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

我们发现富勒烯C&lt；60&gt；在氯代烷(RCL)中与大量过量的AlCl3发生亲电加成反应，以较高的产率得到加合物RC&lt；60&gt；-Cl。中间体烷基富勒烯基阳离子(RC_&lt；60&gt；^)可通过富勒烯醇(RC_&lt；60&gt；OH)在CF_3SO_3H和H_2SO_4等强酸中溶解而生成类长离子。核磁共振谱表明正电荷主要位于C-2上，结构具有C_S对称性。阳离子中心的化学位移(175-180ppm)表明R基氯原子(S)与阳离子中心的配位较弱。阳离子RC_&lt；60&gt；也可通过与AlCl3从氯化物RC_&lt；60-&gt；Cl中提取氯离子而原位生成。当反应在苯甲醚中进行时，溶剂分子与RC_&lt；60&gt；^发生亲核加成反应，得到相应的加合物RC_&lt；60&gt；-C_6H_4OCH_3-p。氯离子也能被AgBF_4萃取。在醇(R‘OH)中，反应可以进行，生成相应的醚类化合物RC_&lt；60&gt；-OR’。氯化物RC_&lt；60&gt；-Cl(R=氯烷基)在苯甲醚-三氟乙醇混合溶剂(1：9v/v)中发生溶剂分解，生成S_N1反应产物RC_&lt；60&gt；-Y(Y=对-苯甲酰基和三氟乙氧基)。其活化能仅略低于叔丁基氯的活化能(25℃时为24-25千卡/摩尔)，表明阳离子RC_(60)与叔丁基阳离子的稳定性接近，并根据相应富勒烯醇电离平衡常数确定了阳离子RC_(60)的pKR^值。所得结果与叔丁基阳离子的pK_R值相当。这一结果也支持RC_&lt；60和叔丁基阳离子在稳定性上的相似性。

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.