The hydrolysis of the anhydride of 2-cyano-2-phenylpropanoic acid triggers the repeated back and forth motions of an acid–base operated molecular switch

This work aimed to render phenomenologically autonomous the otherwise stepwise operation of a catenane-based molecular switch, which is chemically triggered by the decarboxylation of 2-cyano-2-phenylpropanoic acid (2). Given that any amount of 2 in stoichiometric excess with respect to the catenane is consumed in a side reaction, the authors resorted to the corresponding anhydride 5, the slow hydrolysis of which, due to adventitious water in dichloromethane, continuously produces in situ the actual fuel 2. As a consequence, the machine does not require a reloading after each cycle, but switches back and forth as long as fuel is present.