Stimuli-responsive dendrimers. Towards tunable catalysts (DENDSWITCH)
Zusammenfassung der Projektergebnisse
About 90% of the chemicals produced industrially (including drugs) employ a catalytic reaction in at least one synthetic step. In spite (or because) of this universal industrial use, catalysis is one of the main basic research areas. Here, catalysts based on dendrimers can combine the advantages and minimise the disadvantages of homogeneous and heterogeneous catalysts. In this joint ANR-DFG project, we have prepared an unprecedented, original type of catalysts: dendritic catalysts with modifiable properties under the influence of an external stimulus. The dendrimers and the ferrocenyl phosphines were synthesised separately and in a final step combined to give dendritic ferrocenyl phosphines. These were used as ligands for the catalytically active ruthenium complexes. The starting materials and products were fully characterised. The electrochemistry of the dendritic ferrocenyl phosphines and their ruthenium complexes was also studied. The two metals have different redox potentials giving the possibility to oxidise them separately. The catalytic properties of these giant molecules (diameters of several nanometers) are reversibly modified under the influence of an external stimulus. Thus, the electronic changes induced by oxidation of the ferrocene moiety are conferred via the linker to the catalytically active site, turning off its catalytic properties, as a true switch would do. The proof of concept has been provided by the catalytic isomerisation of 1- octen-3-ol using a dendritic complex. The catalytic reaction is highly efficient when the ferrocene moiety is neutral (ON), but switched OFF when the ferrocene moiety is oxidised. This phenomenon is reversible: reduction of the ferrocenium moiety to ferrocene re-activates the catalytic efficiency of the dendritic complex. The possibility to control the catalytic efficiency of these dendritic ferrocenyl phosphine complexes by employing an external stimulus offers great perspectives for a better mastery of catalytic processes.
