PREPARATION AND STRUCTURAL CHARACTERIZATION OF ETA(5)-PENTAMETHYLCYCLOPENTADIENYLCOBALT(III) COMPLEXES OF ALPHA-AMINO-ACIDS WITH COORDINATING SIDE-CHAINS

The complexes [(eta5-Cp)CoCl(L-phe)] (3) and [(eta5-Cp*)COCl(L-pro)] (4), which contain bidentate alpha-amino acidate ligands, were prepare d by the reaction of [(eta5-Cp)Co(mu-Cl)3Co(eta5-Cp*)]FeCl4 (1) with the appropriate alpha-amino acid at room temperature. An analogus CoMp lex [(eta5-Cp)CoCl(DL-pipe)] (DL-pipeH = DL-pipecolinic acid) was syn thesized, as were the remaining complexes, using [(eta5-Cp)Co(mu-Cl)C I]2 (2) instead of 1 and its structure was established by an X-ray stu dy. Tridentate coordination of the cobalt atoms by alpha-amino acidate ligands is observed for [(eta5-CP)Co(L-his)]PF6 (6b), [eta5-CP*)Co(L -aspH-1)] (7a), [(eta5-Cp)Co(L-penH-1)] (8) and [(eta5-Cp*)Co(L-met)] FeCl4 (9a). An X-ray study of 9a confirmed an N, 0, S coordination of the chiral cobalt atom. In [(eta5-Cp)Co(L-aspH-1)] . LiCl . 3H2O (7b) the [L-aspH-1]2- dianion adopts a mu3-(1kappa3N,O,O':2kappa1O':3kappa 1O') coordination mode in bridging the cobalt and two lithium atoms. A mu2-(1kappa3N,O,S:2kappa1O') mode is displayed by the [L-S-Mecys] ani on in [(eta5-CP)Co(mu-L-S-Mecys)CoCl3] (11), which contains Co(III) a nd Co(II) atoms.