Digallane with Redox-Active Diimine Ligand: Dualism of Electron-Transfer Reactions

The reactivity of digallane (dpp-Bian)­Ga–Ga­(dpp-Bian) (<b>1</b>), which consists of redox-active ligand 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene (dpp-Bian), has been studied. The reaction of <b>1</b> with I₂ proceeds via one-electron oxidation of each of two dpp-Bian ligands to a radical-anionic state and affords complex (dpp-Bian)­IGa–GaI­(dpp-Bian) (<b>2</b>). Dissolution of complex <b>2</b> in pyridine (Py) gives monomeric compound (dpp-Bian)­GaI­(Py) (<b>3</b>) as a result of a solvent-induced intramolecular electron transfer from the metal–metal bond to the dpp-Bian ligands. Treatment of compound <b>3</b> with B­(C₆F₅)₃ leads to removal of pyridine and restores compound <b>2</b>. The reaction of compound <b>1</b> with 3,6-di-<i>tert</i>-butyl-<i>ortho</i>-benzoquinone (3,6-Q) proceeds with oxidation of all the redox-active centers in <b>1</b> (the Ga–Ga bond and two dpp-Bian dianions) and results in mononuclear catecholate (dpp-Bian)­Ga­(Cat) (<b>4</b>) (Cat = [3,6-Q]^2–). Treatment of <b>4</b> with AgBF₄ gives a mixture of [(dpp-Bian)₂Ag]­[BF₄] (<b>5</b>) and (dpp-Bian)­GaF­(Cat) (<b>6</b>), which both consist of neutral dpp-Bian ligands. The reduction of benzylideneacetone (BA) with <b>1</b> generates the BA radical-anions, which dimerize, affording (dpp-Bian)­Ga–(BA–BA)–Ga­(dpp-Bian) (<b>7</b>). In this case the Ga–Ga bond remains unchanged. Within 10 min at 95 °C in solution compound <b>7</b> undergoes transformation to paramagnetic complex (dpp-Bian)­Ga­(BA–BA) (<b>8</b>) and metal-free compound C₃₆H₄₀N₂ (<b>9</b>). The latter is a product of intramolecular addition of the C–H bond of one of the <i>i</i>Pr groups to the CN bond in dpp-Bian. Diamagnetic compounds <b>3</b>, <b>5</b>, <b>6</b>, and <b>9</b> have been characterized by NMR spectroscopy, and paramagnetic complexes <b>2</b>, <b>4</b>, <b>7</b>, and <b>8</b> by ESR spectroscopy. Molecular structures of <b>2</b>–<b>7</b> and <b>9</b> have been established by single-crystal X-ray analysis