Precursors to new molecular tube ligands. 1. Double-capped trinuclear cobalt complexes of aminoethanethiol

Co(SCH2CH2NH2)(3) has been capped on the facial amines through protection of the thiolates by coordination of two such complexes to a central Co(III) ion. The trinuclear species forming the framework is the complex ion [Co{Co(SCH2CH2NH2)(3)}(2)](3+), 1, in meso and rac forms which have been chromatographically separated and identified. Hexaimine derivatives of 1, [Co{Co(SCH2CH2N=CH2)(3)}(2)](3+), 2, have been synthesized in good yield by reaction with excess paraformaldehyde and base in CH3CN. The hexaimines have been reacted with NH3 to yield dicapped aza species [Co{Co(SCH2CH2NHCH2)(3)N}(2)](3+), 3, Or reacted with nitromethane to yield the nitro-capped ions [Co{Co(SCH2CH2NHCH2C)(3)CNO2}(2)](3+), 4. The reactions are retentive; i.e., meso reactant yields meso product. All of the products have been characterized by H-1 NMR, C-13 NMR, and UV-vis spectroscopy. Electrochemical measurements (CV and de coulometry) in CH3CN indicate that the central Co(III) ion in all of the species is reduced first, followed by the two terminal Co(III) centers. The formal potentials show that the Co(III) oxidation state is stabilized by the six thiolate bridging ligands in comparison to six thioether donor atoms, whereas capping has a destabilizing effect.