Ferrocene-containing [2]- and [3]rotaxanes. Preparation via an end-capping cross-metathesis reaction and electrochemical properties

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Cross-metathesis reactions of terminal olefins with acrylic esters catalyzed by a Ru-carbene complex ((H2IMes)(PCy3)Cl2Ru = CHPh, H2IMes = N,N-bis(mesityl)-4,5-dihydroimidazol-2-ylidene) were applied to the end-capping of [2]pseudorotaxanes composed of dibenzo[24]crown-8 (DB24C8) and ferrocenylmethylammonium derivatives as the macrocyclic and axle components. A [3]rotaxane consisting of two DB24C8s and an axle molecule having ferrocenyl groups at both ends was obtained from the cross-metathesis reaction of two [2]pseudorotaxanes with Fe(C5H4CH2OCOCH = CH2)2. Cyclic voltammograms of the ferrocene-containing rotaxanes show reversible redox reactions whose potentials vary depending on the presence or absence of cationic dialkylammonium groups in the vicinity of the ferrocene units.