FULLERIDES OF PYRROLIDINE-FUNCTIONALIZED C-60

The spectral characteristics of the fulleride(1-) anions of pyrrolidin e-functionalized C-60 derivatives have been investigated in order to a ssess the degree to which the parent C-60 moiety retains its distincti ve redox and chromophoric properties upon functionalization. Such comp arison data are necessary if C-60 is to fulfill its anticipated role a s a versatile electron-accepting chromophore and a multielectron reser voir. Three systems have been investigated: a simple, monomeric, N-met hylpyrrolidine derivative, 1, a pyrrolidine-linked tetraphenylporphyri n/C-60 dyad, 2, and a pair of bifullerenes, 3 and 4, with adjacent and remote dispositions of the C-60 moieties, respectively. Near infrared spectra of the fulleride(1-) ions of these derivatives are notably si milar to C-60(1-) with only small energy shifts of the band envelope. H-1 and C-13 NMR data on 1(1-) are consistent with unpaired spin densi ty confined largely to the C-60 moiety rather than delocalized onto th e pyrrolidine functionality. The EPR spectra of all of the pyrrolidine -functionalized fulleride(1-) species are characterized by sharp doubl ets (Delta H = 1-2 G) and g values less than the free electron value. Unlike the EPR spectrum of C-60(1-), there is little temperature depen dence of the line width. EPR evidence for ball-to-ball spin-spin inter actions are observed in the fulleride of 3 but not in 4 or in the Cu-I I/C-60(1-) metalated porphyrin dyad. The X-ray crystal structure of th e porphyrin-C-60 dyad 2 has been determined. It is the first X-ray str uctural characterization of a pyrrolidine-functionalized C-60 species and confirms that the azamethine ylide addition has occurred across a 6:6 ring juncture. The crystal packing of the dyad reveals an intermol ecular interaction of the C-60 ball nestled in remarkably close approa ch to the porphyrin plane. The closest approach of a fullerene carbon atom to the mean plane of the porphyrin is ca. 2.75 Angstrom. This int eraction is notably similar to that envisaged for porphyrin-functional ized chromatographic supports used to separate fullerenes. A novel don or/acceptor relationship is proposed to account for this close interac tion.