Isolation of a Metastable Geometrical Isomer of a Hexacoordinated Dihydrophosphate : Elucidation of Its Enhanced Reactivity in Umpolung of a Hydrogen Atom of Wate
Isolation of a Metastable Geometrical Isomer of a Hexacoordinated Dihydrophosphate : Elucidation of Its Enhanced Reactivity in Umpolung of a Hydrogen Atom of Wate
复制标题
六配位二氢磷酸亚稳态几何异构体的分离：阐明其在水氢原子的反极性中增强的反应性
DOI：
10.1021/ic2012765
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发表时间：
2011
影响因子：
4.6
通讯作者：
Takayuki Kawashima
中科院分区：
文献类型：
--
作者：
Hideaki Miyake;Naokazu Kano;Takayuki Kawashima
两个五个可能的几何异构体的hexacoordinated二氢磷酸轴承两套双齿配体进行了研究。对1a-TPP和1b-TEA两种异构体的X射线晶体学分析表明，它们分别具有C2和C1对称性的八面体构型，这与NMR谱相一致。异构体1b-TEA在无任何添加剂的DMSO中在室温下进行醛的氢化物还原和与水的质子交换。在上述条件下，1b-TEA与D2 O和醛或酮的两种反应的一锅反应成功地进行，得到氘代醇。因此，在比与另一种异构体1a-TEA反应中所用的条件温和得多的条件下，用1b-TEA对水的氢原子进行极化。在室温下，在甲醇中1b-TEA发生定量异构化为1a-TEA。对磷酸二氢盐阴离子部分的五种可能的几何异构体的计算表明，它们相对稳定，这合理地解释了异构化，以及位于氧原子反式位置的原子上的较大负电荷。NMR谱中位于氧原子后部的P-H键和P-C键的耦合常数较小，导致这些键具有较小的s特征。1a-TEA和1b-TEA之间的脱氢和质子交换反应性的差异可以分别用氢原子的原子电荷的差异和最初形成的正膦中间体的稳定性差异来解释。
Two of five conceivable geometrical isomers of a hexacoordinated dihydrophosphate bearing two sets of a bidentate ligand were investigated. X-ray crystallographic analysis of both of isomers,1a-TPPand1b-TEA, revealed their octahedral geometries ofC2andC1symmetry, respectively, which were consistent with the NMR spectra. The isomer1b-TEAunderwent both hydride reduction of an aldehyde and proton exchange with water at room temperature in DMSO without any additive. A one-pot reaction of both of the reactions of1b-TEAwith D2O and an aldehyde or a ketone under the above conditions proceeded successfully to give the deuterated alcohol. Thus, umpolung of a hydrogen atom of water with1b-TEAwas achieved under much milder conditions than those used in the reaction with another isomer,1a-TEA. Quantitative isomerization of1b-TEAto1a-TEAoccurred in methanol at room temperature. Calculations on the five conceivable geometrical isomers of the anionic part of the dihydrophosphate revealed their relative stability, which reasonably explained the isomerization, and the larger negative charge at the atoms located at the trans positions of the oxygen atoms. The smaller coupling constants of the P–H and P–C bonds located at the rear of an oxygen atom in the NMR spectra resulted in the smaller s character of these bonds. The differences in both hydride-donation and proton-exchange reactivities between1a-TEAand1b-TEAcould be explained by the differences in the atomic charge of the hydrogen atom and the stability difference of the initially formed phosphorane intermediates, respectively.