Ferrocene bisphosphines

Figure 1. Structures of chiral ferrocene bisphosphine and tetraphosphine ligands. Results and Discussion...

Most catalysts that have been developed for asymmetric catalysis contain chiral C2-symmetric bisphosphines.7 The development of chiral ferrocenylphosphines ventures away from this conventional wisdom. Chirality in this class of ligands can result from planar chirality due to 1,2-unsymmetrically ferrocene structure as well as from various chiral substituents. Two classes of ferrocenylbisphosphines exist two phosphino groups substituted at the l,l -position about the ferrocene backbone (51) and both phosphino groups contained within a single cyclopentadienyl (Cp) ring of ferrocene (4).9... 

A chiral bisphosphine containing two ferrocene moleeules has been prepared using Ugi s lithiation as a key step (Scheme 2-9) [20]. Thus, the diphenylphosphinyl group is introduced at the ferrocenylmethyl position of the iodide obtained from lithiated ferrocene 2. Oxidative coupling of the iodoferrocene followed by reduction of the phosphine oxide gives the bisferrocene-bisphosphine 15. The bisphosphine is unique in that a tra j-chelate is formed on its coordination to a metal. 

Metalation of sulfinylferrocene (338) to give the lithiated species, followed by transmetalation to give either the isolable boron analog (348) or the nonisolable zinc analog (349), is an approach used to access yet another class of ferrocene derivatives (equation 79)Palladium-catalyzed coupling of (348) or (349) with aryl iodides affords planar chiral aryl ferrocenes that are converted by standard transformations into planar chiral monophosphine aryl ferrocenes (350) that are also useful ligands in asymmetric catalysis. With appropriate ort/ o-substitution on the aryl ring, ferrocenes that possess axial chirality as well as planar chirality are prepared if the orfAo-substitutent is a second phosphine unit, access to a bisphosphine aryl ferrocene is achieved. ... 

Arylation of alkynes via addition of arylboronic acids to alkynes represents an attractive strategy in organic synthesis. The first addition of arylboronic acids to alkynes in aqueous media catalyzed by rhodium was reported by Hayashi et al. They found that rhodium catalysts associated with chelating bisphosphine ligands, such as 1,4-(>/5(diphenyl-phosphino)butane (dppb) and l,l -Z A(diphenylphosphino)ferrocene... 

Sammakia and Uemara, the development of the 1,5-bisphosphine Taniaphos by Knochel and coworkers, and more recently by Fu for the preparation of chiral heterocycles, ferrocene-based ligands in asymmetric catalysisJ For a specialized recent review concerning apphcations of chiral ferrocene ligands in asymmetric catalysis, the reader may consult a review by Carretero et alP ... 

Genet C, Canlpa SJ, O Brien P, Taylor S (2006) Catalytic asymmetric synthesis of ferrocenes and P-stereogenic bisphosphines. J Am Chem Soc 128 9336-9337... 

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). 

S,fl)-JOSIPHOS Scheme 12.14 Bisphosphine alkyl and ferrocene ligands. 

Figure 15.3. A selection of chiral bisphosphines based on a ferrocene backbone.

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