Novel Bismethanofullerenes and Ethenofullerene from the Reaction of Propiolates with C60 in the Presence of Triphenylphosphine

Methyl propiolate reacts with C60 in the presence of triphenylphosphine in toluene to give a bismethanofullerene 2. Compound 2 is an adduct of two methyl propiolate units to a C60 moiety and consists of two methano bridges across two 6,6-ring junctions of the same six-membered ring on the fullerene moiety. Similarly, ethyl propiolate reacts with C60 in the presence of PPh3 to yield bismethanofullerene 3. Detailed analysis of the products from the reaction of methyl propiolate with C60 shows, in addition to 2 and C60, an ethenofullerene 4 and an unidentified insoluble material were isolated. Compound 4, which may be viewed as a [2 + 2] cycloaddition adduct of C60 and methyl propiolate, consists of a cyclobutene ring fused to the carbons on a 6,6-ring junction of the C60 moiety. On the basis of the known chemistry of phosphine with electron-withdrawing alkynes and C60, mechanisms are proposed to account for the formation of the bismethanofullerenes 2 and 3 and ethenofullerene 4.