Specially Functionalised Ligands and Coordinating Supports which Facilitate Dissolution of Catalytic Transition Metal Species in Non-Polar 'Green' Solvents, such as ScCO_2

摘要

For environmental, economic and moral reasons, the chemical industry is increasingly seeking to engage cleaner, sustainable processes where appropriate, in place of older more polluting technologies. In some cases, a means by which this might be achieved is via the substitution of organic solvents, which present a variety of environmental hazards, for "green" solvents. Non-toxic, largely inert supercritical carbon dioxide (scCO_2) which contributes zero net VOC emissions is an example of such a solvent. In spite of some highly successful applications of scCO_2, in general it is an extremely poor solvent, very non-polar and lacking the ability to dissolve all but the smallest molecules of any significant polarity. Dissolution of inorganic salts and the vast majority of metal complexes is therefore difficult and consequently homogeneous catalysis employing such compounds is not possible in the same way as in more conventional solvents. One strategy for improving the solubility of catalysts is the functionalisation of ligands with non-polar substituents. Such groups include trimethylsilyl groups, carbosilane dendrimers and polydimethylsiloxane (PDMS).