Acyl radical reactions in fullerene chemistry: direct acylation of [60]fullerene through an efficient decatungstate-photomediated approach.
A versatile and highly efficient photochemical methodology for the direct acylation of C(60) has been developed. This approach utilizes a wide variety of acyl radicals derived from aldehydes through a hydrogen atom abstraction process mediated by tetrabutylammonium decatungstate [(n-Bu(4)N)(4)W(10)O(32)]. The single addition reaction of these acyl radicals to [60]fullerene proceeded selectively to afford a novel class of previously unexplored fullerene-based materials. Product analysis of this reaction showed that decarbonylation and acylation pathways compete when a tertiary or phenylacetyl aldehyde is the starting material. However, a decrease of the reaction temperature was found to be effective in overcoming the decarbonylation encountered in certain acyl radical additions to C(60); the carbonyl radical addition precedes decarbonylation even in the cases where the decarbonylation rate constant exceeds 10(6) s(-1) (i.e., phenylacetaldehyde). The regiochemistry of the t-butyl radical addition was also found to be thermally controlled. The present methodology is directly applicable even in the cases of the cyclopropyl-substituted aldehydes, where rapid rearrangement of the cyclopropyl acyl radical intermediate can potentially occur. A mechanistic approach for this new reactivity of C(60) has been also provided, based mainly on intra- and intermolecular deuterium isotope effect studies.
Tzirakis
Manolis D
MD
Department of Chemistry, University of Crete, 71003 Voutes, Heraklion, Crete, Greece.
Orfanopoulos
Michael
M