Coordination complexes, ionic liquids metal ions

Coordination numbers of 2-6 are found for mononuclear metal complex ionic liquid anions, mostly with halide ions. 

Transition metal catalysis in liquid/liquid biphasic systems principally requires sufficient solubility and immobilization of the catalysts in the IL phase relative to the extraction phase. Solubilization of metal ions in ILs can be separated into processes, involving the dissolution of simple metal salts (often through coordination with anions from the ionic liquid) and the dissolution of metal coordination complexes, in which the metal coordination sphere remains intact. 

Ionic liquids can be used as replacements for many volatile conventional solvents in chemical processes see Table A-14 in the Appendix. Because of their extraordinary properties, room temperature ionic liquids have already found application as solvents for many synthetic and catalytic reactions, for example nucleophilic substitution reactions [899], Diels-Alder cycloaddition reactions [900, 901], Friedel-Crafts alkylation and acylation reactions [902, 903], as well as palladium-catalyzed Heck vinylations of haloarenes [904]. They are also solvents of choice for homogeneous transition metal complex catalyzed hydrogenation, isomerization, and hydroformylation [905], as well as dimerization and oligomerization reactions of alkenes [906, 907]. The ions of liquid salts are often poorly coordinating, which prevents deactivation of the catalysts. 

Decreasing the solubility of ionic liquids in water plays an important role in ionic liquid-based extraction. The anion has the primary effect on water miscibility, whilst the cation seems not to affect miscibility much (Seddon et al. 2000). The order of increasing hydrophobicity for the anions is Br , Cl < [BFJ < [PFe] < [NTfa] (Toh et al. 2006). Metal ions are poorly soluble in ILs except when coordinated with, or solvated by, hydrophobic molecules added to the IL phase, or with hydrophilic complexing anions that can facilitate metal ion transport into the IL phase. 

---