Selective syntheses and fragmentation reactions of cationic cyclo-Phosphanes

• Applicant: Professor Dr. Jan J. Weigand
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 420176248

Next to the element carbon, phosphorus has the highest affinity to build-up homo atomic ring and cluster compounds. This fact mirrors already in the diverse element modifications of phosphorus, from which the P4 molecule is the most reactive modification. The tendency to form comparatively strong P–P single bonds (200 kJ/mol) also reflects the diverse and versatile class of compounds of polyphosphanes. In this regard, the chemistry of monocyclic polyphosphanes featuring the general formula PnRn (R = alkyl, aryl) is also well documented in literature and thus, a fascinating and abundant field of phosphorus chemistry already for decades. However, there is not very much known about the synthesis and the reactivity of cationic cyclo-phosphanes featuring the general formula LnPnn+ and LnRmPn+mn+ where the onio-substituent L derives from N-heterocyclic carbenes (NHC) or cyclic alkyl(amino)carbenes (cAAC). With our synthesis of the cationic tetraphosphetane, we hope to establish a novel route to a whole library of cationic cyclo-phosphanes, for which the ring size is mostly controlled by the substituents at the phosphorus atom. Also the substitution pattern (electronic and steric properties) of the substituents L and R will control the ring size for the synthesis of the cationic cyclo-phosphanes. Next to the development of novel strategies to form cationic cyclo-phosphanes, we will focus on in-depth reactivity studies. At the end of this project, we hope to gain a profound and fundamental understanding of the presented methods to synthesize cationic cyclo-phosphanes via efficient and rational routes. Regarding the reactivity studies on the symmetric and mixed-substituted cyclo-phosphanes, we will focus on reactions with main group element compounds. Different reaction models such as fragmentation reactions, insertion- and transfer reactions, ring expansion reactions and redox reactions will be developed. As this project is of fundamental and explorative nature, we will herewith enter new areas in the field of cyclo-phosphanes and thus, many of our proposed reactions are not a priori predictable. We believe that many of our suggested reaction pathways will independently lead to interesting and exciting phosphorus compounds. A general constitution of the reaction behavior of symmetric and mix-substituted cyclo-phosphanes will be developed and will be a major result of this project. In this regard, the implementation of in-depth mechanistic studies owns a significant impact in order to identify reactive intermediates and side-products.

• DFG Programme: Research Grants
• International Connection: Spain
• Cooperation Partner: Professor Dr. Antonio Frontera