It is a conjunction of factors. I suppose that it is highly cited because it provides an updated review of one of the most investigated and active areas of chemistry of recent years: room-temperature ionic liquids. These compounds possess highly interesting physical-chemical properties that may lead to them being considered as one of the first "real" green solvents. They are now highly popular in all areas of chemistry, used and investigated in a plethora of subjects in both industry and academia. Our group was one of the pioneers on the syntheses and applications on this class of compounds in the early 1990s, and in order to keep myself updated with the latest developments I periodically write reports on the subject; therefore, we were in a privileged position to write the review. It is evident that some people are more comfortable citing a single paper than a list of original papers.

The paper was primary intended to provide a major update on the synthesis and characterization of room-temperature ionic liquids and their application in organometallic catalysis. However, during the writing process it became clearer that in order to touch in-depth on the selected topic it was necessary to critically discuss (mostly raising unsolved questions) the properties of ionic liquids and to try to apply and correlate them with known important principles and models such as those of supramolecular chemistry and nano-structured materials.

At the beginning of 1990, our group had started developing projects on homogeneous organometallic catalysis applied to fine chemistry. Although homogeneous catalysis has several advantages compared with heterogeneous catalysis it also has serious disadvantages—mainly linked to the use of solvents that in most cases are not environmentally friendly. One of the approaches involved in solving this problem is the use of biphasic catalysis such as an aqueous-phase organometallic process. We had planned to engage our efforts in this direction. I can remember that at the same time my friend and colleague Roberto F. de Souza brought to my attention the landmark paper of Y. Chauvin describing the use of organo-aluminate molten salts as media for the biphasic nickel-catalyzed oligomerization of alfa-olefins. Since then we (Roberto’s group and my Laboratory) have started a collaboration project in the ionic liquid area, which has proven to have much broader applications than merely "solvents."

For economical and ecological reasons, synthetic chemists are confronted with the increasing obligation of optimizing their synthetic methods. Maximizing efficiency and minimizing costs in the production of chemicals and materials constitutes one of the most exciting challenges of modern chemistry. The ideal synthesis would produce the desired product in 100% yield and selectivity, in a safe and environmentally acceptable process. It is evident that catalysis stands at the center of ecologically sound chemistry and that ionic liquid phase organometallic catalysis will certainly play an important role in this process. As in any other domain of science, only basic research can lead to true innovations and to possible applications for the generation of improved processes and products.