Stoichiometric C-H Bond Cleavage Reaction in a Bis(carboxylato)ruthenium(II) Complex and Its Application to the Catalytic H-D Exchange Reaction of Carboxylic Acids

摘要

A cationic complex [Ru{OC(O)CMeCH2-2O,O}(PMe3)4]+CH2CMeCO2 (5a) and its related carboxylato complexes are newly prepared by the reaction of [cis-RuH2(PMe3)4] (4) with carboxylic acids in methanol in 76100% yield. Complex 5a reversibly transforms to the neutral form [cis-Ru{OC(O)CMeCH2-1O}2(PMe3)4] (2a) in nonpolar solvents. Complex 2a reversibly liberates a PMe3 group to give [Ru{OC(O)CMeCH2-1O}{OC(O)CMeCH2-2O,O}(PMe3)3] (12a) from which a stereoselective CH bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMeCH-2O,C}(PMe3)4] (1a) from the release of methacrylic acid. Complexes 2a and 5a also give 1a but the prior dissociation of a PMe3 is indispensable for the CH bond cleavage reaction. Complex 1a establishes an equilibrium with 2a (or 5a) in solution. In this reaction, one coordinated carboxylato ligand is engaged in the CH bond cleavage reaction as a proton acceptor, but neither the added carboxylato anion nor typical proton acceptors such as proton sponge assist the reaction. In [D4]MeOH, a catalytic stereospecific deuteration of carboxylic acids has been achieved by 4, in which the equilibrium between 5a and 1a plays a key role.