Ionic Rotors. Preparation, Structure, and Dynamic Solid-State ~2D NMR Study of the 1,4-Diethynylbenzenebis(triphenylborate) Dianion

摘要

The incorporation of moving parts into molecular compounds is a topic of current interest with regard to the development of molecular machines. This interest is fueled in part by the desire to manipulate matter on the small scale. Since macroscale gyroscopes can be used in guidance systems, similar functions can be envisioned in micro- or nanoscale devices. Therefore, research into developing molecular "gyroscopes" has attracted considerable interest as of late. Molecular gyroscopes consist of rotors encased in a protective scaffold to allow freedom of motion to the internal component. Recently, elegant work by Garcia-Garibay's group on systems with a diethynylphenylene rotor connected between two trityl groups (middle of Figure 1) has shown that it is possible to control the rate that the central phenyl ring rotates in the solid state by appropriately substituting groups on the ligand periphery. Crystal packing interactions (such as CH-π and π-π interactions) involving these charge-neutral compounds or their solvates dictate the rotational velocity of the central phenylene ring; the more substituted the trityl/trypticenyl end groups, the more isolated the central rotors, and the faster the central phenylene rotation. This is clearly evident in the 10 increase in room temperature phenylene rotation rates between the p-(Ph_3CC_2)_2C_6H_4 and p-[(3,5-~tBu_2C_6H_3)_3-CC_2)_2C_6H_4 derivatives.