Optically active transition metal compounds .112. Synthesis of chiral carbonylnitrosylcobalt complexes with bidentate PP*, PN* and NN* ligands

The substitution of two carbonyl groups in Co(CO)(3)(NO) by optically active unsymmetrical bidentate ligands LL* yields pairs of diastereomers Co(CO)(NO)(LL*), which differ only in the configuration at the Co atom. LL* can be a bisphosphane, trisphosphane, phosphaneimine or pyridineimine. For the complexes 2 (LL* = (S,S)-norphos), 3 (LL* = (R)-1,2,4-triphos) and 4 (LL* = (R)-1,2,5-triphos) the diastereomer ratios of 45:55 (2a:2b), 83:17 (3a:3b) and 63:37 (4a:4b) respectively indicate an optical induction from the Ligand to the metal configuration during the synthesis. By crystallization it is possible to separate the diastereomers of 1 (LL* = (R)-prophos), 2 and 3. 1a and 3a are obtained as pure diastereomers, 2a as an enriched sample (2a:2b 73:27). The crystal structures and absolute configurations of (S-Co,R-C)-1a and (S-Co,R-C)-3a were determined by X-ray analysis. In 3a the cobalt center is configurationally stable at room temperature, whereas 1a epimerizes in benzene-d(6) at 35 degrees C with a half-life of tau(1/2) = 141 min and 2a in CDCl3 at 24 degrees C with tau(1/2) = 160 min. (C) 1997 Elsevier Science S.A.