Exploring the photoinduced electron transfer reactivity of aza[60]fullerene iminium cation Manolis M. Roubelakis a , Georgios C. Vougioukalakis b , Leanne C. Nye c , Thomas Drewello c , Michael Orfanopoulos a, * a Department of Chemistry, University of Crete, Campus Voutes, Heraklion 71003, Greece b Institute of Physical Chemistry, NCSR ‘Demokritos’, Agia Paraskevi Attikis, Athens 15310, Greece c Department of Chemistry and Pharmacy, University of Erlangen-Nurnberg, Erlangen D-91058, Germany article info Article history: Received 9 June 2010 Received in revised form 6 September 2010 Accepted 4 October 2010 Available online 13 October 2010 Keywords: Aza[60]fullerene Photoinduced electron transfer Iminium cation Benzyltrimethylsilanes Electron-rich olefins abstract Photolysis of (C 59 N) 2 solutions in the presence of neutral p-donors, such as arenes and electron-rich alkenes leads to a series of novel aza[60]fullerene monoadducts. The key step of the reaction involves a photoinduced electron transfer from the donor molecule to the iminium cation of aza[60]fullerene, followed by radical coupling of the resulting aza[60]fullerenyl radical with an intermediate stabilized radical derived from the substrate. This type of reactivity has been proven efficient with arenes having oxidation potential higher than about 1.5 V. Simple olefins, such as tri- and tetra-methylethylene, as well as cyclohexene, can also participate in this kind of photoinduced electron transfer-initiated reaction with C 59 N þ , affording the corresponding aza[60]fullerene derivatives. In the case of 2-methoxyprop-1-ene, 2,4-hexadiene, and b,b-dimethylstyrene, [2þ2] cycloaddition reactions with the aza[60]fullerene carbon shell dominate, leading to a mixture of unidentified multiadducts. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Despite the very rich chemistry of C 60 and the great number of functionalization techniques that have been developed over the years, 1 similar progress regarding its nitrogen substituted coun- terpart, aza[60]fullerene (1, Fig. 1), has been hampered thus far by the low symmetry of the heterofullerene sphere and by the fact that aza[60]fullerene is isolated as a dimer (2, Fig. 1). 2 In other words, the typical fullerene reactions can take place on any of the [6,6] double bonds of the two balls, affording complicated mixtures of isomers that are impossible to isolate and characterize. For exam- ple, one single addition on a [6,6] double bond in 2 can lead to 16 distinct isomers. As a result, only a few methods for the synthesis of well-defined aza[60]fullerene adducts are known at present. 3 The trapping of the azafullerenyl radical 1 was initially utilized to afford adducts 3 and 4 (Fig. 2); radical 1 was produced from dimer 2 either thermally or photochemically in the presence of a hydrogen atom donor, such as tributyl-tinhydride 4 or diphenylmethane, 5 respectively. In the same way, 9-alkyl-substituted fluorenes, 9,10- dihydroanthracene, and xanthene gave the corresponding mono- adducts 5, 6, and 7 (Fig. 2). 6 A free radical chain mechanism has been proposed for the production of these aza[60]fullerene derivatives. 57 However, the most efficient way to prepare aza[60]fullerene monoadducts involves the thermal treatment of the dimeric (C 59 N) 2 in the presence of air and excess toluene-p-sulfonic acid (p- TsOH), a procedure that oxidizes the produced azafullerenyl radical 1 to aza[60]fullerene iminium cation C 59 N þ (8, Scheme 1), which is isoelectronic to C 60 . This entity can be easily trapped by nucleo- philes, such as electron-rich aromatics, 8,9 enolizable carbonyl compounds, 10 as well as alcohols and olefins, 11 furnishing the cor- responding azafullerene derivatives (Scheme 1). The presence of both the oxygen and the acid is crucial for the above reactions to take place. It has been proposed that oxygen acts as the oxidizing agent, whereas toluene-p-sulfonic acid probably traps the reduced oxygen species and adjusts the solution’s pH. 8 N 1 (C s ) 2 N N Fig. 1. Azafullerenyl radical C 59 N  (1) and azafullerene dimer (C 59 N) 2 (2). * Corresponding author. Tel.: þ30 2810 545030; fax: þ30 2810 545001; e-mail address: orfanop@chemistry.uoc.gr (M. Orfanopoulos). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2010.10.006 Tetrahedron 66 (2010) 9363e9369