Metal-Micelle Interaction Leading to Spontaneous Formation of Ligand-Free Palladium(0) Nanoparticles: Highly Efficient Catalysis Enabling Biaryl Ketone Formation from Carboxylic Acid Derivatives

Aqueous Micelles as Solvent, Ligand, and Reaction Promoter in Catalysis

Water is considered to be the most sustainable and safest solvent. Micellar catalysis is a significant contributor to the chemistry in water. It promotes pathways involving water-sensitive intermediates and transient catalytic species under micelles' shielding effect while also replacing costly ligands and dipolar-aprotic solvents. However, there is a lack of critical information about micellar catalysis. This includes why it works better than traditional catalysis in organic solvents, why specific rules in micellar catalysis differ from those of conventional catalysis, and how the limitations of micellar catalysis can be addressed in the future. This Perspective aims to highlight the current gaps in our understanding of micellar catalysis and provide an analysis of designer surfactants' origin and essential components. This will also provide a fundamental understanding of micellar catalysis, including how aqueous micelles can simultaneously perform multiple functions such as solvent, ligand, and reaction promoter.

Aqueous micellar technology: an alternative beyond organic solvents

Solvents are the major source of chemical waste from synthetic chemistry labs. Growing attention to more environmentally friendly sustainable processes demands novel technologies to substitute toxic or hazardous solvents. If not always, sometimes, water can be a suitable substitute for organic solvents, if used appropriately. However, the sole use of water as a solvent remains non-practical due to its incompatibility with organic reagents. Nonetheless, over the past few years, new additives have been disclosed to achieve chemistry in water that also include aqueous micelles as nanoreactors. Although one cannot claim micellar catalysis to be a greener technology for every single transformation, it remains the sustainable or greener alternative for many reactions. Literature precedents support that micellar technology has much more potential than just as a reaction medium, i.e., the role of the amphiphile as a ligand obviating phosphine ligands in catalysis, the shielding effect of micelles to protect water-sensitive reaction intermediates in catalysis, and the compartmentalization effect. While compiling the powerful impact of micellar catalysis, this article highlights two diverse recent technologies: (i) the design and employment of the surfactant PS-750-M in selective catalysis; (ii) the use of the semisynthetic HPMC polymer to enable ultrafast reactions in water.