Phosphorus(V) Porphyrin-Based Molecular Turnstiles

A new cationic molecular
turnstile based on a P­(V) porphyrin backbone bearing two pyridyl interaction
sites, one at the meso position of the porphyrin and the other on
the handle connected to the porphyrin through P–O bonds, was
designed and synthesized. The dynamic behavior of the turnstile 2, investigated by 1D and 2D 1H NMR techniques,
showed that in the absence of an effector, the turnstile is in its
open state and undergoes a free rotation of the rotor (the handle)
around the stator (the porphyrin backbone). In the presence of an
external effector such as Ag+ cation or H+,
the turnstile is switched to its closed states 2-Ag+ and 2-H+, respectively. The locking/unlocking
process is reversible and may be achieved by precipitation of AgBr
upon addition of Et4NBr in the case of the silver-locked
turnstile or by addition of Et3N in the case of the proton-locked
turnstile.