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

A cationic complex [Ru{OC(O)CMeCH 2 ‐κ 2 O , O ′}(PMe 3 ) 4 ] + CH 2 CMeCO 2 − ( 5 a ) and its related carboxylato complexes are newly prepared by the reaction of [ cis ‐RuH 2 (PMe 3 ) 4 ] ( 4 ) with carboxylic acids in methanol in 76–100 % yield. Complex 5 a reversibly transforms to the neutral form [ cis ‐Ru{OC(O)CMeCH 2 ‐κ 1 O } 2 (PMe 3 ) 4 ] ( 2 a ) in nonpolar solvents. Complex 2 a reversibly liberates a PMe 3 group to give [Ru{OC(O)CMeCH 2 ‐κ 1 O }{OC(O)CMeCH 2 ‐κ 2 O , O ′}(PMe 3 ) 3 ] ( 12 a ) from which a stereoselective CH bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMeCH‐κ 2 O , C }(PMe 3 ) 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 PMe 3 is indispensable for the CH 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 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 [D 4 ]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.