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

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

本研究针对由氧化还原活性配体1,2-双[(2,6-二异丙基苯基)亚氨基]苊（1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene，缩写dpp-Bian）构成的二镓烷(dpp-Bian)Ga–Ga(dpp-Bian)（化合物1）的反应活性展开了系统探究。化合物1与碘单质（I₂）发生反应时，两个dpp-Bian配体各经单电子氧化转变为自由基阴离子态，生成配合物(dpp-Bian)IGa–GaI(dpp-Bian)（化合物2）。将化合物2溶解于吡啶（pyridine，缩写Py）中，因溶剂诱导发生分子内电子转移——金属-金属键将电子转移至dpp-Bian配体，得到单核化合物(dpp-Bian)GaI(Py)（化合物3）。用三(五氟苯基)硼（B(C₆F₅)₃）处理化合物3，可脱除吡啶并重新得到化合物2。化合物1与3,6-二叔丁基邻苯醌（3,6-di-tert-butyl-ortho-benzoquinone，缩写3,6-Q）的反应会氧化1中所有氧化还原活性中心（Ga–Ga键与两个dpp-Bian二阴离子），最终生成单核儿茶酚酸根配合物(dpp-Bian)Ga(Cat)（化合物4，其中Cat = [3,6-Q]²⁻）。用四氟硼酸银（AgBF₄）处理化合物4，可得到[(dpp-Bian)₂Ag][BF₄]（化合物5）与(dpp-Bian)GaF(Cat)（化合物6）的混合物，二者均包含中性dpp-Bian配体。用化合物1还原亚苄基丙酮（benzylideneacetone，缩写BA），可得到BA自由基阴离子并发生二聚，生成(dpp-Bian)Ga–(BA–BA)–Ga(dpp-Bian)（化合物7），此过程中Ga–Ga键未发生变化。该溶液在95 ℃下放置10分钟后，化合物7会发生转化，生成顺磁性配合物(dpp-Bian)Ga(BA–BA)（化合物8）与不含金属的化合物C₃₆H₄₀N₂（化合物9）。化合物9是其中一个异丙基（iPr）基团的C–H键对dpp-Bian中的C=N键发生分子内加成的产物。本研究通过核磁共振波谱（NMR）对反磁性化合物3、5、6与9进行了表征，通过电子顺磁共振波谱（ESR）表征了顺磁性配合物2、4、7与8；通过单晶X射线衍射分析确定了化合物2~7与9的分子结构。