Binaphthyl ligands

A series of chiral binaphthyl ligands in combination with AlMe3 has been used for the cycloaddition reaction of enamide aldehydes with Danishefsky s diene for the enantioselective synthesis of a chiral amino dihydroxy molecule [15]. The cycloaddition reaction, which was found to proceed via a Mukaiyama aldol condensation followed by a cyclization, gives the cycloaddition product in up to 60% yield and 78% ee. 

Similar reactions have been used for substitution by alkoxide and phenoxide nucleophiles. Hindered binaphthyl ligands have proven useful in substitutions by alcohols.173... 

Buchwald has designed a hindered dialkylphosphino-binaphthyl ligand (3) that is much more active than the original ligand for asymmetric arylation of ketone enolates. Reactions occur at room temperature using only 2 mol % catalyst with enantioselectivities up to 94% [41]. Additionally, the Buchwald group has developed an electron-rich monodentate ligand (4) capable of vinylation of ketone enolates with up to 92% ee [42]. 

Catalytic asymmetric hydrosilylation of terminal olefins has been developed, using palladium coordinated to the novel binaphthyl ligands (MOP). In all cases (MOPa-d), the enantioselectivity is excellent ( 90% e.e.). The products can be converted into the corresponding secondary alcohols with retention of configuration446. 

Fig. 1. Monodentate (A) and chelating (B) binaphthyl ligands on a metal center and their effect on the stereoselective occupation of the squares.

The amount of catalyst can be reduced to 5 mol % using the binaphthyl-derived Ti-com-plex 32 [11]. Only 2 mol% of Carreira s [12] catalyst 35 is necessary to obtain good yields and high ee values. However, the chiral binaphthyl ligand for 35 is not commercially available. 

The new binaphthyl ligands 49 [22] and 50 [23] have led to a breakthrough in the copper catalyzed 1,4-addition of organozinc reagents to a,jff-unsatu-rated ketones, a reaction which has proved to be difficult if carried out enantioselectively. Selectivities up to 96 % ee have been reached with cyclic substrates, while acyclic substrates still leave room for further improvement. 50 has also been successfully employed in palladium-catalyzed alkylations of allyl acetates [24]. 

The stereodirecting effect of the axially chiral 1,1 -binaphthyl ligand is assisted by the bulky wingtip group of the carbene (Mes) and the additional substituents of the benzylide-nyl ligand that features prominently in the Grubbs catalyst (see Figure 5.12). 

Homogeneous catalytic asymmetric hydrogenation has become one of the most efficient methods for the synthesis of chiral alcohols, amines, a and (3-amino acids, and many other important chiral intermediates. Specifically, catalytic asymmetric hydrogenation methods developed by Professor Ryoji Noyori are highly selective and efficient processes for the preparation of a wide variety of chiral alcohols and chiral a-amino acids.3 The transformation utilizes molecular hydrogen, BINAP (2,2 -bis(diphenylphosphino)-l,l -binaphthyl) ligand and ruthenium(II) or rhodium(I) transition metal to reduce prochiral ketones 1 or olefins 2 to their corresponding alcohols 3 or alkanes 4, respectively.4... 

It is clear that electron-withdrawing alkoxides in M(NAr)(CHR)(OR )2 complexes dramatically increase the rate of reaction of an olefin with the M=CHR bond. In fact, no other X ligands in M(NAr)(CHR)X2 complexes are as successful as alkoxides for sustained metathesis activity, [66] either because they are not bulky enough to stabilize an electron deficient metal center and prevent bimolecular decomposition (e.g., halides) or because they donate too much electron density to the metal in a a and/or Ji fashion (e.g., amides or thiolates). A recent example is Mo(NAr)(CHR)(diamide) where the diamide is a N,N -disubstituted-2,2 -bisamido-l,r-binaphthyl ligand no ready reaction was observed between this complex and ethylene or even benzaldehyde. [108] Alkylidene complexes are now known for all metals in groups 4, 5, and 6, plus rhenium. For example, it was shown that Cp2Ti(CH2) could be trapped... 

The same group also reported that when cadmium nitrate or perchlorate salts were used in the preparation of the MOF, two different MOF structures can be obtained with the same chiral binaphthyl ligand [130]. This diversity in crystal structures seemed to arise from the participation of the anion accompanying Cd " " in the structure. The chiral MOF prepared from nitrate acts as an efficient heterogeneous catalyst for the room-temperature asymmetric addition of diethylzinc to a series of aromatic aldehydes, with ee values up to 90% at 100% substrate conversion. Conversely, the MOFs derived from the perchlorate salt were inactive under the same conditions. 

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