Yury I. Lyakhovetsky

Homolytic reactive mass spectrometry of fullerenes: interaction of C60 and C70 with organo- and organoelement mercurials in the electron impact ion source of a mass spectrometer; EPR, CIDEP, and MS studies of several analogous reactions of C60 performed in solution.

Interaction of C(60) with organo- and organoelement mercurials (CF(3)HgBr, PhHgBr, p-CH(3)C(6)H(4)HgBr, p-CH(3)OC(6)H(4)HgCl, CF(3)HgPh, Ph(2)Hg, (o-carborane-9-yl)(2)Hg, (m-carborane-9-yl)(2)Hg, (p-carborane-9-yl)(2)Hg, and (m-carborane-9-yl)HgCl) in the ionization chamber (IC) of the electron impact (EI) ion source of a mass spectrometer at 250-300 degrees C results in the transfer of the corresponding organic or organoelement radicals from the mercurials to the fullerene. Some of the processes are accompanied by hydrogen addition. C(70) reacts with Ph(2)Hg and (o-carborane-9-yl)(2)Hg at 300 degrees C in a similar fashion. A homolytic reaction path is considered for the reactions. It suggests both the thermal and EI initiated homolytic dissociation of the mercurials to the intermediate organic or organoelement radicals followed by their interaction with the fullerenes at the metallic walls of the IC. When EI is involved, the dissociation is supposed to occur via superexcited states (the excited states with the electronic excitation energies higher than the first ionization potentials) of the mercury reagents, with possible contribution of the process proceeding via their molecular ions. In line with the results obtained in the IC, C(60) reacts with Ph(2)Hg and (o-carborane-9-yl)(2)Hg under UV-irradiation in benzene and toluene solutions to furnish phenyl and carboranyl derivatives of the fullerene, respectively, some also containing the acquired hydrogen atoms. EPR monitoring of the processes has shown the formation of phenylfullerenyl and o-carborane-9-yl-fullerenyl radicals. g-Factors and hyperfine coupling (hfc) constants with (10)B, (11)B, and (13)C nuclei of both the latter and m-carborane-9-yl-fullerenyl radical formed in the reaction of C(60) with (m-carborane-9-yl)(2)Hg have been determined by the special EPR studies. The unusually great chemically induced dynamic electron polarization (CIDEP) of the latter radical where even the (13)C satellite lines are polarized has been observed and is discussed in terms of both radical-triplet-pair and radical-pair mechanisms. The similar CIDEP effect is also intrinsic to the o-carborane-9-yl-fullerenyl radical obtained under the same conditions. The analogous transfer of the carboranyl radicals from (o-carborane-9-yl)(2)Hg to C(60) occurs when their mixture is boiled in (t)BuPh for 10-15 h.

Trifluoromethylation of [60]- and [70]Fullerene in the Ionization Chamber of a Mass Spectrometer

Abstract Both [60]- and [70]fullerene react with either the Scherer radical (perfluorodiisopropylethylmethyl, C9F19), a mixture of branched perfluorononenes (C9F18, the product of hexafluoropropene trimerization), or β-fluorosulphatotetrafluoroethyldiheptafluoroisopropylmethyl radical (C9F18OSO2F) in the ionization chamber of a mass spectrometer to give the positive parent ions of trifluoromethylation products, the reaction being accompanied by hydrogen addition. The reaction occurs at least partly on the walls of the ionization chamber, by a radical mechanism employing CF3 radicals formed from the radical reactants both thermally and under electron impact; only the latter route occurs with the perfluorononenes.

Trifluoromethylation of C60 and C70 with Mercury(II) Trifluoroacetate

Fullerenes C60 and C70 are shown to react with Hg(CF3COO)2 in the ionization chamber of the electron impact source of a mass spectrometer at 300 and 310°C, yielding trifluoromethylated derivatives of the fullerenes with up to six and two CF3 addends, respectively. For some of the products the reactions are accompanied by hydrogen addition. Based on previous mechanistic studies of the analogous reactions of C60 with the Scherer radical (C9F19•), a mixture of perfluoronones (C9F18), and acetone, a plausible scheme is proposed for the processes. It involves formation of the intermediate CF3 radicals owing to electron impact or thermally initiated homolytic dissociation of the mercury(II) salt, and their further reaction with the fullerenes at the surface of the ionization chamber. Heating mixtures of the reagents under argon at 300–310°C also yields trifluoromethylated fullerenes, in agreement with the results obtained with the ionization chamber. *Deceased on 1 February 2006

Homolytic Reactive Mass Spectrometry of Fullerenes: Interaction of C60 and C70 with Ketones in the Electron Impact Ion Source of a Mass Spectrometer and the Comparison of Results with Those of Photochemical Reactions of C60 with Several Ketones in Solution

