SUPRAMOLECULAR HETEROGENEOUS CATALYSIS

Work package:
The effects of ligands coordinated to transition metals on catalysis are well documented,[1] and rational ligand modification to control activity and selectivity of homogeneous catalysts is also well explored. In order to increase the level of control in transition metal catalysis, supramolecular substrate orientation has been recently introduced.[2] In such a strategy, the substrate is oriented with respect to the active site by means of supramolecular interactions such as hydrogen bonds. This level of selectivity is more challenging to achieve in heterogeneous catalysis.[3] Single-atom catalysts (SACs) are emerging materials in the field of catalysis, due to its straightforward synthesis and the possibility to modify supports to control the stability, local environment, and electronic properties of the isolated atoms, therefore open the door to tailor their properties as heterogeneous catalysts.[4] Modification of the support with supramolecular strategies will allow to further predetermine the local environment of the isolated metallic atom and pre-organization of the desired substrate. The project aims at control the selectivity of single-atom catalysts through supramolecular substrate-ligand interactions. This strategy is especially appealing for controlling selectivity in hydroformylation (HF) reaction using SACs. The use of Rh-based SACs for HF has seen significant advancement in recent years.[5] This growing interest is largely due to certain catalytic systems demonstrate activity levels comparable to those of homogeneous catalysts. Nevertheless, these examples are scarce, and in all cases described for this kind of catalysts (except the ones using phosphorus ligand moieties, such as porous organic polymers), the origin of selectivity, if any, is unknow. Few examples in HF reaction catalysed by Rh-based SACs on solid supports display high selectivity. For instance, for styrene HF, l/b ratios observed for Rh- based SACs are in the range of 0.5 to 1, the highest one to date displaying an l/b of 1.6 for Rh single atoms on carbon nitride (C3N4).[6] In order to control selectivity, we plan to use straightforward and inexpensive organic transformations on a carbonaceous support (ideal for this aim), to keep the advantages of heterogeneous catalysts (straightforward, scalable synthesis), while incorporating concepts of supramolecular chemistry. The project is part of a collaboration with J. Reek (University of Amsterdam),[7] and will count with the additional supervision of Hiroya Ishikawa.[8]