Abstract
Herein, a bis-amido tris-amine macrocycle and five bipyridine-based bidentate chelating ligands were investigated towards various divalent transition metal ion (Ni
II
, Co
II
, Cu
II
, and Zn
II
)-templated syntheses of metallo [2]pseudorotaxanes. The formation of these ternary complexes was elucidated
via
different spectroscopic techniques such as ESI-MS, absorption spectroscopy, EPR spectroscopy, and single-crystal X-ray diffraction studies wherever possible. Azide-terminated Ni
II
, Co
II
, Cu
II
, Zn
II
-templated [2]pseudorotaxanes were explored to generate [2]rotaxane,
ROT
,
via
reaction with an alkyne-terminated triphenylene unit as a stopper under the mild reaction condition of the Cu
I
-catalyzed azide–alkyne cycloaddition reaction. Ni
II
-templated [2]pseudorotaxane was found to be the best precursor towards the high-yield synthesis of
ROT
. The interpenetrative nature of the center piece in metal-free rotaxane was also established through various spectroscopic techniques such as ESI-MS and 1D and 2D (COSY, NOESY, ROESY, and DOSY) NMR spectroscopy. Furthermore,
ROT
was functionalized
via
tri-acetylation as
AcROT
to incorporate three tertiary amides at the tris-amine centers; this
AcROT
exhibited rotamer-induced molecular motions in an interpenetrated system
via
the formation of multiple conformers/co-conformers. Additionally, the existence of multiple rotamers was established
via
variable-temperature NMR spectroscopic studies. Li
+
and 12-crown-4 were found to be suitable for the reversible conformation/co-conformation fixation of tri-acetylated bis-amido tris-amine macrocyclic wheel-based rotaxane.