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

Ligand “Brackets” for Ga–Ga Bond

The reactivity of digallane (dpp-Bian)­Ga–Ga­(dpp-Bian) (<b>1</b>) (dpp-Bian = 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene) toward acenaphthenequinone (AcQ), sulfur dioxide, and azobenzene was investigated. The reaction of <b>1</b> with AcQ in 1:1 molar ratio proceeds via two-electron reduction of AcQ to give (dpp-Bian)­Ga­(μ₂-AcQ)­Ga­(dpp-Bian) (<b>2</b>), in which diolate [AcQ]^2– acts as “bracket” for the Ga–Ga bond. The interaction of <b>1</b> with AcQ in 1:2 molar ratio proceeds with an oxidation of the both dpp-Bian ligands as well as of the Ga–Ga bond to give (dpp-Bian)­Ga­(μ₂-AcQ)₂Ga­(dpp-Bian) (<b>3</b>). At 330 K in toluene complex <b>2</b> decomposes to give compounds <b>3</b> and <b>1</b>. The reaction of complex <b>2</b> with atmospheric oxygen results in oxidation of a Ga–Ga bond and affords (dpp-Bian)­Ga­(μ₂-AcQ)­(μ₂-O)­Ga­(dpp-Bian) (<b>4</b>). The reaction of digallane <b>1</b> with SO₂ produces, depending on the ratio (1:2 or 1:4), dithionites (dpp-Bian)­Ga­(μ₂-O₂S–SO₂)­Ga­(dpp-Bian) (<b>5</b>) and (dpp-Bian)­Ga­(μ₂-O₂S–SO₂)₂Ga­(dpp-Bian) (<b>6</b>). In compound <b>5</b> the Ga–Ga bond is preserved and supported by dithionite dianionic bracket. In compound <b>6</b> the gallium centers are bridged by two dithionite ligands. Both <b>5</b> and <b>6</b> consist of dpp-Bian radical anionic ligands. Four-electron reduction of azobenzene with 1 mol equiv of digallane <b>1</b> leads to complex (dpp-Bian)­Ga­(μ₂-NPh)₂Ga­(dpp-Bian) (<b>7</b>). Paramagnetic compounds <b>2</b>–<b>7</b> were characterized by electron spin resonance spectroscopy, and their molecular structures were established by single-crystal X-ray analysis. Magnetic behavior of compounds <b>2</b>, <b>5</b>, and <b>6</b> was investigated by superconducting quantum interference device technique in the range of 2–295 K

Ligand “Brackets” for Ga–Ga Bond

The reactivity of digallane (dpp-Bian)­Ga–Ga­(dpp-Bian) (<b>1</b>) (dpp-Bian = 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene) toward acenaphthenequinone (AcQ), sulfur dioxide, and azobenzene was investigated. The reaction of <b>1</b> with AcQ in 1:1 molar ratio proceeds via two-electron reduction of AcQ to give (dpp-Bian)­Ga­(μ₂-AcQ)­Ga­(dpp-Bian) (<b>2</b>), in which diolate [AcQ]^2– acts as “bracket” for the Ga–Ga bond. The interaction of <b>1</b> with AcQ in 1:2 molar ratio proceeds with an oxidation of the both dpp-Bian ligands as well as of the Ga–Ga bond to give (dpp-Bian)­Ga­(μ₂-AcQ)₂Ga­(dpp-Bian) (<b>3</b>). At 330 K in toluene complex <b>2</b> decomposes to give compounds <b>3</b> and <b>1</b>. The reaction of complex <b>2</b> with atmospheric oxygen results in oxidation of a Ga–Ga bond and affords (dpp-Bian)­Ga­(μ₂-AcQ)­(μ₂-O)­Ga­(dpp-Bian) (<b>4</b>). The reaction of digallane <b>1</b> with SO₂ produces, depending on the ratio (1:2 or 1:4), dithionites (dpp-Bian)­Ga­(μ₂-O₂S–SO₂)­Ga­(dpp-Bian) (<b>5</b>) and (dpp-Bian)­Ga­(μ₂-O₂S–SO₂)₂Ga­(dpp-Bian) (<b>6</b>). In compound <b>5</b> the Ga–Ga bond is preserved and supported by dithionite dianionic bracket. In compound <b>6</b> the gallium centers are bridged by two dithionite ligands. Both <b>5</b> and <b>6</b> consist of dpp-Bian radical anionic ligands. Four-electron reduction of azobenzene with 1 mol equiv of digallane <b>1</b> leads to complex (dpp-Bian)­Ga­(μ₂-NPh)₂Ga­(dpp-Bian) (<b>7</b>). Paramagnetic compounds <b>2</b>–<b>7</b> were characterized by electron spin resonance spectroscopy, and their molecular structures were established by single-crystal X-ray analysis. Magnetic behavior of compounds <b>2</b>, <b>5</b>, and <b>6</b> was investigated by superconducting quantum interference device technique in the range of 2–295 K

