Metal-organic frameworks as selective or chiral oxidation catalysts

Since the discovery of Metal Organic Frameworks (MOFs) in the early 1990s, the amount of new structures has grown exponentially. A MOF typically consists of inorganic nodes that are connected by organic linkers to form crystalline, highly porous structures. MOFs have attracted a lot of attention lately, as the versatile design of such materials holds promises of interesting applications in various fields. In this review, we will focus on the use of MOFs as heterogeneous oxidation catalysts. MOFs are very promising candidates to replace homogeneous catalysts by sustainable and stable heterogeneous catalysts. The catalytic active function can be either the active metal sites of the MOF itself or can be introduced as an extra functionality in the linker, a dopant or a "ship-in-a-bottle" complex. As the pore size, pore shape, and functionality of MOFs can be designed in numerous ways, shape selectivity, and even chiral selectivity can be created. In this article, we will present an overview on the state of the art of the use of MOFs as a heterogeneous catalyst in liquid phase oxidation reactions

Mechanistic investigation on oxygen transfer with the manganese-salen complex

The best-known application of salen complexes is the use of a chiral ligand loaded with manganese to form the Jacobsen complex. This organometallic catalyst is used in the epoxidation of unfunctionalized olefins and can achieve very high selectivities. Although this application was proposed many years ago, the mechanism of oxygen transfer remains a question until now. In this paper, the epoxidation mechanism is investigated by an ab initio kinetic modeling study. First of all a proper DFT functional is selected that yields the correct ordering of the various spin states. Our results show that the epoxidation proceeds via a radical intermediate. If we start from the radical intermediate, these results can explain the experiments with radical probes. The subtle influences in the transition state using the full Jacobsen catalyst explain the product distribution observed experimentally

Chemical sensors based on nano-sized lanthanide-grafted periodic mesoporous organosilica hybrid materials

In this work we introduce the use of nano-sized (50-70 nm) lanthanide-grafted periodic mesoporous organosilicas for both metal ion sensing and solvent sensing. For this study a PMO constructed from the N,N-bis(trimethoxysilylpropyl)-2,6-pyridine dicarboxamide linker and tetraethyl orthosilicate (at a 5 : 95 ratio) was employed. This material was grafted with Eu3+, Tb3+ or a mixture of Eu3+-Tb3+ chloride salts to obtain strongly emitting nano-sized luminescence materials. To further enhance the luminescence properties of the materials two different co-ligands were used - 1,10-phenanthroline (phen) and 5,5 '-dimethyl-2,2 '-dipyridyl (bpy). The luminescence properties of the developed series of hybrid materials were studied in detail in the solid-state and after dispersing in water. The materials were investigated for their use as ion sensors, with the Eu3+ and Tb3+ phen and bpy co-grafted materials showing selective "turn on" fluorescence for Pb2+ and Cr3+ ions (at a 10 ppm concentration of the ions). The Eu3+-Tb3+ co-grafted materials showed solvatochromism and could be used as a solvent sensor to distinguish between protic and aprotic solvents