Towards Redox-Driven Unidirectional Molecular Motion

Redox‐driven molecular motion is an attractive alternative to light‐driven processes. Here, the ability of an overcrowded alkene‐based unimolecular light‐driven rotary motor (A) to be driven by oxidation/reduction cycles is explored. We show that two‐electron oxidation of A is followed by irreversible deprotonation and reduction to form a monocationic species D+, in which the stereogenic center is lost. This latter species was isolated through preparative electrolysis and its structure was confirmed by using single‐crystal X‐ray analysis. However, at short timescales and in the absence of Brønsted acids, these processes can be outrun and the oxidation of A to a dicationic species B2+ occurs, in which the central double bond (the axle of the molecular motor) becomes a single bond; when followed by rapid reduction, it results in the reformation of A, potentially in both its stable and unstable conformations. The latter conformation, if formed, undergoes thermal helix inversion, completing a rotary cycle. The data obtained regarding these reactions provide a window of opportunity for the motor to be driven electrochemically, without degradation from chemical reactions of the oxidized motor. Motion granted: Redox‐driven switching between conformational states competes with electrochemical oxidation on the path to a unidirectional redox‐driven molecular rotary motor.