A Fast‐Moving Copper‐Based Molecular Shuttle: Synthesis and Dynamic Properties

Abstract

Fast-track changes: The synthesis of a new copper-based molecular shuttle is described, with a coordinating macrocycle based on a nonhindering but endocyclic ligand (see scheme), which makes the ligand exchange easier, and thus the motions of the ring along the thread faster.The present report deals with the synthesis of a two-station [2]rotaxane consisting of a dpbiiq-incorporating macrocycle (dpbiiq: 8,8'-diphenyl-3,3'-biisoquinoline) threaded by a coordinating fragment whose complexing units are a dpp and a terpy ligand (dpp: 2,9-diphenyl-1,10-phenanthroline; terpy: 2,2',6',2"-terpyridine). The [2]rotaxane was prepared in 11 steps from commercially available or easy-to-make molecules, without taking into account the preparation of the dpbiiq-containing 39-membered ring, which was available in our group. The ring-incorporated bidentate chelate is at the same time endocyclic and sterically nonhindering, which is a specific property of the dpbiiq-coordinating unit. This unique feature has a profound influence on the rate of the ring-and-copper translation motion between the two stations of the axle. Based on an analogous multistep strategy, a related molecular shuttle has also been prepared that contains exactly the same axle and stoppers as the first compound but whose threaded ring incorporates the sterically hindering dpp chelate. The translation motions of this other system are several orders of magnitude slower than the corresponding movements of the dpbiiq-based compound. The motion corresponding to the rearrangement of the unstable five-coordinate copper(I) form of the compounds is relatively fast for both shuttles; the half lifetime of the five-coordinate Cu(I) species being below 20 ms for the dpbiiq-containing system and below 1 s for the dpp-based molecule. The reverse motion corresponding to the rearrangement of the four-coordinate copper(II) complexes is much slower, especially for the dpp-based system. It is of the order of several hours for the dpp-based shuttle and only one second or less for the dpbiiq system, under exactly the same conditions. The remarkable difference between the motion rates for the two two-station shuttles demonstrates that the use of a very open chelate such as dpbiiq is extremely beneficial in the context of fast-moving molecular machines.

Fast Pirouetting Motion in a Pyridine Bisamine‐Containing Copper‐Complexed Rotaxane

“…10 These interconversions can be induced by the application of an electrochemical potential and are characterized to be near quantitative. However, when compared with the purely organic systems, their major drawback is their long response times 11–13. A great synthetic effort has been devoted to overcome this handicap.…”

Toward unidirectional switches: 2-(2-Hydroxyphenyl)pyridine and 2-(2-methoxyphenyl)pyridine derivatives as pH-triggered pivots

“…Numerous examples of switches [15–18], rotors [19–22] and shuttles [23–28] that can be controlled chemically, electrochemically, thermally or by illumination have been described. One of the most challenging aspects in the design of molecular devices is the creation of synthetic molecular motors, which utilize the unidirectional movements of smaller parts thereof and which, thus, should be able to perform a physical task [2].…”

Two‐Color Reversible Switching in a Photochromic Ruthenium Sulfoxide Complex

“…[1][2][3] A desirable trigger is light, as it provides an ample amount of energy in a short burst of time. Although light is commonly employed for the formation of many different types of metastable states, [4][5][6][7][8] in practice it is difficult to employ light to regenerate the initial ground state.…”