The influence of nuclearity and charge of chiral Rh diene complexes on the activity and enantioselectivity in catalytic asymmetric 1,2-additions of organoboron reagents to N-tosylimines and 1,4-additions to enones was investigated. For this purpose, cationic dimeric Rh(I) complex [(Rh(1))₂Cl]SbF₆ and cationic monomeric Rh(I) complex [RhOH₂(2)]SbF₆ were synthesized from oxazolidinone-substituted 3-phenylnorbornadiene ligands 1 and 2, which differ in the substitution pattern at oxazolidinone C-5′ (CMe₂ vs CH₂) and compared with the corresponding neutral dimeric and monomeric Rh(I) complexes [RhCl(1)]₂ and [RhCl(2)]. Structural, electronic, and mechanistic insights were gained by X-ray crystallography, cyclic voltammetry (CV), X-ray absorption spectroscopy (XAS), and DFT calculations. CV revealed an increased stability of cationic vs neutral Rh complexes toward oxidation. Comparison of solid-state and solution XAS (extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES)) data showed that the monomeric Rh complex [RhCl(2)] maintained its electronic state and coordination sphere in solution, whereas the dimeric Rh complex [RhCl(1)]₂ exchanges bridging chloro ligands by dioxane molecules in solution. In both 1,2- and 1,4-addition reactions, monomeric Rh complexes [RhCl(2)] and [RhOH₂(2)]SbF₆ gave better yields as compared to dimeric complexes [RhCl(1)]₂ and [(Rh(1))₂Cl]SbF₆. Regarding enantioselectivities, dimeric Rh species [RhCl(1)]₂ and [(Rh(1))₂Cl]SbF₆ performed better than monomeric Rh species in the 1,2-addition, while the opposite was true for the 1,4-addition. Neutral Rh complexes performed better than cationic complexes. Microemulsions improved the yields of 1,2-additions due to a most probable enrichment of Rh complexes in the amphiphilic film and provided a strong influence of the complex nuclearity and charge on the stereocontrol. A strong nonlinear-like effect (NLLE) was observed in 1,2-additions, when diastereomeric mixtures of ligands 1 and epi-1 were employed. The pronounced substrate dependency of the 1,4-addition could be rationalized by DFT calculations.

中文翻译：

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单体与二元恶唑烷酮铑降冰片二烯配合物在催化不对称1,2-和1,4-加成中的作用的实验和理论研究

研究了手性Rh二烯配合物的核化和电荷对有机硼试剂向N-甲苯胺的催化不对称1,2-加成反应和对烯酮的1,4-加成反应的活性和对映选择性的影响。为此，由恶唑烷酮取代的3-苯基降冰片二烯配体合成了阳离子二聚Rh（I）络合物[（Rh（1））₂ Cl] SbF ₆和阳离子单体Rh（I）络合物[RhOH ₂（2）] SbF ₆ 1和2，在恶唑烷酮C-5'处的取代方式不同（CMe ₂与CH ₂）并与相应的中性二聚体和单体Rh（I）配合物[RhCl（1）] ₂和[RhCl（2）]进行比较。通过X射线晶体学，循环伏安法（CV），X射线吸收光谱法（XAS）和DFT计算获得了结构，电子和机械方面的见识。CV显示阳离子与中性Rh配合物对氧化的稳定性提高。固态和溶液XAS（扩展X射线吸收精细结构（EXAFS），X射线吸收近边缘结构（XANES））数据的比较表明，单体Rh配合物[RhCl（2）]保持其电子状态和配位溶液中的球形，而二聚体Rh复合物[RhCl（1）] ₂通过溶液中的二恶烷分子交换架桥氯配体。在1,2-和1,4-加成反应中，单体Rh复合物[RhCl（2）]和[RhOH ₂（2）] SbF ₆与二聚体复合物[RhCl（1）] ₂和[ （Rh（1））₂ Cl] SbF ₆。关于对映选择性，二聚Rh种类[RhCl（1）] ₂和[（Rh（1））₂ Cl] SbF ₆在1,2-加成中，其性能优于单体Rh物种，而在1,4-加成中则相反。中性Rh络合物的性能优于阳离子络合物。由于两亲膜中最可能的Rh配合物富集，微乳液提高了1,2-加成的收率，并提供了复杂的核和电荷对立体控制的强烈影响。当使用配体1和epi - 1的非对映异构混合物时，在1,2-加成中观察到强烈的类非线性效应（NLLE）。1,4-加成的明显的底物依赖性可以通过DFT计算来合理化。