Fixing the chirality and trapping the transition state of helicene with atomic metal glue.

By combining the intriguing geometrical properties of two classes of well-established molecules, the metallocenes and the helicenes, we propose a hybrid class of structures-the metallohelicenes. In these, the outer most aryl groups of a specific helicene are glued together by a complexing metal atom. This effectively fixes the chirality of the parent helicene, which otherwise easily undergoes thermal racemization. The fixed chirality suggests several interesting applications, ranging from building blocks of stable molecules with high circular dichroism and optical activity to chiral ligands and catalysts. Alternatively, the metal glue can trap the non-chiral transition state structure of helicene. High-level quantum chemical calculations show the readiness of formation and stability of the proposed complexes.