Dehydrocoupling of Dimethylamine Borane Catalyzed by Rh(PCy3)2H2Cl

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• 作者：Laura J. Sewell ; Miguel A. Huertos ; Molly E. Dickinson ; Andrew S. Weller ; Guy C. Lloyd-Jones
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：April 15, 2013
• 年：2013
• 卷：52
• 期：8
• 页码：4509-4516
• 全文大小：411K
• 年卷期：v.52,no.8(April 15, 2013)
• ISSN：1520-510X

文摘

The Rh(III) species Rh(PCy₃)₂H₂Cl is an effective catalyst (2 mol %, 298 K) for the dehydrogenation of H₃B路NMe₂H (0.072 M in 1,2-F₂C₆H₄ solvent) to ultimately afford the dimeric aminoborane [H₂BNMe₂]₂. Mechanistic studies on the early stages in the consumption of H₃B路NMe₂H, using initial rate and H/D exchange experiments, indicate possible dehydrogenation mechanisms that invoke turnover-limiting N鈥揌 activation, which either precedes or follows B鈥揌 activation, to form H₂B鈺怤Me₂, which then dimerizes to give [H₂BNMe₂]₂. An additional detail is that the active catalyst Rh(PCy₃)₂H₂Cl is in rapid equilibrium with an inactive dimeric species, [Rh(PCy₃)H₂Cl]₂. The reaction of Rh(PCy₃)₂H₂Cl with [Rh(PCy₃)H₂(H₂)₂][BAr^F₄] forms the halide-bridged adduct [Rh(PCy₃)₂H₂(渭-Cl)H₂(PCy₃)₂Rh][BAr^F₄] (Ar^F = 3,5-(CF₃)₂C₆H₃), which has been crystallographically characterized. This dinuclear cation dissociates on addition of H₃B路NMe₂H to re-form Rh(PCy₃)₂H₂Cl and generate [Rh(PCy₃)₂H₂(畏²-H₃B路NMe₂H)][BAr^F₄]. The fate of the catalyst at low catalyst loadings (0.5 mol %) is also addressed, with the formation of an inactive borohydride species, Rh(PCy₃)₂H₂(畏²-H₂BH₂), observed. On addition of H₃B路NMe₂H to Ir(PCy₃)₂H₂Cl, the Ir congener Ir(PCy₃)₂H₂(畏²-H₂BH₂) is formed, with concomitant generation of the salt [H₂B(NMe₂H)₂]Cl.