Chiral metal complexes part 37. A new stereospecific N4 tetradentate, N,N′-di(2-picolyl)-N′-methyl-2S-aminomethylpyrrolidine, S-picpyrrMe, and the crystal structures of its ternary Λ-α1-[ConIII(S-picpyrrMe)(L)]2+ ions (LS-or R-alaninate)

Ronald R. Fenton, Frederick S. Stephens, Robert S. Vagg*, Peter A. Williams

*Corresponding author for this work

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

A new linear N4 tetradentate with terminal pyridyl groups, N,N′-di(2-picolyl)-N′-methyl-2-aminomethylpyrrolidine, S-picpyrrMe, has been synthesized via a six-step process in 19% yield from the naturally-occurring α-amino acid S-proline. The ligand stereospecifically adopts a λ-α topology on coordination to cobalt(III) when isolated as the dichloro complex. This configuration is retained on substitution of the chloro ligands by nitrite or R- or S-alaninate ions. The products were characterised by their electronic absorption and chiroptical properties and by 1H NMR. The low-temperature crystallographic analyses of the R- and S-alaninate complexes are reported. λ- α1-[Co(S-picpyrrMe)(R-ala)](ClO4)2 crystallises in the monoclinic space group P21 with a =10.888(4), b=10.243(4), c=12.365(6) Å,β=109.37(3)° and Z=2; λ-α1-[Co(S-picpyrrMe)(S-ala)](ClO4)2· 1 2H2O crystallises in the orthorhombic space group P212121 with a =10.580(8), b= 14.391(8), c=18.078(7) Å and Z=4. The structures were refined by full-matrix least-squares procedures to R=0.046 for 1662 reflections and R=0.046 for 1771 reflections, respectively. In each case the amino acid coordinates as a N,O-bidentate, completing a CoN5O octahedral coordination sphere with α1 topology. The average CoN(pyridine) distance is 1.955(8) Å and the CoN(tertamine) distances are 1.996(8) and 1.979(8) Å for the methylated and pyrrolidine amines, respectively. The R-alaninate chelate ring is considerably flattened due to a steric interaction between its methyl group and a pyridyl ring of the tetradentate, whereas the S-alaninate has an unstrained puckered conformation.

Original languageEnglish
Pages (from-to)233-242
Number of pages10
JournalInorganica Chimica Acta
Volume197
Issue number2
DOIs
Publication statusPublished - 15 Jul 1992

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