Preparation and structural characterization of η5-pentamethylcyclopentadienylcobalt(III) complexes of α-amino acids with coordinating side chains

The complexes [(η 5 -Cp★)CoCl( l -phe)] ( 3 ) and [(η 5 -Cp★)CoCl( l -pro)] ( 4 ), which contain bidentate α-amino acidate ligands, were prepared by the reaction of [(η 5 -Cp★)Co(μ-Cl) 3 Co(η 5 -Cp★)]FeCl 4 ( 1 ) with the appropriate α-amino acid at room temperature. An analogous complex [(η 5 -Cp★)CoCl( dl -pipe)] ( dl -pipeH = dl -pipecolinic acid) was synthesized, as were the remaining complexes, using [(η 5 -Cp★)Co(μ-Cl)Cl] 2 ( 2 ) instead of 1 and its structure was established by an X-ray study. Tridentate coordination of the cobalt atoms by α-amino acidate ligands is observed for [(η 5 -Cp★)Co( l -his)]PF 6 ( 6b ), [(η 5 -Cp★)Co( l -aspH −1 )] ( 7a ), [(η 5 -Cp★)Co( l -penH −1 )] ( 8 ) and [(η 5 -Cp★)Co( l -met)] FeCl 4 ( 9a ). An X-ray study of 9a confirmed an N, O, S coordination of the chiral cobalt atom. In [(η 5 -Cp★)Co( l -aspH −1 ) ]·LiCl·3H 2 O ( 7b ) the [ l -aspH −1 ] 2− dianion adopts a μ 3 -(1κ 3 NO , O′ :2κ 1 O′ :3κ 1 O′ ) coordination mode in bridging the cobalt and two lithium atoms. A μ 2 -(1κ 3 N , O , S :2κ 1 O′ ) mode is displayed by the [ l -S-Mecys] anion in [(η 5 -Cp★)Co(μ- l -S-Mecys)CoCl 3 ] ( 11 ), which contains Co III and Co II atoms.