Redox-active Metalladiphosphine Ligands for Catalysis

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The main topic of the research proposal is the development and utilization of redox-active diphosphine ligands based on alkynes, which are substituted by phosphine groups. Alkynes bearing P-atoms in both alpha-positions are excellent bridging ligands. The unsaturated character of the alkyne bridges involves a high electronic cooperativity of the linked metals, which is particularly strong in the side-on carbon phosphine chelate coordination mode. Such cooperativity in dinuclear complexes allows either fast intramolecular electron transfers or even delocalized states over both metals. Accordingly, from an academic prospective the specific electronic structure in those complexes is an intriguing matter of investigation. The systematic development of metalla-acetylenediphosphine ligands and their coordination chemistry is directed to an improvement of catalytic activity of catalytically active P,P-coordinated metals by the electronic coupling of the metals involved. Redox-active phosphines offer the possibility to either switch the donor strength within the catalytic cycle by an intramolecular electron transfer (relay function) or to serve as an electron reservoir for oxidative addition and as a sink for reductive elimination. The latter is particularly interesting for first row transition metals in order to overcome the one-electron redox step limit. In addition, on this basis paramagnetic catalytic systems might become accessible, which are usually diamagnetic in combination with standard phosphines due to their character as strong field ligands. The kind of impact of this virtually distal paramagnetism on the catalytic processes belongs to the central issues of the project. Accordingly, alkyne complexes with terminal phosphine groups are potentially functional ligands; and the use of which in catalysis is generally promising.