Phosphane-Based Cyclodextrins as Mass Transfer Agents and Ligands for Aqueous Organometallic Catalysis

Sébastien Tilloy,Eric Monflier,Hervé Bricout,Stéphane Menuel,Cécile Binkowski-Machut

doi:10.3390/molecules171113062

Abstract

The replacement of hazardous solvents and the utilization of catalytic processes are two key points of the green chemistry movement, so aqueous organometallic catalytic processes are of great interest in this context. Nevertheless, these processes require not only the use of water-soluble ligands such as phosphanes to solubilise the transition metals in water, but also the use of mass transfer agents to increase the solubility of organic substrates in water. In this context, phosphanes based on a cyclodextrin skeleton are an interesting alternative since these compounds can simultaneously act as mass transfer agents and as coordinating species towards transition metals. For twenty years, various cyclodextrin-functionalized phosphanes have been described in the literature. Nevertheless, while their coordinating properties towards transition metals and their catalytic properties were fully detailed, their mass transfer agent properties were much less discussed. As these mass transfer agent properties are directly linked to the availability of the cyclodextrin cavity, the aim of this review is to demonstrate that the nature of the reaction solvent and the nature of the linker between cyclodextrin and phosphorous moieties can deeply influence the recognition properties. In addition, the impact on the catalytic activity will be also discussed.

Highlights

Green chemistry is a movement whose goal is to develop more environmentally friendly methods for the chemical industry and to reduce its environmental impact
Various CD-mono, di, tri or tetra-phosphanes have been described in the literature [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27], but only some CD-functionalized by one or two phosphorous moieties were exploited in aqueous organometallic catalytic processes [28,29,30,31,32,33,34,35,36]. While their coordinating properties towards a transition metal and their catalytic properties were fully detailed, their mass transfer agent properties were much less discussed. As these mass transfer agent properties are directly linked to the recognition capacities, the aim of this review is to demonstrate that the nature of the reaction solvent and the nature of the linker between cyclodextrin and phosphorous moieties can deeply influence the availability of the CD cavity
This group has proposed three different types of CD-diphosphanes (Figure 2; CD-diphosphanes 1–3) in order to combine phase transfer catalysis and transition metal catalysis. To establish whether these phosphane-CDs functioned as supramolecular catalysts, an equimolar mixture of 1-decene and 4-phenyl-1-butene were subjected to competition experiments. This mixture was hydrogenated in DMF by rhodium complexes based on these CD-diphosphanes

Summary

Introduction

Green chemistry is a movement whose goal is to develop more environmentally friendly methods for the chemical industry and to reduce its environmental impact. Replacement of hazardous solvents with water is one of the main points of this movement [1]. In this field, aqueous organometallic catalysis occupies a prominent place [2]. Mass transfer agents, such as cyclodextrins (CDs) [3], are necessary to increase the low water-solubility of organic substrates and secondly, water-soluble ligands, such as phosphanes [4], are necessary to solubilise the metal in water In this context, cyclodextrin-functionalized phosphanes are an interesting alterative since these compounds can simultaneously act as mass transfer agents and as coordinating species (Figure 1)

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Conclusion