Accessing Metalloradical-Type Reactivity from Dinuclear Pd(I) Catalysts

• Applicant: Professorin Dr. Franziska Schoenebeck
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555706376

Recent advancements within the fields of synthesis and catalysis have showcased the value of dinuclear Pd(I) as robust and versatile catalysts, capable of facilitating numerous cross-coupling and isomerisation processes, which had previously proven challenging-to-accomplish under conventional Pd(0)/Pd(II) catalytic approaches. The key to the Pd(I) dimers’ versatility, as determined by computational and mechanistic studies, has been its ability to access three different reactivity modes, which includes: (1) releasing low-coordinate Pd(0) species; (2) directly engaging in dinuclear reactivity; and (3) acting as a reservoir for Pd(II)–H. In all three cases, the reaction pathways invoked are two-electron processes, and to date, there has been no indication that Pd(I) radical monomers are either formed or involved in any of the reported transformations. This is in stark contrast to what has been established within our research programme for analogous Ni(I) dimers, which have been shown to engage in metalloradical-type reactivity in the presence of olefin-containing substrates. Therefore, it is the goal of this research proposal to investigate the fundamental differences in reactivity between Ni(I) and Pd(I) dinuclear complexes and establish whether it is possible to generate Pd(I) metalloradicals from Pd(I) dimer precursors, in preference over the established modes of activation. We aim to build upon our expertise in transition metal catalysis, organic synthesis and computational chemistry to determine whether changes to the ligand sphere of the Pd(I) dimer complexes or external stimuli, such as visible light, are necessary to trigger this unprecedented metalloradical reactivity. Our preliminary work, guided by machine learning (ML) predictions and literature precedent, has focussed on establishing a library of Pd(I) dimer candidates, whose potential for radical-type reactivity we propose to further study in three stages. In the first stage, we will use computational tools and spectroscopic techniques to identify Pd(I) complexes most likely to exhibit metalloradical reactivity. In the second stage, we will utilise vinylcyclopropanes (VCP), which were previously employed in our study of the Ni(I) dimer system, as radical probes to assess the Pd(I) dimers’ capacity to engage in single electron processes. Finally, in the third stage, we aim to apply our findings towards the development of Pd(I) radical-enabled transformations, such as isomerisations and remote functionalisations of terminal alkene substrates. Through this work, we aspire to broaden the scope and range of transformations enabled by Pd(I) dinuclear catalysis, which will subsequently enable us to improve the state-of-art of transition metal catalysis and methodology development as a whole.

• DFG Programme: Research Grants