Nanoconfinement Effects of Micellar Media in Asymmetric Catalysis

Abstract

Replacement of organic solvents, in particular chlorinated, aromatic, and polar aprotic ones, is an emerging issue that can find a solution in the development of catalytic reactions in water. Nature performs a multitude of chemical transformations in water under mild conditions mediated by enzymes. In particular the nanoconfinement effects of the enzymes ensure high activity and impressive stereoselectivities. Micellar catalysis is nowadays a real alternative approach to catalysis in traditional organic media, enabling good activity under mild conditions, with the advantage of possible catalyst and micellar medium recycling. Micellar media emerged also as good nano‐environments for stereoselective reactions, with many examples of chemical transformations mediated by metal and organo‐catalysts for which improvements of stereoselectivity were observed with respect to the same reaction under homogeneous conditions in traditional organic solvents. More specifically, both the catalytically active site and the micelles provided by the surfactant can contribute to the asymmetric induction, partially resembling what known in terms of stereoselectivity imparted by the active site of enzymes and metallo‐enzymes.

Surfactant Micellar and Vesicle Microenvironments and Structures under Synthetic Organic Conditions

“…Together, these experiments provide size, partitioning, microenvironment, and system evolution-upon-reaction information that was not previously reported and could not have been learned through previously ex situ, low-concentration-required, or nonspatially resolved/ensemble-averaged analytical techniques. These findings enable immediate revision of models of size (micro for all surfactants rather than nano), internal environments (substantially dictated by organic substrate, variations pinpointed to specific reagents), and partitioning (dependent on each surfactant) in these systems, suitable for improving the development of sustainable aqueous–organic reactions. ,− ,,− …”

Aqueous micellar technology: an alternative beyond organic solvents

“…Future work using more abundant metals like copper, nickel, cobalt, and iron will further increase the popularity of micellar catalysis. At the moment, asymmetric reactions using chiral micelles are still underdeveloped, 53 and micelles of PS-750-M, which are chiral, have only been used for achiral reactions. Thus, the application of PS-750-M or development of the second generation of this additive for asymmetric synthesis could be anticipated in the following years to ensure more environmentally friendly cross-coupling reactions.…”

Recent Developments and Trends in Asymmetric Organocatalysis

“…Furthermore, confined catalysts and media have also been envisioned for the development of novel organocatalytic processes (Scheme 7 B). [39] Thus, the use of enzyme mimicking catalysts with confined active sites, heterogenized organocatalytic decorated metal‐organic frameworks (MOFs) and cages [40] or use of micellar environment [41] provides a unique confined reaction media that allows for unusual conformational restricted geometries and/or highly selective processes.…”