Stable CI3+ salts and attempts to prepare CHI2+ and CH2I+

摘要

The room-temperature stable CI3+ salts [CI3](+)[pftb](-) 1 and [CI3](+)[al-f-al](-) 2 ([pftb](-) = [Al(OC(CF3)(3))(4)](-); [al-f-al](-) = [((CF3)(3)CO)(3)Al-F-Al(OC(CF3)(3))(3)](-)) were prepared in quantitative yields from purified CI4 and the corresponding silver aluminates with total exclusion of light (NMR, IR, UV-VIS, X-ray diffraction). The isolated CI3+ cation is trigonal planar with a sum of angle(I-C-I) = 360.0 degrees (1) and 359.9 degrees (2). Attempts to prepare CHI2+ and CH2I+ salts from CHI3 or CH2I2/Ag[pftb] mixtures remained unsuccessful; the reaction with CH2I2 leads to the formation of the adduct [Ag(CH2I2)(3)](+)[pftb](-) 3, while for HCI3, dismutation with formation of 1 as well as 3 was observed. All particles were also calculated at the MP2/TZVPP level to predict the vibrational and electronic spectra as well as to calculate the Gibbs free energies of all reactions (Delta G degrees, gas phase and CH2Cl2 solution). Quantum chemical calculations were also used to investigate the stability of the [ pftb]- anion against the electrophilic attack of the CX3+ and CHnX3-n+ cations (X = F-I, n = 1-3). The strength of the Lewis acidity of these cations and of the isoelectronic boron halides BX3 and BHnX3-n have been established on the basis of their fluoride ion affinities (FIAs). The FIAs of the carbon and the boron containing compounds show opposite trends, with fluorinated halomethyl cations being stronger acids than their heavier congeners but iodinated holoboranes being stronger acids than their lighter homologues.