ABSTRACT Formic acid is a promising hydrogen carrier. Herein, we synthesized and profiled a series of manganese‐based complexes containing a quinoline‐pyridinium amidate N,N′‐bidentate coordinating ligand, MnX(CO) 3 (N,N’), for catalytic formic acid dehydrogenation. The activity of these novel manganese complexes was dependent on the metal‐bound halide as well as the motif of the donor‐flexible pyridinium amidate ligand. The ortho′‐methylated ortho‐pyridinium amidate system Mn3 showed highest activity and reached up to 400 turnovers and a turnover frequency of 1100 h −1 . Modification of the catalytic conditions unveiled the importance of the water concentration and a direct temperature dependence, with a large activation enthalpy (ΔH ‡ = 99 kJ mol −1 ) and a close to zero activation entropy (ΔS ‡ = –37 J K −1 mol −1 ). Mechanistic investigation further suggest that the process is homogeneous, and that the turnover‐limiting step is the β–hydride elimination of formate from a catalytically active species that comprises both the halide and the PYA ligand bound to the manganese center.
Reuge et al. (Thu,) studied this question.