1265632-17-4Relevant academic research and scientific papers
Synthesis and reactivity of o-benzylphosphino- and o-α- methylbenzyl(N, N-dimethyl)amine-boranes
Heiden, Zachariah M.,Schedler, Michael,Stephan, Douglas W.
experimental part, p. 1470 - 1479 (2011/04/23)
The series of o-benzylphosphino-boranes, o-(R2B)C 6H4CH2PtBu2 (R = Cl 3, Ph 4, Cy 6, C6F5 7, Mes 8) and o-(BBN)C6H 4CH2PtBu2 (5), were synthesized from reactions of the respective chloroboranes with the lithiated benzyl-phosphine. In an analogous fashion, the α-methylbenzyl(N,N-dimethyl)amine-boranes o-(R 2B)C6H4CH(Me)NMe2 (R = Cl 10, Ph 11, Cy 12, C6F5 13, Mes 14) were prepared. While these species were inactive in the catalytic hydrogenation of tBuN≡CHPh, compounds 7, 8, and 14 did react with H2 at elevated temperatures (100 °C), resulting in the elimination of HC6F5 and mesitylene, respectively. In the latter case, the species o-((Mes)HB)C 6H4CH(Me)NMe2 15 was isolated. 14 was also shown to react with H2O to give the species o-((Mes)(HO)B)C 6H4CH(Me)NMe2 16 with the loss of mesitylene. The structure of these compounds and the nature of these reactions were also probed spectroscopically, crystallographically, and computationally. The energies for the products of hydrogenation, the phosphonium and ammonium hydridoborates, were computed. In all cases, these products were endothermic with respect to the precursor phosphine-boranes and amine-boranes and H 2. The barriers to H2 activation were found to be in the range of 24-38 kcal/mol. These theoretical studies also demonstrate that the steric bulk around the boron center dramatically affects the activation barrier for H2 activation, while the Lewis acidity of the borane has the largest effect on the stabilization of the resulting onium-borohydride. In the case of the elimination reactions, the driving forces appear to be the loss of arene byproduct and formation of a strong donor-acceptor bond.
