title: Approaches to open fullerenes: synthesis and kinetic stability of diels-alder adducts of substituted isobenzofurans and C60.
abstract: We have examined the reactions of 1,3-disubstituted isobenzofurans with the fullerene C60 in the context of an approach to open a large orifice on the fullerene framework. A variety of substituted isobenzofurans (6a-h), generated from the reaction of 1,4-substituted 1,4-epoxynaphthalenes 3a-h with 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (4a) or 1,2,4,5-tetrazine (4b), were added to C60 to afford the Diels-Alder adducts 7a-h. The thermal stability of these adducts toward retro-Diels-Alder fragmentation differs greatly in solution from that in the solid state. In solution, the relatively facile retro-Diels-Alder fragmentation of monoadducts 7a and 7c, to give C60 and the free isobenzofurans 6a and 6c, have rate constants (and activation barriers) of k=9.29x10(-5) s-1 at 70 degrees C (Ea=32.6 kcal mol-1) and k=1.36x10(-4) s-1 at 40 degrees C (Ea=33.7 kcal mol-1), respectively, indicating that the addition of isobenzofurans to C60 is readily reversible at those temperatures. In the solid state, thermogravimetric analysis of adduct 7a indicates that its decomposition occurs only within the temperature range of 220-300 degrees C. As a result, these compounds can be stored at room temperature in the solid state for several weeks without significant decomposition but have to be handled within several hours in solution.
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
authors: Shih-Ching
authors: SC
authors: Chuang
authors: Michael
authors: M
authors: Sander
authors: Thibaut
authors: T
authors: Jarrosson
authors: Scott
authors: S
authors: James
authors: Eugene
authors: E
authors: Rozumov
authors: Saeed I
authors: SI
authors: Khan
authors: Yves
authors: Y
authors: Rubin
mesh_terms: D001572:Benzofurans / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D003500:Cyclization; D037741:Fullerenes / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D001572:Benzofurans; D037741:Fullerenes; C069837:fullerene C60