Topological transformation of a trefoil knot into a [2]catenane

Abstract

Topological transformation of a zinc-templated trefoil knot, Zn-TK, into a zinc-templated [2]catenane, Zn-[2]C, was studied. The net reaction 2 Zn-TK→3 Zn-[2]C was accomplished in 89% yield by heating a solution of Zn-TK in DO. Kinetic investigation by H NMR spectroscopy and high resolution mass spectrometry revealed that the mechanism is complex, involving a large pool of intermediates that form after imine bond cleavage. Bromide ions, which can occupy the central cavity of Zn-TK, inhibited the reaction. Two similar transformations were also studied, one of a cadmium-containing trefoil knot, Cd-TK, into a cadmium-containing catenane, Cd-[2]C, and the other of Cd-TK into Zn-[2]C. The latter transformation could be achieved in one step at high temperature or in two steps via transmetallation to form Zn-TK at room temperature followed by topological conversion of Zn-TK to Zn-[2]C at high temperature.

Self‐Assembly of Molecular Trefoil Knots Featuring Pentadecanuclear Homoleptic AuI‐, AuI/AgI‐, or AuI/CuI‐Alkynyl Coordination

“…The reversible interconversion between Au x (possibly Au 12 ‐1 [2]catenane) and the Au 15 trefoil knot at room temperature is different from a previously reported transformation from a Zn 3 trefoil knot to a Zn 2 catenane upon heating (based on HRMS and 1 H NMR analysis), [7d] for which the reverse process was not reported. Notably, the dynamic equilibrium between the Au 15 trefoil knot and proposed Au 12 [2]catenane in solution allows facile isolation of each of the two ensembles simply by changing the solvent, revealing the importance of such an equilibrium in self‐assembly.…”

Transformation networks of metal–organic cages controlled by chemical stimuli

“…In this review, we detail transformations between discrete architectures, where at least one of the species in the network is a three-dimensional metal-organic cage. Novel examples of transformations involving other types of self-assembled structures, 42 including helicates, 43,44 macrocycles, 45,46 other one-and two-dimensional assemblies, 47,48 and extended structures 49 such as metal-organic frameworks, 50 metallopolymers [51][52][53] and soft materials, 54 fall beyond the scope of this review. As others 41 and our group 40 have recently reviewed strategies to covalently modify coordination assemblies after their formation, we do not treat this type of chemical transformation herein.…”

Ion‐Mobility Mass Spectrometry for the Rapid Determination of the Topology of Interlocked and Knotted Molecules

“…A change of conditions, for example, temperature, pH, concentration, or solvent, may then lead to shifts of the equilibrium to other topologies . For example, Prakasam et al . observed a transformation of a trefoil knot into a Hopf link, when the temperature was raised.…”

“…[13] Ac hange of conditions,f or example,t emperature, pH, concentration, or solvent, may then lead to shifts of the equilibrium to other topologies. [2] Fore xample,P rakasam et al [14] observed at ransformation of at refoil knot into aH opf link, when the temperature was raised. Pentecost et al [15] showed how sensitive such libraries can be to small changes.Borromean rings formed when the ligands used were equilibrated with either Zn II or Cu II templating metal ions.In marked contrast, aSolomon link forms when Zn II and Cu II are both added simultaneously.S uch interconversions may prevent the separation of the desired compounds in order to obtain single crystals or good spectroscopic data.…”