Cavitands as Containers for α,ω-Dienes and Chaperones for Olefin Metathesis.

Described herein is the behavior of α,ω-dienes sequestered within cavitands in aqueous (D2 O) solution. Hydrophobic forces drive the dienes into the cavitands in conformations that best fill the available space. Shorter dienes (C9 and C10) bind in compressed conformations that tumble rapidly in the cavitands. Longer dienes induce capsule formation between cavitands with self-complementary hydrogen bonding sites, where the dienes exist in extended conformations. In cavitands unable to form capsules, longer dienes adopt folded structures. The wider open ends allow the synthesis of medium-sized cycloalkenes by ring-closing metathesis reactions with the Hoveyda-Grubbs-II catalyst. Yields of cycloheptene and cyclooctene were enhanced by the chaperones in water when compared with reactions of the free dienes in either aqueous media or chloroform, and even cyclononene could be prepared within the cavitand.

Cavitands as Chaperones for Monofunctional and Ring-Forming Reactions in Water.

Cyclic processes involving medium-sized rings show low rates because internal strains-torsions and transannular interactions-are created during the reactions. High dilution is often used to slow the competing bi- and higher-molecular processes but cannot accelerate the desired cyclization reaction. Here we apply cavitands to the formation of medium- to large-sized rings through conversion of long-chain diisocyanates to cyclic ureas. The reactions take place in aqueous (D2O) solution, where hydrophobic forces drive the starting materials into the cavitands in folded conformations. The guest assumes the shape to fill the space properly, which brings the reacting ends closer together than they are in bulk solvent. Complexation overcomes some of the internal strains involved in precyclization shapes of the guest molecules and accelerates the cyclization. The results augur well for applications of water-soluble cavitands to related processes such as remote functionalization reactions.

Hierarchical Self-Assembly of Discrete Organoplatinum(II) Metallacycles with Polysaccharide via Electrostatic Interactions and Their Application for Heparin Detection.

In recent past years, investigation of hierarchical self-assembly for constructing artificial functional materials has attracted considerable attention. Discrete metallacycles based on coordination bonds have proven to be valid scaffolds to fabricate various supramolecular polymers or smart soft matter through hierarchical self-assembly. Here, we present the first example of the hierarchical self-assembly of discrete metallacycles by taking advantage of the positive charges of the organoplatinum(II) metallacycle skeleton through multiple electrostatic interactions. Heparin, a sulfated glycosaminoglycan polymer that has been widely used as an anticoagulant drug, was selected to induce hierarchical self-assembly because of the existence of multiple negative charges. To investigate the hierarchical self-assembly process, an aggregation-induced emission (AIE) active moiety, tetra-phenylethylene (TPE), was introduced onto the metallacycle via coordination-driven self-assembly. Photophysical studies revealed that the addition of heparin to the tris-TPE metallacycles solution resulted in dramatic fluorescence enhancement, which supported the aggregation between metallacycle and heparin driven by multiple electrostatic interactions. Moreover, the entangled pearl-necklace networks were obtained through hierarchical self-assembly as detected by SEM, TEM, and LSCM experiments. In particular, single bead-like chains were observed in the AFM and TEM images, which provided direct, visual evidence for the aggregation of positively charged metallacycles and negatively charged heparin. More interestingly, further optical study demonstrated that this TPE-decorated metallacycle could function as a turn-on fluorescent probe for heparin detection with high sensitivity and selectivity. Thus, this research presents the first example of counter polyanion-induced hierarchical self-assembly of discrete metallacycles and provides a "proof-of-principle" method for heparin sensing and binding.

A neutral branched platinum-acetylide complex possessing a tetraphenylethylene core: preparation of a luminescent organometallic gelator and its unexpected spectroscopic behaviour during sol-to-gel transition.

A neutral branched platinum-acetylide complex TPA possessing a tetraphenylethylene core was successfully prepared, which was found to form luminescent organometallic gels in ethyl acetate. Stimulated by temperature or F(-), the reversible gel-sol transition was realized. More interestingly, TPA exhibited an unexpected blue shift of the emission during the sol-to-gel transition.

Design and preparation of ethynyl-pyrene modified platinum-acetylide gelators and their application in dispersion of graphene.

A series of new ethynyl-pyrene modified platinum-acetylide gelators were prepared, some of which were found to be able to incorporate graphene into the metallogel matrix.

Hierarchical self-assembly of a discrete hexagonal metallacycle into the ordered nanofibers and stimuli-responsive supramolecular gels.

A discrete hexagonal metallacycle decorated with multiple amide groups and long hydrophobic alkyl chains was constructed via [3+3] coordination-driven self-assembly, from which the ordered nanofibers and stimuli-responsive supramolecular gels were successfully obtained via hierarchical self-assembly.

Hierarchical self-assembly of supramolecular hydrophobic metallacycles into ordered nanostructures.

We describe herein the hierarchical self-assembly of discrete supramolecular metallacycles into ordered fibers or spherical particles through multiple noncovalent interactions. A new series of well-defined metallacycles decorated with long alkyl chains were obtained through metal-ligand interactions, which were capable of aggregating into ordered fibroid or spherical nanostructures on the surface, mostly driven by hydrophobic interactions. In-depth studies indicated that the morphology diversity was originated from the structural information encoded in the metallacycles, including the number of alkyl chains and their spatial orientation. Interestingly, the morphology of the metallacycle aggregates could be tuned by changing the solvent polarity. These findings are of special significance since they provide a simple yet highly controllable approach to prepare ordered and tunable nanostructures from small building blocks by means of hierarchical self-assembly.