Cycling a Tether into Multiple Rings: Pt‐Bridged Macrocycles for Differentiated Guest Recognition, Pseudorotaxane Transformations, and Guest Capture and Release

Abstract

Macrocycle engineering is a key topic in supramolecular chemistry. When synthesizing a ring, one can obtain either complex mixtures of macrocycles of different sizes or a single ring if a template is utilized. Here, we unite these approaches along with postsynthetic modifications to transform a single tether into multiple rings-up to five per tether. The macrocycles contain two bridged phenylpyridine ligands that are connected through a Pt atom, which defines the rings' shape, size, and host activity. All rings undergo redox reactions (between Pt II and Pt IV ) that allow for large conformational changes. Their reactivity, together with their host performance, is a convenient way to control the capture and release of guests, to mediate ring transformations, and to control pseudorotaxane-to-pseudorotaxane conversions. This novel approach could serve to assemble other libraries of small ring molecules, create cyclic polymers bridged by responsive-at-metal nodes, and produce processable mechanically interlocked molecules. Since Pedersen's seminal work on crown ethers, [1,2] the synthesis of macrocycles has been central to supramolecular chemistry. [3] The library of known ring molecules is vast, encompassing diverse compositions, geometries and sizes. [4][5][6][7][8][9] Macrocycles are being investigated for applications [10] such as sensing, [11] molecular delivery, [12] molecular machinery, [13] and more. [14] Macrocycle synthesis relies on one of the approaches depicted in Figure 1. The statistical approach proceeds under kinetic control and yields mixtures of linear and cyclic oligomers; [15] template-assisted syntheses operate under thermodynamic control, favoring one particular ring; [16] and post-synthetic modifications serve to alter preassembled rings. [17,18] Although these approaches are used disjointedly, we envisioned that by applying all three in tandem, a single precursor-the tether-could be transformed into multiple rings. Forming and isolating many macrocycles from one tether is not only economical but can also lead to rings with distinct cavity sizes, and hence differentiated host activity.Labile and inert metal-organic compounds have been crucial in recent developments of supramolecular chemistry. [19][20][21] Phenylpyridine (phpy) derivatives are important in the synthesis of cyclometalated complexes (e.g., with