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Cooperative Catalysis: Using Interdisciplinary Chemical Systems to Develop New Cooperative Catalysts

Periodic Reporting for period 2 - CoopCat (Cooperative Catalysis: Using Interdisciplinary Chemical Systems to Develop New Cooperative Catalysts)

Reporting period: 2019-08-01 to 2021-01-31

The main problem tackled by this project is the limitation of our current industrial chemical processes to face key challenges as chemical sustainability. Industry highly relies on catalytic processes, but from a technical point of view, most of the available ones are not proficient enough regarding several fundamental aspects such as activity, selectivity, substrate scope or cost efficiency.
The importance of catalysis to chemical industry is evinced by the fact that 75% of all chemicals currently require catalysts at some stage in their production, with catalytic processes generating €1,000 Bn in products world-wide. Therefore, the development and fundamental understanding of innovative catalysts will have direct and long-term benefits to the chemical manufacturing sector and to the broader knowledge-based economy.
The overall aim of this ERC project is to develop innovative cooperative catalysts using interdisciplinary chemical systems based on main group elements, transition metals and molecular clusters to achieve better efficiency and improve chemical scope and sustainability of key chemical transformations. To achieve this aim, the main objectives of the project are:
- To explore bond activation and catalysis using Frustrated Lewis Pairs constructed around transition metals (TM-FLPs).
- To synthesize hybrid systems based on low-valent main group elements and transition metals (Hybrid TM/MG) to investigate their catalytic applications through synergistic effects.
- To design and characterize a library of supramolecular Intercluster Compounds (ICCs) to be used as heterogeneized materials for Green Catalysis.
- To build innovative chemical super-architectures capable of performing unprecedented catalytic transformations.
The following paragraphs cover the work carried out within this ERC project from February 2018 to July 2020 (see Figure).

Objective 1: Transition metal frustrated Lewis pairs. We have extended our preliminary results on the FLP-type activation of small molecules by gold/platinum couples to other combinations of transition metals that include the use of Pd, Ni, Rh, Ru and Ir as metallic bases, and Ag, Cu, Zn and Yb as the corresponding acids. Much of this work is still under development, but to date we have acquired a deep understanding on how these bimetallic pairs operate. We have demonstrated that some of these pairs are capable of activating not only the H-H or the acidic C-H bonds in alkynes, but also other polar bonds less amenable to cleavage by transition metals such as O-H and N-H bonds in water and ammonia, respectively (Chem. Commun. 2019, 55, 8812; Angew. Chem. Int. Ed. 2020, DOI: 10.1002/anie.202008442). In addition, our mechanistic investigations allowed us to provide evidence for the genuine frustrated character of our gold/platinum TMFLPs (Chem. Eur. J. 2020, 26, 5982), while subtle modifications of the ligands permit rational control of regioselectivity (Organometallics 2020, 39, 13, 2534). Our Lewis acid/base bimetallic combinations have also allowed us to identify the non-innocent character of a very common organometallic ligand (pentamethylcyclopentadienyl, Cp*) in a Rh(I) species (Angew. Chem. Int. Ed. 2020, DOI: 10.1002/anie.202008442) a behaviour that was supposed to be restricted to early transition metals. In the same area we have demonstrated remote and reversible C-H and C-C bond formation/cleavage for the same ligand in a related Ir(I/III) system (J. Am. Chem. Soc. 2019, 141, 2205). As pointed out by some authors, even homobimetallic species with multiple metal-metal bonds can exhibit FLP-like reactivity. In this vein, our exploration of the ambiphilic behavior of dimolybdneum species has shown highly interesting results in terms of small molecule activation (Chem. Commun. 2018, 54, 9186) and unusual bonding (two manuscripts in preparation).

Objective 2: Hybrid main group/transition metal elements. We have synthesized a family of transition metal/germylene species stabilized by a series of phosphinoamide bifunctional ligands. We have found, however, that all prepared complexes are inactive towards small molecule activation and thus catalysis. In parallel, we have examined the coordination chemistry of sterically congested germylene compounds with a variety of transition metals. Although this approach was started more recently, we have already accumulated important results. For instance, we have obtained dynamic information from X-ray diffraction studies on π-interactions in cationic metalogermlenium cations. We believe that these studies demonstrate the importance of these overlooked type of contacts in low-valent tetrylene chemistry (work under review). In addition, we have explored the reactivity of a gold/platinum frustrated Lewis pair towards tetrylene dihalides (combining WP1 and W2), revealing an interesting Sn-mediated phosphine exchange reaction and formation of hybrid clusters (Dalton Trans. 2019, 48, 9127). With the same spirit of combining WP1 and WP2 we have explored the bonding in metal-only Lewis pairs formed between a Rh(I) Lewis base and a series of main group Lewis bases (Chem. Eur. J. 2020, 10.1002/chem.202003167).

Objective 3: We have prepared a number of transition metal clusters of Ir and Ru, as well as others based on Rh and Au. We have combined cationic versions of these clusters with commercial polyoxometalates and obtained a family of heterogeneous intercluster compounds. Despite our success in synthetic aspects, the prepared materials do not show remarkable results in terms of catalysis yet. We will continue exploring other related systems, as described in our contingency plans, in the following months. In the meantime we have also examined one of our contingencies for this WP, consisting in the preparation of polydentate ligands to access polynuclear complexes that could also be later heterogeneized in combination with polyoxometalates. As such, our first results on the coordination chemistry of versatile trisphosphinite ligands was recently reported (Molecules, 2020, 25, 593).
The following paragraphs cover progress beyond the state of the art within this ERC project from February 2018 to July 2020. It has been divided in three sections as per Objectives 1-3 described above, providing a bullet list of achievements that go beyond the state of the art.

Objective 1:
- We have gained solid mechanistic support for the first truly frustrated system entirely based on transition metals.
- We have reported the first bimetallic system that efficiently activates both O-H and N-H bonds in water and ammonia, respectively.
- We have demonstrated that subtle modifications of steric parameters in bimetallic frustrated Lewis pairs can have dramatic effects on regioselectivity during bond activation processes.
- We have extended the library of bimetallic frustrated Lewis pairs far beyond their previous development.
- We have evinced the usefulness of using bimetallic approaches to isolate otherwise fleeting intermediates.
- We have provided further evidence of the non-innocence character of the widespread pentamethylcyclopentadienyl ligand, with prior unreported transformations.

Objective 2:
- We have isolated the first examples of hybrid transition metal/low-valent heavier main group elements based on NP bifunctional ligands
- We have synthesized a number of transition metal/tertrylene systems with unprecedented structural features and reactivity
- We have made use of structural data from X-ray diffraction studies to gather fundamental information on dynamic processes for arene π-bonding in tetrylenes

Objective 3:
- We have demonstrated that the combination of cationic and anionic clusters produce highly insoluble intercluster compounds that show potential for catalytic applications.
- We have provided a robust and versatile method to access trimetallic complexes based on trisphosphinite ligands.

Overall, expected results for the next future in the three aforementioned objectives will involve the implementation of already investigated bond activation processes into catalytic applications.
General image of the work done