Synthesis and crystal structures of a family of bimetallic complexes with phenyl-substituted bridging tetraoxolene ligands

Seven dinuclear metal complexes and one trinuclear metal complex have been synthesized using the redox-active diphenyl-substituted tetraoxolene 2,5-dihydroxy-3,6-diphenyl-1,4-benzoquinone (H₂Ph₂dhbq, C₁₈H₁₂O₄) as a bridging ligand and tris[(pyridin-2-yl)methyl]amine (TPA, C₁₈H₁₈N₄) as a tetradentate terminal ligand. Single-crystal X-ray diffraction data confirm the final redox states of all components, revealing both expected and unexpected redox behavior across the eight reported complexes. Metal complexes with the formula [M^II₂(Ph₂dhbq²⁻)(TPA)₂]²⁺ can be synthesized from Mn, Fe, Co, Ni, Zn, and Ru, using either the oxidized ligand H₂Ph₂dhbq or a combination of the reduced ligand H₄Ph₂dhbq and an in-situ oxidant. Additionally, switching to Group 13 elements, such as Ga, facilitates the formation of the related [M^III₂(Ph₂dhbq⁴⁻)(TPA)₂]²⁺ complex, wherein the ligand remains in its initial reduced state.