Chiral ferrocene based phosphine

Figure 9.10 Chiral ferrocene based phosphine phosphoramidite ligands (PPFAPhos) developed within our group.

Most syntheses continue to use the chiral-directing group approach or the use of chiral-protecting groups for metallation. The synthesis and application of a new family of air-stable, highly unsymmetrical ferrocene-based phosphine-phosphoramidites, exemplified by 37, has been described, and their use in Rh-catalyzed asymmetric... 

Fig. 25.1 Structures of Ugi s amine and the first ferrocene-based chiral phosphine ligands.

Asymmetric hydroboration of prochiral alkenes has been achieved using transition metal catalysts and chiral phosphines as ligands to obtain enantiomerically pure alkyl boronates <1997CC173>. Catalysts such as Rh(COD)2+BF4 , Rh(COD)2+Cl, Rh+BF4 , etc., in combination with chiral phosphines like DIOP 71, BINAP 72, CHIRAPHOS 73, DIPAMP 74, BDPP 75, ferrocene-based diphosphines 76<1999TL4977>, etc., have been employed for the asymmetric hydroboration of prochiral alkenes with moderate to high ee (DIOP = 2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane BINAP = 2,2-bis(diphenyl-phos-phanyl)-l,1-binaphthyl CHIRAPHOS = 2,3-bis(diphenylphosphino)butane DIPAMP = l,2-bis[(2-methoxyphe-nyl)phenylphosphino]ethane BDPP = 2,4-bis(diphenylphosphino)pentane). 

Asymmetric hydroformylation of styrene has been studied with a range of bidentate phosphines, van Leeuwen reported phosphorus-chiral ferrocenyl-based diphosphines, the hydride complexes of which showed varying ee-ea ratios depending on ligand basicity, as determined by HP-IR and HP-NMR. This contrasted to the clear ea preference shown by complexes of the achiral l,l -bis(diphenylphosphino)ferrocene (dppf) ligand. Claver and van Leeuwen " " " investigated BDPP [(2A,4A)-bis(diphenylphosphino)pentane] and CHIRAPHOS [(2R,3R)-bis (diphenylphosphino)butane] for the same transformation. High pressure spectroscopic data for the catalytic species... 

Chen WP, Mbafor W, Roberts SM, Whittall J (2006) A very simple, highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands. J Am Chem Soc 128 3922-3923... 

In the area of asymmetric hydrogenation chiral dighosphines have played a center role since and many applications have been developed. Important new ligands that have been introduced comprise Noyori s BINAP [28], DuPhos (Burk) [29], Takaya s BINAPHOS [30], and Ci-symmetric ferrocene-based ligands introduced by Togni [31]. Industrial products, of which the synthesis uses enantioselective phosphine-derived metal-catalysts are for instance menthol, metolachlor, biotin, and several alcohols, e.g. (R)-1,2-propanedioI, For details about the applications the reader is referred to reviews and references therein [32, 33]. Substituents and backbones have an enormous influence on the performance of the ligands, but usually rationalizations are lacking. 

NMR spectroscopy was applied in the enantiomeric excess determination of (iV,iV-dimethyl-(2,2,2-trifluoro-l-phenylethyl)amine-C,A)palladium complexes of a-amino acids.Dunina et al. used NMR spectroscopy and a P -chiral phosphapalladacycle for the enantiomeric purity determination of a-amino acids. P NMR spectroscopy was also used in the enantiomeric excess determination of N,C o///5< -palladated complexes of P-chiral phosphines. A ferrocene-based reagent (i p,successfully designed for the chiral recognition of /3-hydroxyphosphines and the discrimination of ( )-bis(diphenylphosphino)-1,1 -binaphthyl. 

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... 

Phosphorus is a key element in catalysis, and the last two Nobel prizes in molecular chemistry were awarded to Noyori, Sharpless and Knowles (2001) for their work on enantioselective catalysis and to Grubbs, Schrock and Chauvin (2005) for their work on the chemistry of transition metal carbene complexes and their applications in metathesis. In both cases the development of highly efficient, specifically tailored phosphorus based ligands are of paramount importance The book opens with an account of the recent studies on a new family of air-stable chiral primary phosphines based on the binaphthyl backbone and their applications in asymmetric hydrosilylations (Chap. 1). The concept of applying phosphorus ligands to enantioselective catalysis is also the main subject of Chaps. 5 and 10, dealing with P-based planar chiral ferrocenes and chiral phosphorus ligands for enantioselective enyne cycloisomerizations, respectively. 

A series of chiral chelate phosphine ligands, mainly based on the ferrocene backbone (Figure 6.9), have been tested in [C4Ciim][PF6] as catalysts for enantioselective allylic alkylation reactions and results are listed in Table 6.9.[134]... 

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