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Aluminum chloride is a widely used acid catalyst. It exhibits the highest efficiency when used with promoters, namely, either protic (water, hydrogen halides) [1,2] or aprotic (acyl halides [3], mono-and polyhaloalkanes [3][4][5], transition metal salts [5][6][7]) organic or inorganic compounds. Thus, the catalyst systems become superacidic; in particular, they activate alkanes under relatively mild conditions [3][4][5][6][7]. The mechanism of action of promoting additives is not entirely clear to date. A promising way of elucidating the features of promoter action and the mechanism of transformations is apparently to study catalysis at low temperatures, when the contribution of the side reactions is low and it is, in principle, possible to isolate and study particular steps of a complex process.In this work, we studied the catalytic properties of promoted aluminum chloride at low temperatures (170-230 K) under conditions of restricted molecular mobility toward the conversion of paraffins. It was found for the first time that, depending on the promoter (an alkyl halide or a transition metal salt), the transformation of alkanes develops according to two mechanisms. An unusual route of paraffin transformation, resulting in normal alkanes containing one carbon atom less, was identified.Samples containing aluminum chloride, a promoter, and an excess of alkane ( n -octane) were prepared by vacuum cocondensation of reactant vapors onto the cooled (80 K) mirror surface of the copper block of the optical reactor described previously in [8]. The reagent ratios in the AlCl 3 /CoCl 2 or AlCl 3 /BuCl catalyst systems were varied from 0.3 to 10. The dilution with a saturated hydrocarbon ( ë 8 ç 18 /AlCl 3 ) varied from 3 to 50. The film thickness was 5-15 µ m.The dynamics of formation of the catalyst system and alkane transformations were studied in situ by IR spectroscopy in the temperature range 80-290 K and ex situ by analyzing the reaction products by GLC and GC/MS. The samples were heated at a rate of 2-3 K/min and were kept at an intermediate temperature of 170 K for 30-60 min. The volatile reaction products were collected in a liquid nitrogen-cooled tube attached to the reactor. Comparative experiments on the conversion of alkanes under standard conditions (liquid phase, room temperature) were carried out in sealed glass tubes containing a suspension of aluminum chloride in the liquid hydrocarbon (15 : 1) under continuous stirring for 30-120 min.The reaction selectivity toward each of the products was determined from GLC data by normalizing the peak areas using the calibration coefficients found preliminarily with standard compounds.IR spectra in the 4000-400 cm -1 range were recorded on Specord 75 IR and Infralum FT-801 spectrophotometers. The products were analyzed on an LKhM 3700 instrument with a flame ionization detector and on a Finnigan MAT-112S GC/MS instrument (ionizing energy, 80 eV).In octane/aluminum chloride cocondensates, lowtemperature transformations started in the 170-220 K range, giving rise to new IR...

Low temperature FT IR studies of products of co condensation of aluminum chloride and cobalt chloride in hydrocarbon matrices were carried out in the temperature range 80-250 К. DFT quantum mechanical calculations of the geometry and vibrational frequencies of alumi num chloride/cobalt chloride polynuclear molecular and ionic complexes of different compositon were carried out. Isomeric labile complexes Аl 2 Cl 6 •СoCl 2 were detected under partial matrix isolation conditions and their behavior was monitored. The interaction of the 1 : 1 and 2 : 1 aluminum halide/cobalt halide molecular complexes at 120-170 К produces catalytically active species in low temperature conversion of alkanes. According to the data of in situ spectral studies and to the results of quantum chemical calculations, these species represent ionic associates which simultaneously contain Co and Al atoms in both cationic and anionic fragments.

Sec butyl and tert butyl cations were first stabilized upon cocondensation of aluminum chloride and haloalkanes (2 chlorobutane and 2 chloro 2 methylpropane, respectively) and their IR spectra and thermal stability investigated. Aluminum chloride anions participating in stabilization of carbenium ions were revealed. Ionic complexes and both 1:1 and 2:1 molecular complexes of reagents were detected and their IR spectra studied. Quantum chemical calcula tions at the PBE level of density functional theory with inclusion of electron correlation were employed to optimize the geometric parameters and to determine the vibrational frequencies of aluminum chloride, butyl chlorides, and their complexes of various compositions. The struc tures of the associates observed were determined on the basis of comparison of the experimental and calculated vibrational spectra.

Density functional calculations of binary and ternary propane complexes with aluminum and cobalt(II) chlorides were carried out. Interaction of metal chloride complexes with the methylene and methyl groups of propane is coupled with strong polarization of С-Н bonds. The direction of polarization is opposite to that observed under interaction with the typical Lewis acids including aluminum halides. In the interaction of bimetallic (transition met al/aluminum) complexes with saturated С-Н bonds, the key role is played by the transition metal ion rather than the stronger Lewis center (Al). The negative atomic charge on carbon increases, which may facilitate the formation of metal alkyl compounds with a carbanion type organic radical.Aluminum chloride is a widely used catalyst of hydro carbon conversion, which is particularly efficient in the presence of promoting dopants. Among them, of special interest are transition metal salts whose synergistic effect on the catalytic activity of Lewis acids in the isomeriza tion and cracking of paraffins and alkylation of unsaturat ed and aromatic compounds is known since the late 1970s. 1-4 Synergism is mostly attributed to the enhanced acidity of the Lewis acid, i.e., aluminum halide. 1,2,5 At the same time there are experimental data suggesting the pos sibility of direct interaction of promoter cations with or ganic substrates. In particular, this is indicated by the com position of products of low temperature (170-220 К) con version of С 7 -С 10 paraffins which was first performed with the promoted aluminum chloride in our recent study. 6 It was found that conversion in the presence of transition metal halides led not only to iso alkanes, but also high yields of n alkanes with the carbon chain one atom short er than in the starting alkane (these products are atypical of acid catalysts). 6 The yield of cracking products in this process was at most 5% vs. 70-80% obtained with alumi num chloride (either untreated or promoted by organic halides). This effect of transition metal salts on the pro cess selectivity in the presence of Lewis acids was reported in studies of liquid phase conversion of paraffins. 1,4 In certain aspects this resembles the action of transition met al ions introduced into zeolites. Modification of zeolites by, e.g., zinc or cobalt cations, also considerably changes the reaction selectivity. 7,8 According to IR data, 9-11 co ordinatively unsaturated cations appear in these systems, which leads to formation of new active centers (existing along with acidic catalytic centers) which impart a bi functional character to the catalyst and favor changes in the direction of the reaction. One can assume by analogy that transition metal cations in bimetalic aluminum ha lide complexes play a key role in the activation of hydro carbons. This follows from a correlation between the struc ture of polynuclear aluminum and cobalt halide complexes and their catalytic activity in the low temperature reac tions of alkanes. 12,13 The data of in situ IR measurements and the resul...