Stepwise helicity inversions by multisequential metal exchange.

Development of artificial helical molecules that can undergo responsive helicity inversion has been a challenging research target in functional molecular chemistry. However, most reported helicity inversions are based on a single-mode transition, i.e., the conversion between right- and left-handed states. We report here the first molecular system that allows stepwise multisequential helicity inversion utilizing metal exchange of helical complexes derived from a hexaoxime ligand, H6L(1). The ligand H6L(1) underwent a four-step conversion (H6L(1) → L(1)Zn3 → L(1)Zn5 → L(1)Zn3Ba → L(1)Zn3La) upon sequential metal addition (Zn(2+), Ba(2+), then La(3+)). Associated with the conversion, three-step helicity inversion took place (L(1)Zn3, right-handed → L(1)Zn5, left-handed → L(1)Zn3Ba, right-handed → L(1)Zn3La, left-handed). This is the first example of stepwise multimode helicity inversion of a discrete molecule, which could be useful as a platform for construction of dynamic regulation systems with multiple asymmetric functions.