News about the diagonal relationship between phosphorus and carbon: development of 5-phosphasemibullvalene derivatives and their application as P(III)-Ligands in homogeneous catalysis

• Applicant: Professor Dr. Christian Müller
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 336307444

The di-π-methane rearrangement of 1-phosphabarrelenes to 5-phosphasemibullvalene derivatives, which we first described by us in 2016, represents a new and interesting diagonal relationship between the elements phosphorus and carbon in the periodic table of the elements. It provides an easy and selective access to chiral, sterically demanding, rigid and configurationally stable organophosphorus(III) compounds. In the first funding period (2017-2020), the photoinduced formation of 5-phosphasemibullvalene derivatives was investigated fundamentally and systematically. In doing so, we were not only able to obtain important results regarding the synthesis, coordination chemistry and separation of enantiomers of these phosphorus compounds, but also important information about their stereoelectronic properties as well as their use as ligands in Au(I)-catalysed cyclization reactions and in the Rh-catalyzed hydroformylation of terminal and internal alkenes could be gained. Furthermore, valuable information on the mechanism of di-π-methane rearrangement of complex-bound 1-phosphabarrelenes was obtained by means of DFT calculations. Parts of the results have already been published in four peer-reviewed journals or presented in a series of lectures. At least two further publications are in preparation. Also, the di-π-methane rearrangement of 1-phosphabarrelenes to 5-phosphasemibullvalene derivatives in the coordination sphere of metals was acknowledged as a "highlight". Furthermore, a dissertation was written on this project. The focus of the second funding period is in particular i) the development of bidentate/chelating 5-phosphasemibullvalene; ii) di-π-methane rearrangement in coordination compounds; iii) access to still unknown 2-phosphasemibullvalenes; iv) mechanistic investigations; v) the establishment of (enantionmerically pure) 5-phosphasemibullvalenes in the enantioselective hydroformylation of prochiral alkenes. The focus is on the enantioselective Rh-catalyzed hydroformylation of internal and less reactive alkyl-alkenes to the corresponding chiral (internal) aldehydes. For this extremely challenging reaction, there are so far only very few selective molecular catalyst systems known in the literature.

• DFG Programme: Research Grants