Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

Waste CO 2 at atmospheric pressure can be used to trigger dramatic changes in the properties of certain switchable materials. Compared to other triggers such as light, acids and oxidants, CO 2 has the advantages that it is inexpensive, nonhazardous, non-accumulating in the system, easily removed, and it does not require the material to be transparent. Known CO 2 -triggered switchable materials now include solvents, surfactants, solutes, catalysts, particles, polymers, and gels. These have also been described as ''smart'' materials or, for some of the switchable solvents, ''reversible ionic liquids''. The added flexibility of switchable materials represents a new strategy for minimizing energy and material consumption in process and product design.

We report a new class of CO 2 binding organic liquids that chemically capture and release CO 2 much more efficiently than aqueous alkanolamine systems. Mixtures of organic alcohols and amidine/ guanidine bases reversibly bind CO 2 chemically as liquid amidinium/guanidinium alkylcarbonates. The free energy of CO 2 binding in these organic systems is very small and dependent on the choice of base, approximately À9 kJ mol À1 for DBU and Barton's base and +2 kJ mol À1 for 1,1,3,3tetramethylguanidine. These CO 2 capturing agents do not require an added solvent because they are liquid, and therefore have high CO 2 capacities of up to 19% by weight for neat systems, and slightly less when dissolved in acetonitrile. The rate of CO 2 uptake and release by these organic systems is limited by the rate of dissolution of CO 2 into and out of the liquid phase. Gas absorption is selective for CO 2 in both concentrated and dilute gas streams. These organic systems have been shown to bind and release CO 2 for five cycles without losing activity or selectivity.

In situ(11)B NMR monitoring, computational modeling, and external trapping studies show that selectivity and extent of H(2) release in metal-catalysed dehydrogenation of ammonia borane, NH(3)BH(3), are determined by coordination of reactive aminoborane, NH(2)BH(2), to the metal center.