A Catenane Assembled through a Single Charge‐Assisted Halogen Bond

Abstract

Interlocked molecules have captured chemists imagination owing to their nontrivial topology and the promise of their potential nanotechnological uses as molecular machines [1] and in chemical sensor applications.[2] The synthesis of such sophisticated architectures is a challenge, and as a consequence this has necessitated the implementation of imaginative cation, [3] anion, [4] and neutral [5] templation methodologies, which use a combination of complementary Lewis acid-base, electrostatic, and hydrogen-bonding interactions for component assembly. Halogen bonding (XB) is the attractive highly directional, noncovalent interaction between an electron-deficient halogen atom and a Lewis base.[6] The scope of XB in solid-state crystal engineering has been intensively explored for a number of years, [7] however, in spite of the complementary analogy to ubiquitous hydrogen bonding, it is only in recent times that investigations into the application of solution-phase XB interactions to molecular recognition processes, self-assembly, and catalysis have resulted in this field developing rapidly.[8] Indeed, in conjunction with anion templation, we have used XB to assemble interpenetrated and interlocked molecular frameworks. [8b-d] By incorporating a suitable neutral Lewis base XB acceptor, such as pyridine, [7b, 9] into a macrocyclic framework, we demonstrate herein that a single charge-assisted XB interaction can be utilized for pseudorotaxane assembly and, importantly, in the synthesis of a novel interlocked catenane.The synthetic strategy employed to construct the target catenane is outlined in Figure 1. An acyclic positively charged XB-donor component threads through a complementary XBaccepting pyridine-containing macrocycle, thereby forming an orthogonal interpenetrative assembly that is stabilized by a charge-assisted XB interaction. In addition to the incorporated pyridine XB-acceptor motif, the macrocycle component 1 contains electron-rich hydroquinone groups to facilitate supplementary secondary aromatic donor-acceptor interactions with electron-deficient positively charged heterocyclic XB-donor threading derivatives. A range of bromo-and iodofunctionalized triazolium and pyridinium compounds were chosen as potential threading components, containing terminal vinyl functional groups, which after successful pseudorotaxane assembly with macrocycle 1, could be used for catenane synthesis through ring-closing metathesis (RCM) cyclization (Scheme 1). Macrocycle 1 and halo-functionalized triazolium and pyridinium derivatives were prepared by using Figure 1. Cartoon of orthogonal halogen-bond-templated pseudorotaxane species. X = halogen atom. Scheme 1. Structures of macrocycle 1 and threading components 2-6·BF 4 .

Halogen‐ and Hydrogen‐Bonding Catenanes for Halide‐Anion Recognition

“…Macrocycle 1 8 and functionalised pyridinium derivatives 2 – 4⋅BF 4 were prepared by using multistep synthetic procedures reported previously (Figure 2). 6e…”