Department of Chemistry, University of York, Heslington, York, YO10 5DD UK.
CNRS, LCC (Laboratoire de Chimie de Coordination), Université de Toulouse, UPS, INPT, 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France CNRS.
Dalton Trans. 2023 Feb 21;52(8):2495-2505. doi: 10.1039/d2dt04036k.
The reaction between [IrCl(COD)] and dppe in a 1 : 2 ratio was investigated in detail under three different conditions. [IrCl(COD)(dppe)], 1, is formed at room temperature in the absence of base. In the presence of a strong base at room temperature, hydride complexes that retain the carbocyclic ligand in the coordination sphere are generated. In isopropanol, 1 is converted into [IrH(1,2,5,6-η:η-COD)(dppe)] (2) on addition of KOBu, with = (1.11 ± 0.02) × 10 s, followed by reversible isomerisation to [IrH(1-κ-4,5,6-η-CH)(dppe)] (3) with = (3.4 ± 0.2) × 10 s and = (1.1 ± 0.3) × 10 s to yield an equilibrium 5 : 95 mixture of 2 and 3. However, when no hydride source is present in the strong base (KOBu in benzene or toluene), the COD ligand in 1 is deprotonated, followed by β-H elimination of an Ir-CH intermediate, which leads to complex [IrH(1-κ-4,5,6-η-CH)(dppe)] (4) selectively. This is followed by its reversible isomerisation to 5, which features a different relative orientation of the same ligands ( = (3.92 ± 0.11) × 10 s; = (1.39 ± 0.12) × 10 s in CD), to yield an equilibrated 32 : 68 mixture of 4 and 5. DFT calculations assisted in the full rationalization of the selectivity and mechanism of the reactions, yielding thermodynamic (equilibrium) and kinetic (isomerization barriers) parameters in excellent agreement with the experimental values. Finally, in the presence of KOBu and isopropanol at 80 °C, 1 is transformed selectively to K[IrH(dppe)] (6), a salt of an anionic tetrahydride complex of Ir. This product is also selectively generated from 2, 3, 4 and 5 and H at room temperature, but only when a strong base is present. These results provide an insight into the catalytic action of [IrCl(COD)(LL)] complexes in the hydrogenation of polar substrates in the presence of a base.
在三种不同条件下，详细研究了[IrCl(COD)]与 dppe 以 1:2 的比例的反应。在不存在碱的情况下，室温下形成[IrCl(COD)(dppe)]，1。在室温下存在强碱时，保留配位球中环己二烯配体的氢化物复合物被生成。在异丙醇中，加入 KOBu 后，1 转化为[IrH(1,2,5,6-η:η-COD)(dppe)]（2），速率常数为 = (1.11 ± 0.02) × 10 s，随后可逆异构化为[IrH(1-κ-4,5,6-η-CH)(dppe)]（3），速率常数为 = (3.4 ± 0.2) × 10 s 和 = (1.1 ± 0.3) × 10 s，生成 2 和 3 的平衡 5:95 混合物。然而，当强碱（苯或甲苯中的 KOBu）中不存在氢化物源时，1 中的 COD 配体被去质子化，随后 Ir-CH 中间体发生β-H 消除，导致选择性地生成配合物[IrH(1-κ-4,5,6-η-CH)(dppe)]（4）。然后，它可逆异构化为 5，其具有相同配体的不同相对取向（在 CD 中，速率常数为 = (3.92 ± 0.11) × 10 s； = (1.39 ± 0.12) × 10 s），生成 4 和 5 的平衡 32:68 混合物。密度泛函理论（DFT）计算有助于完全解释反应的选择性和机制，得到与实验值非常吻合的热力学（平衡）和动力学（异构化势垒）参数。最后，在 80°C 下存在 KOBu 和异丙醇时，1 选择性地转化为 K[IrH(dppe)]（6），这是 Ir 的阴离子四氢化物配合物的盐。该产物也可从 2、3、4 和 5 以及 H 在室温下选择性生成，但仅当存在强碱时。这些结果提供了对[IrCl(COD)(LL)]配合物在存在碱的情况下对极性底物氢化催化作用的深入了解。
