Optically active transition metal compounds 113 - Synthesis of chiral carbonylnitrosylcobalt complexes with four different unidentate ligands

In a two step synthesis pairs of diastereomers Co(CO)(NO)(L)(L*), which differ only in the configuration at the cobalt atom, are obtained from Co(CO)(3)(NO). L is a monodentate phosphite or phosphane and L* a monodentate optically active phosphane or isocyanide. For complex 8 (L = PPh3, L = phenyl-tarpholane) a diastereomer ratio of 55:45 (8a:8b) is found after the synthesis. For all other complexes this ratio is 50:50. By crystallization it is possible to obtain samples enriched in one of the diastereomers of 1 (L = P(OMe)(3), L* = PPh2N(Me)CH(Me)(Ph)), 2 (L = PPh3, L* = CNCH(Me)Ph)), 7 (L = PMe2Ph, L* = glyphos) and 8. The ratios achieved are 74:26 (1a:1b), 79:21 (2a:2b), 71:29 (7a:7b) and 74:26 (8a:8b). The crystal structures of six complexes were determined. For (S-Co,S-C)-2a, (R-Co,S-C)-3b and (S-Co,R-C,R-C)-8a the absolute configuration could be established. The cobalt center is configurationally stable at room temperature. Epimerization is observed only at higher temperatures, 1a epimerizes in toluene-d(8) at 82.2 degrees C with a half life of tau(1/2) = 43 h, 2a in benzene-d(6) at 72.9 degrees C with tau(1/2) = 83 min and 7a in benzene-d(6) at 70.0 degrees C with tau(1/2) = 77 min. (C) 1998 Elsevier Science S.A. All rights reserved.