Endohedral fullerene with μ3-carbido ligand and titanium-carbon double bond stabilized inside a carbon cage

In all metallofullerenes known before this work, metal atoms form single highly polar bonds with non-metal atoms in endohedral cluster. This is rather surprising for titanium taking into account the diversity of organotitanium compounds. Here we show that the arc-discharge synthesis of mixed titanium-lutetium metallofullerenes in the presence of ammonia, melamine or methane unexpectedly results in the formation of TiLu 2 C@ I h -C 80 with an icosahedral I h (7) carbon cage. Single-crystal X-ray diffraction and spectroscopic studies of the compound reveal an unprecedented endohedral cluster with a μ 3 -carbido ligand and Ti-C double bond. The Ti(IV) in TiLu 2 C@ I h -C 80 can be reversibly reduced to the Ti(III) state. The Ti=C bonding and Ti-localized lowest unoccupied molecular orbital in TiLu 2 C@ I h -C 80 bear a certain resemblance to titanium alkylidenes. TiLu 2 C@ I h -C 80 is the first metallofullerene with a multiple bond between a metal and the central, non-metal atom of the endohedral cluster. Metallofullerenes typically have polar single bonds between metals and non-metals. Here, through arc-discharge experiments, the authors observe the formation of an endohedral fullerene with an encapsulated tri-coordinate μ 3 -carbon centre and a stable titanium-carbon double bond.