Development of the method of alkylation of C_<60> by way of alkylfullerenyl cation

我们发现富勒烯C_1<60>在氯代烷烃（RCl）中与过量的AlCl_3发生亲电加成反应，得到了较好的加成产物<60>RC_1-Cl。富勒<60>烯醇（RC_<60>OH）在强酸（如CF_3SO_3H和H_2SO_4）中溶解，可生成长寿命的烷基富勒烯阳离子（RC_ ^+）。通过NMR和维斯/近红外光谱观察到这些阳离子作为长寿命物种。~ 1C <13>NMR谱表明，正电荷主要位于C-2位，结构具有C_s对称性。阳离子中心的化学位移（175-180 ppm）表明R基团中的氯原子与阳离子中心弱配位，<60>也可通过AlCl_3从氯化物RC_ Cl中夺取氯离子原位生成阳离子RC_ ^+<60->。当反应在苯甲醚中进行时，溶剂分子与RC ^+发生亲核加成<60>，得到相应的加合物RC<60>-C_6H_4OCH_3-p。用此试剂在醇（R ′ OH）中进行反应，得到相应的醚类化合物RC_<60>-OR ′，氯化物RC_<60>-Cl（R=氯代烷基）在苯甲醚-三氟乙醇（1：9 v/v）混合溶剂中发生溶剂分解，得到S_N1反应产物RC_<60>-Y（Y=对苯甲醚和三氟乙氧基）。活化自由能（24-25 kcal/mol，25℃）仅略低于叔丁基氯的活化自由能，表明阳离子RC <60>^+具有与叔丁基氯相近的稳定性，阳离子RC ^+的pK_R^+值<60>也由相应富勒醇的电离平衡常数确定。所得值与叔丁基阳离子的pK_R ~+相当。这一结果也支持了RC_ ^+与叔丁基阳离子在稳定性上的相似性<60>。

We found that fullerene C_<60> undergoes electrophilic addition when treated with a large excess of AlCl_3 in chloroalkanes (RCl), giving adducts RC_<60>-Cl in good yields. The intermediate, alkylfullerenyl cations (RC_<60>^+), could be generated as long-likved ions by dissolving fullerenols (RC_<60>OH) in strong acids such as CF_3SO_3H and H_2SO_4. These cations were observed by NMR and vis/NIR spectra as long-lived species. The ^<13>C NMR spectra indicated that the positive charge is located mainly on C-2, and the structure has C_s symmetry. The chemical shift of the cationic center (175-180 ppm) suggested a weak coordination of chlorine atom(s) in the group R to the cationic center.Cations RC_<60>^+ could be also generated in situ by the abstraction of a chloride ion from chlorides RC_<60-> Cl with AlCl_3. When the reactions were carried out in anisole, nucleophilic addition of a solvent molecule to RC_<60>^+ occurred, giving the corresponding adducts RC_<60>-C_6H_4OCH_3-p. The chloride ion can be also abstracted by AgBF_4. With this reagent the reaction could be carried out in alcohols (R'OH), giving the corresponding ethers RC_<60>-OR' in good yiels.Chlorides RC_<60>-Cl (R=chloroalkyl) were found to undergo solvolysis in anisole-trifluoroethanol mixed solvent (1:9 v/v) to give S_N1 reaction products, RC_<60>-Y(Y=p-anisyl and trifluoroethoxy). The free energies of activation (24-25 kcal/mol at 25℃) were only slightly lower than that for the tert-butyl chloride, indicating that cations RC_<60>^+ have stabilities close to that of the tert-butyl cation.The pK_R^+ values of cations RC_<60>^+ were also determined from the equilibrium constants for the ionization of the corresponding fullerenols. The obtained values are comparable to the pK_R+ of the tert-butyl cation. Thsi result also support the similarity in stability between RC_<60>^+ and the tert-butyl cation.