Chiral Recognition of α-Amino Acids by an Optically Active (2S,5S,8S,11S)-2,5,8,11-Tetraethyl Cyclen Cobalt(III) Complex

The optically active cobalt(III) complex with chiral cyclen, (2S,5S,8S,11S)-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane, preferentially binds to d-phenylglycine (d-Phg) or d-t-leucine (d-t-Leu) rather than l-Phg or l-t-Leu, respectively, with 20% de in dimethyl sulfoxide at 293 K. Comparative studies on the crystal structures of cobalt(III) complexes with d-Phg and l-Phg revealed that the diastereoselectivity is due to the difference in the steric hindrance that should occur between the amino group of Phg and the ethyl group of cyclen.