Synthesis chiral metallocenes

More recently, a very efficient asymmetric carbolithiation of N,N-dimethyl-aminofulvene 30, leading to a chiral cyclopentadienide anion, was reported by Hayashi et al. [6] for the synthesis of chiral metallocenes (Scheme 6). By adding an aryl lithium such as 31 complexed with a chiral ligand on fulvene 30, a cyclopentadienide ion 32 bearing a stereogenic center at the a position was generated. This anion was reacted with [RhCl(nbd)]2 to yield... 

Chiral active pharmaceutical ingredients, 18 725-726. See also Enantio- entries Chiral additives, 6 75—79 Chiral alcohols, synthesis of, 13 667-668 P-Chiral alcohols, synthesis of, 13 669 Chiral alkanes, synthesis of, 13 668-669 Chiral alkenes, synthesis of, 13 668—669 Chiral alkoxides, 26 929 Chiral alkynes, synthesis of, 13 668-669 Chiral ammonium ions, enantiomer recognition properties for, 16 790 Chiral ansa-metallocenes, 16 90 Chiral auxiliaries, in oxazolidinone formation, 17 738—739... 

Metal complexes of pinene-fused boratabenzene ligands, analogous to chiral metallocenes that have found application in catalysis and enantioselective synthesis, have been prepared.122-124 With late transition metals such as Mn and Fe, the complexes are obtained as mixtures of diastereomers (e.g., 97) with the sterically less congested exo form predominating, but the bis(ligand) Zr complex 98 was obtained as the pure exo,exo product.124 A lithium... 

A. Togni in New Chiral Ferrocenyl Ligands for Asymmetric Catalysis in Metallocenes. Synthesis, Reactivity, Applications , eds. A. Togni and R. L. Halterman, Weinheim, 1998, Vol. 2, p. 685. 

Halterman, R. L. Synthesis of chiral titanocene and zirconocene dichlorides. In Metallocenes— Synthesis, Reactivity and Applications, Togni, A., Halterman, R. L., Eds. Wiley-VCH Weinheim, 1998 pp 455-544. 

Halterman, R. L. Ramsey, T. M. Asymmetric synthesis of a stericaUy rigid binaphthyl-bridged chiral metallocene Asymmetric catalytic epoxidation of unfunctionalized aUcenes. OrganometalUcs 1993, 12, 2879-2880. 

Schaverien, C. Ernst, R. Schut, R Skiff, W. Resconi, L. Barhassa, E. Balhoni, D. et al. Anew class of chiral bridged metallocene Synthesis, structure, and olefin (co)polymerization behavior of rac- and meio-l,2-CH2CH2 4-(7-Me-indenyl) 2ZrCl2. J. Am. Chem. Soc. 1998,120, 9945-9946. 

Nickel-0- and palladium-O-complexes are very active catalysts for the polymerization of norbornene and also for cyclopentene [552-554], Nickel catalysts produce soluble polymers with a molecular weight of over one million while polymers obtained with palladium or metallocene complexes are insoluble. The soluble polymers have an atactic structure. The microstructure of the polynorbornene depends on the catalyst used and is isotactic by synthesis with chiral metallocenes. 

Ziegler-Natta catalysts based on chiral metallocenes in combination with aluminoxane allow the synthesis of isotactlc polyolefins ). A high activity is given with the ethylene(bisindenyl)-zirconlumdlchloride catalyst as well as the ethylene(bistetra-... 

Previous polypropylenes found to favor the y-modification, which are thermally unstable with respect to the a-modification, were very low in MW the values were 2600 for thermally degraded polymers and 740 to 3900 by special synthesis.This is compared with s of 9,000 to 90,000 for the present anisotactic polypropylenes. Therefore, the ani-PP formed by the chiral metallocene catalyst, which crystallizes preferentially in the thermally stable y-form, probable are comprised of chains containing frequent with discontinuity in their helical configurations. 

Ziegler Natta catalysts exhibit varying degrees of selectivity in the vinylic polymerization of cycloolefins, strongly depending on the nature of the catalyst and reaction conditions [198]. When chiral catalysts (e.g., chiral metallocenes in combination with aluminoxanes) are used, the synthesis of stereoregular polycycloolefins is possible [205]. 

Baker s yeast seems to be compatible with several metal-containing or organometal-lic species, as shown for the reduction of ferrocenyl derivatives [459], arylketone-Cr(CO)3 complexes [460], indanone-Cr(CO)3 complexes [460], and a planar chiral metallocene aldehyde [461]. This approach allowed the synthesis of all four enantio-pure stereoisomers of l-ferrocenyl-l,3-butanediol [462] and of 1,1-disubstituted ferrocenyl amino alcohols [463]. The reduction of porphyrins and hemoglobins by baker s yeast is long known there are only a few reports for the reduction of inorganic materials [17]. 

Recently the ylide 16 or the corresponding protonated ligands allowed, in presence of metallated bases of groups I and II (Li, K, Ba), the synthesis of the first phosphonium bridged metallocene 17 (dicyclopentadienylide) (Scheme 12). Chiral kalocene and barocene, observed only in racemic forms, have thus been obtained [57]. 

The studies summarized above clearly bear testimony to the significance of Zr-based chiral catalysts in the important field of catalytic asymmetric synthesis. Chiral zircono-cenes promote unique reactions such as enantioselective alkene alkylations, processes that are not effectively catalyzed by any other chiral catalyst class. More recently, since about 1996, an impressive body of work has appeared that involves non-metallocene Zr catalysts. These chiral complexes are readily prepared (often in situ), easily modified, and effect a wide range of enantioselective C—C bond-forming reactions in an efficient manner (e. g. imine alkylations, Mannich reactions, aldol additions). 

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