Coordination Chemistry of the Redox Non‐Innocent Ligand Bis(2‐amino‐3, 5‐di‐tert‐butylphenyl)amine with Group 10 Metal Ions (Ni, Pd, Pt). Issue 16 (22nd March 2018) - Leconte, Nicolas
Abstract : The pincer ligand H3 L 3N, bis(2‐amino‐3, 5‐di‐ tert ‐butylphenyl)amine}, was chelated to Ni II, Pd II, and Pt II . Square‐planar complexes of stoichiometry 2:1 (ligand/metal) formed, wherein the ligand coordinates in a bidentate fashion. By X‐ray diffraction we established that each ligand molecule coordinates in its diiminosemiquinone radical form in the neutral Ni II, Pd II, and Pt II complexes (1, 2, and3, respectively). The resulting systems are singlet diradical species, with a predicted J value in the range –1062 to –1764 cm –1 . These diradicals display an intense LLCT transition involving the diiminosemiquinone moieties: 860, 852, and 760 nm for1, 2, and3, respectively. Complex1, 2, and3 exhibit reversible oxidation waves in their CV curves. Cations1 +, 2 +, and3 + are ( S = 1/2) systems with g values close to 2. The increase in the intensity of the resonance in the order1 + <2 +, 3 + is consistent with the easy comproportionation of1 + . X‐ray diffraction analysis discloses that3 + is a mixed‐valent radical mononuclear complex. An intense IVCT is observed at low energy (1536, 1656, and 1256 nm for1 +, 2 +, and3 +, respectively), confirming that this classification applies to all the cations. Dications1 2+, 2 2+, and3 2+ are closed‐shell bis(diiminobenzoquinone) species. The crystal structure of3 2+ shows that this complex exhibits the shortest mean C–N bond lengths within the series. Abstract : The o ‐diaminobenzene‐based pincer ligand H3 L 3N, bis(2‐amino‐3, 5‐di‐ tert ‐butylphenyl)amine}, coordinates metals in a bidentate fashion, affording homoleptic square‐planar complexes of stoichiometry 2:1 (ligand/metal) with two pendent aniline groups. The complexes can undergo two reversible oxidations, affording mixed‐valent iminosemiquinone/diiminoquinone and bis(diiminoquinone) species.