Paracyclophanes bidentate ligands

A) Planar Chiral Paracyclophane-Based Bidentate Ligands. As paracaclophane has to some extent similar characteristics as ferrocene, it allows the preparation of bidentate phosphines with planar chirality. First the paracyclophane-based diphosphine ligand, [2.2]Phane-Phos (83, R = Ph), was synthesized by Pye and coworkers.Both Rh- and Ru-complexes of PhanePhos... 

FIGURE 29.8. Paracyclophane-based planar chiral bidentate ligands. 

Bolm and coworkers very recently tested the iridium(I) complex derivatives 57a-57c in asymmetric hydrogenation [105]. These complexes contain a bidentate carbene-phosphine ligand with a chiral pseudo-ortho-[2,2]paracyclophane unit built into its backbone (Fig. 13). 

Bidentate oxazoline-imidazolylidene ligands, in which both units are linked by a chiral paracyclophane, have been studied in Bolm s group [129]. In this case, the planar chirality of the pseudo-orfho-paracyclophane is combined with the central chirality of an oxazoline (Scheme 48). Compounds 70 were tested in the asymmetric hydrogenation of olefins displaying moderate selectivity (ee s of up to 46% for dimethylitaconate in the presence of 70b). 

Complex 33, containing a partially reduced 1,10-phenantroline-based monodentate NHC ligand led to 97% yield and 81% ee in the hydrogenation of methyl acetamidoacrylate (Figure 13.4). A bidentate NHC bearing a PPh2 unit with a chiral pseudo-o-[2.2]paracyclophane linker (34) was found to be a selective catalysts for non-functionalized trisubstituted alkenes, although functionalized alkenes were found to be sensitive to the H2 pressure. Also, the... 

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