Selective Bond Cleavage Reactions by Low-valent Ruthenium Complexes

摘要

Reactions of zero-valent ruthenium complex [Ru(eta~4-1,5-COD)(eta~6-1,5-COD)(eta~6-1,3,5-COT)] (1) (COD=cyclooctadiene, COT=cyclooctatriene) with a series of monodentate tertiary phosphines cause selective displacement of the COD ligand to give Ru(COT) complexes, in which the COT ligand coordinates to the Ru either by eta~4 or eta~1:eta~3 fashion [[Ru(1-4-eta~4-1,3,5-COT)L_3] {L=PEt_3(2a), PBu_3(2b), PEt_2Ph(2c)}, [Ru(6-eta~1 : 1-3-eta~3-COT)L_3] {L=PMe_3(3a), PMe_2Ph(3b)}]. The highly reduced zero-valent complex 2a-c, shows higher activity toward C-O bond cleavage reaction of alkenyl carboxylate than 1 and 1/phosphine system. Complex 1/phosphine system shows high activity toward versatile bond cleavage reactions such as C-O bond of vinylic and allylic carboxylates or ethers, C-S bond of sulfide or thiophenes, and sp~3 C-H bond of ortho substituted phenols or carboxylic acids. Oxidative addition of C-H bond in active methylene compounds takes place to give hydrido (enolato) ruthenium(II) complexes, where zwitterionic structure of the enolato ligand derived from cyanoesters enhances their nucleophilic character to act as an active intermediate in Murahashi aldol and Michael reactions catalyzed by low-valent ruthenium complex.