ISOMERIZATION OF FULLEROID C60 CONTAINING AN ADAMANTANE FRAGMENT, INTO METHANOFULLERENE UNDER THE ACTION OF ULTRASOUND

The synthesis of a fullerene derivative conjugated with adamantane is based on an original catalytic selective method for the functionalization of carbon clusters with the participation of diazo compounds, previously devel oped in the laboratory of catalytic synthesis of the Institute of Petrochemistry and Catalysis of the Ufa Federal Research Center of the Russian Academy of Sciences. In the cycloaddition reaction of adamantane derivative hy drazone to fullerene C60 under metal complex catalysis conditions in the presence of Pd(PPh3)2Cl2, a single [5,6] open isomer was obtained: a hexaadduct of fulleroid containing ethyl and adamantane fragments on the methylene bridge with a quantitative yield (the molar ratio of reagents C60:Pd(PPh3)2Cl2:adamantane hydrazone 7:MnO2 = 1:0.05:10:30). The scheme of synthesis of the initial hydrazone of adamantane derivative includes three succes sive stages based on the synthesis of adamantanecarboxylic acid chloride, its interaction with C2H5MgBr and the condensation reaction of the obtained adamantane ketone with hydrazine hydrate. The hydrazone of the adamantane derivative plays a dual role in this reaction: firstly, it is a reducing agent for the divalent palladium ion in Pd(PPh3)2Cl2, i.e. it generates the active form of the catalyst; secondly, it is a reagent from which a diazo compound is formed in situ in the presence of the oxidizer MnO2, which is attached to the fullerene framework to form a single [5,6]-open isomer. It was found that the resulting compound does not undergo isomerization into the [6,6]-closed one under thermal conditions (100 hours, 180°C), but undergoes isomerization under mild conditions under the action of ultrasound (air, room temperature, 1.5 hours). Atmospheric oxygen does not affect the sonochemical isomerization reaction: conducting reactions under anaerobic conditions does not change the yield of the reaction product. The obtained compounds were identified by the combined use of mass, UV, one- and two-dimensional NMR spectrometry. Identification of two isomeric forms of adamantane adducts of fullerene C60 ([5,6]-open and [6,6]-closed) was carried out using 13C NMR spectra: the [5,6]-open isomer does not have signals of sp3-hybridized carbon atoms in the 70–90 ppm region; the [6,6]-closed isomer contains two signals of sp3-hybridized atoms of the fullerene sphere in the 70–90 ppm region.