Organometallic rotaxane dendrimers with fourth-generation mechanically interlocked branches

Abstract

Mechanically interlocked molecules, such as catenanes, rotaxanes, and knots, have applications in information storage, switching devices, and chemical catalysis. Rotaxanes are dumbbell-shaped molecules that are threaded through a large ring, and the relative motion of the two components along each other can respond to external stimuli. Multiple rotaxane units can amplify responsiveness, and repetitively branched molecules-dendrimers-can serve as vehicles for assembly of many rotaxanes on single, monodisperse compounds. Here, we report the synthesis of higher-generation rotaxane dendrimers by a divergent approach. Linkages were introduced as spacer elements to reduce crowding and to facilitate rotaxane motion, even at the congested periphery of the compounds up to the fourth generation. The structures were characterized by 1D multinuclear ( 1 H, 13 C, and 31 P) and 2D NMR spectroscopy, MALDI-TOF-MS, gel permeation chromatography (GPC), and microscopy-based methods including atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM and TEM studies of rotaxane dendrimers vs. model dendrimers show that the rotaxane units enhance the rigidity and reduce the tendency of these assemblies to collapse by self-folding. Surface functionalization of the dendrimers with ferrocenes as termini produced electrochemically active assemblies. The preparation of dendrimers with a well-defined topological structure, enhanced rigidity, and diverse functional groups opens previously unidentified avenues for the application of these materials in molecular electronics and materials science.rotaxane dendrimer | controllable divergent approach | platinum acetylide | surface modification | dynamic supramolecular systems D endritic molecules containing rotaxane components are a recently developed subset of mechanically bonded supermolecules (1-3). The combination of the characteristics of both rotaxanes (sliding and rotary motion) and dendrimers (repetitive branching with each generation) provides the resultant rotaxane dendrimers with unusual topological features and potentially useful properties. For example, the introduction of stimuli-responsive rotaxanes (4) such as muscle-like bistable rotaxanes or daisy chains can impart switchable features to the resultant dendrimers that are "smart" to external inputs. The applications of dendrimers in materials science (5, 6) suggest that rotaxane dendrimers could serve as supramolecular dynamic materials.A variety of rotaxane dendrimers have been designed and constructed over the past few years. For examples, mechanically interlocked units were used either as cores or end groups, by Vögtle and coworkers (7), Stoddart and coworkers (8-13), Gibson et al. (14), Kim and coworkers (15,16), and Kaifer and coworkers (17,18). Compared with these simpler systems, rotaxane dendrimers with interlocking ring components on the branches or at the branch points are rare. Specifically, Kim et al. (16) and Leung et al. (19) have reported the only two cases of rotaxane branched dendrimers u...

Our Expedition in Linear Neutral Platinum-Acetylide Complexes: The Preparation of Micro/nanostructure Materials, Complicated Topologies, and Dye-Sensitized Solar Cells

“…To the best of our knowledge, no case of third‐ or higher‐generation rotaxane dendrimers equipped with mechanically interlocked functions on the branches was reported before the year 2015. Inspired by the fact that neutral platinum‐acetylide could be used as a readily derivatized linker to construct the complicated topologies, more recently, we synthesized the organometallic [2]rotaxane 40 containing a neutral platinum‐acetylide group from three components in good yield (86%) on a gram scale 43. Then, by incorporating mechanically interlocked rotaxanes on the branches, the divergent growth of organometallic dendrimers was carried out.…”

Integrative Self‐Sorting: One‐Pot Synthesis of a Hetero[4]rotaxane from a Daisy‐Chain‐Containing Hetero[4]pseudorotaxane

“…Thanks to the rapid development of supramolecular chemistry, especially macrocycle‐based host–guest chemistry, the noncovalent interactions between hosts and guests have been well investigated and understood, significantly advancing the progress of novel and efficient supramolecular templates for the construction of MIMs . Rotaxanes, the most common species in the family of MIMs, evolve their interlocked structures from the primitive dumbbell‐like [2]rotaxanes into various elegant structures with high structural complexity, such as [1]rotaxanes, [ c 2]daisy chains, hetero[ n ]rotaxanes, and dendrimer [ n ]rotaxanes . Meanwhile, the increasing structural complexity fundamentally advances the capability of rotaxanes towards more superior assignments and functions…”

Programmed Synthesis of Molecular Wires with Fixed Insulation and Defined Length Based on Oligo(phenylene ethynylene) and Permethylated α‐Cyclodextrins

“…Yang et al. applied iterative reactions to synthesize rotaxane dendrimers . In 2016, Goldup and co‐workers developed an iterative procedure for [ n ]rotaxanes ( VIII → IX ), whereby multiple macrocycles could be precisely introduced in the desired sequences (Figure c) .…”