Hydrogen bonding motifs in structurally characterized salts of the tris(ethylenediamine) cobalt trication, [Co(en)3]3+; An interpretive review, including implications for catalysis
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© 2017 Elsevier B.V. Werner tris(1,2-diamine) cobalt(III) complexes have emerged as a powerful class of hydrogen bond donor catalysts for enantioselective organic synthesis. Mechanistic insight is sought by examining the structures of salts of the parent trication [Co(en)3]3+ (en = ethylenediamine), more than 150 of which have been crystallographically characterized. First, fundamental stereochemical features of the trication (symmetry, cobalt configuration, chelate conformation), and its resolution into enantiomers, are reviewed. Interactions between the trication and counter anions are then analyzed in detail. Hydrogen bonding is always observed, even when the anions are poor hydrogen bond acceptors, and a systematic nomenclature is developed. Some hydrogen bonding patterns recur, and a few are conspicuously absent. However, there are no “conserved motifs”. This suggests that this catalyst family is capable of varied types of interactions with organic substrates, and diverse modes of catalytic activation.
author list (cited authors)
Ghosh, S. K., Ehnbom, A., Lewis, K. G., & Gladysz, J. A.