Mechanism of chiral asymmetry generation by chiral autocatalysis in the preparation of chiral octahedral cobalt complex

✍ Scribed by Kouichi Asakura; Dilip K. Kondepudi; Reesheda Martin

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 125 KB
• Volume: 10
• Category: Article
• ISSN: 0899-0042
• DOI: 10.1002/(sici)1520-636x(1998)10:4<343::aid-chir9>3.0.co;2-8

✦ Synopsis

Chiral asymmetry generation, the predominant production of one enantiomer in a non-chiral environment, could occur in the production of the chiral complex cis-[CoBr(NH 3 )(en) 2 ]Br 2 by the reaction of [Co(H 2 O) 2 {(OH) 2 Co(en) 2 } 2 ](SO 4 ) 2 with ammonium bromide in an aqueous medium. The main kinetic steps in the reaction system have been determined. During the reaction, the product crystallizes at an early stage. When a very small amount of crystalline enantiomer was added to the reaction system at an early stage, the same enantiomer was produced preferentially; in addition, the enantiomeric excess of the product increased with increasing the stirring rate. Thus, it seems that each enantiomer generates chiral crystals that could self-replicate through secondary nucleation when the solution is stirred; these crystals in turn enhance the production of the same enantiomer. With a computer code that simulates such a kinetic mechanism, it is shown that enantiomeric excess observed in the experiments could be reproduced.