Chiral complexes 2,2 -paracyclophane

There are a limited number of group VHI-X metal-based catalytic systems active and selective in asymmetric hydrosilylation of 0=0 bond. These few systems include Fe(OAc)2/DUPHOS active in hydrosilylation of aryl methyl ketones with (EtO)2MeSiH or PMHS (301,302), ruthenium complexes bearing oxazolinylferrocenephosphine ligand (303), or chiral bis(paracyclophane)-substituted (NHC) ligands in hydrosilylation of aryl alkyl ketones with H2SiPh2 (304) and iridium(I)/DIPOF system active in hydrosilylation of acetophenone with diphenylsilane. 

In 2004, Bolm et al. reported the use of chiral iridium complexes with chelating phosphinyl-imidazolylidene ligands in asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee [17]. These complexes were synthesized from the planar chiral [2.2]paracyclophane-based imida-zolium salts 74a-c with an imidazolylidenyl and a diphenylphosphino substituent in pseudo ortho positions of the [2.2]paracyclophane (Scheme 48). Treatment of 74a-c with t-BuOLi or t-BuOK in THF and subsequent reaction of the in situ formed carbenes with [Ir(cod)Cl]2 followed by anion exchange with NaBARF afforded complexes (Rp)-75a-c in 54-91% yield. The chela-... 

By using a similar method, we can prove that the cell complexes of the molecules [m [n]paracyclophane [22] and triple layered cyclophane [23] are also intrinsically chiral. Figure 30 illustrates these molecules... 

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). 

As unique C2-symmetric transition metal complexes, the atropisomeric (Rp,Rp)-2,2 -bi([2]paracyclo[2]-5,8-quinolinophane) (52) and (Rp,Rp)-1,1 -bi([2]paracyclo [2]-5,8-isoquinolinophane) (53) were prepared from (/ p)-4-amino- and (Rp)-4-carboxy-[2.2]paracyclophanes, respectively. The CD spectra of 52 and 53 were significantly different from each other (Fig. 14) [60]. The bisquinoline moieties are in almost planar orientation in 2,2 -isomer 52 and the origin of chirality is ascrib-able primarily to the paracyclophane structure. In contrast, the main source of chirality in l,l -isomer 53 is the distorted bisquinoline chromophores (i.e., the axial chirality). 

Formyl-5-hydroxy[2.2]paracyclophane (153) was used as a chiral auxiliary in the synthesis of a-amino acids [98]. The reported enantiomeric excess was in the range of 90-98%. Racemic 153 was first prepared by Hopf and Barrett [99]. To separate the enantiomers, their Schiff bases with the dipeptide (S)valyl-(S)valine was prepared. The diastereomeric copper(II) complexes of this compound show different solubility in 2-propanol. Alternatively they can be separ-... 

We were able to synthesize chiral dendri- rations. In addition, the circular dichrograms mers with stable planar-chiral building blocks clearly indicate that chiral dendrimers based to avoid racemisation. [47] In contrast to the on derivatives of [2.2]paracyclophanes can results of Seebach et al. these dendrimers be employed for complexation of certain show increasing chirality with inreasing gene- metal cations. 

Very recently, Ma and coworkers prepared a planar-chiral Af-heterocyclic carbene silver complex based on [2.2]-paracyclophane (Scheme 3.18) [37]. The... 

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... 

Dahmen and Erase demonstrated the first highly enantioselective diethylzinc addition to imines in the absence of other metal catalysts such as Ti, Zr, and Cu complexes (Scheme 4.46) [40]. A simple method that uses only a catalytic amount of chiral N,0-ligand (132) based on [2,2] paracyclophane without an additional central metal is notable. Although they used a specific N-protected a-(p-Ts)benzylamine (130) as the highly reactive N-protected imine precursor (133) via an in situ preparation, the reaction was catalyzed by only 2 mol% of (132) for various functionalized aromatic imines. While the corresponding Et adducts (131) were obtained in almost quantitative yields and excellent enantiomeric excesses, 3 equiv of diethylzinc was used. 

A new family of catalysts has recently produced dramatically improved results for both enantioselective aUcoxy-and hydroxycarbonylation. When diphosphine ligands based on the planar chiral paracyclophane backbone are treated with two equivalents of [PdCl2(PhCN)2], they can form very rare halide-bridged dipalladium complexes (Scheme 14.29). °°... 

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... 

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