MICELLAR EFFECTS UPON REACTION OF COBALT COMPLEXES WITH ALKYL-HALIDES

[The reactions of Co(I) complexes with alkylating agents to give alkyl Co(III) complexes are models for the transfer of alkyl groups mediated by vitamin B12. The effects of micellized surfactants on these reactions were studied to simulate the conditions under which these model reactions take place under biological conditions, e.g. at membrane surfaces.] The reactions of the cobaloxime Co (DH)2 and the related propane derivative. Co(DOH)DOpn0 are strongly catalyzed by cationic micelles of cetyltrimethylammonium bromide (CTABr). The rate enhancements for the cobaloxime reaction and for that of Co (DOH)DOpn0 (in parentheses) are: EtBr .apprx. 1 (8.5); n-C5H11Cl, 220 (200); ClCH2CO2, 420 (173); ClCH2CH2CO2, 373. Anionic micelles of sodium lauryl sulfate inhibit the reaction of Co(DOH)DOpn0 with ClCH2CO2, but do not affect that with n-C5H11Cl. The reactions of Co(DOH)DOpn0, like those of the cobaloxime, are SN2 displacements and in the absence of surfactant in MeOH n-PrBr is more reactive than iso-PrBr.