Carbó J J, Maseras F, Bo C, van Leeuwen P W
Unitat de Química Física, Edifi C.n, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
J Am Chem Soc. 2001 Aug 8;123(31):7630-7. doi: 10.1021/ja0101678.
The origin of regioselectivity in rhodium diphosphine catalyzed hydroformilation was investigated by means of hybrid QM/MM calculations using the IMOMM method. The roles of the diphosphine bite angle and of the nonbonding interactions were analyzed in detail by considering rhodium systems containing xantphos-type ligands, for which a correlation between the natural bite angle and regioselectivity has been recently reported. From the pentacoordinated equatorial--equatorial HRh(CO)(alkene)(diphosphine) key intermediate, eight possible reaction paths were defined and characterized through their respective transition states (TS). We succeeded in reproducing the experimentally observed trends for the studied diphosphines. By performing additional calculations on model systems, in which the steric effects induced by the phenyl substituents of xantphos ligands were canceled, we were able to separate, identify, and evaluate the different contributions to regioselectivity. These additional calculations showed that regioselectivity is governed by the nonbonding interactions between the diphenylphosphino substituents and the substrate, whereas the effects directly associated to the bite angle, what we call orbital effects, seem to have a smaller influence.
采用IMOMM方法通过混合量子力学/分子力学（QM/MM）计算研究了铑二膦催化氢甲酰化反应中区域选择性的起源。通过考虑含有联二萘酚型配体的铑体系，详细分析了二膦咬角和非键相互作用的作用，最近报道了其天然咬角与区域选择性之间的相关性。从五配位的赤道-赤道HRh(CO)(烯烃)(二膦)关键中间体出发，定义了八条可能的反应路径，并通过各自的过渡态（TS）对其进行了表征。我们成功地再现了所研究二膦的实验观察趋势。通过对模型体系进行额外计算，其中联二萘酚配体的苯基取代基引起的空间效应被消除，我们能够分离、识别和评估对区域选择性的不同贡献。这些额外计算表明，区域选择性受二苯基膦取代基与底物之间的非键相互作用控制，而与咬角直接相关的效应，即我们所说的轨道效应，似乎影响较小。
