Evolution of late transition-metal-catalyzed intermolecular reductive coupling reaction of [60]fullerene and N-sulfonylaldimines: Competing formation of hydrobenzylated [60]fullerenes and 1,2-dihydrofullerene

A system based on late transition-metal halides, phosphanes, water, and reducing agents in 1,2-dichlorobenzene can efficiently catalyze the intermolecular reductive coupling of [60]fullerene with N-sulfonylaldimines to afford novel 1,2-hydrobenzylated [60]fullerene derivatives. We found that both group VII B metals (cobalt, rhodium, iridium) and group VIII B metals (nickel, palladium, platinum) perform this coupling reaction. A control experiment in the absence of aldimines produced C ₆₀H ₂, which showed that the reaction might proceed via a [60]fullerene metal complex [M(η ²-C ₆₀)(ligand)]. An isotope labeling experiment with D ₂O as deuterium source resulted in deuterioaryzilation with deuterium bonded to the sp ³-carbon of C ₆₀, providing evidence of a five-membered azametallacycle intermediate. Evaluation of the scope of reductive coupling reaction with versatile aldimines gave access to the hydroaryzilation products. All the reductive coupling products were completely characterized by IR and NMR spectroscopy and ESI mass spectrometry. A possible reaction mechanism based on these results is proposed. This discovery of the formation of reductive coupling compounds and metal-catalyzed formation of C ₆₀H ₂ are both new to metal catalysis and fullerene chemistry. A system based on late transition-metal halides, phosphanes, water, and reducing agents in o-DCB can efficiently catalyze intermolecular reductive coupling between [60]fullerene and N-sulfonylaldimines to afford new 1,2-hydrobenzylated [60]fullerene derivatives. The reaction yields are moderate, due to the formation of C ₆₀H ₂ as a byproduct. A possible reaction mechanism is proposed.