Thermally Stable Heteroleptic Trans‐Bis(Chelate) Ruthenium(II) Complex Bearing 2,2'‐Bipyridine and Acetylacetonato: Synthesis, Isomerization, and Crystal Structure.

Thermally stable trans‐bis(chelate)‐type Ru(II) complexes are challenging to prepare owing to steric hindrance between the two chelate ligands. Herein, we investigated the isomerization of a heteroleptic cis‐bis(chelate) complex to obtain its trans form. cis‐[Ru(acac)(bpy)(dmso‐S)2](OTf)⋅0.5H2O (1⋅(OTf)⋅0.5H2O; acac−=acetylacetonato; bpy=2,2'‐bipyridine; dmso=dimethyl sulfoxide; OTf−=CF3SO3−) was prepared by reacting trans(O,S)‐[Ru(bpy)(dmso‐S)2(dmso‐O)2](OTf)2 (P0) with Li(acac) in acetone at 298 K. In 1⋅(OTf)⋅0.5H2O, the two labile dmso‐O ligands of P0 were replaced by an acac− ligand. The dihedral angle between the chelate rings of bpy and acac− in 1+ was 76.7°, suggesting steric hindrance between ligands owing to the two bulky dmso‐S ligands at the cis position. 1⋅(OTf)⋅0.5H2O was thermally stable in DMSO and acetone; however, in methanol and water, a dmso‐S ligand was dissociated from 1+, and the complex isomerized to trans‐[Ru(acac)(bpy)(dmso‐S)(solvent)]+. Refluxing of 1⋅(OTf)⋅0.5H2O in methanol for 18 h, evaporation to dryness under vacuum, and treatment with water yielded trans‐[Ru(acac)(bpy)(dmso‐S)(OH2)](OTf) (2⋅(OTf)) with excellent purity. 2⋅(OTf) was characterized by X‐ray crystallography, elemental analysis, and 1H NMR spectroscopy. As expected, steric hindrance was not observed between the trans‐arranged bpy and acac−, and the two chelates laid flat on the equatorial plane in 2+. [ABSTRACT FROM AUTHOR]