Ligand “Brackets” for Ga–Ga Bond

The reactivity of digallane (dpp-Bian)­Ga–Ga­(dpp-Bian) (<b>1</b>) (dpp-Bian = 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene) toward acenaphthenequinone (AcQ), sulfur dioxide, and azobenzene was investigated. The reaction of <b>1</b> with AcQ in 1:1 molar ratio proceeds via two-electron reduction of AcQ to give (dpp-Bian)­Ga­(μ₂-AcQ)­Ga­(dpp-Bian) (<b>2</b>), in which diolate [AcQ]^2– acts as “bracket” for the Ga–Ga bond. The interaction of <b>1</b> with AcQ in 1:2 molar ratio proceeds with an oxidation of the both dpp-Bian ligands as well as of the Ga–Ga bond to give (dpp-Bian)­Ga­(μ₂-AcQ)₂Ga­(dpp-Bian) (<b>3</b>). At 330 K in toluene complex <b>2</b> decomposes to give compounds <b>3</b> and <b>1</b>. The reaction of complex <b>2</b> with atmospheric oxygen results in oxidation of a Ga–Ga bond and affords (dpp-Bian)­Ga­(μ₂-AcQ)­(μ₂-O)­Ga­(dpp-Bian) (<b>4</b>). The reaction of digallane <b>1</b> with SO₂ produces, depending on the ratio (1:2 or 1:4), dithionites (dpp-Bian)­Ga­(μ₂-O₂S–SO₂)­Ga­(dpp-Bian) (<b>5</b>) and (dpp-Bian)­Ga­(μ₂-O₂S–SO₂)₂Ga­(dpp-Bian) (<b>6</b>). In compound <b>5</b> the Ga–Ga bond is preserved and supported by dithionite dianionic bracket. In compound <b>6</b> the gallium centers are bridged by two dithionite ligands. Both <b>5</b> and <b>6</b> consist of dpp-Bian radical anionic ligands. Four-electron reduction of azobenzene with 1 mol equiv of digallane <b>1</b> leads to complex (dpp-Bian)­Ga­(μ₂-NPh)₂Ga­(dpp-Bian) (<b>7</b>). Paramagnetic compounds <b>2</b>–<b>7</b> were characterized by electron spin resonance spectroscopy, and their molecular structures were established by single-crystal X-ray analysis. Magnetic behavior of compounds <b>2</b>, <b>5</b>, and <b>6</b> was investigated by superconducting quantum interference device technique in the range of 2–295 K

Ytterbium and Europium Complexes of Redox-Active Ligands: Searching for Redox Isomerism

The reaction of (dpp-Bian)­Eu^II(dme)₂ (<b>3</b>) (dpp-Bian is dianion of 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene; dme is 1,2-dimethoxyethane) with 2,2′-bipyridine (bipy) in toluene proceeds with replacement of the coordinated solvent molecules with neutral bipy ligands and affords europium­(II) complex (dpp-Bian)­Eu^II(bipy)₂ (<b>9</b>). In contrast the reaction of related ytterbium complex (dpp-Bian)­Yb^II(dme)₂ (<b>4</b>) with bipy in dme proceeds with the electron transfer from the metal to bipy and results in (dpp-Bian)­Yb^III(bipy)­(bipy^–̇) (<b>10</b>) – ytterbium­(III) derivative containing both neutral and radical-anionic bipy ligands. Noteworthy, in both cases dianionic dpp-Bian ligands retain its reduction state. The ligand-centered redox-process occurs when complex <b>3</b> reacts with <i>N</i>,<i>N</i>′-bis­[2,4,6-trimethylphenyl]-1,4-diaza-1,3-butadiene (mes-dad). The reaction product (dpp-Bian)­Eu^II­(mes-dad)­(dme) (<b>11</b>) consists of two different redox-active ligands both in the radical-anionic state. The reduction of 3,6-di-<i>tert</i>-butyl-4-(3,6-di-<i>tert</i>-butyl-2-ethoxyphenoxy)-2-ethoxycyclohexa-2,5-dienone (the dimer of 2-ethoxy-3,6-di-<i>tert</i>-butylphenoxy radical) with (dpp-Bian)­Eu^II(dme)₂ (<b>3</b>) caused oxidation of the dpp-Bian ligand to radical-anion to afford (dpp-Bian)­(ArO)­Eu^II(dme) (ArO = OC₆H₂-3,6-<i>t</i>Bu₂-2-OEt) (<b>12</b>). The molecular structures of complexes <b>9</b>–<b>12</b> have been established by the single crystal X-ray analysis. The magnetic behavior of newly prepared compounds has been investigated by the SQUID technique in the range 2–310 K. The isotropic exchange model has been adopted to describe quantitatively the magnetic properties of the exchange-coupled europium­(II) complexes (<b>11</b> and <b>12</b>). The best-fit isotropic exchange parameters are in good agreement with their density functional theory-computed counterparts