Bimetallic complexes of photoswitchable phosphines and uses in catalysis – Switch-Phos

Our first objective was to prepare phosphorous ligands and the corresponding bimetallic complexes, from nitrogen-containing skeletons whose geometry changes under the effect of UV irradiation. Our working hypothesis foresaw that only one of the two forms of the catalyst would generate a synergy between the two metal centres and that, consequently, its reactivity would be profoundly different from that of the other isomer. This study of fundamental chemistry intended first to validate this hypothesis and to develop then original applications.
Thus, in the framework of this project, we first synthesized non-fluorinated azobenzene based diphosphines, then fluorinated ones, and the corresponding gold complexes. Subsequently, these bimetallic complexes were used as catalysts in an intramolecular hydroamination reaction. Preliminary laboratory results showed that it was indeed possible to control the kinetic of this reaction using light as an external stimulus. Thus, the isomeric form of the catalyst that favours double activation of the substrate was found to be more active than the “monometallic” form. This illustrates a catalytic “ON/OFF” process. In order to have a more efficient catalytic system, we subsequently developed a new photo-switch skeleton with a cyclic azobenzene structure, called triazonine. The corresponding gold complexes have enabled, for the first time, the so-called “ON/ON”catalytic processes, where the two interconverting isomers of the catalyst lead to two different products from the same substrate. The photophysical properties of these new light reactive species were investigated at the ENS Paris-Saclay.

After synthesizing, characterizing, and using in catalysis gold bimetallic complexes with fluorinated (Catal. Sci. Technol. 2018) and non-fluorinated (Dalton Trans 2021) skeletons, we focused on developing triazonines as new photoswitch molecular scaffolds (Chem. Commun 2021). As part of this project, a review has been written that provides a comprehensive overview of phosphorus species possessing a photoswitch skeleton, whether or not they are used in catalysis (ChemCatChem 2020).

Further impactful studies are currently being finalized and will be published shortly.

The Switch-Phos project is a fundamental research project coordinated by Arnaud Voituriez (ICSN). He also associates Angela Marinetti (ICSN), as well as Joanne Xie, Rémi Métivier, Nicolas Bogliotti and Stéphane Maisonneuve of ENS Paris-Saclay. The project began in early 2018 and lasted 52 months. It received an ANR support of 423 K€ for a total cost of around 900 K€.

The objective of this project is to develop an unprecedented series of photoswitchable phosphine complexes, namely bimetallic species, for uses in catalysis. In particular, we will investigate catalytic processes known to necessitate bimetallic activation. We intend to demonstrate that light induced changes of the geometrical features of these ligands will either modulate or, in the best case, induce an on-off switch of the catalytic activity. Such switchable catalysts are of prominent interest for the development of sequential multicatalytic systems, inspired by the catalytic cascades of natural biological processes. Moreover, bimetallic photoswitchable catalysts will afford unprecedented probes for mechanistic investigations on cooperative effects in bimetallic catalysis.