Stopper ferrocenyl

Threading such an oriented ring onto a dumbbell end capped with two different stoppers will give rise to two diastereoisomers, as shown schematically in Figure 2.12c. Such rotaxanes were actually described by Isnin and Kaifer, and were characterized as CDX-positional isomers (Figure 2.17).41 Thus reaction of ferrocenyl derivative 40 (1 equiv) with 2 equiv of a-CDX, and potassium 5-amino-2-naphthalene sulfonate 41 in water, in the presence of EDC (EDC = l-(3-[dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride) as a catalyst, afforded a mixture of diastereoisomeric [2]-rotaxanes 42a and 42b in 15% yield and 6 4 ratio. 

In other studies, the above research group synthesised a number of related one-and two-station, photoactive [2]-rotaxanes incorporating either ferrocene or anthracene stoppers or a combination of each type. In these systems, the terminal stoppers associate with the exterior of the bis(4-4 -bipyridinium)cyclophane tetracation via 7U-stacking. Such proximity has obvious implications for the required rapid electron-transfer to a terminal (ferrocenyl) group in order to be competitive with the simple charge recombination process discussed previously. The relationship between the photoactivity, electron-transfer behaviour and concomitant configurational charges in the above systems has now been described in some detail. " ... 

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