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Multiple Adducts of C 60 by Tether‐Directed Remote Functionalization and synthesis of soluble derivatives of new carbon allotropes C n (60+5)
Author(s) -
Isaacs Lyle,
Diederich François,
Haldimann Richard F.
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800202
Subject(s) - chemistry , adduct , intramolecular force , regioselectivity , cycloaddition , fullerene , surface modification , stereochemistry , medicinal chemistry , organic chemistry , catalysis
Abstract 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 C n (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 π‐electron chromophore of the fullerene is reduced as a result of increasing functionalization; this analysis is the subject of the directly following paper.