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)⋅0.5H 2 O ( 1 ⋅(OTf)⋅0.5H 2 O; acac − =acetylacetonato; bpy=2,2’‐bipyridine; dmso=dimethyl sulfoxide; OTf − =CF 3 SO 3 − ) 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)⋅0.5H 2 O, 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)⋅0.5H 2 O 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)⋅0.5H 2 O in methanol for 18 h, evaporation to dryness under vacuum, and treatment with water yielded trans ‐[Ru(acac)(bpy)(dmso‐ S )(OH 2 )](OTf) ( 2 ⋅(OTf)) with excellent purity. 2 ⋅(OTf) was characterized by X‐ray crystallography, elemental analysis, and 1 H 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 + .