Multiple adducts of C-60 by tether-directed remote functionalization and synthesis of soluble derivatives of new carbon allotropes Cn(60+5)

A comprehensive series of multiple adducts of C-60 was prepared by tether-directed remote functionalization. When the tether-reactive-group conjugates 2 and 10 were attached to methano[60]fullerenecarboxylic acid (= cyclopropafullerene- C-60-I-h-carboxylic acid) and C-60, respectively, the e-bis-adducts 4 and 9 (Schemes 1 and 2) were obtained with complete regioselectivity as predicted by semi-empirical PM3 calculations (Fig. 2). Attachment of the anchor-tether-reactive-group conjugate 13 to C-60 by Bingel reaction, followed by double intramolecular Diels-Alder, cycloaddition afforded the tris-adduct 12 (Scheme 3). Starting from 12, a series of selective e-additions led to the tetrakis-adducts 16 and 19 (Scheme 4), pentakis-adducts 20-23 (Scheme 5), and, ultimately, to hexakis-adducts 24 and 25 (Scheme 6), and 29, and 30 (Scheme 7) with a pseudo-octahedral addition pattern on the fullerene core. Oxidative cyclization of diethynylmethanofullerene 30 under Eglinton-Glaser conditions afforded the trimeric and tetrameric acetylenic macrocycles 26, with three, and 27, with four appended C-60 moieties, respectively (Scheme 8). These multinanometer-sized compounds are the first soluble derivatives of C-195 and C-260, two members of a new class of fullerene-acetylene hybrid C-allotropes with the general formula Cn(60+5). The matrix-assisted laser-desorption time-of-flight mass spectra of 26 and 27 showed a remarkable fragmentation; the sequential loss of fullerene spheres led to the formation of ions corresponding to mono-fullerene adducts of the cyclocarbons cyclo-C-15 and cyclo-C-20 (Fig. 4). Large solvent effects were observed in the Bingel addition of 2-bromomalonates to higher adducts of C-60, with the use of polar solvents enhancing the reaction rate without loss of regioselectivity. Experimental evidence for the enhanced reactivity of e(face) over e(edge) bonds was obtained, which had previously been predicted in computational studies. The correlated series of mono- to hexakis-adducts of C-60 allowed identification of the changes in reactivity and physical properties that occur, when the conjugated pi-electron chromophore of the fullerene is reduced as a result of increasing functionalization; this analysis is the subject of the directly following paper.