Synthesis, characterization and stereochemical preferences of cobalt(II) ternary amino acid complexes containing N-((2-pyridyl)methyl)- 2((2-aminoethyl)thio)acetamide, a stereospecific linear NSNN tetradentate ligand

Paul J. Toscano, Kimberly A. Belsky, Tze Chen Hsieh, Terrence Nicholson, Jon Zubieta

Research output: Contribution to journalArticle

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Abstract

The preparation, isolation and characterization of cis-β-[Co(pyge)(AA)]PF6 [pygeH = N-((2-pyridyl)methyl)-2-((2-aminoethyl)thio) acetamide; AA = gly, L-ala, L-ile, L-leu, sarcosine (sar), α-aminoisobutyric acid (aiba) and β-ala] are described. 1H and 13C NMR spectra of the new cobalt complexes strongly suggest that one geometrical isomer is obtained with very high stereoselectivity. β1- [Co(pyge)(gly)]PF6·2H2O (1) crystallized in the monoclinic space group P21/c with a = 14.518(2), b = 14.583(2), c = 19.783(3) Å, β = 98.51(1)° and Z = 8 and was refined to R = 0.080. In both of the two independent cations in the asymmetric unit, the gly chelate had the β1 configuration with respect to the pyge ligand. The complex β-[Co(pyge)(Cl)(NO2)]·H2O was prepared; recrystallization of this complex provided single crystals of β-[Co(pyge)(Cl)(NO2)]·[Co(pyge)(NO2)2]·2H2O (2). Complex 2 crystallized in the triclinic space group P1 with a = 7.850(1), b = 13.346(2), c = 15.998(2) Å, α = 106.45(1), β = 99.07(1), γ = 104.78(1)° and Z = 2, and was refined to R = 0.052. The chlorine ligand was found to be trans to the amido donor of the pyge ligand, suggesting that the β1 configuration found for the amino acid complexes stems from kinetically-based substitutions. The complex β-[Co(pyge)Cl2]·H2O promotes the hydrolysis of amide and ester bonds of dipeptides and amino acid esters to again give β1-[Co(pyge)(AA)]PF6. Finally, evidence is presented for sar and L-ala, that the diastereomeric β1 complex that predominates at equilibrium is the isomer with the ligand methyl group hydrophobically interacting with the pyridyl moiety of the pyge ligand.

Original languageEnglish (US)
Pages (from-to)977-991
Number of pages15
JournalPolyhedron
Volume10
Issue number9
DOIs
StatePublished - 1991
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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