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We compared the chemical reactivity of D(23)-C and that of ScC@D(23)-C, 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(23)-C carbon cage is altered drastically by endohedral ScC doping. The reaction of empty D(23)-C with the diazirine under photoirradiation yields two adamantylidene (Ad) adducts. NMR spectroscopic studies revealed that the major Ad monoadduct (C(Ad)-A) has a fulleroid structure and that the minor Ad monoadduct (C(Ad)-B) has a methanofullerene structure. The latter was also characterized using X-ray crystallography. C(Ad)-A is stable under photoirradiation, but it interconverted to C(Ad)-B by heating at 80 °C. In contrast, the reaction of endohedral ScC@D(23)-C with diazirine under photoirradiation affords four Ad monoadducts (ScC@C(Ad)-A, ScC@C(Ad)-B, ScC@C(Ad)-C, and ScC@C(Ad)-D). The structure of ScC@C(Ad)-C was characterized using X-ray crystallography. Thermal interconversion of ScC@C(Ad)-A and ScC@C(Ad)-B to ScC@C(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(Ad)-B and ScC@C(Ad)-C are thermodynamically favorable products. Their different chemical reactivities derive from ScC doping, which raises the HOMO and LUMO levels of the D(23)-C carbon cage.

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Additions of adamantylidene (Ad) to M N@I -C (M=Sc, Lu) and Sc N@D -C have been accomplished by photochemical reactions with 2-adamantyl-2,3'-[3H]-diazirine (1). In M N@I -C , the addition led to rupture of the [6,6]- or [5,6]-bonds of the I -C cage, forming the [6,6]-open fulleroid as the major isomer and the [5,6]-open fulleroid as the minor isomer. In Sc N@D -C , the addition also proceeded regioselectively to yield three major isomeric Ad mono-adducts, despite the fact that there are nine types of C-C bonds in the D -C cage. The molecular structures of the seven Ad mono-adducts, including the positions of the encaged trimetallic nitride clusters, have been unambiguously determined through single-crystal XRD analyses. Furthermore, results have shown that stepwise addition of Ad to Lu N@I -C affords several Ad bis-adducts, two of which have been isolated and characterized. The X-ray structure of one bis-adduct clearly revealed that the second Ad addition took place at a [6,6]-bond close to an endohedral metal atom. Theoretical calculations have also been performed to rationalize the regioselectivity.