CHIRAL METAL-COMPLEXES .37. A NEW STEREOSPECIFIC N4 TETRADENTATE, N,N'-DI(2-PICOLYL)-N'-METHYL-2S-AMINOMETHYLPYRROLIDINE, S-PICPYRRME, AND THE CRYSTAL-STRUCTURES OF ITS TERNARY LAMBDA-ALPHA(1)-[CO(III)(S-PICPYRRME)(L)]2+ IONS (L = S-ALANINATE OR R-ALANINATE)

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 alpha-amino acid S-proline. The ligand stereospecifically adopts a LAMBDA-alpha 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 H-1 NMR. The low-temperature crystallographic analyses of the R- and S-alaninate complexes are reported. LAMBDA-alpha1-[Co(S-picpyrrMe)(R-ala)](ClO4)2 crystallises in the monoclinic space group P2(1) with a = 10.888(4), b = 10.243(4), c = 12.365(6) angstrom, beta = 109.37(3)-degrees and Z = 2; LAMBDA-alpha1-[Co(S-picpyrrMe)(S-ala)](ClO4)2.1/2H2O crystallises in the orthorhombic space group P2(1)2(1)2(1) with a = 10.580(8), b = 14.391(8), c = 18.078(7) angstrom 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 alpha1 topology. The average Co-N(pyridine) distance is 1.955(8) angstrom and the Co-N(tert-amine) distances are 1.996(8) and 1.979(8) angstrom 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.