Imidazolinylidene ligand

Chiral N-arylated imidazolinylidene ligands have been employed in the palladium(II) catalyzed aerobic oxidation of secondary alcohols to the corresponding ketones [55]. The chiral variant of this reaction, which does not generate a new element of chirality, is again based on the kinetic resolution of racemic mixtures. The active catalyst is formed in situ by a combination of two precursors, a dinuclear NHC-palladium(II) complex and an achiral (acetate) or chiral base ((-)-sparteine) (Scheme 18). 

A novel chiral bidentate imidazolinylidene ligand (26) has recently been developed in Helmchen s group [57]. It is related to Grubbs imidazolinyli-... 

The use of imidazolinylidene ligands 1 has been shown to be particularly useful to enhance the reactivity of the cross-couplings of aryl chlorides [35] and fluorides [36] with aryl Grignard reagents. 

In 2002, Hoveyda et al. reported the synthesis, structure and reactivity of a chiral bidentate Ru-based catalyst 65, bearing a binaphthyl moiety, for olefin metathesis [33]. Preference for a bidentate chiral imidazolinylidene was based on the hypothesis that such a ligand would induce chirality more efficiently. This catalyst was designed by analogy with similar achiral complexes 66 that... 

In conclusion, while the first chiral imidazolinylidenes tested in asymmetric catalysis only gave a moderate chiral induction, more recent results have clearly indicated that the encoding of chiral information in the backbone of the heterocycle may give rise to highly efficient stereodirecting ligands. The potential versatility of this approach is apparent in a recent contribution... 

Alternatively, Dorta and co-workers used SINap ligands in order to improve the activity and stability of second-generation ruthenium metathesis catalysts (14). Effects of NHC backbone substitution on imidazolinylidene-derived ligands were studied by Grubbs et who also replaced the imidazole-based N-heterocycles with their thiazole analogues.Because these modifications were also applied to oxygen-chelated alkylidene catalysts, they are discussed in more details in the next Section. 

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