Structures and interligand interaction pattern of phosphoramidite Pd complexes by NMR spectroscopy: modulations in extended interaction surfaces as stereoselection mode of a privileged class of ligands.
Structures and interligand interaction pattern of phosphoramidite Pd complexes by NMR spectroscopy: modulations in extended interaction surfaces as stereoselection mode of a privileged class of ligands.
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通过核磁共振波谱分析亚磷酰胺钯配合物的结构和配体间相互作用模式：扩展相互作用表面的调制作为一类特殊配体的立体选择模式
DOI：
10.1002/chem.201300095
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
R. M. Gschwind
中科院分区：
文献类型：
--
作者：
E. Hartmann;M. M. Hammer;R. M. Gschwind
During the last decade, phosphoramidites have been established as a so‐called privileged class of ligands in various transition metal catalyses. However, the interactions responsible for their favorable properties have hitherto remained elusive. To address this issue, the formation trends, structural features, and interligand interaction patterns of severaltrans‐ andcis‐[PdLL′Cl2] complexes have been investigated by NMR spectroscopy. The energetic contribution of their interligand interactions has been measured experimentally using the supramolecular balance for transition‐metal complexes. The resulting energetics combined with an analysis of the electrostatic potential surfaces reveal that in phosphoramidites not only the aryl groups but the complete (CH)CH3Ph moieties of the amine side chains form extended quasi‐planar CH‐π and π‐π interaction surfaces. Application of the supramolecular balance has shown that modulations in these extended interaction surfaces cause energetic differences that are relevant to enantioselective catalysis. In addition, the energetics of these interligand interactions are quite independent of the actual structures of the complexes. This is shown by similar formation and aggregation trends of complexes with the same ligand but different structures. The extended quasi‐planar electrostatic interaction surface of the (CH)CH3Ph moiety explains the known pattern of successful ligand modulation and the substrate specificity of phosphoramidites. Thus, we propose modulations in these extended CH‐π and π‐π interaction areas as a refined stereoselection mode for these ligands. Based on the example of phosphoramidites, this study reveals three general features potentially applicable to various ligands in asymmetric catalysis. First, specific combinations of alkyl and aryl moieties can be used to create extended anisotropic interaction areas. Second, modulations in these interaction surfaces cause energetic differences that are relevant to catalytic applications. Third, bulky substituents with matching complementary interaction surfaces should not only be considered in terms of steric hindrance but also in terms of attractive and repulsive interactions, a feature that may often be underestimated in asymmetric catalysis.
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