Iridium complexes with α-diimines: Catalytic hydrogen transfer from isopropanol to cyclohexanone

Article abstract of DOI:10.1016/0277-5387(95)00194-W

[Ir(COD)Cl]₂ (COD = 1.5-cyclooctadiene) reacted with α-diimines (LL) derived from glyoxal (GLL) or biacetyl (BLL) giving different types of compounds depending on the ligand and on the stoichiometric ratios employed, i.e. [Ir₂(COD)₂Cl₂(GLL)] when [Ir(COD)Cl]₂/GLL = 1:1 or IrCl(COD)(LL) when [Ir(COD)Cl]₂/LL = 1:2. Solutions of [Ir₂(COD)₂Cl₂(GLL)] contain ionic [Ir(COD)(GLL)]⁺[Ir(COD)Cl₂]^- species and dimeric [Ir(COD)Cl]₂(μ-GLL) species with bridging LL groups in equilibrium. IrCl(COD)(LL) compounds are pentacoordinated in the solid state and undergo rearrangements in solution. In the presence of bulky anions, cationic [Ir(COD)(LL)]A species were formed. When the reactions were performed in the presence of SnCl₂, pentacoordinated Ir(SnCl₃)(COD)(LL) compounds were obtained, which in solution showed static or dynamic behaviour depending on the ligand. The different compounds are active catalysts in the homogeneous hydrogen transfer from isopropanol to cyclohexanone. The cationic species show higher activity and the most active cation is the compound containing biacetyloximehydrazone. Copyright