2,2'-Diphosphinotolanes and Their Multifaceted Reactivities: On the Edge Between [PCCP]-Pincer Ligands and P-Heterocyclic Carbenes

• Applicant: Privatdozent Dr. Joachim Ballmann
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 406990896

Within the bounds of this research project, exploratory studies are to be conducted in order to shine light on 2,2'-diphosphinotolanes and their coordination chemistry. In preliminary experiments, these systems were found to exhibit bifurcated reactivities, which are governed by the employed metal ions and precursors, respectively. In general, the divergent reaction pathways may either lead to rigid [PCCP]-pincer complexes or to PHC-coordinated species (PHC = P-heterocyclic carbene). To allow for a controlled and selective synthesis of these different types of complexes, an in-depth analysis of the later discovery is required. This analysis certainly represents one of the most important milestones to be reached over the course of this research project. In the case of [PCCP]-pincer scaffolds, the focus will be set on early transition metal complexes and on their reactivities. Given that simple theoretic considerations indicate that such [PCCP]-pincer complexes are well-suited for the stabilization of M=E- and M≡E-motifs (E = CR2, NR and CR), the synthesis of group 4, group 5 and group 6 alkylidenes and alkylidynes is intended. In turn, these complexes are to be examined with respect to their application in different catalytic processes, such as alkene or alkyne metathesis. The aforementioned P-heterocyclic carbenes, however, seem to be particularly well-suited for the synthesis of late transition metal complexes. In this context, the focus will be set on selected precious metals (Ruthenium, Rhodium and Palladium and their heavier homologs), as their PHC-complexes hold great promise for various applications in homogeneous catalysis (inter alia for catalytic transfer hydrogenations, alkene metathesis and allylic substitution reactions). To exploit the underlying concept for the preparation of PCH-complexes, the synthesis of bis-PHC-complexes is intended as well. Consecutively, these complexes have to be evaluated with respect to their applications in homogeneous catalysis, which paves the way for entering entirely uncharted scientific terrain.

• DFG Programme: Research Grants