be completely inactive towardamine-borane dehydrogenationr
- Robertson, Alasdair P. M.,Suter, Riccardo,Chabanne, Laurent,Whittell, George R.,Manners, Ian
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p. 12680 - 12691
(2012/02/15)
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- Homogeneous catalytic dehydrocoupling/dehydrogenation of amine-borane adducts by early transition metal, group 4 metallocene complexes
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The efficient catalytic dehydrocoupling of a range of amine-borane adducts, R'RNH·BH3 (R' = R = Me 1a; R' = R = Pr 1b; R' = Me, R = CH2Ph 1c) by a series of group 4 metallocene type precatalysts has been demonstrated. A reduction in catalytic activity was detected upon descending the group and also on substitution of the cyclopentadienyl (Cp) ligands with sterically bulky or electron-donating substituents. Precatalysts Cp2TiCl2/2nBuLi and Cp2Ti(PMe 3)2, which are believed to act as precursors to [Cp 2Ti], were found to promote the transformation of 1a to [Me 2N-BH2l2 (3a) in a homogeneous catalytic process. Mechanistic studies identified the linear dimer Me2NH- BH2-NMe2-BH3 (2a) as a reaction intermediate, which subsequently undergoes further catalytic dehydrogenation to form cyclic dimer 3a. Synthesis of the 2H-isotopologues of 1a allowed the extraction of phenomenological kinetic isotope effects for 1a → 2a and 2a → 3a from initial rate data, which permitted the proposal of a catalytic cycle with plausible intermediates. Support for the presence of an active Ti(II) catalyst was provided by the lack of reactivity of Ti(III) complexes TiCl 3 and Cp2TiCl or Ti(O) in the form of THF soluble colloids or bulk Ti powder toward 1a or 1b. Modeling of the rates of consumption of 1a and formation of 3a during catalysis by Cp2Ti(PMe3) 2 supported this conclusion and allowed the proposal of a two cycle, four step reaction mechanism. The proposed first cycle generates 2a in a two step process. In the second cycle, interaction of 2a with the same catalyst then results in a catalytic dehydrogenative ring closing reaction to form 3a, also in a two step process.
- Sloan, Matthew E.,Staubitz, Anne,Clark, Timothy J.,Russell, Christopher A.,Lloyd-Jones, Guy C.,Manners, Ian
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p. 3831 - 3841
(2010/05/15)
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- Dehydrocoupling reactions of borane-secondary and -primary amine adducts catalyzed by group-6 carbonyl complexes: Formation of aminoboranes and borazines
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Photoirradiation of a solution of BH3·NHR2 (1a: R = Me, 1b: R = 1/2C4H8, 1c: R = 1/2C 5H10, 1f: R = Et) containing a catalytic amount of a group-6 metal carbonyl complex, [M(CO)6] (M = Cr, Mo, W), led to dehydrogenative B-N covalent bond formation to produce aminoborane dimers, [BH2NR2]2 (2a-c, f), in high yield. During these reactions a borane σ complex, [M(CO)5(η1- BH3·NHR2)] (3), was detected by NMR spectroscopy. Similar catalytic dehydrogenation of bulkier amineboranes, BH 3·NHiPr2 (1d) and BH3· NHCy2 (1e, Cy = cyclo-C6H11), afforded monomeric products BH2=NR2 (4d, e). The reaction mechanism of the dehydrocoupling was investigated by DFT calculations. On the basis of the computational study, we propose that the catalytic dehydrogenation reactions proceed via an intramolecular pathway and that the active catalyst is [Cr(CO)4]. The reaction follows a stepwise mechanism involving NH and BH activation. Dehydrocoupling of borane-primary amine adducts BH 3·NH2R (1g: R = Me, 1h: R = Et, 1i: R = tBu) gave borazine derivatives [BHNR]3 (5g-i).
