Nickel complex compounds, with resolution

Optical resolution of some hydrocarbonds and halogeno compounds by inclusion complexation with the chiral host (9a) has been accomplished.11,12 Preparation of optically active hydrocarbons is not easy and only a few example of the preparation of optically active hydrocarbons have been reported. For example, optically active 3-phenylcyclohexene has been derived from tartaric acid through eight synthetic steps.11 Although one-step synthesis of optically active 3-methylcyclohexene from 2-cyclo- hexanol by the Grignard reaction using chiral nickel complex as a catalyst has been reported, the enantiomeric purity of the product is low, 15.9%.11 In this section, much more fruitful results by our inclusion method are shown. 

Study of the structures of metal-amino acid complexes is a classical problem initiated by the school of Pauling in the 40s, with the nickel-glycine compound. Many authors have worked in this direction with increasing resolution and details. This paper describes the single-crystal structure of [bis(L-alaninato)diaqua] Nickel(II) dihydrate. 

If one enantiomer obtained by resolution is the desired one, the other recovered from the mother liquor of the resolution should be racemized to use for the next resolution. In general, whether the racemization method for unwanted enantiomer is known or not will be key to producing optically active compounds on an industrial scale. In most cases, optical resolution and racemization are non-divisable for the realization of a practical and economical process. For instance, nickel chloride complex of DL-a-amino-e-caprolactam has been successfully resolved. The complex, dissolved in ethanol, was heated and inoculated with enantiopure complex, then racemization and crystallization of the complex occurred at the same time. As a result,... 

Wilke and coworkers showed that trialkylaluminum compounds reduce nick-el(II) complexes to nickel(O) and they proposed that complexation of the sec-busal to the aluminum, to generate a chiral aluminum species, could also be responsible for the observed effects [12]. Giacomelli and coworkers later reported that the use of a chiral amine, as a Lewis base complex with the trialkylalane, gave products with a small optical rotation in the attempted resolution of some racemic olefins, although as above, the enantioselectivities were extremely low (<1%) [18]. Notably, the authors mention that the use of (-)-(DIOP)NiCl2 (DI-OP=2,3-0-isopropylidene-2,3-dihydroxy-l,4-bisdiphenylphosphinobutane) as a precatalyst gave products lacking an optical rotation. 

Kirschner and Ahmadhave applied the Pfeiffer effect to the resolution of complex inorganic compounds. These authors allowed a Pfeiffer effect to develop in the initially racemic nickel(II) tris(2,2 -dipyridyl) complex in levo-mahc acid, and then succeeded in freezing out the non-equimolar mixture of enantiomers from the system by means of precipitation of the enantiomers as the relatively insoluble perchlorates. These insoluble perchlorates were then redissolved by allowing an aqueous suspension of them to come in contact with Amberlite IRA-400 anion exchange resin in the chloride form, and the optical rotation of a solution of the soluble complexes (as chlorides) was then read on a photoelectric polarimeter. Table 2 shows the optical rotations of this complex, and Fig. 7 shows a comparison of the... 

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