title: Werner Complexes with ω-Dimethylaminoalkyl Substituted Ethylenediamine Ligands: Bifunctional Hydrogen-Bond-Donor Catalysts for Highly Enantioselective Michael Additions.
abstract: The racemic carbonate complex [Co(en)2 O2 CO](+) Cl(-) (en=1,2-ethylenediamine) and (S)-[H3 NCH((CH2 )n NHMe2 )CH2 NH3 ](3+) 3 Cl(-) (n=1-4) react (water, charcoal, 100 °C) to give [Co(en)2 ((S)-H2 NCH((CH2 )n NHMe2 )CH2 NH2 )](4+) 4 Cl(-) (3 a-d H(4+) 4 Cl(-) ) as a mixture of Λ/Δ diastereomers that separate on chiral-phase Sephadex columns. These are treated with NaOH/Na(+) BArf (-) (BArf =B(3,5-C6 H3 (CF3 )2 )4 ) to give lipophilic Λ- and Δ-3 a-d(3+) 3 BArf (-) , which are screened as catalysts (10 mol %) for additions of dialkyl malonates to nitroalkenes. Optimal results are obtained with Λ-3 c(3+) 3 BArf (-) (CH2 Cl2 , -35 °C; 98-82 % yields and 99-93 % ee for six β-arylnitroethenes). The monofunctional catalysts Λ- and Δ-[Co(en)3 ](3+) 3 BArf (-) give enantioselectivities of <10 % ee with equal loadings of Et3 N. The crystal structure of Δ-3 a H(4+) 4 Cl(-) provides a starting point for speculation regarding transition-state assemblies.
authors.affiliation: Department of Chemistry, Texas A&M University, PO Box 30012, College Station, TX, 77842-3012, USA.
authors.forename: Subrata K
authors.initials: SK
authors.lastname: Ghosh
authors.affiliation: Institut für Organische Chemie and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Henkestrasse 42, 91054, Erlangen, Germany.
authors.forename: Carola
authors.initials: C
authors.lastname: Ganzmann
authors.affiliation: Department of Chemistry, Texas A&M University, PO Box 30012, College Station, TX, 77842-3012, USA.
authors.forename: Nattamai
authors.initials: N
authors.lastname: Bhuvanesh
authors.affiliation: Department of Chemistry, Texas A&M University, PO Box 30012, College Station, TX, 77842-3012, USA. gladysz@mail.chem.tamu.edu.
authors.forename: John A
authors.identifier: http://orcid.org/0000-0002-7012-4872
authors.initials: JA
authors.lastname: Gladysz
keywords: Michael additions; cobalt complexes; enantioselective catalysis; hydrogen bonding; nitroalkenes