Ferrocene based diphosphine ligands

The authors note that under their conditions, involving relatively high temperatures and low pressures, many steps of the cycle have similar rates, as die kinetics are rather complex. The best results were obtained when an excess of phosphine was employed. A ligand to metal ratio of 1.5 was preferred, as at higher ratios the selectivity did not improve further. 

This led Unruh and Christenson to the conclusion that the most selective species was one containing more than two phosphorus ligands, while the current view was, Wilkinson s view, that complexes containing two phosphines were the ones leading to high l b ratios of 20. They propose that the most selective species contains three phosphorus atoms, one dppf as a bidentate on one metal and one dppf bridging between two metals. The two metals are to function independently in the catalysis. 

Re-examination of the dppf-Rh system has shown that the coordination behavior under syn-gas is different [42]. Both NMR spectra and in situ IR ([Rh] = 8 mM, [dppf] = 17 mM, p(CO) = 20 bar, 40 C) spectra show that the only species under these conditions is RhH(dppf)(CO)2 being a mixture of rapidly equilibrating 2ae (approximately 80 %) and 2ee (20 %). The l b 

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H.U. Blaser, M. Lotz, F. Spindler, "Asymmetric Catalytic Hydrogenation Reactions with Ferrocene Based Diphosphine Ligands" in Handbook of Chiral Chemicals, 2nd Edition, D. J. Ager (Ed.), CRC Press, Boca Raton 2005... 

Asymmetric Catalytic Hydrogenation Reactions with Ferrocene-Based Diphosphine Ligands... 

Blaser H-U, Lotz M, Spinder R Asymmetric catalytic hydrogenation reactions with ferrocene-based diphosphine ligands. 

The benchmark ligand for this reaction, which is also the one used for the industrial-scale reaction, is the Xyliphos ligand, a ferrocene-based diphosphine bearing the same stereochemical features and substitution pattern as ligand... 

Subsequently, Landis studied the coordination of the ferrocene-based diphosphine-benzoxaborolidine ligands 53 with the aim of supporting secondary interactions between the pendant Lewis acid and an external Lewis base.63 Stable platinum complexes 63a-c were formed by reacting... 

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). 

In 1998, Hamann and Hartwig reported that electron-rich, ferrocene-based diphosphines such as 13 allowed for the coupling of cyclic amines with aryl chlorides [72,73]. The known ligand 13 proved to be most generally useful for this transformation, Eq. (42). The 13/Pd-catalyzed arylation reaction was performed with cyclic amines as well primary amines, however, no reactions with acyclic secondary amines were reported. 

Hartwig and co-workers reported that several ferrocene-based diphosphines are useful in the arylation of primary amines with aryl chlorides [72]. Known ligands 20 [104] and 21 [105] are particularly effective in the coupling of chloroarenes and primary aliphatic amines, Eq. (102). 

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 29.9. Selection of ferrocene-based chiral ligands (A) ferrocene-based diphosphines with planar chirality only (B) bidentate ferrocene-based ligands with ntixed planar and central chirality and (C) ligands with planar and axial chirality as well as planar, central, and axial chirahty. 

Azanorbornyl-3-methanol (93) shows its value as a chiral ligand in Ru-catalyzed transfer hydrogenation. On binding to Ru, C2-symmetric diphosphines (94, 95, etc.) and the ferrocene-based ligand 96 are able to exert their steric influences during hydrogenation of 1,3-diketones. 

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, McCormack PJ, Mohammed K, Mbafor W, Roberts SM, Whittall J (2007) Stereoselective synthesis of ferrocene-based c2-symmetric diphosphine ligands application to the highly enantioselective hydrogenation of a-substituted cinnamic acids. Angew Chem Int Ed 46 4141 144... 

Platinum-chiral bidentate ligand-tin(ll)chloride catalysts have been used in hydroformylation reactions. MeOBlPHEP, BlNAP-hemioxide, and diphosphites containing 2,4-pentanediyl and 1,3-diphenyl-1,3-propanediyl moieties have been used as a bidentate ligand (288). Pt-complexes with ferrocene-based chiral diphosphines have been screened in enantioselective hydroformylation of styrene (289). 

TriFer Ferrocene-based C2-symmetric diphosphine ligand... 

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