Polyhalomethanes combined with aluminum halides as generators of superelectrophiles of a novel type

Semi-empirical (AM1) and ab initio (MO LCAO SCF-RHF/6-31G) quantum chemical calculations of CCl4 . nAlCl(3)(n = 1, 2) and CCl3+AlCl3 systems were performed to elucidate the nature of complexes responsible for the superelectrophilicity of tetrachloromethane in the presence of aluminum chloride. The results of the calculations do not allow us to relate the high activity of these systems with formation of the species Cl2CCl+-->AlCl3. The CCl4 . nAlCl(3) systems were shown to be generators of the superelectrophiles of a novel type, namely the electron deficient 'chlorenium' cations Cl2C-Cl+ and dications Cl+-C-Cl+ which are different from the known chloronium cations R-Cl+-R. The capability of forming mono-, di- and tridentate ionic complexes, wherein Cl+ of the CCl3+ cation is bonded with one, two or three Cl- of AlCl4-, is a peculiarity of the CCl3+AlCl4- system. The bidentate complex CCl3+AlCl4- with positive charge 0.54a.u. on the Cl atom (instead of 0.33 a.u. in a free CCl3+) seems to be the best candidate for the role of key superelectrophile in the CCl4 . nAlCl(3) systems. (C) 1997 Elsevier Science S.A.