5314-85-2Relevant academic research and scientific papers
B-Methylated Amine-Boranes: Substituent Redistribution, Catalytic Dehydrogenation, and Facile Metal-Free Hydrogen Transfer Reactions
Stubbs, Naomi E.,Sch?fer, Andr,Robertson, Alasdair P.M.,Leitao, Erin M.,Jurca, Titel,Sparkes, Hazel A.,Woodall, Christopher H.,Haddow, Mairi F.,Manners, Ian
supporting information, p. 10878 - 10889 (2015/11/27)
Although the dehydrogenation chemistry of amine-boranes substituted at nitrogen has attracted considerable attention, much less is known about the reactivity of their B-substituted analogues. When the B-methylated amine-borane adducts, RR'NH·BH2Me (1a: R = R' = H; 1b: R = Me, R' = H; 1c: R = R' = Me; 1d: R = R' = iPr), were heated to 70 °C in solution (THF or toluene), redistribution reactions were observed involving the apparent scrambling of the methyl and hydrogen substituents on boron to afford a mixture of the species RR'NH·BH3-xMex (x = 0-3). These reactions were postulated to arise via amine-borane dissociation followed by the reversible formation of diborane intermediates and adduct reformation. Dehydrocoupling of 1a-1d with Rh(I), Ir(III), and Ni(0) precatalysts in THF at 20 °C resulted in an array of products, including aminoborane RR'N=BHMe, cyclic diborazane [RR'N-BHMe]2, and borazine [RN-BMe]3 based on analysis by in situ 11B NMR spectroscopy, with peak assignments further supported by density functional theory (DFT) calculations. Significantly, very rapid, metal-free hydrogen transfer between 1a and the monomeric aminoborane, iPr2N=BH2, to yield iPr2NH·BH3 (together with dehydrogenation products derived from 1a) was complete within only 10 min at 20 °C in THF, substantially faster than for the N-substituted analogue MeNH2·BH3. DFT calculations revealed that the hydrogen transfer proceeded via a concerted mechanism through a cyclic six-membered transition state analogous to that previously reported for the reaction of the N-dimethyl species Me2NH·BH3 and iPr2N=BH2. However, as a result of the presence of an electron donating methyl substituent on boron rather than on nitrogen, the process was more thermodynamically favorable and the activation energy barrier was reduced.
N-(2,4,6-trimethylborazinyl)-substituted boron, aluminum and titanium compounds
Gemünd, Birgit,Günther, Berndt,Knizek, J?rg,N?th, Heinrich
, p. 23 - 36 (2008/09/21)
The N-lithioborazine LiH2N3B3Me 3, 1, reacts with organoboron halides not only to the respective borazinyl organylboranes but also by Me/halogen exchange. (Me2N) 2B-H2N3B3Me3 was obtained from 1 and (Me2N)2BCl. A new ten-membered B 6N4 ring system, 5, results on treatment of Cl(Me 2N)B-B(NMe2)Cl with 1. The B-N-borazinyl borazines 6-8 can be prepared from 1 and B-monohalo borazines. The synthesis of 2,4,6-trimethylborazinyl-aluminum and -titanium compounds is achieved only with mononuclear monohalides of Al(III) and Ti(IV). The 2,4,6-trimethylborazinyl- bis(piperidino)alane 9 and the tris(2,6-diisopropylphenoxo)-2,4,6- trimethylborazinyltitanium 10 were characterized by X-ray structure analysis. The distortion of the borazine ring by B and N substitution is discussed. In case of the N-substituted borazines YH2N3B 3Me3 the B-N bonds of the YNB2 units are elongated, e. g. for Y = PBr2 or (RO)3Ti, while N lithiation leads to a shortening of these B-N bond. These changes of bond lengths are also reflected by changes in the B1-N2 and B3-N3 bond lengths which become shorter in the presence of electron-withdrawing groups, but longer in case of Li substitution. Also, the bond angles B1-N2-B2 and B2-N3-B3 are affected by an increase of up to 128°.
