23273-02-1Relevant academic research and scientific papers
Reactions of amine-and phosphane-borane adducts with frustrated Lewis pair combinations of Group 14 triflates and sterically hindered nitrogen bases
Whittell, George R.,Balmond, Edward I.,Robertson, Alasdair P. M.,Patra, Sanjib K.,Haddow, Mairi F.,Manners, Ian
experimental part, p. 3967 - 3975 (2011/01/11)
The ability of trialkyl Group 14 triflates in combination with amine and pyridine bases to dehydrogenate amine-and phosphane-borane adducts has been investigated. By using multinuclear NMR spectroscopy, it has been shown that Me2NH ·BH3 (11) is efficiently converted to [Me2N-BH2]2 (12) by the so-called "frustrated Lewis pair" (FLP) of nBu3SnOTf (4, -OTf = -OSO2CF3) and 2,2,6,6-tetramethylpiperidine (6). Within the scope of the study, exchange of the Lewis acid effects the rate of dehydrogenation in the order: 4 gt; Me3Si-OTf (2) gt; Et 3SiOTf (3). Exchange of the Lewis base for 2,6-di-tert-butylpyridine (5) has also been shown to reduce the rate of reaction, whereas 1,3-di-tert-butylimidazol-2-ylidene (7) reacted directly with 2 to afford 1,3-bis-tert-butyl-4-(trimethylsilyl)imidazolium triflate (8[OTf]). For FLP combinations for which dehydrogenation reaction times are longer, detectable quantities of [H2B(μ-H)(μ-NMe2)BH2] (14) are observed. Both the dehydrogenation reaction and competitive formation of this product are proposed to proceed by initial hydride abstraction by the Lewis acid, followed by deprotonation by the Lewis base, or combination with further dimethylamine-borane and elimination of [Me2NH2]OTf (18[OTf]), respectively. In contrast to 11, MeNH2·BH 3 (22) was not found to cleanly dehydrogenate to either [MeNH-BH 2]3 or [MeN-BH]3 under the same conditions. An alternative reaction pathway was observed with either 2 or 4 and 6 with Ph 2PH ·BH3 (23), resulting in P-silylation or P-stannylation of the phosphane-borane, respectively.
Dehydrocoupling reactions of borane-secondary and -primary amine adducts catalyzed by group-6 carbonyl complexes: Formation of aminoboranes and borazines
Kawano, Yasuro,Uruichi, Mikio,Shimoi, Mamoru,Taki, Seitaro,Kawaguchi, Takayuki,Kakizawa, Taeko,Ogino, Hiroshi
, p. 14946 - 14957 (2010/01/16)
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).
Hydrogen elimination in dimethylamine-borane
Ryschkewitsch,Wiggins
, p. 314 - 317 (2007/10/12)
The elimination of hydrogen from dimethylamine-borane was studied at 100° by observing the hydrogen isotope distribution in the products resulting from reactants with different hydrogen isotopes on nitrogen and/or boron. The results clearly eliminate the possibility of a unimolecular elimination and favor a bimolecular reaction. Different deuterium isotope effects on the elimination rates were deduced, depending on whether the nitrogen atom or the boron atom was substituted (kN- H/kN- D = 3.5; kB- H/kB- D = 1.2). Various possible isotopic exchange reactions which could have complicated the study were investigated.
