14708-83-9Relevant articles and documents
Mechanisms of the thermal and catalytic redistributions, oligomerizations, and polymerizations of linear diborazanes
Robertson, Alasdair P. M.,Leitao, Erin M.,Jurca, Titel,Haddow, Mairi F.,Helten, Holger,Lloyd-Jones, Guy C.,Manners, Ian
supporting information, p. 12670 - 12683 (2013/09/23)
Linear diborazanes R3N-BH2-NR2-BH 3 (R = alkyl or H) are often implicated as key intermediates in the dehydrocoupling/dehydrogenation of amine-boranes to form oligo- and polyaminoboranes. Here we report detailed studies of the reactivity of three related examples: Me3N-BH2-NMe2-BH3 (1), Me3N-BH2-NHMe-BH3 (2), and MeNH 2-BH2-NHMe-BH3 (3). The mechanisms of the thermal and catalytic redistributions of 1 were investigated in depth using temporal-concentration studies, deuterium labeling, and DFT calculations. The results indicated that, although the products formed under both thermal and catalytic regimes are identical (Me3N·BH3 (8) and [Me2N-BH2]2 (9a)), the mechanisms of their formation differ significantly. The thermal pathway was found to involve the dissociation of the terminal amine to form [H2B(μ-H)(μ-NMe 2)BH2] (5) and NMe3 as intermediates, with the former operating as a catalyst and accelerating the redistribution of 1. Intermediate 5 was then transformed to amine-borane 8 and the cyclic diborazane 9a by two different mechanisms. In contrast, under catalytic conditions (0.3-2 mol % IrH2POCOP (POCOP = κ3-1,3-(OPtBu 2)2C6H3)), 8 was found to inhibit the redistribution of 1 by coordination to the Ir-center. Furthermore, the catalytic pathway involved direct formation of 8 and Me2Ni - BH2 (9b), which spontaneously dimerizes to give 9a, with the absence of 5 and BH3 as intermediates. The mechanisms elucidated for 1 are also likely to be applicable to other diborazanes, for example, 2 and 3, for which detailed mechanistic studies are impaired by complex post-redistribution chemistry. This includes both metal-free and metal-mediated oligomerization of MeNHi - BH2 (10) to form oligoaminoborane [MeNH-BH 2]x (11) or polyaminoborane [MeNH-BH2] n (16) following the initial redistribution reaction.
Catalytic redistribution and polymerization of diborazanes: Unexpected observation of metal-free hydrogen transfer between aminoboranes and amine-boranes
Robertson, Alasdair P. M.,Leitao, Erin M.,Manners, Ian
, p. 19322 - 19325 (2012/01/13)
Ir-catalyzed (20 °C) or thermal (70 °C) dehydrocoupling of the linear diborazane MeNH2-BH2-NHMe-BH3 led to the formation of poly- or oligoaminoboranes [MeNH-BH2]x (x = 3 to >1000) via an initial redistribution process that forms MeNH 2?BH3 and also transient MeNH=BH2, which exists in the predominantly metal-bound and free forms, respectively. Studies of analogous chemistry led to the discovery of metal-free hydrogenation of the B=N bond in the "model" aminoborane iPr2N=BH2 to give iPr2NH?BH3 upon treatment with the diborazane Me3N-BH2-NHMe-BH3 or amine-boranes RR′NH?BH3 (R, R′ = H or Me).
Intermediates in the formation of N-methylaminoborane trimer and N,N-dimethylaminoborane dimer
Beachley Jr.
, p. 870 - 874 (2007/10/05)
Experimental evidence for the intermediates in the formation of N-methylaminoborane trimer, (H2BNHCH3)3, and N,N-dimethylaminoborane dimer, (H2BN(CH2)2)2, has been obtained by synthetic methods and trapping procedures. The pyrolysis of methylamine borane, H3BNH2CH3, yields the six-membered ring of (H2BNHCH3)3 by initially forming H2B(NH2CH3)2+BH 4-, then [H2CH3NBH2NHCH3BH2NH 2CH3]+BH4- through a series of successive dehydrogenation condensation reactions. The final step of the proposed mechanism is ring closure by dehydrogenation. The new compound, [H2CH3NBH2NHCH3BH2NH 2CH3]+Cl-, was prepared by heating a mixture of H2B(NH2CH3)2+Cl - and H3BNH2CH3 and was characterized by elemental analysis, its reactions with FeCl3 and NaBH4, and its pmr spectrum. The experimental evidence for the intermediates during the pyrolysis of dimethylamine borane to form (H2BN(CH3)2)2 is consistent with monomeric H2BN(CH3)2 species which then associate to give the dimer.
