Off-Equilibrium Speed Control of a Multistage Molecular Rotor: 2-Fold Chemical Fueling by Acid or Silver(I)

Driving conformational motion in defined off-equilibrium oscillations can be achieved using chemical fuels. When the ultrafast turnstile 1 (k₂₉₈> 10¹² Hz) was fueled with 2-cyano-2-phenylpropanoic acid (Fuel 1), the diprotonated rotor [H₂(1)]²⁺ (k₂₉₈ = 84.0 kHz) formed as a transient regaining the dynamics of the initial turnstile after consumption of the fuel (135 min). Upon addition of silver(I) (Fuel 2) to turnstile 1, the metastable rotor [Ag₂(1)]²⁺ (k₂₉₈ = 1.57 Hz) was initially furnished, but due to a consequentially triggered S_N2 reaction, the Ag⁺ ions were consumed as insoluble AgBr along with regeneration of 1 (within 3 h). The off-equilibrium fast ⇆ slow rotor conversions fueled by acid and silver(I) were directly monitored by fluorescence and ¹H NMR. In addition, metal ion exchange was fueled enabling off-equilibrium oscillations between rotors [Li₂(1)]²⁺ ⇆ [Ag₂(1)]²⁺. In the end, both sustainability and efficiency of the process were increased in unison by using the interfering proton waste in the formation of a [2]pseudorotaxane.