Catalysis in Supramolecular Systems: the Case of Gel Phases

Abstract

Dedicated to Prof. Franco Cozzi in the occasion of his 70th birthday.Supramolecular gels are a fascinating class of materials, originated by the self-assembly of low molecular weight molecules. Underpinned by non-covalent interactions, they find application in a diverse range of fields. Among these, supramolecular gels can be considered as organized, nonconventional reaction media, able to influence reactivity in a radically different way, compared with what happens in solution. This short review will focus on this aspect, covering literature from 2010 onwards, addressing the application of supramolecular gels as reaction media. In particular, in the first section we explore organocatalytic reactions in gel phase, with wide synthetic relevance, such as aldol and Mannich reactions as well as Friedel Crafts or ester hydrolysis processes. Subsequently, focus is laid on metal-catalysed reactions, among which relevance is given to widely used reactions like crosscoupling and click reactions. Then, the final sections describe the use of supramolecular gels as reaction media for photoand biocatalysed processes.

Natural eutectogels: sustainable catalytic systems for C–C bond formation reactions

“…The reaction was also performed in the presence of cyclohexanone that gave 73% of yield with low enantioselectivities (96% de, syn 29%, ee). Unfortunately, changing the nature of the maleimide gave only traces in product (entries [11][12][13][14][15]. Also in this case, the obtained trend can be ascribed to the higher structural organisation and rigidity of the maleimides, which with more difficulty can reach the catalytic site to promote the reaction.…”

“…In this context, also supramolecular gels have been considered as suitable and environmentally friendly opportunities. [12][13][14][15][16] Supramolecular gels are emerging materials originated by the self-assembling of small molecules (Low Molecular Weight Gelators, LMWGs) in dilute solution. 17,18 The structure of the gel is formed by non-covalent interactions (hydrogen bonding, van der Waals, A6 @ established between the low molecular weight gelator and the solvent.…”

Advances in the Structural Strategies of the Self-Assembly of Photoresponsive Supramolecular Systems

“…Lately, the efficiency of supramolecular gels used in catalytic processes has been corroborated in an exhaustive study presented by Professor D’Anna and her collaborators [ 43 ]. In another instance, light responsive components might include the biological systems, as established by Chen Wang, who performs a unique review about DNA-based hydrogels with transient behaviors by responding to self-regulating chemistry.…”

Photocatalyst-Incorporated Cross-Linked Porous Polymer Networks

“…Their reversible nature, based on assembly−disassembly equilibrium via noncovalent interactions (hydrogen bonding, p−p stacking, donor−acceptor interactions, metal coordination, hydrophobic forces, van der Waals interactions) allows further reactions in confined spaces, which plays a key role in tuning photocatalytic activity of desired materials. 106 Low-molecular-weight com-…”