Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom.
Inorg Chem. 2013 Apr 15;52(8):4509-16. doi: 10.1021/ic302804d. Epub 2013 Apr 1.
The Rh(III) species Rh(PCy3)2H2Cl is an effective catalyst (2 mol %, 298 K) for the dehydrogenation of H3B·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·NMe2H, using initial rate and H/D exchange experiments, indicate possible dehydrogenation mechanisms that invoke turnover-limiting N-H activation, which either precedes or follows B-H activation, to form H2B═NMe2, 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(F)4] forms the halide-bridged adduct [Rh(PCy3)2H2(μ-Cl)H2(PCy3)2Rh][BAr(F)4] (Ar(F) = 3,5-(CF3)2C6H3), which has been crystallographically characterized. This dinuclear cation dissociates on addition of H3B·NMe2H to re-form Rh(PCy3)2H2Cl and generate [Rh(PCy3)2H2(η(2)-H3B·NMe2H)][BAr(F)4]. 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(η(2)-H2BH2), observed. On addition of H3B·NMe2H to Ir(PCy3)2H2Cl, the Ir congener Ir(PCy3)2H2(η(2)-H2BH2) is formed, with concomitant generation of the salt [H2B(NMe2H)2]Cl.
Rh(III)配合物 Rh(PCy3)2H2Cl 是一种有效的催化剂（2 mol %，298 K），可将 H3B·NMe2H（在 1,2-F2C6H4 溶剂中 0.072 M）脱氢，最终得到二聚氨基硼烷[H2BNMe2]2。使用初始速率和 H/D 交换实验对 H3B·NMe2H 消耗的早期阶段进行的机理研究表明，可能存在涉及周转限制的 N-H 活化的脱氢机制，该机制要么先于要么后于 B-H 活化，形成 H2B═NMe2，然后二聚化得到[H2BNMe2]2。另一个细节是，活性催化剂 Rh(PCy3)2H2Cl 与无活性的二聚体 Rh(PCy3)H2Cl2 处于快速平衡中。Rh(PCy3)2H2Cl 与[Rh(PCy3)H2(H2)2][BAr(F)4]反应形成卤化物桥联加合物[Rh(PCy3)2H2(μ-Cl)H2(PCy3)2Rh][BAr(F)4]（Ar(F) = 3,5-(CF3)2C6H3），已通过晶体学进行了表征。该双核阳离子在添加 H3B·NMe2H 后解离，重新形成 Rh(PCy3)2H2Cl 并生成[Rh(PCy3)2H2(η(2)-H3B·NMe2H)][BAr(F)4]。还讨论了低催化剂负载（0.5 mol %）下催化剂的命运，观察到形成无活性硼氢化物物种 Rh(PCy3)2H2(η(2)-H2BH2)。向 Ir(PCy3)2H2Cl 中添加 H3B·NMe2H，生成 Ir 同系物 Ir(PCy3)2H2(η(2)-H2BH2)，同时生成盐[H2B(NMe2H)2]Cl。
