MULTIPLE METAL ADDITIONS TO C-60 - AN AB-INITIO STUDY OF [M(PH3)(2)]C-N(60) (M=PT AND PD N=1, 2, AND 6)

A full geometry optimization at the HF level has been carried out for the fullerene platinum complexes [Pt(PH3)(2)]C-n(60), n = 1, 2, and 6, and for the hexasubstituted palladium derivative [Pd(PH3)(2)]C-6(60). The computed geometries are in good agreement with those determined b y X-ray diffraction. When there is just one platinum bound to C-60, th e binding energy is found to be 11.7 kcal/mol higher than the calculat ed Pt-ethylene binding energy. The interaction between the metal and C -60 is basically local. As a matter of fact, the dissociation energy o f the first metal group in [Pt(PH3)(2)]C-2(60) is just 2.7 kcal/mol lo wer than the dissociation energy of the Pt(PH3)(2) fragment in the mon osubstituted derivative. The total binding energy of the six platinum groups in [Pt(PH3)(2)]C-6(60) has been computed to be 30.4 kcal/mol (5 .1 kcal/mol per group). An important charge transfer from the metal gr oup to the C-60 core has been detected, about 0.5e for the monosubstit uted derivative and 2.2e for the hexasubstituted platinum complex. The Pd(PH3)(2) group has been determined to be more labile than the corre sponding platinum group. The M-C-60 bond strength is noticeably weaken ed if the complex is reduced. Hence, the loss of C-60(-) from [Pt(PH3) (2)](2)(C-60)(-) is 12.5 kcal/mol more favorable than the loss of C-60 from its neutral partner.