(Cyclopentadienyl)chromiumtricarbonyl dimers as a source of metal-centered free-radicals to form stable η2-bonded spin-adducts with fullerenes

Spin-adducts (I, IIb–c) of C60 and C70 with metal-centered free radicals CpCr(CO)3 (I, IIa) have been generated in toluene via interaction between fullerenes and the weakly metal–metal bonded dimeric complexes [CpCr(CO)3]2 (Cp = η5-C5H5 (I); Cp = η5-C5Me5 (II)). Their structures have been investigated using ESR spectroscopy and DFT-PBE calculations and η2-bonding to the Cdouble bond; length as m-dashC bond between two hexagons in C60 has been established. Calculations have been extended to investigate the nature of the intermediate η2-coordinated toluene chromium complexes (I, IId).