A Transition Metal Containing Rotaxane in Motion: Electrochemically Induced Pirouetting of the Ring on the Threaded Dumbbell
作者:Laurence Raehm、Jean-Marc Kern、Jean-Pierre Sauvage
DOI:10.1002/(sici)1521-3765(19991105)5:11<3310::aid-chem3310>3.0.co;2-r
日期:1999.11.5
In this work we describe a rotaxane in which a new type of motion, pirouetting of the wheel around its axle, can be electrochemically triggered. The rotaxane was synthesized by using the three-dimensional effect of copper(I). It incorporates both a hetero-biscoordinating ring (containing both 2,9-diphenyl-1,10-phenanthroline and 2,2':6',2"-terpyridine units) and a molecular string which contains only one 2,9-diphenyl-1,10-phenanthroline. Both ends of the string are functionnalized by a bulky stopper ( tris(p-tert-butylphenyl) (4-hydroxypbenyl)methane). Large molecular motions have been induced electrochemically in this molecule and were detected by using cyclic voltammetry. The driving force of the two rearrangement processes observed is the high stability of two markedly different coordination environments for copper(I) and copper(II) ions. In the copper(I) state, two phenanthroline units tone of the ring, one of the string) interact with the metal in a tetrahedral geometry (Cu-(4)(I)), whereas in the copper(II) state the five-coordinate geometry (Cu-(5)(II)) is due to the phenanthroline of the string and to the terpyridine of the ring. The kinetic rate constants of the two molecular motion processes (from Cu-(5)(I)) to Cu-(4)(II)) and fom Cu-(4)(II)) to Cu-(5)(II))) have been determined and both rates are much faster than the ones in previously studied analoguous systems. In addition, the rate of the pirouetting motion depends greatly on the copper oxidation state. The divalent four-coordinate copper complex (Cu-(4)(II))) rearranges in tens of seconds, whereas the monovalent five-coordinate copper system leads to the four-coordinate complex in the millisecond time scale.