Rotaxanes of a macrocyclic ferrocenophane with dialkylammonium axle components

Abstract

Octaoxa[22]ferrocenophane, 1, was synthesized and employed as the macrocyclic component of [2]rotaxanes. [2]Pseudorotaxanes composed of macrocyclic molecule 1 and dialkylammonium derivatives with a terminal vinyl group undergo end-capping via cross-metathesis of the terminal group with bulky acrylates. The [2]rotaxanes of 1 with axle components having bulky terminal groups, such as 3,5-dimethylphenyl, 9-anthryl, and ferrocenyl groups, maintain an interlocked structure in CDCl₃ solution, but they are gradually converted into a mixture of the individual components via dethreading of the end groups in polar solvents such as CD₃CN and dmso-d₆. The reaction rate varies depending on the end group and solvent. The cationic rotaxane with an anthryl end group of the axle component, [(1){AnCH₂NH₂CH₂C₆H₄-4-OCH₂CH₂CHCHCOOC₆H₄-4-C(C₆H₄-4-tBu)₃}](BAr_F) (An = 9-anthryl, BAr_F = B{C₆H₃-3,5-(CF₃)₂}₄) shows weak emission upon excitation of the anthryl group (12b, λ_em = 419 nm, quantum yield, ϕ = 0.012). The quantum yield is lower than that of the neutral rotaxane 13b (ϕ = 0.030) formed by N-acetylation of 12b and a physical mixture of the corresponding free axle molecule, AnCH₂N(Ac)CH₂C₆H₄-4-OCH₂CH₂CHCHCOOC₆H₄-4-C(C₆H₄-4-tBu)₃ (8), and 1 (ϕ = 0.34). The efficiency of the quenching caused by the ferrocenylene group caused by energy transfer is affected significantly by the relative positions of the anthryl and ferrocenylene groups in the rotaxane. The rotaxane with axles having a secondary ammonium moiety has a redox potential E_1/2 = −0.03–0.02 V (vs. Ag⁺/Ag), which is lower those of than compound 1 (E_1/2 = −0.10 V) and the neutral [2]rotaxanes with the N-acetylated axle components (E_1/2 = −0.11 and −0.22 V).