Current research on room-temperature ionic liquids as lubricants is described. Ionic liquids possess excellent properties such as non-volatility, non-flammability, and thermo-oxidative stability. The potential use of ionic liquids as lubricants was first proposed in 2001 and approximately 70 articles pertaining to fundamental research on ionic liquids have been published through May 2009. A large majority of the cations examined in this area are derived from 1,3-dialkylimidazolium, with a higher alkyl group on the imidazolium cation being beneficial for good lubrication, while it reduces the thermo-oxidative stability. Hydrophobic anions provide both good lubricity and significant thermo-oxidative stability. The anions decompose through a tribochemical reaction to generate metal fluoride on the rubbed surface. Additive technology to improve lubricity is also explained. An introduction to tribology as an interdisciplinary field of lubrication is also provided.

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The tribological properties of trifluorotris(pentafluoroethyl) phosphate [(C 2 F 5 ) 3 PF 3 -, FAP]-derived ionic liquids were evaluated under boundary conditions. The anion is hydrophobic in comparison with bis(trifluoromethylsulfonyl)imide [(CF 3 SO 2 ) 2 N -, TFSI]. 1,3-Dialkyli midazolium salts of FAP provided much lower friction than 1,3-dialkylimidazolium salts of TFSI. In addition, the FAP salts exhibit better anti-wear properties than the TFSI salts. Another advantage of the FAP anion is availability of several cations to prepare ionic liquids. For example, tetraalkyl phosphonium, N,N-dialkylpyrrolidium, and tetramethylisouronium salts of FAP provided friction coefficient of approximately 0.1. Straight-chain carboxylic acids as model friction-reducing additives improved the tribological properties of the FAP salts. Surface analyses were conducted to study the boundary film formed by rubbing. It was found that the boundary film is composed of adsorbed anion on uppermost surfaces and reacted anion on sub-surfaces. The model friction-reducing additives were found on the rubbed surfaces.

The tribological properties of room temperature ionic liquids containing tetraalkylphosphonium cations were evaluated on the basis of the chemical structure of their salts. The tribochemistry of these ionic liquids was discussed on the basis of the results of tribo-tests and surface analyses. The tribological properties of the tetraalkylphosphonium salts examined in this work were observed to be better than those of 1,3-alkylimidazolium salts. The structure of the alkyl group in the phosphonium cation also has a slight effect on the tribological properties of the salts. During a friction test carried out under lowload conditions, the phosphonium cation was oxidized to phosphate to form a boundary film. This film inhibited the reaction of the bis(trifluoromethanesulfonyl)amide anion that yielded metal fluoride on the rubbed surfaces. The combination of the phosphonium cation with a phosphate anion or thiophosphate anion resulted in a better lubricant than 1,3-alkylimidazolium bis(trifluoromethanesulfonyl)amide. The reactions of the phosphate anion and thiophosphate anion yielded a phosphate boundary film that exhibited better tribological properties than those of the fluoride boundary film.

Allylation of /3-keto esters or malonates was carried out in good yields under neutral conditions by using allylic carbonates in the presence of palladium-phosphine catalyst. Although simple ketones, esters, nitriles, and sulfones hardly react with allylic carbonates, -alkenyl or -aryl ketones, esters, nitriles, and sulfones were also allylated by using palladium-bis(diphenylphosphino)ethane catalyst under neutral conditions.We have reported the reaction of (v-allyljpalladium chloride (1) with carbonucleophiles such as malonates, acetoacetates, and enamines as a new method for carbon-carbon bond formation1 (Scheme I, eq 1). Later, in situ formation of (T-allyl)palladium complexes 2 as in-

This review aims at introducing an engineering field of lubrication to researchers who are not familiar with tribology, thereby emphasizing the importance of lubricant chemistry in applied science. It provides initial guidance regarding additive chemistry in lubrication systems for researchers with different backgrounds. The readers will be introduced to molecular sciences underlying lubrication engineering. Currently, lubricant chemistry, especially "additive technology", looks like a very complicated field. It seems that scientific information is not always shared by researchers. The cause of this is that lubrication engineering is based on empirical methods and focuses on market requirements. In this regard, engineering knowhow is held by individuals and is not being disclosed to scientific communities. Under these circumstances, a bird's-eye view of lubricant chemistry in scientific words is necessary. The novelty of this review is to concisely explain the whole picture of additive technology in chemical terms. The roles and functions of additives as the leading actors in lubrication systems are highlighted within the scope of molecular science. First, I give an overview of the fundamental lubrication model and the role of lubricants in machine operations. The existing additives are categorized by the role and work mechanism in lubrication system. Examples of additives are shown with representative molecular structure. The second half of this review explains the scientific background of the lubrication engineering. It includes interactions of different components in lubrication systems. Finally, this review predicts the technical trends in lubricant chemistry and requirements in molecular science. This review does not aim to be a comprehensive chart or present manufacturing knowhow in lubrication engineering. References were carefully selected and cited to extract "the most common opinion" in lubricant chemistry and therefore many engineering articles were omitted for conciseness.

In 1965 we reported that (ir-allyl)palladium chloride reacts with carbonucleophiles such as malonates, acetoacetates, and enamines, thereby offering a new method for carbon-carbon bond formation1,2 (see Scheme I). Later synthetic applications of this reaction have been explored mainly by Trost.3 Certain allylic compounds, such as allylic acetates, react with Pd(0) complexes to form (Tr-allyl)palladium complexes in situ; these, without being isolated, react with carbonucleophiles. On the basis of these reactions, a catalytic allylation of carbonucleophiles with allylic esters has been developed,4,5 and this catalytic process is now widely used for carbon-carbon bond formation in organic synthesis3,6 (see Scheme II). In addition to allylic esters, many other allylic compounds such as allylic ethers, phosphates, amines, nitro compounds, sulfones, and halides can also be used for catalytic allylation in the presence of bases.Thus far, the main synthetic application of (x-allyl)palladium chemistry has been the catalytic allylation of carbonucleophiles using allylic acetates. Recently, however, we have broadened the scope and usefulness of (ir-allyl) palladium chemistry by discovering several new reactions using allyl carbonates and allyl /3-keto carboxylates. We have found that allyl alkyl carbonates 1, allyl /3-keto carboxylates 2, and allyl vinylic carbonates 3 are very reactive substrates and undergo a number of reactions that are difficult to achieve with allylic acetates under mild conditions. These substrates, which react with Pd(0) complexes to form ( -allyl)palladium alkoxides 5 or enolates 12a and 12b after facile decarboxylation, undergo various transformations depending on reaction conditions. The major reactions paths can be summarized in Scheme III. All these reactions proceed with facile decarboxylation. Mechanistically, they are closely related to each other and are discussed from common viewpoints in this Account. Reactions of Allyl Alkyl CarbonatesAllylation reaction of carbonucleophiles with various allylic compounds has now seen widespread use in organic synthesis.3,6 Allylic acetates are mainly used in the presence of bases. Several years ago we and Trost Jiro Tsuji obtained his B.S. from Kyoto University and then came to the U.S., where he obtained his Ph.D. at Columbia working with G. Stork in 1960. After returning to Japan, he worked at Basic Research Laboratories, Toray Industries Inc., and moved In 1974 to Tokyo Institute of Technology as a professor. Development of new reactions catalyzed by transition-metal complexes, particularly palladium complexes, and application of these new catalytic reactions to total synthesis of natural products are his major research programs.

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