Creation of Novel Environmentally Benign Low-Valent Ruthenium Catalysts

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The creation of novel transition metal complexes which show high catalytic performance is essential for development of highly atom-economical and environmentally benign synthetic methods without the formation of byproducts. In this study, we first succeeded in preparation of novel Ru(0) complexes bearing arenes, p-quinones, and tridentate pyridyl ligands via selective displacement of either 1,3,5-cyclooctatriene (cot) or dimethyl fumarate (dmfm) ligands in Ru(η^6-cot)(η^2-dmfm)_2 (1). The stoichiometric reaction of 1 with phenol gave novel Ru(II) phenolate complexes, while the reaction of 1 with water in the presence of 1,2-bis(diphenylphosphino)ethane (dppe) gave a novel chiral Ru(0) aqua complex, Ru(η^2-dppe)(η^2-dmfm)_2(H_2O) (2). The structures of all novel complexes were clearly determined by X-ray crystallography. Optical resolution of rac-2 was successfully performed by HPLC equipped with a chiral column.In addition, we have developed the following novel catalytic reactions characteristic to ruthenium ; 1)formal [4+2] cycloaddition of alkynes with electron-deficient alkenes to cyclohexenedicarboxylates via isomerization of alkynes and successive Diels-Alder reaction, 2)[2+2+2] cocyclotrimerization of three different alkynes (dimethyl acetylenedicarboxylate, 1-decyne and 3-hexyne), 3)regio- and stereoselective linear codimerization of 2-norbornenes with acrylic compounds, 4)synthesis of 2-alkylidenetetrahydrofurans by codimerization of dihydrofurans with α,β-unsaturated esters. All these ruthenium-catalyzed reactions offered the synthetic methods for novel functional monomers with high atom-efficiency.