Rotaxane metal complex

Intramolecular mobility of metal complexes of rotaxanes and catenanes with macroheterocyclic fragments 98ACR611. 

Electrochemically Driven Molecular Machines Based on Transition-metal Complexed Catenanes and Rotaxanes... 

In 1979, Maciejewski et al. also explored Method 3 for the preparation of main-chain poly(vinylidene chloride-/ -CD rotaxane) 35 [74, 75]. Radiation polymerization and AIBN-initiated solution polymerization of the complex of vinyli-dene chloride with 21 gave products with min = 0.34 and 0.49, respectively. However, the polyrotaxane via Method 1 had a much lower min (0.087) with much lower CD/monomer feed ratio than for those via the polymerization of the complex (1 1 ratio). Therefore, the reported min values are not comparable, so the difference between the two methods in terms of threading efficiencies cannot be distinguished. Although the authors did not see any threading via Method 2 for the same polyrotaxanes, Ogino and coworkers prepared a true CD-based polyrotaxane of Type 5 using metal complexes as stoppers [76]. It was also found that... 

There are also chiral topological supramolecular structures in molecular knots, rotaxanes, catenanes, and Borromean rings with metal complexes.73,74... 

The [2]-rotaxane 81 of Figure 2.28 owes its existence to transition metal-complex fragments as stoppers.60 The thread 77 designed for its synthesis... 

Another area of NEMS that is receiving tremendous attention is the mimicry of biological systems, aptly referred to as biomimetics. For instance, in the development of linear molecular muscles that undergo contraction and extension movements. Initial work in this field utilized transition metal complexes containing rotaxanes and catenanes, due to the nondestructive redox processes occurring on the metal centers.Though these complexes were actuated by a chemical reaction, the movement was in a noncoherent manner. In order to better mimic skeletal muscle movement, one has to look at the mode of motion within the most efficient molecular machines - in our human bodies. 

Figure 35 Copper (I)-templated synthesis of metal-complexed [2]-rotaxane (105) bearing...

Figure 43 Principle of transition metal-templated construction of a [2]-rotaxane with two different porphyrinic stoppers (same conventions as in Figure 42). (i) Macrocycle (A) is threaded onto chelate (B), end-blocked by a porphyrin at one extremity and fiaictionalized with a reactive group X, which is a precursor to the second porphyrin stopper, affording prerotaxane (C) (ii) construction of the second porphyrin, leading to metal-complexed [2]-rotaxane (D).

Preliminary experiments showed that the light emission of the zinc porphyrins was strongly quenched in the case of the metallo-rotaxanes, and, remarkably, also in the case of the free [2]-rotaxane. Whereas for the metallo-rotaxanes, the possibility that the central metal-complex ftagment participates in the quenching process cannot be ruled out, for the [2]-rotaxane, it is clear that the only mechanism is through-space electron transfer to the gold(III) porphyrin moiety appended to the macrocycle. 

More recently, a similar approach was taken by Macartney and coworkers to synthesize [2]rotaxanes (Figure 4). Rotaxane 2 is self-assembled efficiently in solution from a-CD, [Fe(CN)5(H20)] and l,l -( f5 -alkanediyl)bis(4,4 -pyridyl-pyridium) ion. The [2]rotaxane is also formed by the addition of a-CD to a solution of the dumbbell component [(CN)5Fe(bpy(CH2)nbpy)Fe(CN)5]. This result infers a slow dissociation of the terminal metal complex, followed by formation of an intermediate pseudorotaxane and reassociation of the metal complex. 

Figure 3 [2]Rotaxanes constructed fn>m a,(o-diaminoalkane, cyclodextrins and metal complex stoppers reported by Ogino.

More recently, the construction of a series a-CD [2]rotaxanes, based on the attachment of stoppers to threads by means of metal complex formation, was described by Macartney et al. [5] They have shown that the self-assembly of rotaxanes of the type [(NC)5Fe R(CH2) R - a-CD Fe(CN)5] -where R and R are bipyridinium or pyrazi-nium (e. g., 1 in Scheme 1) happens irrespective of the order of the addition of the components to the aqueous solution. This observation infers a slow dissociation of one of the [Fe(CN)s] ions, followed by a-CD inclusion and the recomplexation of [Fe(CN)s] ion. Evidence for the formation of [2]rotaxanes is provided by the H NMR spectra, in which the signals of the symme-... 

Transition metal-complexed catenanes and rotaxanes as light-driven molecular machines prototypes 05CL742. 

Fig. 3 The macrocycle A incorporating a coordinating fragment thick line) interacts with a metal center black circle) and an asymmetrical open chain chelate B bearing one porphyrin and a precursor function X which is small enough to pass through the ring after the threaded intermediate C is formed, the additional porphyrin ring is constructed, affording the transition metal-complexed rotaxanes D and E. Demetalation leads to the free-ligand rotaxanes F and G from D and E, respectively...

Fig. 11 Principle of transition metal-templated synthesis of a [2]rotaxane. A thick line represents a dpp chelate, a black dot represents a metal cation, a hatched diamond represents a Au(III) porphyrin and an empty diamond represents a Zn(II) porphyrin. The transition metal controls the threading of Au(III) porphyrin-pendant macrocycle (A) onto chelate (B), to form prerotaxane (C). Construction of the porphyrin stoppers at the X functions leads to the metal complex [2]rotaxane (D). Removal of the template cation forms the free rotaxane (E)...

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