Indole rings are prevalent in natural products and bioactive compounds. Recently, cationic cobalt(III) half-sandwich complexes have shown catalytic activity in intermolecular cyclization reactions with anilines and alkynes to form indole rings. We wanted to explore the use of other cationic Co(III) complexes utilizing C-H bond functionalization for the formation of indole rings. As such, we synthesized trans-dichlorotetrakis(imidazole)cobalt(III) chloride (1) utilizing ligand substitution reactions beginning with the known complex, trans-dichlorotetrakis(pyridine)cobalt(III) chloride. Evidence for the formation of 1 has been obtained through 1H and 13C NMR and elemental analysis. Complex 1 is both cationic and contains a Co(III) metal center leading us to believe that it may be able to catalyze intermolecular cyclization reactions to form indole rings. Interestingly, 1 is structurally very different than the known half-sandwich complexes and would greatly expand the class of cationic Co(III) catalysts that may be utilized. Preliminary 1H NMR data for catalytic testing of 1 shows the formation of an indole product from N-nitrosoaniline and diphenylacetylene starting materials.

Synthesis of a new cationic cobalt(III) coordination complex and its potential applications as an indole ring forming catalyst

253rd National Meeting (2017)

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