Advances in science and technology come from the discovery of new and conceptually innovative ways to control the interactions and behaviour of matter and to extract new functions and applications from them. In this regard, exotic non-covalent interactions such as chalcogen bonds, from the attraction of negative sites to a chalcogen atom, and anion-pi, from the stabilization of anions on electron-deficient aromatic units, have been barely explored and their implementation in functional systems should result in a breakthrough in current science, amplifying the repertoire of supramolecular interactions available up to date.
The main objective of this project is the development of these unorthodox interactions as a tool in oganocatalysis and enzymatic catalysis, controlling the stabilization of reactive intermediates and transition states and modulating the outcome of the chemical transformation.
From here, two different goals are presented:
- Design of new molecular scaffolds able to interact with anions and negatively-charged reactive species through chalcogen bonds and study their performance as catalysts. Implementation of these systems in artificial enzymes would be highly desirable, with the idea of having access to asymmetric catalysis, on one hand, and of introducing this novel interaction in biological systems, on the other hand.
- Amplify the number of molecular scaffolds that shows activity in anion-pi catalysis. So far, small napthalenediimides (NDIs) and related structures have been the only players able to perform efficiently in anion-pi catalysis. Thus, the discovery of other materials that could increase the rather small collection of catalysts, such as electron-deficient fullerenes and/or other carbon allotropes, would result in a tremendous evolution of this research area.
Conclusions:
- Different molecules have been tested in chalcogen bonding catalysis, bearing a common central structure, dithienothiophene, decorated with different electron-withdrawing groups to increase the acidity of the sigma-hole, responsible of the interaction between the chalcogen atom with electron-rich units. Several of these structures have showed good catalytic activity in chemical transformations, with perfect correlation between the strength of the sigma-hole and the performance as catalysts (Figure 1). However, the implementation of this structures in artificial enzymes did not succeed. Chalcogen bonding interactions are not strong enough to activate the substrate in very polar solvents, i.e. water.
- Regading anion-pi catalysis, fullerenes and other carbon allotropes have been implemented in the portfolio of organic materials able to perform with this unconventional type of catalysis (Figure 2 and figure 4). In-depth study has been performed during this action, both related to the optimization of the chemical structure of the catalyst and the understanding of the parameters that govern anion-pi interactions with carbon nanomaterials. From this, a new direction in anion-pi catalysis has emerged, where highly polarizable materials rather than small and very electron-deficient ones reveal very good stabilization of anions and negatively-charged reactive intermediates and, thus, high activity as catalysts (Figure 3).
