GENERATION OF AN OPTICALLY-ACTIVE OCTAHEDRAL COBALT COMPLEX BY A CHIRAL AUTOCATALYSIS

Optically active cis-[CoBr(NH3)(en)(2)]Br-2 could be readily obtained by the reaction of optically inactive [Co(H2O)(2){(OH)(2)Co(en)(2)}(2) ](SO4)(2) with ammonium bromide in a water suspension. The optically a ctive cis-[CoBr(NH3)(en)(2)]Br-2 was not readily racemized in its aque ous solution, indicating it not to be produced by total spontaneous re solution but by asymmetric synthesis. This synthesis was exclusively o bserved when the weight ratio of [Co(H2O)(2){(OH)(2)Co(en)(2)}(2)](SO4 )(2) to water was above 0.31. Since the crystal of each enantiometer o f cis-[CoBr(NH3)(en)(2)]Br-2 introduced into the reaction system lead to the preferential production of the same enantiomer, chiral autocata lysis was shown to be performed during the reaction. In the concentrat ed suspension, crystallization of cis-[CoBr(NH3)(en)(2)]Br-2 that was produced by the reaction would be started during the relatively early stage of the reaction. If several crystals to be initially produced ar e enantiomerically unequivalent by statistical fluctuation, it may cau se the spontaneous generation of the enantiomeric predominance.