Selective cycloaddition of ethylene oxide to CO2 within the confined space of an amino acid-based metal-organic framework

Host-guest chemistry within the confined space of metal-organic frameworks (MOFs) offers an almost unlimited myriad of possibilities, hardly accessible with other materials. Here we report the synthesis and physical characterization, with atomic resolution by single-crystal X-ray diffraction, of a novel water-stable tridimensional MOF, derived from the amino acid S-methyl-L-cysteine, {SrZn6[(S,S)-Mecysmox]3(OH)2(H2O)}·9H2O (1), and its application as a robust and efficient solid catalyst for the cycloaddition reaction of ethylene/propylene oxide with CO2 to afford ethylene/propylene carbonate with yields of up to 95% and selectivity of up to 100%. These results nicely illustrate the great potential of MOFs to be game changers for the selective synthesis of industrially relevant products, representing a powerful alternative to the current heterogeneous catalysts.

Metal-organic frameworks as chemical nanoreactors for the preparation of catalytically active metal compounds

Since the emergence of metal-organic frameworks (MOFs), a myriad of thrilling properties and applications, in a wide range of fields, have been reported for these materials, which mainly arise from their porous nature and rich host-guest chemistry. However, other important features of MOFs that offer great potential rewards have been only barely explored. For instance, despite the fact that MOFs are suitable candidates to be used as chemical nanoreactors for the preparation, stabilization and characterization of unique functional species, that would be hardly accessible outside the functional constrained space offered by MOF channels, only very few examples have been reported so far. In particular, we outline in this feature recent advances in the use of highly robust and crystalline oxamato- and oxamidato-based MOFs as reactors for the in situ preparation of well-defined catalytically active single atom catalysts (SACS), subnanometer metal nanoclusters (SNMCs) and supramolecular coordination complexes (SCCs). The robustness of selected MOFs permits the post-synthetic (PS) in situ preparation of the desired catalytically active metal species, which can be characterised by single-crystal X-ray diffraction (SC-XRD) taking advantage of its high crystallinity. The strategy highlighted here permits the always challenging large-scale preparation of stable and well-defined SACs, SNMCs and SCCs, exhibiting outstanding catalytic activities.

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]@Ag^I₂Na^I₂{Ni^II₄[Cu^II₂(Me₃mpba)₂]₃}·48H₂O [Me₃mpba^4– = 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.

The present work describes the MOF-driven preparation of well-defined ligand-free Ag₂⁰ nanoclusters, which are efficiently stabilized by the MOF channels. The small Ag₂⁰ nanoclusters, prepared in the gram scale, are used as efficient and recoverable catalysts for the Buchner ring expansion reaction. These results expand the toolkit of readily affordable Ag species for heterogeneous catalysis in organic synthesis.