Periodic Reporting for period 4 - YlideLigands (Tailoring Ylidic Compounds as Ligands for Organometallic Chemistry)
Période du rapport: 2021-01-01 au 2021-12-31
This project takes aim at the development and application of novel ylidic, carbon-centred Lewis bases. By means of a smart molecular design, systems with unusual electronic properties and donor capacities will be prepared and their reactivity towards main group element compounds and transition metal complexes will be explored. For example, applications of neutral bisylidic compounds as well as anionic metalated ylides will be studied. Employing experimental and computational methods a fundamental understanding of the electronic structure depending on the actual ligand design and its influence on the donor capacity will be provided. This will allow the manipulation and tailoring of the properties and reactivities of the bases and thus open applications such as their use in bond activation reactions, as strong donors for the stabilization of reactive compounds as well as their application as electronically flexible ligands in catalytically active metal complexes.
By means of a careful molecular design, we succeeded in the isolation of a couple of stabilized systems, which are accessible in gram-scale and thus – for the first time – applicable as isolated reagents. Detailed computational studies on the electronics and bonding situation in metalated ylides in comparison to neutral bisylidic compounds confirmed the special properties of these compounds and allowed for a more profound understanding of these ligand systems, which will help to experimentally tailor their properties for further applications. First reactivity studies already confirmed the excellent applicability of metalated ylides for ylide-functionalization. Owing to the strong nucleophilicity the ylide moiety can be transferred to many different main group elements and thus be used for the manipulation of their properties. This strategy allowed us to isolate the first ylide-substituted boron cation, in which we made use of the strong donor capacity of the yldiide to stabilize a highly electron-deficient compound with novel reactivity.
Besides being excellent reagents for the stabilization of reactive compounds, the yldiides also revealed to be ideal for a facile preparation of ylide-functionalized phosphines (YPhos ligands). Phosphines are amongst the most important ligands in homogenous catalysis. The design of new phosphines has been decisive for crucial developments in homogenous catalysis and contributed to many new synthetic methodologies that nowadays allow for the constructions of complex molecules which are often part in pharmaceuticals or agrochemicals. In a sub-project of this ERC-project, we further developed ylide-functionalized phosphines into a class of ligands with unusual and highly tunable electronic and steric properties which turned out to be ideal for a variety of different transition metal catalyzed reactions. For example, we could demonstrate that due to their strong donor properties, YPhos ligands are excellent ligands for gold-catalyzed hydroamination reactions and palladium-catalyzed C-N coupling reactions. Here, the YPhos-based catalysts were able to operate under unusually mild reactions conditions and showed high activities at low catalyst loadings. Thereby, they could also compete with or even surpass the activity of catalysts based on established ligand systems.
Overall, we were so far able to demonstrate that electronic stabilization of ylidic ligands allows for the allocation of carbon bases with unusual but valuable properties, which can be used in quite different directions, such as for fundamental studies on the stabilization of reactive species but also more applied areas such as in homogenous catalysis. In the second part of our research program we will continue these studies to further broaden the applications of our reagents.