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首页> 外文期刊>Chemistry: A European journal >Theoretical studies of asymmetric hydroformylation using the Rh-(R,S)-BINAPHOS catalyst - Origin of coordination preferences and stereoinduction
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Theoretical studies of asymmetric hydroformylation using the Rh-(R,S)-BINAPHOS catalyst - Origin of coordination preferences and stereoinduction

机译：使用Rh-（R，S）-BINAPHOS催化剂进行不对称加氢甲酰化的理论研究-配位偏爱和立体诱导的起源

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We have undertaken theoretical investigations of the asymmetric hydroformylation of styrene by the [Rh{(R,S)-BINAPHOS}(CO) _2H] catalyst, focusing on the origin of the ligand coordination preferences and stereoinduction. We evaluated the different factors governing the preference of the BINAPHOS ligand to coordinate with the phosphane moiety at the equatorial site and the phosphite moiety at the apical site. The donor-acceptor interactions, obtained using a modified version of energy decomposition analysis (EDA) based on orbital deletion, favour the phosphite moiety at the equatorial site. However, the electronic distortion and the steric effects inverse this tendency. Calculations also suggest that the coordination preference was transferred to the selectivity-determining transition state. We propose a stereochemical model based on quantitative quadrant maps obtained from a new molecular descriptor, the distance-weighted volume (V _W), which is easily computed from ground-state structures. Repulsive interactions between the substrate and the apical phosphite were responsible for the enantiodifferentiation. The axial chirality of the phosphite discriminated one of the competitive equatorial-apical paths, whereas the axial chirality of the backbone discriminated one of the two enantiomers. Transition-state calculations revealed that the placement of phosphane at the apical site would lower enantioselectivity, explaining the poor performance of other phosphane-phosphite ligands. Finally, comparison with previous studies allowed the definition of several prerequisites for diphosphane ligands for high stereoselectivity: 1) specific equatorial-apical coordination bringing chirality to the apical site, 2) combination of two stereogenic centres and 3) rigid structures. The asymmetric hydroformylation of styrene by using the Rh-(R,S)-BINAPHOS catalyst was theoretically investigated. The electronic distortion and the steric effects explained the exceptional ligand coordination with the phosphane and phosphite moieties at the equatorial and apical sites, respectively. The stereochemical model derived from a new descriptor, the distance-weighted volume (V _W), indicates that the combination of the two chiral centres, each discriminating either an equatorial-apical path or the enantiomer, is crucial.
机译：我们已经对[Rh {（R，S）-BINAPHOS}（CO）_2H]催化剂对苯乙烯的不对称加氢甲酰化进行了理论研究，重点是配位体配位偏好和立体诱导的起源。我们评估了控制BINAPHOS配体与赤道部位的膦部分和顶端部位的亚磷酸酯部分配位的偏好的不同因素。使用基于轨道缺失的能量分解分析（EDA）的改进版本获得的供体-受体相互作用，有利于赤道部位的亚磷酸酯部分。但是，电子失真和空间效应使这种趋势逆转。计算还表明，协调偏好已转移到决定选择性的过渡状态。我们基于从新的分子描述子即距离加权体积（V _W）获得的定量象限图提出了一种立体化学模型，该模型很容易从基态结构中计算出来。底物和顶端的亚磷酸酯之间的排斥性相互作用是对映异构的原因。亚磷酸酯的轴向手性区分了竞争性的赤道-顶端途径之一，而主链的轴向手性则区分了两种对映体之一。过渡态计算表明，膦在顶位的位置会降低对映选择性，这说明了其他膦亚磷酸酯配体的性能较差。最后，与先前的研究进行比较，可以定义出具有高立体选择性的二膦配体的几个先决条件：1）特定的赤道-顶配位使手性到达顶位; 2）两个立体中心的结合; 3）刚性结构。理论上研究了使用Rh-（R，S）-BINAPHOS催化剂对苯乙烯的不对称加氢甲酰化反应。电子畸变和空间效应解释了分别在赤道和顶端位置与膦和亚磷酸酯部分的优异配体配位。从一个新的描述符，即距离加权体积（V_W）得出的立体化学模型表明，两个手性中心的组合至关重要，每个中心都可以分辨出赤道-顶峰路径或对映体。

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