Despite being inexpensive and readily available in enantiomerically pure form, there are no applications of Werner complexes in organic synthesis. This derives from their poor solubilities in organic solvents and inaccessibility of metal the center by the substrates. Such complexes can be rendered soluble in organic solvents using large lipophilic anions like BArf– (BArf– = B(3,5-C6H3(CF3)2)4), and the N-H bonds of chiral cobalt-amine complexes can be used to activate the organic substrates by hydrogen bonding. In preliminary studies, we have found that the bifunctional Werner complexes [Co(en)2((S)-H2NCH2CH[(CH2)nNMe2]-NH2)](BArf)3 (n = 2-4), are exceptional catalysts for the Michael additions of dicarbonyls to nitroolefins. Enantioselectivities of up to 97% and yields greater than 99% were obtained in the Michael addition of malonates to nitroolefins with catalyst n = 3. These bifunctional complexes are found to be highly effective for the addition of thiols to α,β-Unsaturated N-Acylated Oxazolidin-2-ones, Friedel-Crafts reaction of ß-naphthol to nitrostyrenes. The dimethylamino group in the functionalized chelate renders an external base unnecessary. These complexes will be applied to wide varieties of organic reactions known to be catalyzed by hydrogen bond donors. This process provides synthetically useful and highly functionalized organic compounds In addition, the simple operational procedure and the use of air stable, inexpensive catalysts made this highly attractive.

Hydrogen bond mediated enantioselective organic transformations by bifunctional Werner complexes

250th National Meeting (2015)

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