Department of Chemistry, Illinois Institute of Technology, Chicago, IL 60616, USA.
Department of Chemistry, University at Albany, State University of New York, Albany, NY, 12222, USA.
Chemistry. 2019 Nov 7;25(62):14140-14147. doi: 10.1002/chem.201902992. Epub 2019 Oct 8.
One-electron reduction of corannulene, C H , with Li metal in diglyme resulted in crystallization of [{Li (diglyme) } (C H ) (C H -C H ) ] (1), as revealed by single-crystal X-ray diffraction. This hybrid product contains two corannulene monoanion-radicals along with a dianionic dimer, crystallized with four Li ions wrapped by diglyme molecules. The dimeric (C H -C H ) anion provides the first crystallographically confirmed example of spontaneous radical dimerization for C H . The C-C bond length between the two C H bowls of 1.588(5) Å is consistent with the single σ-bond character of the linker. The trans-disposition of two bowls in the centrosymmetric (C H -C H ) dimer is observed with the torsion angle around the central C-C bond of 180°. Comprehensive theoretical analysis of formation/decomposition processes of the dimeric dianion has been carried out in order to evaluate the nature of bonding and energetics of the C H coupling. It is found that such σ-bonded dimers are thermodynamically unstable due to large preparation energy and repulsive Pauli component of the bonding, but kinetically persistent due to a high energy barrier provided by the existing spin-crossing point.
一电子还原[corannulene, C H ]与金属锂在二甘醇二甲醚中反应，得到[{Li (diglyme) } (C H ) (C H -C H ) ]（1）的晶体，这一点通过单晶 X 射线衍射得到了揭示。这种混合产物包含两个corannulene 单阴离子自由基和一个二阴离子二聚体，用二甘醇二甲醚分子包裹着四个 Li 离子结晶。二聚体（C H -C H ）阴离子提供了 C H 自由基二聚化的第一个晶体学确证实例。1 中两个 C H 碗之间的 C-C 键长为 1.588(5) Å，与连接体的单个 σ 键特征一致。在中心对称的（C H -C H ）二聚体中观察到两个碗的反式排布，中央 C-C 键的扭转角为 180°。为了评估 C H 键合的本质和能量学，对二聚体二阴离子的形成/分解过程进行了全面的理论分析。结果发现，由于大的制备能和键合的反 Pauli 分量，这种 σ 键合的二聚体在热力学上是不稳定的，但由于现有自旋交叉点提供的高能量势垒，它们在动力学上是稳定的。
