Nickel chiral catalyst

The chiral catalyst was made from Raney nickel, which was prepared by addition in small portions of 3.9 g Raney nickel alloy to 40 ml water containing9 g NaOH. The mixture was kept at 100 C for 1 h, and then washed 15 times with 40 ml water. Chirality was introduced by treatment of the Raney nickel for I h at lOO C with 178 ml water adjusted to pH 3.2 with NaOH and containing 2g (S,S)-tartaric acid and 20 g NaBr. The solution was then decanted, and the modifying procedure was twice repeated. Hydrogenation over this catalyst of acetylacctone (100 atm, 100" C) in THF containing a small amount of acetic acid gave an isolated yield of chiral pentanediol of 44% (99.6% optical purity). 

One of the important conclusions of the early attempts was that it is fruitful to place the functionality near an optically active support. Already in 1958, Isoda and coworkers reported for the first time the enantioselective hydrogenation with a Raney nickel catalyst modified with optically pure amino acids. Optical yields reported at that time were from low (2.5%) to moderate (36%) values (for references see [12]). Subsequently, in 1963, Izumi and coworkers [100] initiated an extended study of the modified Raney nickel system with TA. As a result of their initial researches, this system was the first heterogeneous chiral catalyst to give high enantioselectivities in the hydrogenation of / -ketoesters (95%) [101,102],... 

The cationic aqua complexes of the C2-symmetric trans-chelating tridentate ligand 447 proved also highly effective chiral catalysts. The complexes involving the metal(II) perchlorates of iron, cobalt, nickel, copper and zinc produced the main endo adduct of cyclopentadiene and N - aery loy 1-1,3 -oxazo I i din -2 -one with very high ee values281. 

Using cheaper metals, electron-deficient imines such as sulfinylimine (20) can be reduced by diethylzinc, using a chiral nickel(II) catalyst yields and des >90% can be achieved.53 Interestingly, ketones are unaffected by the process many common reducing agents cannot so discriminate. XH NMR profiling indicates ethylene production, a... 

A particularly successful approach to the catalytic hydrogenation of dialkyl ketones with hydrogen has been the use of the heterogeneous contact catalyst system - Raney nickel chirally modified with tartaric acid [18]. Here too, selectivity is enhanced by branching of the alkyl substituent in the alkyl methyl ketones (e.g., 85 % ee for the hydrogenation of isopropyl methyl ketone). With... 

Catalytic hydrosilylation of alkenes performed in the presence of a chiral catalyst results in the formation of chiral silanes. Initially platinium catalysts of the type L PtCl2, L = (/ )-benzyl-(methyl)phenylphosphine (BMPP) or (/ )-methyl(phenyl)propylphosphine and 1,1-disubstituted prostereogenic alkenes, such as a-methylstyrene, 2,3-dimethyl-l-butene and 2-methyl-l-butene, were used however, the stereoselectivity was low4,5. A slightly higher stereoselectivity is obtained when dichlorobis[(/ )-benzyl(methyl)phenylphosphine]nickel [Ni(BMPP)2Cl2] is used as the catalyst. Note that two chiral silanes are formed in this reaction, both of which are products of anti-Markovnikov addition. The major product is the expected dichlorosilane 3, while the byproduct is an anomalous chlorosilane 4 both products were separated by fractional distillation and the major product methylated to give the trimethylsilanes 56 7. 

In Baeyer-Villiger oxidations catalyzed by (achiral) copper or nickel salts substituted cyclohexanones like 4 (Eq. 3) had been shown to be reactive substrates for the conversion to the corresponding (racemic) lactones in the presence of aldehyde and molecular oxygen [22]. The next step was to develop a chiral catalyst in order to make this reaction proceed in an enantioselective manner, giving optically active oxepanones. Various copper complexes were screened in a search for asymmetric induction in the aerobic Baeyer-Villiger oxidation. The most active and selective catalyst that was eventually found was the copper complex... 

The low solubility of most organometaUic catalysts in COj means that in ideal cases no modification catalyst is required, provided it is suffidenfly soluble in the IL. This was foimd to be the case for the hydrovinylation system which employed a nickel-based chiral catalyst first reported by Wilke and co-workers [23], In the case of the hydroformylation system, however, the activity was foimd to be highest when using [Rh(acac)(CO)2] combined with a sulfonated triphenylphosphine analogue that had an imidazoHum cation as its counterion. In practice it is likely that neutral catalysts may require charged ligands, while those which are themselves charged can be used unmodified. 

Allylic acetates undergo an asymmetric coupling with ArMgX, in the presence of a chiral nickel(II) catalyst, to give (83) in up to... 

In 2008, Hamada and colleagues employed homogeneous chiral nickel-bisphosphine catalysts for DKR. Indeed, hydrogenations through DKR of a series of a-amino-jS-ketoester hydrochlorides into the corresponding anti )S-hydroxy-a-amino esters were achieved using a combination of nickel acetate... 

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