Schorpp Marcel, Krossing Ingo
Institut für Anorganische und Analytische Chemie , Freiburger Materialforschungszentrum (FMF) , Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany . Email:
Chem Sci. 2020 Jan 13;11(8):2068-2076. doi: 10.1039/c9sc06254h. eCollection 2020 Feb 28.
The synthesis of the first unsupported dicationic arene complexes of calcium and strontium [(η-HMB)AE(DFB)] is reported (HMB = hexamethylbenzene; AE = alkaline earth metal; DFB = -difluorobenzene). They were prepared by direct oxidation of the elemental metals employing the ligand-forming radical cation salt [HMB][WCA] as an oxidant (WCA = [Al(OR)] or [μF-{Al(OR)}]; R = C(CF)). In addition, monocationic η-HMB complexes of calcium, strontium and barium supported by coordination of the monodentate anion [F-Al(OR)] are reported. In all examples, almost undistorted η-HMB coordination is observed with rather short M-arene distances approaching those observed with the isoelectronic but negatively charged pentamethylcyclopentadienyl ligand. The structure and bonding, thermodynamic stability and Lewis acidity (fluoride/hydride ion affinities, FIA/HIA) of the generated complexes were assessed by DFT methods. It followed that the gaseous dications [(η-HMB)AE(DFB)] are extremely hard Lewis acids that retain FIAs close to superacidity in solution.
报道了首例钙和锶的无配体二价芳烃配合物[(η-HMB)AE(DFB)]的合成（HMB = 六甲基苯；AE = 碱土金属；DFB = -二氟苯）。它们是通过使用形成配体的自由基阳离子盐[HMB][WCA]（WCA = [Al(OR)]或[μF-{Al(OR)}]；R = C(CF)）直接氧化元素金属制备的。此外，还报道了由单齿阴离子[F-Al(OR)]配位支撑的钙、锶和钡的单阳离子η-HMB配合物。在所有实例中，观察到几乎未变形的η-HMB配位，M-芳烃距离相当短，接近与等电子但带负电荷的五甲基环戊二烯基配体所观察到的距离。通过密度泛函理论（DFT）方法评估了所生成配合物的结构和键合、热力学稳定性以及路易斯酸度（氟化物/氢化物离子亲和力，FIA/HIA）。结果表明，气态二价阳离子[(η-HMB)AE(DFB)]是极强的路易斯酸，在溶液中保持接近超强酸度的氟化物离子亲和力（FIA）。
