Abstract
The reactivity of the __h__exa(N‐__m__ethylidene__i__mine)Co^III^ complex [Co‐hmi‐(taci)~2~]^3+^ (taci = 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) towards the nucleophiles ammonia, aniline and cyanide was investigated and the main products were identified by spectroscopic methods and by a crystal structure analysis. The relative energies of the complexes formed and those of possible stereo isomers were analysed by means of molecular mechanics calculations. In the reaction with NH~3~, two condensation products, [Co(L^a^)]^3+^ and [Co(L^b^)]^3+^, were identified with the two taci moieties linked by one or two N=CH–N(H)‐CH~2~–NH bridges, respectively. The reaction with aniline yielded the complex [Co(L^c^)(L^d^)]^3+^ (where L^c^ is a mono‐N‐methylated and L^d^ a phenylformamidine‐substituted taci), whereas the reaction with cyanide resulted in the formation of [Co(L^e^)]^3+^ having an NH–CH~2~–C(NH~2~)=N bridge between the two taci subunits. A mechanism that accounts for the different types of products can be suggested as follows: In [Co(L^a^)]^3+^, [Co(L^b^)]^3+^ and [Co(L^c^)(L^d^)]^3+^, N‐methylation was observed and this can be interpreted in terms of an intramolecular Cannizzaro type hydride shift. For [Co(L^a^)]^3+^ and [Co(L^b^)]^3+^ two subsequent addition steps of the nucleophile to adjacent imino groups must take place prior to the hydride shift, whereas for [Co(L^c^)(L^d^)]^3+^ the hydride shift appears to have already occurred after the first addition step of aniline to an imino group. Formation of [Co(L^e^)]^3+^ can be explained in terms of a nucleophilic attack of CN^–^ to an imino group and a subsequent attack of a deprotonated amino group (which must have previously been formed by hydrolysis of a methylideneimino group) to the nitrile C‐atom. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)