Search for: All records

Although catenanes comprising two ring-shaped components can be made in large quantities by templation, the preparation of three-dimensional (3D) catenanes with cage-shaped components is still in its infancy. Here, we report the design and syntheses of two 3D catenanes by a sequence of S N 2 reactions in one pot. The resulting triply mechanically interlocked molecules were fully characterized in both the solution and solid states. Mechanistic studies have revealed that a suit[3]ane, which contains a threefold symmetric cage component as the suit and a tribromide component as the body, is formed at elevated temperatures. This suit[3]ane was identified as the key reactive intermediate for the selective formation of the two 3D catenanes which do not represent thermodynamic minima. We foresee a future in which this particular synthetic strategy guides the rational design and production of mechanically interlocked molecules under kinetic control. 

Complexation between a viologen radical cation (V^.+) and cyclobis(paraquat‐p‐phenylene) diradical dication (CBPQT^2(.+)) has been investigated and utilized extensively in the construction of mechanically interlocked molecules (MIMs) and artificial molecular machines (AMMs). The selective recognition of a pair ofV^.+using radical‐pairing interactions, however, remains a formidable challenge. Herein, we report the efficient encapsulation of two methyl viologen radical cations (MV^.+) in a size‐matched bisradical dicationic host — namely, cyclobis(paraquat‐2,6‐naphthalene)^2(.+), i.e.,CBPQN^2(.+). Central to this dual recognition process was the choice of 2,6‐bismethylenenaphthalene linkers for incorporation into the bisradical dicationic host. They provide the space between the two bipyridinium radical cations inCBPQN^2(.+)suitable for binding twoMV^.+with relatively short (3.05–3.25 Å) radical‐pairing distances. The size‐matched bisradical dicationic host was found to exhibit highly selective and cooperative association with the twoMV^.+in MeCN at room temperature. The formation of the tetrakisradical tetracationic inclusion complex — namely, [(MV)₂⊂CBPQN]^4(.+)– in MeCN was confirmed by VT¹H NMR, as well as by EPR spectroscopy. The solid‐state superstructure of [(MV)₂⊂CBPQN]^4(.+)reveals an uneven distribution of the binding distances (3.05, 3.24, 3.05 Å) between the three differentV^.+, suggesting that localization of the radical‐pairing interactions has a strong influence on the packing of the twoMV^.+inside the bisradical dicationic host. Our findings constitute a rare example of binding two radical guests with high affinity and cooperativity using host‐guest radical‐pairing interactions. Moreover, they open up possibilities of harnessing the tetrakisradical tetracationic inclusion complex as a new, orthogonal and redox‐switchable recognition motif for the construction of MIMs and AMMs.

 

Complexation between a viologen radical cation (V^.+) and cyclobis(paraquat‐p‐phenylene) diradical dication (CBPQT^2(.+)) has been investigated and utilized extensively in the construction of mechanically interlocked molecules (MIMs) and artificial molecular machines (AMMs). The selective recognition of a pair ofV^.+using radical‐pairing interactions, however, remains a formidable challenge. Herein, we report the efficient encapsulation of two methyl viologen radical cations (MV^.+) in a size‐matched bisradical dicationic host — namely, cyclobis(paraquat‐2,6‐naphthalene)^2(.+), i.e.,CBPQN^2(.+). Central to this dual recognition process was the choice of 2,6‐bismethylenenaphthalene linkers for incorporation into the bisradical dicationic host. They provide the space between the two bipyridinium radical cations inCBPQN^2(.+)suitable for binding twoMV^.+with relatively short (3.05–3.25 Å) radical‐pairing distances. The size‐matched bisradical dicationic host was found to exhibit highly selective and cooperative association with the twoMV^.+in MeCN at room temperature. The formation of the tetrakisradical tetracationic inclusion complex — namely, [(MV)₂⊂CBPQN]^4(.+)– in MeCN was confirmed by VT¹H NMR, as well as by EPR spectroscopy. The solid‐state superstructure of [(MV)₂⊂CBPQN]^4(.+)reveals an uneven distribution of the binding distances (3.05, 3.24, 3.05 Å) between the three differentV^.+, suggesting that localization of the radical‐pairing interactions has a strong influence on the packing of the twoMV^.+inside the bisradical dicationic host. Our findings constitute a rare example of binding two radical guests with high affinity and cooperativity using host‐guest radical‐pairing interactions. Moreover, they open up possibilities of harnessing the tetrakisradical tetracationic inclusion complex as a new, orthogonal and redox‐switchable recognition motif for the construction of MIMs and AMMs.