• deuterium;
  • C[BOND]H activation;
  • metallacycles;
  • P ligands;
  • ruthenium


A cationic complex [Ru{OC(O)CMe[DOUBLE BOND]CH22O,O′}(PMe3)4]+CH2[DOUBLE BOND]CMeCO2 (5 a) and its related carboxylato complexes are newly prepared by the reaction of [cis-RuH2(PMe3)4] (4) with carboxylic acids in methanol in 76–100 % yield. Complex 5 a reversibly transforms to the neutral form [cis-Ru{OC(O)CMe[DOUBLE BOND]CH21O}2(PMe3)4] (2 a) in nonpolar solvents. Complex 2 a reversibly liberates a PMe3 group to give [Ru{OC(O)CMe[DOUBLE BOND]CH21O}{OC(O)CMe[DOUBLE BOND]CH22O,O′}(PMe3)3] (12 a) from which a stereoselective C[BOND]H bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMe[DOUBLE BOND]CH-κ2O,C}(PMe3)4] (1 a) from the release of methacrylic acid. Complexes 2 a and 5 a also give 1 a but the prior dissociation of a PMe3 is indispensable for the C[BOND]H bond cleavage reaction. Complex 1 a establishes an equilibrium with 2 a (or 5 a) in solution. In this reaction, one coordinated carboxylato ligand is engaged in the C[BOND]H 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 5 a and 1 a plays a key role.