Ce@C(82) is isolated by high-performance liquid chromatography (HPLC) and the cage symmetry is determined as C(2)(v)() by measuring the (13)C NMR spectra of its anion. The (13)C NMR peaks of [Ce@C(82)](-) show temperature-dependent shifts ascribed to the f electron remaining on the Ce atom. Both Ce@C(82) and [Ce@C(82)](-) are silent in electron spin resonance spectroscopy (ESR) because of the highly anisotropic g matrix as well as of the fast relaxation process originating from the orbital angular momentum of the f electron. This is the complementary relationship to the observation of the paramagnetic shift in (13)C NMR. [Ce@C(82)](-) has lower stability in air than [La@C(82)](-).

Photolysis and thermolysis of diazirines have been widely used to produce carbenes. 1 Bonneau and Liu have reported that these reactions yield not only a singlet carbene but also a diazo compound as an intramolecular rearrangement product. 2 The nature of the specific substituents on the diazirine determines the formation of the corresponding diazomethane as an intermediate, which may or may not be observed. 3 These authors also reported on the quantum yields of the formation of carbene and diazo compounds derived from the photolysis of diazirines by means of laser flash photolysis. 2 Numerous chemical transformations have been developed since the isolation of C 60 in preparatively useful quantities. 4 C 60 has a unique reactivity, which differs significantly from that of classical planar aromatics. 5 C 60 reacts with diazomethane to yield fulleroid. 5d,6 Carbene generated from the thermolysis of precursors such as diazirines, 7 sodium trichloroacetate, 8 cyclopropene, 9 oxadiazole, 10 and tosylhydrazone 11 adds onto C 60 , affording methanofullerene. 4 These differences might be useful in differentiating whether carbene or diazo compound is involved as the reactive intermediate. In this context, we have carried out the photolysis of diazirine in the presence of C 60 .Our report demonstrates that C 60 acts as a mechanistic probe for the formation of carbene and diazo compound in the photolysis of diazirine. As well, our experiment offers the first redox data of methanofullerene and fulleroid bearing the same substituent at the bridging carbon atom on the C 60 moiety.Irradiation of a benzene solution of 2-adamantane-2,3′-[3H]-diazirine (1, 2.5 × 10 -4 M) and C 60 (2.5 × 10 -3 M) with a highpressure mercury arc lamp (cutoff < 300 nm) at 15°C in a Pyrex tube resulted in the formation of the corresponding adduct C 60 -Ad (2) in 80% yield, which was purified by preparative HPLC with a GPC column. Adduct 2 can be readily separated into two isomers, 2a and 2b, by preparative HPLC with a Buckyprep column (Scheme 1). The isomeric ratio of 2a and 2b is 49/51. FAB mass spectrometry of 2a and 2b gives a molecular ion peak (C 70 H 14 requires m/z 854) at m/z 858-854, as well as a peak for C 60 at m/z 724-720, which arises from the loss of the adamantyl group. The UV-visible absorption spectra of 2a and 2b are virtually identical to that of C 60 , except for a subtle difference in the 400-650 nm region. These results suggest that 2a and 2b retain the essential electronic and structural character of C 60 . The UV-visible absorption spectrum of 2a has an absorption at 434 nm, which is a characteristic feature of a 6,6-adduct of C 60 . 12 The spectral data of 1 H and 13 C NMR and 2D NMR (HMQC and HMBC) clearly suggest that 2a has C 2V symmetry. 13 Meanwhile, the analysis of 1 H and 13 C NMR(HMQC and HMBC) has offered crucial evidence for the identification of C s symmetry of 2b as a 5,6-adduct of C 60 . 14 We carried out density functional calculations at the BLYP/ 3-21G level for 2a and 2b with the Gaussian 98 program. 15 ...