Bond Activation and Catalysis by Transition Metal Frustrated Lewis Pairs

Periodic Reporting for period 1 - TM-FLPS (Bond Activation and Catalysis by Transition Metal Frustrated Lewis Pairs)

Reporting period: 2016-10-01 to 2018-09-30

This proposal has focused on developing a novel approach in the hot field of cooperative catalysis by merging fundamental concepts of main group and transition metal chemistry. Catalysis is critical to the delivery of future growth in the manufacturing sector, with catalytic processes generating around €1,000 Bn in products world-wide. Thus, the development and fundamental understanding of innovative new catalyst systems, such as the ones investigated in this proposal, has clear, direct and long-term benefits to the chemical manufacturing sector and to the broader knowledge-based economy. Moreover, catalytic science is a multidisciplinary and significant enabling discipline crucial to the advance of many priority areas such as the search of future energy systems, solar technologies, sustainable chemistry, synthetic biology or healthcare.

Nature catalytic designs outperform most synthetic approaches in terms of activity, selectivity or substrate scope, while relying on cooperative architectures in which neighbouring set of atoms crucially assist the metal to achieve a certain catalytic transformation. A paradigmatic approach in the area of synthetic cooperative chemistry is the development of Frustrated Lewis Pairs (FLPs), in which sterically encumbered combinations of Lewis acid/base (LA/B) couples are not quenched, but act cooperatively to activate a wide variety of small molecules. Drawing on this theme, the overall objective of this proposal was combining the rich chemistry of transition metals with the powerful reactivity offered by FLP systems by designing TM-FLPs after substituting at least one LA/B component by a transition metal and then demonstrating its usefulness for the activation and functionalization of small molecules.

Overall, the project has been highly successful. We have been able to demonstrate, for the first time, that it is possible to design a FLP system entirely based on transition metals (which we have coined with the term “TMOFLP”). We achieved this important goal by combination of two sufficiently bulky transition-metal based fragments of acidic and basic Lewis character (Figure 1). The bulkiness of the phosphine ligands quench Lewis adduct formation and confer high potential for small molecule activation. These results were published in JACS as a single-author paper (2017, 139, 2944).

Figure1. Activation of H2 and C2H2 by a TMOFLP based on Au(I) and Pt(0) complexes stabilized by bulky phosphine ligands. ORTEP diagrams for compounds 3a, 4a and 5a are represented.

One of the advantages of incorporating transition metals into FLP designs derives from the easiness of steric and electronic tuning by ligand modification, in stark contrast with the often difficult synthetic protocols to access acidic boranes typically used in traditional FLPs. We have demonstrated that by slight tuning of the steric properties of terphenyl phosphine ligands it is easy to alter the regioselectivity of the aforementioned transformations (Figure 2). In addition, we have elucidated the reaction mechanisms by a joint experimental/computational effort, results that will be shortly published.

Figure 2. Selectivity in the activation of acetylene by our TMOFLP system.

Overview of the dissemination of results
Publications

1. Campos, J.*. Dihydrogen and Acetylene Activation by a Gold(I)/Platinum(0) Transition Metal Only Frustrated Lewis Pair, J. Am. Chem. Soc. 2017 (single-author paper), 139, 2944.
(Repository: https://idus.us.es/xmlui/handle/11441/55206)

2. Campos, J.* Pares de Lewis frustrados basados en metales de transición. An. Quím. 2017, 113, 224-230. (Open Access)

3. Hidalgo, N.; Pérez-Jiménez, M.; Moreno, J. J.; López-Serrano, J.; Carmona, E.*; Campos, J.* Tuning the Selectivity of Alkyne Activation by a Transition Metal Only Frustrated Lewis Pair. Manuscript in preparation.

Dr. Campos has submitted two other papers that are now under review and are related to the present project by the central idea of developing novel cooperative catalysts.
4. Moreno, J. J.; Espada, M. F.; Krüger, E.; López-Serrano, J.; Campos, J.*; Carmona, E. Ligand Rearrangement and Hemilability in Rhodium(I) and Iridium(I) Complexes Bearing Terphenyl Phosphines, 2018, submitted to EurJIC.
5. Campos, J.* Dehydrogenation of alcohols and polyols from a hydrogen production perspective. 2018, submitted to Physical Sciences Reviews (Open Access).

Other dissemination activities
Invited seminars: 4 invited seminars at the Universities of Granada and Vigo and by the Royal Academy of Sciences of Sevilla.
Conferences: 2 Plenary talks at the XIV Young Researchers Symposium (Badajoz) and the 1st Conference of PhD students (Sevilla)
Outreach activities: 4 invited talks in different events such as the European Researchers´ Night.

Other relevant achievements
Dr. Campos carried out a secondment period at the University of Oxford within the group of Prof. Simon Aldridge. During that stay Dr. Campos was able to elucidate the nature of a silicon species that was very recently reported to be a cAAC-silicon(I) radical (Angew. Chem. Int. Ed. 2017, 56, 7573). Instead of being a radical the reported purple compound could be a silicon(II) dimer with a Si-H termini that would better fit with all experimental observations. We are currently preparing a manuscript to report these results.

The most important outcome from this Marie Curie project it perhaps the fact that it served as the experimental seed that justify a later ERC Starting Grant proposal prepared by Dr. Campos and recently funded (CoopCat). This proposal focuses on developing innovative cooperative strategies for catalysis. The results derived from this Marie Curie IF, mainly the demonstration that a TMOFLP can be prepared, was certainly very important to get the ERC project funded. This latter achievement is in fact the reason to request an early termination for the Marie Curie proposal, but the science behind it will continuously develop over the following years under the umbrella of Dr. Campos’ ERC StG.

As stated above, we have made an important scientific achievement beyond the current state-of-the-art in the fields of cooperative chemistry and frustrated Lewis pairs by designing the first TMOFLP and demonstrating its capacity to activate small molecules. We have also demonstrated how we can tune the selectivity of the metallic pair by ligand modification, a strategy more versatile than the classic modification of boranes typically employed in traditional FLPs. These results constitute the experimental seed that allowed Dr. Campos for being awarded with an ERC StG grant that builds upon these results. The more complex cooperative systems that will emerge from future studies will likely have an important impact not only on the field of cooperative chemistry, but also in related areas linked to catalysis. The wider societal implications are frontierless, since catalysis is a fundamental piece in many of the most important scientific challenges for the future, such as the use of renewable raw materials in industry or the implementation of a novel sustainable energy paradigm.

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Periodic Reporting for period 1 - TM-FLPS (Bond Activation and Catalysis by Transition Metal Frustrated Lewis Pairs)

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