Rotaxane slippage

Concept Rotaxane-like entities are created by the slippage protocol in which the cavities of macrocyclic polyethers dilate", at elevated temperatures, so as to allow their passage over the relatively bulky stoppers of chemical dumbbells (see Cartoon below). Similarly,... 

Several years ago in our research laboratories, a novel route to the synthesis of kinetically stable rotaxane-like19121 spedes was discovered,1131 which relies upon the aforementioned balance between kinetics and thermodynamics. This route is termed slippage inasmuch as the rotaxane-like species are obtained when a preformed macrocycle bears a cav-... 

Scheme 2. Rotaxane synthesis combining different meth- threading-followed-by-stopperingthen (2) slippage...

F. M. Raymo, J. F. Stoddart, Slippage-A Simple and Efficient Way to Self-Assemble Ini Rotaxanes , Pure Appl Chem. 1997, 69,1987-1997, and references dted therein. 

P. R. Ashton, M. Belohradsky, D. Philp, J. F. Stoddart, Slippage-An Alternative Method for Assembling [2] Rotaxanes , J. Chem. Soc. Chem. Commun. 1993,1269-1274. 

Scheme 12a-d There are several general methods to prepare rotaxanes a threading followed by capping b clipping c slippage d snapping... 

The clipping reaction used in [52, 53, 55] to synthesize tetralactam-based squaraine rotaxanes such as 14 and 15 afforded only moderate yields (ca. 28-35%) of the rotaxanes, possibly because of the unavoidable presence of nucleophiles that react with the chemically unstable squaraines during the reaction. The slippage approach [62] minimizes the squaraine dye s contact with nucleophiles during the rotaxane formation process and therefore can be used to efficiently encapsulate a squaraine dye such as 23 in a macrocycle such as 25 [63],... 

Hsueh S Y, Lai CC, Liu YH, Wang Y, Peng SM, Chiu SH (2007) Protecting a squaraine near-IR dye through its incorporation in a slippage-derived [2]rotaxane. Org Lett 9 4523 1526... 

Assembling [2] rotaxanes (wheel and axle) can involve three basic processes (Scheme 13). One of these (93CC1269) involves slippage, in which the axle (115) is linked by a 4,4 -bipyridine, and the wheel (116) is a bisparaphenylene-34-crown-10 ether. Heating the two components in acetonitrile at 60°C yields the rotaxane, which can be characterized by FABMS and H and l3C NMR, but extrusion of the wheel occurs at 100°C. In other developments (94NAT(369)133), the pyridine component may be incorporated in the wheel, as in structure (117), where two bipyridinium units are connected by p-xylyl groups, and here the rotaxane acts as molecular switch. At room temperature in acetonitrile the wheel... 

In other studies, matched complementarity between the cavity size of the macro-cyclic component and the size of the bulky stopper groups has been exploited to allow preparation of rotaxanes by means of the slippage mechanism mentioned previously. 

The above results indicate that there is little difference between the rates of formation of the three rotaxanes (with R equal to H, CH3 or CjH ), suggesting that the steric hindrance to slippage is similar in all three cases. When the rotaxane with R = H was heated in deutero-dimethyl sulfoxide, there was loss of the crown component from the assembly - at 60 °C, the loss was less than 25% after six hours. 

Other rotaxanes have been prepared using the slippage strategyOne such example consists of a linear component (terminated by carbohydrate stoppers) that contained a hydroquinone recognition site. This was demonstrated to interact with cyclobis(paraquat-/7-phenylene) tetrachloride in D O over one week at room temperature to yield the corresponding water-soluble catenane. ... 

The slippage procedure lends itself to the preparation of [n]-rotaxanes that are based on longer linear fragments incorporating more than one dicationic binding site and fitted with stoppers of appropriate size. The successful synthesis of the [3]-rotaxane 29 has been achieved by this means. This product, which is formed in good yield when the crown macrocycle is present in substantial excess, was... 

The construction of even more elaborate structures has proved possible using the slippage procedure. These include three novel rotaxanes incorporating one, two and three bis-/ -phenylene-34-crown-10 macrocycles, respectively. Each of these... 

Rotaxanes are synthesized by two basically different methods (Figure 3) threading (or slippage ), and clipping [47], In the threading strategy a macrocycle is threaded onto a molecular axle at first then the stoppers are attached to the ends of the axle. In a variant, the molecular axle is end-blocked at one extremity prior to... 

Figure 3 The three methods of rotaxane construction (a) threading and stoppering (h) slippage (c) clipping and cyclization.

Figure 8 Statistical threading (temperature-controlled slippage). Preparation of [2]-rotaxane (10) [38],...

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