Time-resolved control of nanoparticle integration in titanium-organic frameworks for enhanced catalytic performance.

Among the multiple applications of metal-organic frameworks (MOFs), their use as a porous platform for the support of metallic nanoparticles stands out for the possibility of integrating a good anchorage, that improves the stability of the catalyst, with the presence of a porous network that allows the diffusion of substrates and products. Here we introduce an alternative way to control the injection of Au nanoparticles at variable stages of nucleation of a titanium(iv) MOF crystal (MUV-10). This allows the analysis of the different modes of nanoparticle integration into the porous matrix as a function of the crystal formation stage and their correlation with the catalytic performance of the resulting composite. Our results reveal a direct effect of the stage at which the Au nanoparticles are integrated into MUV-10 crystals not only on their catalytic activity for the cyclotrimerization of propargyl esters and the hydrochlorination of alkynes, but also on the selectivity and recyclability of the final solid catalyst, which are far superior than those reported for the same reactions with TiO2 supports.

Silver-Exchanged Zeolite Y Catalyzes a Selective Insertion of Carbenes into C-H and O-H Bonds.

Commercially available zeolite Y modulates the catalytic activity and selectivity of ultrasmall silver species during the Buchner reaction and the carbene addition to methylene and hydroxyl bonds, by simply exchanging the counter cations of the zeolite framework. The zeolite acts as a macroligand to tune the silver catalytic site, enabling the use of this cheap and recyclable solid catalyst for the in situ formation of carbenes from diazoacetate and selective insertion in different C-H (i.e., cyclohexane) and C-O (i.e., water) bonds. The amount of catalyst in the reaction can be as low as ≤0.1 mol % silver. Besides, this reactivity allows deeply drying the HY zeolite framework by making the strongly adsorbed water molecules react with the in situ formed carbenes.

Ag2(0) dimers within a thioether-functionalized MOF catalyze the CO2 to CH4 hydrogenation reaction.

Ultrasmall silver clusters in reduced state are difficult to synthesize since silver atoms tend to rapidly aggregate into bigger entities. Here, we show that dimers of reduced silver (Ag2) are formed within the framework of a metal-organic framework provided with thioether arms in their walls (methioMOF), after reduction with NaBH4 of the corresponding Ag+-methioMOF precursor. The resulting Ag2-methioMOF catalyzes the methanation reaction of carbon dioxide (CO2 to CH4 hydrogenation reaction) under mild reaction conditions (1 atm CO2, 4 atm H2, 140 °C), with production rates much higher than Ag on alumina and even comparable to the state-of-the-art Ru on alumina catalyst (Ru-Al2O3) under these reaction conditions, according to literature results.

MOF-Triggered Synthesis of Subnanometer Ag02 Clusters and Fe3+ Single Atoms: Heterogenization Led to Efficient and Synergetic One-Pot Catalytic Reactions.

The combination of well-defined Fe3+ isolated single-metal atoms and Ag2 subnanometer metal clusters within the channels of a metal-organic framework (MOF) is reported and characterized by single-crystal X-ray diffraction for the first time. The resulting hybrid material, with the formula [Ag02(Ag0)1.34FeIII0.66]@NaI2{NiII4[CuII2(Me3mpba)2]3}·63H2O (Fe3+Ag02@MOF), is capable of catalyzing the unprecedented direct conversion of styrene to phenylacetylene in one pot. In particular, Fe3+Ag02@MOF─which can easily be obtained in a gram scale─exhibits superior catalytic activity for the TEMPO-free oxidative cross-coupling of styrenes with phenyl sulfone to give vinyl sulfones in yields up to >99%, which are ultimately transformed, in situ, to the corresponding phenylacetylene product. The results presented here constitute a paradigmatic example of how the synthesis of different metal species in well-defined solid catalysts, combined with speciation of the true metal catalyst of an organic reaction in solution, allows the design of a new challenging reaction.

Highly Efficient MOF-Driven Silver Subnanometer Clusters for the Catalytic Buchner Ring Expansion Reaction.

The preparation of novel efficient catalysts─that could be applicable in industrially important chemical processes─has attracted great interest. Small subnanometer metal clusters can exhibit outstanding catalytic capabilities, and thus, research efforts have been devoted, recently, to synthesize novel catalysts bearing such active sites. Here, we report the gram-scale preparation of Ag20 subnanometer clusters within the channels of a highly crystalline three-dimensional anionic metal-organic framework, with the formula [Ag20]@AgI2NaI2{NiII4[CuII2(Me3mpba)2]3}·48H2O [Me3mpba4- = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. The resulting crystalline solid catalyst─fully characterized with the help of single-crystal X-ray diffraction─exhibits high catalytic activity for the catalytic Buchner ring expansion reaction.