Synthesis and chemistry of fullerene derivatives bearing phosphorus substituents.: Unusual reaction of phosphines with electron-deficient acetylenes and C60

A unique method to introduce phosphorus substituents onto C-60 is based on the reaction of phosphines with acetylenes and C-60. Treatment of C-60 with phosphines (PR3) and electron-deficient acetylenes (A) in toluene at ambient temperature gave fullerene derivatives (1, R = C6H5 and A = MeO2CC=CCO2Me; 2, R = C6D5 and A = MeO2CC=CCO2Me; 3, R = C6H5 and A = EtO2CC=CCO2Et; 4, R = p-CH3C6H5 and A = MeO2CC=CCO2Me; 6, R = C6H5 and A trans-MeO2CC=CCH=CHCO2Me) consisting of a phosphorus ylide group and a cyclopropane ring on the fullerene moiety in good to excellent yields. The structures of these ylide derivatives are determined on the basis of their spectral data and single-crystal X-ray diffraction measurements. Al these ylides show temperature-dependent, NMR spectra that can be rationalized on the basis of interchange between two Z,E isomers and restricted rotation of the substituents on the fullerene moiety. Based on the known chemistry of phosphines and acetylenes, we propose a mechanism to account for the formation of these ylide derivatives. Phosphine ylides 1 and 4 readily undergo protonation and decarboxylation in the presence of acid to give phosphonium salts 7 and 8, respectively.