Ultrastable and Highly Catalytically Active N-Heterocyclic-Carbene-Stabilized Gold Nanoparticles in Confined Spaces.

Controlling the size and surface functionalization of nanoparticles (NPs) can lead to improved properties and applicability. Herein, we demonstrate the efficiency of the metal-carbene template approach (MCTA) to synthesize highly robust and soluble three-dimensional polyimidazolium cages (PICs) of different sizes, each bearing numerous imidazolium groups, and use these as templates to synthesize and stabilize catalytically active, cavity-hosted, dispersed poly-N-heterocyclic carbene (NHC)-anchored gold NPs. Owing to the stabilization of the NHC ligands and the effective confinement of the cage cavities, the as-prepared poly-NHC-shell-encapsulated AuNPs displayed promising stability towards heat, pH, and chemical regents. Most notably, all the Au@PCCs (PCC=polycarbene cage) exhibited excellent catalytic activities in various chemical reactions, together with high stability and durability.

On/off fluorescence emission induced by encapsulation, exchange and reversible encapsulation of a BODIPY-guest in self-assembled organometallic cages.

A dynamic guest-binding study of BODIPY-derivative 3 (3 = 1,3,5,7,8-pentamethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) with two Cp*RhIII-based organometallic cages [Cp*6Rh6(µ-CA)3(tpt)2](OTf)61 (H2CA = chloranilic acid, tpt = 2,4,6-tripyridyl-1,3,5-triazine) and [Cp*6Rh6(µ-DHNA)3(tpt)2](OTf)62 (H2DHNA = 6,11-dihydroxynaphthacene-5,12-dione) have been demonstrated. While guest 3 displays a strong green fluorescence emission, the host-guest complexes 3⊂1 and 3⊂2 exhibit almost no emission. However, fluorescence emission can be again 'turned on' by adding coronene (4) or pyrene (5) into the solution of 3⊂1 and 3⊂2. Guests 4 and 5 show stronger binding affinities toward the organometallic cages 1 and 2 due to the strong electrostatic interactions between the electron-rich guest and electron-deficient tpt resulting in the displacement of 3 by 4 or 5, which eventually helps the fluorescence enhancement. Further guest-binding studies using a Job's plot experiment illustrate the formation of discrete 1 : 1 host-guest complexes which are also supported by 1H NMR spectroscopy and ESI mass spectrometry. The anion-exchange study with sodium chloride reveals that the chloride ion can effectively disassemble the host frameworks of 1 and 2 releasing the fluorescent guest 3 which can be again encapsulated into the cavity of reassembled cages promoted by the addition of silver triflate.

Chelating Bis(N-Heterocyclic Carbene) Palladium-Catalyzed Reactions.

N-Heterocyclic carbenes (NHCs) have been widely employed in the construction of various metal complexes and applied in the field of catalysis. In this review, a series of palladium complexes comprising chelating bis(NHC) donors (Pd-bis(NHC) complexes) are outlined according to their application in homogeneous catalysis. Examples of metal-organic frameworks containing Pd-bis(NHC) moieties are briefly discussed, in terms of their use in heterogeneous catalysis. The catalytic applications of Pd-bis(NHC) complexes (or moieties in heterogeneous catalysts) are mainly focused on the Mizoroki-Heck, Suzuki-Miyaura, and Sonogashira coupling reactions. Another 14 types of reactions are also summarized beyond these three types of reactions.