THEORETICAL INVESTIGATION OF THE ORIGIN OF REGIOSELECTIVITY IN THE FORMATION OF METHANOFULLERENES BY ADDITION OF DIAZO-COMPOUNDS - A MODEL STUDY

The thermal extrusion of dinitrogen from the adduct of benzene with di azomethane 11 was investigated by ab initio and density functional met hods as a model reaction for the thermal extrusion of dinitrogen from the adducts of fullerenes with diazomethane to form 6-5-open methanofu llerenes, The calculations provided evidence that the reaction of 11 t owards norcaradiene (12) proceeds via a Mobius aromatic transition sta te 12a with an activation energy of approximately 20 kcalmol(-1) This transition state is characterized by a high anisotropy in the magnetic susceptibility of Delta(chi) approximate to 88 cgs-ppm, The transitio n state 13a of the alternative dinitrogen extrusion pathway from 11 to the thermodynamically more stable product toluene (13) is approximate ly 5 kcalmol(-1) higher in energy: hence, norcaradiene (12) is the kin etically favored product, Analoguous calculations on a larger, more ri gid system indicated no change in the mechanism of the reaction, This is in agreement with the observed regioselectivity in the thermal extr usion of dinitrogen from the pyrazoline-fused [60]fullerene 3 to form the 6-5-open methanofullerene 2.