Ligand and substrate effects on the mechanism of rhodium-catalyzed hydrogenation of enamides.
Ligand and substrate effects on the mechanism of rhodium-catalyzed hydrogenation of enamides.
复制标题
配体和底物对铑催化烯酰胺氢化机理的影响。
DOI：
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发表时间：
2007
影响因子：
3.6
通讯作者：
O. Wiest
中科院分区：
文献类型：
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作者：
Patrick J. Donoghue;P. Helquist;O. Wiest
采用B3LYP/LACVP**理论水平，对一系列配体和底物进行了Rh催化的烯胺加氢反应研究。以1，2-双(二甲基膦)乙烷(DMPE)和(Z)-1，2-双(二甲基膦)乙烯(ZDMP)为模型配体，(R，R)-MeDuPHOS和(R，R)-四甲基双氧杂环己烷(TMBOP)为模型底物，考察了两种模型双齿膦配体对α-甲酰胺基丙烯腈的加氢反应。然后研究了ZDMP配体对三种附加底物的作用：N-(2-丙烯基)甲酰胺、(Z)-3-甲氨基-2-丁烯腈和(E)-3-甲氨基-2-丁烯腈。用QM/MM(ONIOM)方法计算的四种配体和α-甲酰胺基丙烯腈的势能面与以前的计算结果基本一致，但相对势垒始终较高而不是较低。不同底物与同一配体的氢化反应势能面的计算结果表明，不同底物的氢化反应存在一定的机械性变化。氢转移到两个烯烃碳的顺序是根据衬底电子学计算而改变的。这对不同底物对映体选择性的起源有很大影响，因为第一次氢化物转移到底物的计算对于所有底物都是不可逆的，与它发生在烯烃的α碳还是β碳无关。
The rhodium-catalyzed hydrogenation reaction of enamides is studied computationally using the B3LYP/LACVP** level of theory for a range of ligands and substrates. Two model bidentate phosphine ligands, 1,2-bis(dimethylphosphino)ethane (DMPE) and (Z)-1,2-bis(dimethylphosphino) ethene (ZDMP), and two chiral bidentate phosphine ligands, (R,R)-MeDuPHOS and (R,R)-tetramethylbisoxaphospinane (TMBOP), are investigated in the hydrogenation of alpha-formamidoacrylonitrile as a model substrate. The ZDMP ligand is then studied for three additional substrates: N-(2-propenyl)formamide, (Z)-3-formamido-2-butenenitrile, and (E)-3-formamido-2-butenenitrile. The potential-energy surfaces calculated for the four ligands and alpha-formamidoacrylonitrile are in general agreement with previous computational studies using QM/MM (ONIOM) methods but show consistently higher relative barriers rather than lower. The calculated potential-energy surfaces of hydrogenations of various substrates with a common ligand indicate a mechanistic change based on substrate. The sequence of hydrogen transfer to the two olefinic carbons is calculated to change based on substrate electronics. This has a significant impact on the origins of enantioselectivity for such varied substrates as the first hydride transfer to the substrate is calculated to be irreversible for all substrates, independent of whether it occurs at the alpha or beta carbon of the olefin.