摘要：

Situated in the middle of the second row of the transition-metal series, ruthenium lies at the heart of the Periodic Table. This central location bestows upon ruthenium properties that are common to both its early- and late-transition-metal cousins. Harnessing the best of both world,ruthenium benefits from a confluence of desirable properties, amounting to a winning combination for catalysis. Borrowing the high reactivity of elements to its left and the less oxophilic and Lewis acidic nature of those to its right, it results in a special array of properties, which led to refer to ruthenium as an element for the connoisseur.Of all the elements of the Periodic Table, ruthenium has the widest scope of oxidation states (from –2 in Ru(CO)42– to +8 in RuO4), and various coordination geometries in each electron configuration, which is in contrast to the narrow scope of oxidation states and simple squareplanar structure of palladium. For instance, in the principal lower oxidation states of 0, II, and III, ruthenium complexes normally prefer trigonal-bipyramidal and octahedral structures, respectively. Such a variety of ruthenium complexes has great potential for the exploitation of novel catalytic reactions and synthetic methods; however, as a consequence of the difficulties ofmatching the catalysts and substrates, ruthenium chemistry has lagged behind palladium chemistry by almost decade. Indeed, until the 1980s the reported useful synthetic methods using ruthenium catalysts were limited to a few reactions which include oxidations with RuO4,hydrogenation reactions, and hydrogen transfer reactions. As the coordination chemistry of ruthenium complexes has progressed, specific characters of ruthenium have been made clear. Ruthenium is relatively inexpensive in comparison with the other Group 8 transition metals such as rhodium, and a wide variety of ruthenium complexes have been prepared. RuCl3·nH2O is frequently used as the starting material in the preparation of most of ruthenium complexes. The ruthenium complexes can be roughly divided into five groups according to their supporting ligands: carbonyl, tertiary phosphines, cyclopentadienyl, arene/dienes, and carbenes. These ligands have proven to serve effectively as the activating factors such as generation of coordinatively unsaturated species by the liberation of ligands, and stabilization of reactive intermediates. It has been understood that the precise control of coordination sites and redox sequences of the intermediacies are especially important in the case of ruthenium to design specific organic transformations. Moreover, ruthenium complexes also demonstrate a variety of useful characteristics, which include low redox potential, high electron transfer ability, high coordination ability to heteroatoms, Lewis acid acidity, unique reactivity of metallic species andintermediates such as oxo-metals, metallacycles, and metal carbene complexes. Therefore, a large number of novel, useful reactions have begun to be developed using catalytic amounts of ruthenium complexes. The great influence of ruthenium chemistry on organic synthesis in recent years has now elevated the metal's importance to the same level as palladium, or even higher.Indeed, some ruthenium-catalyzed reactions have become industrial processes, with typical examples including a combination of the ruthenium-catalyzed asymmetric hydrogenation of 2-benzamidomethyl-3-oxobutanate via kinetic resolution and the ruthenium-catalyzed oxidationof (1R',3S)-3-[1'-(tert-butyldimethylsilyloxy)ethyl]azetidin-2-one. The latter process provides an important industrial scheme for the synthesis of 4-cetoxyazetidinone, which is a versatile and key intermediate in the synthesis of carbapenem antibiotics. Grubb's ruthenium carbenecomplexes [...] have also been used for industrial ring-opening metathesis polymerization (ROMP).Recent progress in the ruthenium carbine complex-catalyzed carbon-carbon double bond formation for organic synthesis is outstanding, and has become extremely important. Theruthenium catalysts involve hydrogenatio

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