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Sais derivados do cátion 1,3-dialquilimidazólio são uma das mais populares e investigadas classes de líquidos iônicos a temperatura ambiente. Embora, em vários casos, suas propriedades físico-químicas e/ou o resultado dos processos que ocorrem nesses líquidos diferem significantemente daqueles obtidos em solventes orgânicos dipolares, estes ainda podem ser descritos como simples solventes orgânicos. Nesta revisão, será introduzido o conceito que líquidos iônicos derivados do cátion 1,3-dialquilimidazólio são mais convenientemente descritos como estruturas poliméricasn-} n onde DAI representa o cátion 1,3-dialquilimidazólio e X o ânion. Este padrão estrutural é observado geralmente em sólidos e mantido em grande extensão no estado líquido e mesmo em fase gasosa. A introdução de outras moléculas ou macromoléculas no líquido iônico provoca a perturbação da rede de ligações de hidrogênios podendo gerar, em alguns casos, nano-estruturas com regiões polares e apolares onde compostos de inclusão podem ser formados.

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Ionic liquids (ILs), in particular imidazolium-based ILs, have proven to be suitable media for the generation and stabilisation of soluble metal nanoparticles (NPs). Indeed, transition-metal NPs with small sizes, narrow size distribution and different shapes have been prepared by reduction of organometallic compounds with molecular hydrogen, decomposition of transition-metal complexes in the zero-valent state, metal bombardment or simple transfer for previously prepared water- or classical organic solvent-soluble colloids to the ILs. The formation and stabilisation of NPs in these highly hydrogen bonded organised supramolecular fluids occur with the re-organisation of the hydrogen bond network and the generation of nanostructures with polar and non-polar regions, including the NPs. The IL forms a protective layer, which is probably composed of imidazolium aggregates located immediately adjacent to the nanoparticle surface, which provides both steric and electronic protection against aggregation and/or agglomeration. These stable transition-metal NPs immobilised in the ILs have proven to be efficient green catalysts for several reactions in multiphase conditions and also novel materials for chemical sensors. In this critical review, the structural/surface properties of these soluble metal NPs dispersed in ILs and their application in catalysis and as chemical sensors are discussed, with particular attention paid to the stabilisation models proposed to explain the stability and properties of these metal NPs (219 references).

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1-n-Butyl-3-methylimidazolium hexafluorophosphate room-temperature ionic liquid is not only suitable as a medium for the preparation and stabilization of iridium nanoparticles but also ideal for the generation of recyclable biphasic catalytic systems for hydrogenation reactions. Thus, Ir(0) nanoparticles with a mean diameter of 2 nm have been prepared by reduction of Ir(I) dissolved in the ionic liquid with H2. This catalytic solution can be reused several times for the biphasic hydrogenation of olefins under mild reaction conditions.

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