Development of a Generic Mechanism for the Dehydrocoupling of Amine-Boranes: A Stoichiometric, Catalytic, and Kinetic Study of H3B路NMe2H Using the [Rh(PCy3)2
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- 作者：Laura J. Sewell ; Guy C. Lloyd-Jones ; Andrew S. Weller
- 刊名：The Journal of the American Chemical Society
- 出版年：2012
- 出版时间：February 22, 2012
- 年：2012
- 卷：134
- 期：7
- 页码：3598-3610
- 全文大小：674K
- 年卷期：v.134,no.7(February 22, 2012)
- ISSN：1520-5126
文摘
The multistage Rh-catalyzed dehydrocoupling of the secondary amine-borane H3B路NMe2H, to give the cyclic amino-borane [H2BNMe2]2, has been explored using catalysts based upon cationic [Rh(PCy3)2]+ (Cy = cyclo-C6H11). These were systematically investigated (NMR/MS), under both stoichiometric and catalytic regimes, with the resulting mechanistic proposals for parallel catalysis and autocatalysis evaluated by kinetic simulation. These studies demonstrate a rich and complex mechanistic landscape that involves dehydrogenation of H3B路NMe2H to give the amino-borane H2B鈺怤Me2, dimerization of this to give the final product, formation of the linear diborazane H3B路NMe2BH2路NMe2H as an intermediate, and its consumption by both B鈥揘 bond cleavage and dehydrocyclization. Subtleties of the system include the following: the product [H2BNMe2]2 is a modifier in catalysis and acts in an autocatalytic role; there is a parallel, neutral catalyst present in low but constant concentration, suggested to be Rh(PCy3)2H2Cl; the dimerization of H2B鈺怤Me2 can be accelerated by MeCN; and complementary nonclassical BH路路路HN interactions are likely to play a role in lowering barriers to many of the processes occurring at the metal center. These observations lead to a generic mechanistic scheme that can be readily tailored for application to many of the transition-metal and main-group systems that catalyze the dehydrocoupling of H3B路NMe2H.