Lanthanum Complexes with a Diimine Ligand in Three Different Redox States

The reduction of 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene (dpp-Bian) with an excess of La metal in the presence of iodine (dpp-Bian/I₂ = 2/1) in tetrahydrofuran (thf) or dimethoxyethane (dme) affords lanthanum­(III) complexes of dpp-Bian dianion: deep blue [(dpp-Bian)^2–­LaI­(thf)₂]₂ (<b>1</b>, 84%) was isolated by crystallization of the product from hexane, while deep green [(dpp-Bian)­LaI­(dme)₂] (<b>2</b>, 93%) precipitated from the reaction mixture in the course of its synthesis. A treatment of complex <b>1</b> with 0.5 equiv of I₂ in thf leads to the oxidation of the dpp-Bian dianion to the radical anion and results in the complex [(dpp-Bian)^1–­LaI₂(thf)₃] (<b>3</b>). Addition of 18-crown-6 to the mixture of <b>1</b> and NaCp* (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) in thf affords ionic complex [(dpp-Bian)^2–­La­(Cp*)­I]­[Na­(18-crown-6)­(thf)₂] (<b>4</b>, 71%). In the absence of crown ether the alkali metal salt-free complex [(dpp-Bian)^2–­LaCp*­(thf)] (<b>5</b>, 67%) was isolated from toluene. Reduction of complex <b>1</b> with an excess of potassium produces lanthanum–potassium salt of the dpp-Bian tetra-anion {[(dpp-Bian)^4–­La­(thf)]­[K­(thf)₃]}₂ (<b>6</b>, 68%). Diamagnetic compounds <b>1</b>, <b>2</b>, <b>4</b>, <b>5</b>, and <b>6</b> were characterized by NMR spectroscopy, while paramagnetic complex <b>3</b> was characterized by the electron spin resonance spectroscopy. Molecular structures of <b>2</b>–<b>6</b> were established by single-crystal X-ray analysis