title: A mechanistic study of manganese(iii) acetate-mediated phosphonyl group additions to [60]- and [70]-fullerenes: the oxidative-ion-transfer mechanism vs. free radical addition.
abstract: The phosphonylation of C60with HP(O)(OAlk)2and Mn(OAc)3·2H2O has been considered to occur via a free radical (FR) path involving intermediate radicals ˙P(O)(OAlk)2. The present study provides evidence in support of another mechanism for the reactions, oxidative-ion-transfer (OIT). The mechanism involves the change of an acetate group in Mn(OAc)3for the phosphonate group and oxidation of C60by the Mn(OAc)2P(O)(OAlk)2formed to a pair: (C60˙+, Mn(OAc)2P(O)(OAlk)2˙-) followed by the transfer of the phosphonate anion to give the monophposphonylfullerenyl radical. It undergoes reversible dimerization. The polyaddition occurs analogously. Moreover, the compounds Mn(OAc)2P(O)(OAlk)2(Alk = Et and i-Pr) obtained make novel reagents for phosphonylation of fullerenes working by the OIT mechanism. The reactions of C60in benzene with equimolar amounts of Mn(OAc)2P(O)(OPr-i)2or Hg[P(O)(OPr-i)2]2which is known as working by the FR mechanism since it produces radical ˙P(O)(OPr-i)2under UV-irradiation, furnished the same radical ˙C60P(O)(OPr-i)2. However, at a 20-fold molar excess of the reagent toward C60, a single derivative C60[P(O)(OPr-i)2]4and a mixture of derivatives bearing between two and eight phosphonyls were obtained in the former and latter cases, respectively. With C70, the change of the mechanism produced a change in the regioselectivity: 5 and 3 isomers of ˙C70P(O)(OPr-i)2were obtained, respectively. DFT-calculations provided the hyperfine coupling (hfc) constants of the isomers and explained the regioselectivity change.
authors.affiliation: A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, 28 Vavilov St., 119991 GSP-1 Moscow V-334, Russia. yulyakh@ineos.ac.ru.
authors.forename: Boris L
authors.initials: BL
authors.lastname: Tumanskii
authors.forename: Denis S
authors.initials: DS
authors.lastname: Sabirov
authors.forename: Yury I
authors.initials: YI
authors.lastname: Lyakhovetsky