Manganese() acetate-mediated activation of C-H bonds of weak CH-acids; addition of -carborane, its derivatives, and some other CH-acids to [60]-fullerene

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019-02, Vol.48 (6), p.246-258
• Main Authors: Tumanskii, Boris L, Sabirov, Denis S, Solodovnikov, Stanislav P, Lyakhovetsky, Yury I
• Format: Article
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt04565h

o -Carborane, 9-I- o -carborane, 1-Me- o -carborane, and several other CH-acids, 9H-fluorene, 2-Br-9H-fluorene, and trimethylsylylacetylene, have been shown to react with C 60 affording their monoadducts with fullerene, the reaction being mediated by Mn(OAc) 3 ·2H 2 O. In the case of o -carborane, when the molar ratio of C 60  :  o -carborane : Mn(OAc) 3 ·2H 2 O was 1 : 21 : 20, polyaddition occurred to furnish adducts bearing between one and six o -C 2 HB 10 H 10 groups. A distinguishing characteristic of the carboranyl derivatives of C 60 obtained appeared to be that the carboranyl moieties were connected to the fullerenyl one by their carbon atom. No such fullerene derivatives have been known so far. Based on the results previously obtained for the phosphonylation of fullerenes, an oxidative-ion-transfer (OIT) mechanism was suggested for the reactions. The mechanism involves the replacement of an acetate group in Mn(OAc) 3 with the corresponding R of a CH-acid (RH), oxidation of C 60 by Mn(OAc) 2 R with the formation of a pair [C 60 &z.rad; + , Mn(OAc) 2 R&z.rad; − ] followed by the transfer of R − to C 60 &z.rad; + to furnish the radical RC 60 &z.rad;. The radical abstracts a hydrogen atom from another molecule of RH or from the solvent. The polyaddition occurs in an analogous way. This mechanism found support in this study owing to the fact that the reactions of both o -carborane and 9H-fluorene did not proceed with perfluorobenzophenone as a substrate, because it was unable to undergo oxidation. C 70 reacted with o -carborane in a similar way to give the corresponding monoadduct. No reaction of C 60 with m -carborane was observed and this was explained by its insufficient CH-acidity. CH-acids including o -carboranes add to C 60 by a carbon atom via oxidative-ion-transfer reactions mediated by Mn(OAc) 3 .