D_(2d)(23)-C_(84) versus Sc_2C_2@D_(2d)(23)-C_(84): Impact of Endohedral Sc_2C_2 Doping on Chemical Reactivity in the Photolysis of Diazirine

摘要

We compared the chemical reactivity of D_(2d)(23)-C_(84) and that of Sc_2C_2@D_(2d)(23)-C_(84), both having the same carbon cage geometry, in the photolysis of 2-adamantane-2,3'-[3H]-diazirine, to clarify metal-atom doping effects on the chemical reactivity of the carbon cage. Experimental and computational studies have revealed that the chemical reactivity of the D_(2d)(23)-C_(84) carbon cage is altered drastically by endohedral Sc_2C_2 doping. The reaction of empty D_(2d)(23)-C_(84) with the diazirine under photoirradiation yields two adamantylidene (Ad) adducts. NMR spectroscopic studies revealed that the major Ad monoadduct (C_(84)(Ad)-A) has a fulleroid structure and that the minor Ad monoadduct (C_(84)(Ad)-B) has a methanofuller- ene structure. The latter was also characterized using X-ray crystallography. C_(84)(Ad)-A is stable under photoirradiation, but it interconverted to C_(84)(Ad)-B by heating at 80 ℃. In contrast, the reaction of endohedral Sc_2C_2@D_(2d)(23)-C_(84) with diazirine under photoirradiation affords four Ad monoadducts (Sc_2C_2@ C_(84)(Ad)-A, Sc_2C_2@C_(84)(Ad)-B, Sc_2C_2@C_(84)(Ad)-C, and Sc_2C_2@C_(84)(Ad)-D). The structure of Sc_2C_2@C_(84)(Ad)-C was characterized using X-ray crystallography. Thermal interconversion of Sc_2C_2@C_(84)(Ad)-A and Sc_2C_2@C_(84)(Ad)-B to Sc_2C_2@ C_(84)(Ad)-C was also observed. The reaction mechanisms of the Ad addition and thermal interconversion were elucidated from theoretical calculations. Calculation results suggest that C_(84)(Ad)-B and Sc_2C_2@C_(84)(Ad)-C are thermodynamicaUy favorable products. Their different chemical reactivities derive from Sc_2C_2 doping, which raises the HOMO and LUMO levels of the D_(2d)(23)-C_(84) carbon cage.