Nickel-Promoted First Ene−Diyne Cycloaddition Reaction on C60: Synthesis and Photochemistry of the Fullerene Derivatives

A novel method for the construction of a fused cyclohexadiene ring on C 60 based on a nickel-promoted [2+2+2] cycloaddition of 1,6-diynes is described. Treatment of C 60 with terminal 1,6-diynes (HC⋮CCH 2 ) 2 X) in the presence of NiCl 2 (PPh 3 ) 2, Zn, and PPh 3 at 90 °C in toluene afforded [2+2+2] bicyclic hexadiene derivatives (X = C(CO 2 Me) 2 ( 2a ), C(CO 2 Et) 2 ( 2b ), C(COMe) 2 ( 2c ), CH 2 ( 2d ), O ( 2e ), NSO 2 - p -C 6 H 5 CH 3 ( 2f ), C(SO 2 Ph) 2 ( 2g ), and ( 2h ) in good yields. Spectral data for products 2a − h indicated that the cycloaddition of diynes to C 60 occurs across a 6,6-ring junction on the fullerene. On the basis of the established chemistry of metal-mediated [2+2+2] cycloaddition, a mechanism is proposed to account for the present nickel-mediated reaction. All the hexadiene derivatives 2a − h in solution are readily oxidized by molecular oxygen in the presence of light at ambient temperature. The oxidation process of compound 2a in chloroform- d was monitored by 1 H NMR spectroscopy, and the results showed that 2a first reacted with molecular oxygen to form peroxide 3 and was subsequently converted to dialdehyde 4 and C 60 -containing polymeric material. Photochemical properties of some cyclohexadiene derivatives were then investigated. Upon irradiation (350 nm), compounds 2a − c, 2f, and 2h readily underwent [4+4] cycloaddition to give the corresponding bisfulleroids 5a − c, 5f, and 5h in excellent yields.