Ferrocene-containing [1]-, [2]-, [3]- and [4]rotaxanes synthesized from a common precursor

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The Cu-catalyzed reaction of a dialkylammonium, having ferrocenyl and hexynyl end groups, FcCH2NH2CH2C6H4–4-O(CH2)4CCH]PF6 (Fc = Fe(C5H4)(C5H5)), with a crown ether having an azidemethyl side-arm yields a [1]rotaxane composed of a single molecule. The crystal structure of the [1]rotaxane suggests an arrangement where the 1,4-phenylene ring is tilted at 22° close to the catechol ring rather than in a parallel alignment. Another dialkylammonium with ferrocenyl and alkynyl terminal groups, [FcCH2NH2CH2C6H4–4-O(CH2)4CCH]PF6, reacts with aromatic compounds with one to three azide groups in the presence of dibenzo[24]crown-8-ether (DB24C8) and [Cu(MeCN)4]PF6 catalyst, to afford the corresponding [2]–[4]rotaxanes. The products contain DB24C8 molecules as the cyclic components which are bound to the ammonium group of the axle component with NH⋯O hydrogen bonding. The [3]rotaxane having two triazole groups on the axle component reacts with PdCl2(MeCN)2 to yield mono- and di-palladium complexes with different conformations of the axle component.