Chiral ferrocene based ligands

Aminocarbonylation has also been applied to the synthesis of unsymmetrical ferrocene-1,1 -bis-carboxamides. Ferrocene-based chiral ligands are very useful in asymmetric catalysis, and enantiomerically pure ferrocenyl ligands can be obtained by optical resolution of unsymmetrically substituted ferrocenes. However, the synthesis of such unsymmetrical ferrocenes is not an easy task. The use of aminocarbonylation gave a solution to this challenge. For example, the Pd-catalyzed reaction of symmetrical ferrocenyl diiodide 144 with two different amines, morpholine and diethylamine (5 equiv. each) under 39.5 atm of CO, gave the desired unsymmetrically disubstituted ferrocene-biscarboxamide 145 in 85% yield (Equation (11)). ... 

FIGURE 15.2 Starting compound and structures of the first ferrocene-based chiral ligands. 

The synthesis and application of chiral ferrocene derivatives has attracted much interest.358 Hence the ferrocenyldiphosphine (163) (Josiphos) can be prepared by direct HPR2 substitution of the dimethylamino group (Equation (40)).359 Various other ferrocene-based chiral ligands are known (e.g., the TRAP ligands (164)).360-364... 

Very few reports on the asymmetric catalytic Pd reaction have been made to date. However, in 2009, Otha and coworkers reported the application of ferrocene-based chiral ligands in this reaction. Despite obtaining moderate to good yields for the corresponding addition products, the enantiose-lectivity was very low (a maximum of 11% ee was obtained) [49]. 

Based on these considerations on the existence of complexes IV and V, Chen, McCormick et al. have developed a new concept of ferrocene-based chiral ligands [33, 34]. These authors designed and completed stereoselective synthesis of the... 

Asymmetric allylic alkylations of lithium enolates of various alkyl aryl ketones 25 were studied by the group of Hou [18] using ferrocene-based chiral ligands. 

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. 

Recently a novel chiral ferrocene-based amidinato ligand and its rhodium complexes have been described. The chiral N,N -bis(ferrocenyl)-substituted formamidine (N,N -bis[(S)-2- (lR)-l-(diphenylphosphino)ethyl ferrocen-l-yl]for-mamidine was prepared from commercially available (IR)-l-(dimethylamino) ethyl ferrocene by a multistep procedure in an overall yield of 29%. Deprotonation of the ligand with -butyllithium followed by addition of [RhCl2(COD)2] as illustrated in Scheme 167 yielded the corresponding (formamidinato)rhodium(l)... 

Figure 6 Chiral ferrocene-based bisphosphane ligands.

Fu has reported a planar-chiral bisphosphorus ligand 45 with a phosphaferrocene backbone. The ligand has provided enantioselectivity up to 96% ee in the hydrogenation of a-dehydroamino acid derivatives.99 Another planar-chiral ferrocene-based bisphosphorus ligand 46 has been reported by Kagan recently and enantioselectivity up to 95% ee has been obtained in the reduction of dimethyl itaconate.100... 

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

Figure 18.17. Ferrocene-based chiral-planar P-N ligand, and phosphinooxazolines [32]...

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... 

Chiral bis(oxazolines) 51 with an oxalylic acid backbone were used for the Ru-catalyzed enantioselective epoxidation of tran5-stilbene yielding franx-l,2-diphenyloxirane in up to 69% ee [24]. The asymmetric addition of diethylzinc to several aldehydes has been examined with ferrocene-based oxazoline ligand 52 [25], resulting in optical yields from 78-93% ec. The imide 53 derived from Kemp s triacid containing a chiral oxazoline moiety was used for the asymmetric protonation of prochiral enolates [26]. Starting from racemic cyclopentanone- and cyclohexanone derivatives, the enantioenriched isomers were obtained in 77-98 % ee. 

Many chiral ferrocene-based bisphosphane ligands with great structural variations have been developed recently. Togni and Spindler introduced non-Crsymmetric ferrocene-based Josiphos type ligands. Josiphos 38 has been found to be effective for Rh-catalyzed hydrogenation of a-acetamidocinnamate, dimethyl itaconate, and P-keto esters. A class of non-Cj-symmetrical ferrocene-based 1,5-diphosphane ligands (TaniaPhos 39) has also been... 

Compared with asymmetric intramolecular hydroacylation reactions of alkenes, the corresponding intermolecular versions have been relatively less developed. In 2007, Stemmier and Bolm reported the first example of enanti-oselective intermolecular hydroacylation reactions between salicylaldehydes 40 and norbornadiene-type alkenes 41 (Scheme 8.20). It was found that the diastereoselectivity of the reaction could be modulated through changing the chiral ligands. With ferrocene-based bisphosphine ligand L5, the exo-product 42a was obtained exclusively with up to 82% ee. When monodentate phos-phoramidite ligand L6 was employed, the e do-isomer 42b was obtained as major product with moderate enantioselectivity (54% ee). 

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). 

A series of ferrocene-based chiral dmuclear complexes of Pd(n) and Pt(ll), containing the deprotonated form of the ligand (i )-l-[(J)-diphenylphosphino)ferrocenyl]ethyl mercaptan, have been prepared, which further extends the utility of this ligand class. 

A series of non-f, -symmetrical ferrocene-based 1,5-diphosphane ligands (TaniaPhos) has been developed by Knochel.88,88a,88b The ligands have been effectively used in Rh- or Ru-catalyzed asymmetric hydrogenations. The ligand 39, which has an MeO group at the chiral carbon center, has shown excellent applications in the hydrogenation of several olefin and ketone substrates.89 Weissensteiner and Spindler have reported a series of structurally different... 

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