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Issue 42, 2016
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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

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Abstract

The phosphonylation of C60 with HP(O)(OAlk)2 and 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)3 for the phosphonate group and oxidation of C60 by the Mn(OAc)2P(O)(OAlk)2 formed 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 C60 in benzene with equimolar amounts of Mn(OAc)2P(O)(OPr-i)2 or Hg[P(O)(OPr-i)2]2 which is known as working by the FR mechanism since it produces radical ˙P(O)(OPr-i)2 under 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]4 and 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)2 were obtained, respectively. DFT-calculations provided the hyperfine coupling (hfc) constants of the isomers and explained the regioselectivity change.

Graphical abstract: 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

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Publication details

The article was received on 25 Jul 2016, accepted on 12 Sep 2016 and first published on 13 Sep 2016


Article type: Paper
DOI: 10.1039/C6DT02941H
Citation: Dalton Trans., 2016,45, 16838-16849
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    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

    B. L. Tumanskii, D. S. Sabirov and Y. I. Lyakhovetsky, Dalton Trans., 2016, 45, 16838
    DOI: 10.1039/C6DT02941H

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