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

Abstract

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.