Understanding a Hydroformylation Catalyst that Produces Branched Aldehydes from Alkyl Alkenes
Understanding a Hydroformylation Catalyst that Produces Branched Aldehydes from Alkyl Alkenes
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DOI：
10.1021/jacs.7b09164
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发表时间：
2017-11-08
影响因子：
15
通讯作者：
Clarke, Matthew L.
中科院分区：
文献类型：
--
作者：
Dingwall, Paul;Fuentes, Jose A.;Clarke, Matthew L.
本文报道了铑催化的氢甲酰化反应机制的实验和计算研究，该反应选择性地从无偏置的烯烃底物中生成支醛产物。这种极不寻常的选择性依赖于一种称为BOBPHOS的磷酸烷-亚磷酸盐配体。利用原位高压红外（HPIR）和反应过程动力学分析方法进行的动力学研究表明，催化循环涉及两个步骤，以确定周转。发现了CO的负序和烯烃和H-2的正序，并测定了氢和一氧化碳分压对选择性的影响。标记研究发现氢化铑加入烯烃基本上是不可逆的。对活化的氢二羰基铑进行了详细的hir和NMR表征。在没有H-2的情况下，氢化二羰基铑与烯基苯的反应可以进一步详细地表征四配位和五配位的酰基铑。在单次转化条件下，支链酰基与线状酰基的比值保留在醛产物的最终比值中。理论研究揭示了配体和底物之间意想不到的稳定CH-pi相互作用，这种相互作用通过导致潜在的低能量途径变得无效而影响了高支化选择性。能量跨度和TOF控制程度分析有力地支持了实验观察和机制理论。建立了一个三维象限模型来表示区域选择性和对映体选择性的结构来源。
This paper reports experimental and computational studies on the mechanism of a rhodium-catalyzed hydroformylation that is selective for branched aldehyde products from unbiased alkene substrates. This highly unusual selectivity relies on a phospholane-phosphite ligand prosaically called BOBPHOS. Kinetic studies using in situ high pressure IR (HPIR) and the reaction progress kinetic analysis methodology suggested two steps in the catalytic cycle were involved as turnover determining. Negative order in CO and positive orders in alkene and H-2 were found and the effect of hydrogen and carbon monoxide partial pressures on selectivity were measured. Labeling studies found rhodium hydride addition to the alkene to be largely irreversible. Detailed spectroscopic HPIR and NMR characterization of activated rhodium-hydrido dicarbonyl species were carried out. In the absence of H-2, reaction of the rhodium-hydrido dicarbonyl with allylbenzene allowed further detailed spectroscopic characterization of four- and five-coordinate rhodium-acyl species. Under single-turnover conditions, the ratios of branched to linear acyl species were preserved in the final ratios of aldehyde products. Theoretical investigations uncovered unexpected stabilizing CH-pi interactions between the ligand and substrate which influenced the high branched selectivity by causing potentially low energy pathways to become unproductive. Energy span and degree of TOF control analysis strongly support experimental observations and mechanistic rationale. A three-dimensional quadrant model was built to represent the structural origins of regio- and enantioselectivity.