Plenary Lectures

Microporous materials absorbing the mechanisms of homogeneous catalysis for C-H functionalisation of arene compounds

Dirk De Vos

KU Leuven, Belgium. Email: dirk.devos@kuleuven.be

In the search for safe, atom-economic reactions that fit in synthetic routes with improved step economy, microporous materials, and in particular zeolites and MOFs can play a key role. The pore environments of MOFs and zeolites can control the redox chemistry of embedded transition metals; in appropriate coordination environments, stability and TON of the catalysts can be highly improved, and unexpected shape selectivities induced. The lecture will illustrate these general ideas with particular focus on catalytic centres that can activate C-H sp2 bonds. Classically, in homogeneous catalysis, arenes are functionalized using cross-coupling reactions of the Heck or Suzuki type, requiring prefunctionalized, e.g. halogenated reactants. In a more atom-economic approach, the metal centre can directly activate a C-H bond, but this requires that an oxidant is used in the overall reaction, as illustrated for the Pd-catalyzed Fujiwara alkenylation of arenes with olefins to form styrenes. We will highlight several designs of porous catalysts which bring significant benefits to such C-H activating reactions, beyond merely providing immobilization. Starting from the wellknown MOF-808, we docked a S-containing carboxylic ligand to the Zr6 clusters in the structure. This provides an excellent environment for Pd2+/Pd0 to affect the Fujiwara reaction, giving direct access to alkenylated arenes. 1 For synthesizing biaryl motives, Pdzeolites stand out. We proved that in the pores of zeolite Beta, toluene is homocoupled to produce with high selectivity the p,p’-bitolyl isomer, out of 6 possible isomers.2 These reactions are now extended to selective heterocouplings, e.g. of phenyl rings and heteroaromatics. In both cases, the involved active species were studied in detail, with a combination of XAS, NMR and theoretical calculations.

Using similar designs of zeolite-entrapped transition metals, we also present (i) a Rh catalyst for the selective carboxylation of indoles using CO and O2, and (i) a Ru catalyst for the photocatalytic trifluoromethylation of arenes. In the final section, we will reveal an unexpected role of zeolites as equilibrium shifting agentsin the transfer hydrocyanation, allowing a much safer introduction of HCN than when using HCN.

References

[1] Van Velthoven, N et. al. ACS Catal. 2020, 10, 5077–5085. [2] Vercammen, J. et al., Nature Catalysis 2020, 3, 1002–1009.

Custom 3D porous carbon structures from whey

Raúl Llamas Unzueta, Miguel A. Montes-Morán, J. Angel Menéndez

Instituto de Ciencia y Tecnología del Carbono (INCAR-CSIC) c/ Francisco Pintado Fe, 26, 33011 Oviedo, Spain. Email: angelmd@incar.csic.es

Over the past decades, porous carbon technology has evolved to the point that today we can control the nanoscale level, being able to produce activated carbons with tailored porosity and surface chemistry. Interestingly, few advances has been done regarding the shaping of the porous carbons at a macroscale level, being the most "sophisticated" structures relatively simple monoliths or activated carbon cloths. However, the recent development of additive manufacturing techniques makes it possible to produce pre-engineered porous carbon structures. Nevertheless, since most of the materials used in 3D printing are based on thermoplastic polymers that cannot be carbonized (or activated) without losing the shape, 3D printing of tailored porous carbon structures is not an straightforward issue and most of the methods proposed so far are relatively complex. To overcome this problem, we investigate the use of surpluses of whey (a natural and sustainable thermoset polymer) for producing custom 3D porous carbon structures.1 Casting and machining,2,3 selective laser sintering (SLS) and extrusion 3D printing can be used with whey as a precursor for producing geometries that, upon carbonization or activation, give rise to porous carbon structures that preserves the original (with a controlled shrinkage) design (Figure 1). The resulting carbons have outstanding mechanical properties when compared to other similar porous materials. These carbon may perform better that the traditional activated carbons or used in new applications like producing scaffolds for bone tissue engineering.4

Figure 1. Porous carbon structures obtained by casting and machining (top left), SLS (top right) and extrusion 3D printing (bottom left) and porosity of the walls (bottom right).

References

[1] Menéndez, J.A.; Montes-Morán, M.A.; Arenillas, A.; Ramírez-Montoya, L.A.; Llamas-Unzueta, R.; WO2021069770 Patent.[2] Llamas-Unzueta, R.; Menéndez, J.A.; Ramírez-Montoya, J.A.; Viña, J.; Argüelles, A.; Montes-Morán, M.A.; Carbon, 2021, 175, 403- 412. [3] Llamas-Unzueta, R.; Ramírez-Montoya, J.A.; Viña, J.; Argüelles, A.; Montes-Morán, M.A.; Menéndez, J.A. Dyna, 2021, 96, 422-428. [4] Llamas-Unzueta, R.; Suárez, M.; Fernández, A.; Díaz, R.; Montes-Morán, M.A.; Menéndez, J.A.; Biomedicines, 2021, 9, 1091.

Acknowledgments: This research was funded MICINN, grant number PID2020-115334GB-I00 and Principado de Asturias–FICYT-FEDER, grant number IDI/2018/000118. Raúl Llamas thanks the Spanish National Research Council (CSIC) for funding received through the Project PIE 202080E276.

Benign-by-design porous (carbonaceous) materials for catalysis: present and future

Rafael Luque

Departamento de Quimica Orgánica, Universidad de Cordoba, Campus de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396, E14014, Cordoba, Spain. E-mail: rafael.luque@uco.es

Porous materials featuring high surface areas, narrow pore size distribution and tuneable pores diameters have attracted a great deal of attention in recent years due to their promising properties and applications, in various areas including adsorption, separation, sensing and catalysis. Innovation through specific and rational design has led to the development of a wide range of these materials with varying morphologies, porosity, structures (e.g., silicates, carbons, metal oxides) and functionalities that currently makes this field one of the most developed in materials science. However, many advances in the field are recently diversifying this exciting area of work to promising applications in drug delivery, tumoral therapy, biomedicine, etc. This contribution is aimed to provide an overview on the present and future of porous materials (including porous carbonaceous materials) with a particularly focus on benign-bydesign strategies for their preparation in view of their catalytic applications.