Charged ligands for catalyst immobilisation and analysis

Ligands involved in organometallic chemistry have been functionalised at locations somewhat removed from the binding site for diverse reasons, including modification of electronic and steric characteristics, improving solubility, to confer chirality, to add a spectroscopic "handle", to facilitate electron-transfer processes or for spin-labelling. Here, the focus is specifically on catalytically active metal complexes in which a charged or highly polar group has been appended to the periphery of one or more of the ligands. For the most part, the motivation has been to alter the solubility properties of the catalytic metal complex to which it is attached, for the purposes of immobilisation in another phase (water, ionic liquids, etc.) and improvement of the green credentials of the process. However, other uses are also becoming recognised, for example to aid in situ analysis of catalysts by electrospray ionisation mass spectrometry.