Cation-ji interaction

Several comprehensive reviews of the cation-ji interaction were piiblishedj and the reader should consult these for fiirdier details and original references. Especially significant and more recent articles are explicitly cited here. 

Recently, N-methyliraidazole-mediated KR of racemic secondary alcohols during the transfer of a chiral acyl moiety was developed [41]. This resolution process proceeds via chiral acyl imidazolium chlorides 11 with very good selectivity. The discriminating ability between the enantiomers of alcohols was observed only with the N-methylimidazole derivative and not with the parent acid chloride acyl donor. Various acyl imidazolium chlorides were reacted with racemic alcohols to produce the enantiomerically enriched esters and alcohols. Strong non-covalent cation-Ji interactions in a specific conformation of an intermediate cation-)i complex (parallel stacking) provide high selectivity as shown in 12. 

The anion-binding thiourea catalysis was applied further in asymmetric polycyclization of hydroxylactam derivatives 296 (Scheme 2.81). It was found that larger aromatic groups on the pyrrolidine ring of thiomea catalyst produced better results in terms of reactivity and enantioselectivity. The 4-pyrenyl-substituted thiourea 289c was found to be an optimal catalyst to promote polycyclization reactions which involved stabilizing cation-ji interactions to indnce the enantioselectivity [112]. 

Not surprisingly, ILs have been analyzed using alkyl-based reversed phase [20] as well as cation-exchange chromatography [21,22]. However, the rich potential interaction chemistries of ILs may also be inferred from the retention behavior of imidazolium- and pyridinium-based ILs on phenyl-based stationary phases which can supply aromatic ji-ji interaction capability [23]. The multiple modes of interaction between the imidazolium and the phenyl phase are illustrated in Figure 5.1. In this study, it was reported that the role of aromatic ji-ji interactions in the separations of IL cations could be mediated by the addition of acetonitrile. 

Lenthall, J. T. and Steed, J. W., Organometallic cavitands Cation-Jl interactions and anion binding via Ji-metallation , Coord. Chem. Rev. 2007, 251, 1747-1760. 

The structural parameters are included in Table 15. Since these complexes are dimers with planes related to each other by the inversion center, they exhibit ji-jt interactions. Generally, the complexes which show strong ji-ji interaction may have very low values of mean plane separation and lateral shift [10]. Thus, the 7t-jt interaction in cation radical complexes is rather weak as judged by higher values of lateral shift and mean plane separation. A detailed study indicates that the unusual saddle conformations occuring in the 71-cation radical is not electronic but rather steric in origin. The unusual saddle conformation results... 

The cation-TT interaction involves binding of a cation to Ji-electrons (e.g., benzene, acetylene). Early mass spectrometry and ion cyclotron resonance studies have established that alkali-metal cations (e.g., Na+) bind strongly to simple aromatics. Later, Deakyne, and Meolner showed that organic ions (e.g., alkylammoniums) display affinities for aromatics. Moreover, extensive work by Dougherty and CO workers has established models of the cation- n- interaction that have been successfully demonstrated in a variety of synthetic receptors. ... 

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