Alkylation of toluene with dichloromethane in the presence of triisobutylaluminum and perfluorophenylborates
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1H NMR method showed that in systems based on triisobutylaluminum (TIBA) and triphenylcyclopropenylium [Ph3C3]+[B(C6F5)4]–(CPB) or triphenylmethylium [Ph3C]+[B(C6F5)4]–(TB) perfluorophenylborates in a toluene–dichloromethane mixture the Friedel–Crafts process occurs with the formation of ditolylmethane (DTM) accompanied by the complete decomposition of TIBA to form isobutane. 19F NMR spectroscopy showed that the [B(C6F5)4]–anion decomposes in the systems to form B(C6F5)3 and HC6F5. The short-living [AlBu2 i]+ cation formed in the reaction of perfluorophenylborates with TIBA is assumed to be the species initiating the process. It has been shown that CPB is less reactive than TB. The addition of a stoichiometric amount of Ph2CCpFluHfMe2 exerts no effect on the process with the CPB-containing system but inhibits the reaction in the case of TB.
Key wordsFriedel–Crafts reaction toluene dichloromethane alkylation triisobutylaluminum carbenium ions perfluorophenylborates metallocene NMR spectroscopy
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