Our previous investigations showed that homolytic reactions of C60 with a number of perfluoroorganic and organomercury(II) compounds occurring under electron impact (EI) in the ionization chamber (IC) of a mass spectrometer could predict the reactivity of C60 towards these compounds in solution or solid state. To expand the scope of this statement, C60 and C70 have been reacted with ketones RCOR1, where R and R1 are alkyl, aryl, benzyl, and CF3, in an IC under EI to yield products of the addition of R· and R1· radicals to the fullerenes, paramagnetic ones being stabilized by hydrogen addition and loss. Experimental evidence in support of a mechanism involving homolytic dissociation of ketone molecules via superexcited states to afford these radicals that react with the fullerenes at the IC surface has been obtained. As anticipated, the reactions between C60 and several ketones conducted in solution under UV irradiation have afforded Me-, Ph-, and CF3-derivatives of C60. However, some other products have been identified by mass spectrometry and their formation is reasonably explained. When decalin has been employed as a solvent, decalinyl derivatives of the fullerene have been found among the products and the (9-decalinyl)fullerenyl radical has been registered by EPR. Thus, incomplete but reasonable conformity of the results of the reactions of fullerenes with ketones in an IC under EI with those of the reactions of the same reagents in solution under UV irradiation has been demonstrated, and the former results can predict the latter ones to a reasonable extent.

A Comparative Study of Homolytic Reactions of Fullerenes with Aldehydes in a Mass Spectrometer under Electron Impact and in Solution under UV Irradiation

C60 was reacted in the ionization chamber of a mass spectrometer under electron impact (EI) with aldehydes, RCHO (R = Ph, p-FC6H4, F5C6, p-MeOC6H4, α-thienyl, o-HOC6H4, o-BrC6H4, m-BrC6H4 and t-Bu), with the transfer of R• radicals and with Me•-transfer from i-PrCHO and t-BuCHO. Paramagnetic fullerene derivatives were stabilized by the addition of the next R• radical or a hydrogen atom, or hydrogen or bromine atom loss. A detailed study showed that the reaction between C60 and PhCHO occurred via a homolytic mechanism that matches one reported earlier for the reaction with acetone. This suggests the generality of the mechanism for the reactions of fullerenes with other species in ionization chambers under EI at ca 300°C. All aldehydes, except one, had radicals at the carbonyl group which were different from those in the ketones examined earlier in the reactions. This expanded the variety of radicals which can be transferred to fullerenes during reactions in ionization chambers under EI. Due to this and the hydrogen atom at the CO group of aldehydes, some reactions occurred that were not found for the ketones: the formation of cyclic products C60COC6H4 and C60OC6H4 for PhCHO, o-BrC6H4CHO and o-HOC6H4CHO, respectively, and HC60Ph for o- and m-BrC6H4CHO. The reaction with α-formylthiophen gives the first example of transferring an aromatic heterocyclic radical to C60 in an ionization chamber under EI. C70 reacted with PhCHO, p-FC6H4CHO and i-PrCHO similarly to C60. The results for the reactions of C60 with PhCHO and with i-PrCHO were compared with those in solution under UV irradiation. Incomplete but reasonable coincidence was found; in both modes, the addition of Ph•, PhCO• and Me• radicals to C60 occurred, whereas some other products were formed in solution and the explanation is given as to why this occurred. This conformity sup ports the hypothesis based on the results of kindred reactions with ketones and organomercurials: the results of EI-initiated homolytic reactions between fullerenes and other compounds in an ionization chamber can predict the reactivity of the fullerenes toward them in solution.

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

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.

Interaction of Fullerenes with Organosilanes in the Ionization Chamber of a Mass Spectrometer under Electron Impact and the Reaction of C60 with Tetraphenylsilane in Solution under UV Irradiation

C60 was shown to react with organosilanes Me4Si, Ph2SiH2, Ph2MeSiH, Ph4Si, and α-naphthylphenylmethylsilane in the electron ionization ion source of a mass spectrometer with the transfer of the corresponding organic radicals (Me, Ph, and α-naphthyl) from the silanes to the fullerene. The reactions were accompanied by hydrogen addition to some products and hydrogen loss from them. C70 reacted with Me4Si analogously. A reaction mechanism involving homolytic dissociation of the silanes under electron impact to the corresponding organic radicals, which react further with C60 at the surface of the ionization chamber of the mass spectrometer to give the respective adducts, was offered. A mechanistic study of the reaction of C60 with Me4Si supported it. No silicon containing derivatives of the fullerenes were found. C60 reacted with Ph4Si in solution under UV irradiation in a similar fashion furnishing phenyl derivatives of the fullerene. These results provide an additional support to the hypothesis formulated earlier that the homolytic reactive mass spectrometry of fullerenes (the reactions of fullerenes with other species in the ionization chambers of mass spectrometers and their mass spectral monitoring) can predict the reactivity of them toward the same reagents in solution to a significant extent.