- Kawano, Yasuro,Uruichi, Mikio,Shimoi, Mamoru,Taki, Seitaro,Kawaguchi, Takayuki,Kakizawa, Taeko,Ogino, Hiroshi
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p. 14946 - 14957
(2010/01/16)
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- Development of rhenium catalysts for amine borane dehydrocoupling and transfer hydrogenation of olefins
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Five-coordinated rhenium(I) hydride complexes of the type [Re(Br)(H)(NO)(PR3)2] (R = Cy 2a, iPr 2b) were prepared from [Re(Br)2(NO)(PR3)2(η2- H2)] (R = Cy la,. iPr lb) via deprotonation of the η2-H2 ligands with various bases. Filling the vacant site of 2a or 2b by various less bulky two-electron donors produced the 18-electron complexes [Re(Br)(H)(NO)(PR3)2(L)] (L = O 2 3, CH2=CH2 4, acetylene 5, H2 6, CO 7, CH3CN 8). The influence of the trans-coordinated ligand on the Re-H bond was examined. The 1H NMR chemical shift of the hydride depends on L in the order O2 > acetylene > CH 2=CH2 > H2 > CO > CH3CN. The reactions of 2a or 2b with the IMes or SIMes ligands afforded the five-coordinated complex [Re(Br)(H)(NO)(PR3)(NHC)] (NHC = IMes 9 (IMes = 1,3bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), SIMes 10 (SIMes = l,3-bis(2,4,6-trimethylphenyl)4,5-dihydroimidazol-2-ylidene)) via replacement of one phosphine. The reaction of 2a or 2b with n-BuLi leads to the formation of the n-butene-coordinated dihydride complexes [Re(H)2(NO)(PR 3)2(η2-n-CH2=CHC 2H5)] (R = Cy 12a, iPr 12b). Species 1a and 1b reacted also with NaNMe2BH3, affording the tetrahydride complexes [Re(H)4(NO)(PR3)2] (R = Cy 14a, iPr 14b) via the intermediacy of 2a and 2b. The molecular structures of complexes 8b, 10a, and 10b were established by single-crystal X-ray diffraction studies. The five-coordinated rhenium(I) hydride complexes 2a, 2b, 9a, and 9b catalyzed the dehydrocoupling of Me2NHBH3 and the transfer hydrogenation of olefins using Me2NHBH3 as a hydrogen donor, which showed high activities. Mechanistic studies were carried out indicating that these rhenium(I) hydride catalyses allowed formation of dihydrogen hydride complexes. A plausible catalytic cycle for both dehydrocoupling and transfer hydrogenation was proposed, which implies the ability of rhenium(I) complexes to activate B-H and N-H bonds by the facile redox interplay of Re(I) and Re(III) species.
- Jiang, Yanfeng,Blacque, Olivier,Fox, Thomas,Frech, Christian M.,Berke, Heinz
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p. 5493 - 5504
(2009/12/25)
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- Metal Tetarhydidoborates and Tetrahydroborato Metallates, 24 - Solvates of Sodium Bis(borane)dimethylamide
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The reaction of sodium metal with dimethylamine-borane in THF yields Na((H3B)2NMe2) (1) which can be isolated as {Na[(H3B)2NMe2]}5*THF or as Na[(H3B)2NMe2]*15-crown-5 (2) and Na[(H3B)2NMe2]*benzo-15-crown-5 (3) after addition of the appropriate crown ether to the THF solution of 1. Reaction of 1 with ZrCl4 yields Me2HN-BH2-NMe2-BH3 (4), the structure of which has been determined. In THF solution, 1 reduces aldehydes, ketones, acyl chlorides, and esters to the corresponding alcohols. It also reacts slowly with nitriles and allylbenzene. Compound (1)5*THF crystallizes in an extended three-dimensional lattice, in which the Na atoms are coordinated by 6-9 hydridic H atoms, while 3 is a molecular compound in the solid state. Only one hydrogen atom of each BH3 group coordinates to the sodium center. On the other hand, 4 forms dimeric associates in the solid state through N-H...H-B interactions.
- Noeth, Heinrich,Thomas, Steffen
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p. 1373 - 1380
(2007/10/03)
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- Hexamethylenetetramine-borane adducts
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The four possible borane adducts of hexamethylenetetramine (hexamine) were prepared, three of which being hitherto unknown. Synthesis and purification procedures were worked out so that pure samples were available for chemical studies. Pyrolysis of the tetraadduct when controlled proceeded with rearrangement by hydride migration to form dimethylaminoborane derivatives. The adducts were not amenable to borane cation formation; those two cations eventually prepared, (CH2)6N4BH2py+ and (CH2)6N4BH2P(CH3) 3+, were not very stable.
- Riley, Marvin D.,Miller, Norman E.
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p. 707 - 710
(2008/10/08)
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