Dronova Marina S, Bilyachenko Alexey N, Yalymov Alexey I, Kozlov Yuriy N, Shul'pina Lidia S, Korlyukov Alexander A, Arkhipov Dmitry E, Levitsky Mikhail M, Shubina Elena S, Shul'pin Georgiy B
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Ulitsa Vavilova, dom 28, Moscow 119991, Russia.
Dalton Trans. 2014 Jan 14;43(2):872-82. doi: 10.1039/c3dt52508b. Epub 2013 Oct 24.
Two principally different in their molecular architecture isomeric tetranuclear copper(ii) silsesquioxanes, "Globule"-like compound [(PhSiO1.5)12(CuO)4(NaO0.5)4] (1) and "Sandwich"-like derivative [(PhSiO1.5)6(CuO)4(NaO0.5)4(PhSiO1.5)6] (2), were synthesized by the partial cleavage of polymeric copper(ii) silsesquioxane [(PhSiO1.5)2(CuO)]n by tetraphenylcyclotetrasiloxanolate. The route leading to the formation of either 1 or 2 entirely depends on the nature and composition of the solvent used for this reaction. Thus, the process in an ethanol-1-butanol solution gives compound 1. When a 1,4-dioxane-methanol mixture was used, compound 2 was prepared. The structures and unusual crystal packing of the cages were confirmed by the X-ray studies. It has been found that the reaction of benzene with H2O2 in acetonitrile solution at 50 °C catalyzed by 1 requires addition of trifluoroacetic acid (TFA) in low concentration and gives phenol with a turnover number (TON) of 250 after 3 h. The initial reaction rate W0 linearly depends on the concentration of catalyst 2. The oxidation of 1-phenylethanol to acetophenone with hydrogen peroxide catalyzed by complex 1 in the presence of TFA is not efficient. In contrast, 1 exhibited excellent activity in the oxidation with tert-butyl hydroperoxide (TBHP) in the absence of any acid (the yield of acetophenone was close to the quantitative, TON attained 475 after 2 h). A kinetic study of this reaction led to the conclusion that the process occurs with the participation of radicals tert-BuO˙ produced in the Cu-promoted decomposition of TBHP. The mode of dependence of W0 on the initial concentration of TBHP indicates the formation of an intermediate adduct between the catalyst 1 and TBHP (characterized by the equilibrium constant K1≈ 2 M(-1) for the conditions of conducted experiments) followed by subsequent decomposition of the adduct (k2≈ 0.2 s(-1)) to generate an intermediate species tert-BuO˙ which induces the alcohol oxidation.
两种分子结构上主要不同的异构四核铜（II）倍半硅氧烷，“球状”化合物[(PhSiO1.5)12(CuO)4(NaO0.5)4]（1）和“三明治”状衍生物[(PhSiO1.5)6(CuO)4(NaO0.5)4(PhSiO1.5)6]（2），通过四苯基环四硅氧烷醇盐对聚合铜（II）倍半硅氧烷[(PhSiO1.5)2(CuO)]n的部分裂解合成。生成1或2的途径完全取决于用于该反应的溶剂的性质和组成。因此，在乙醇 - 1 - 丁醇溶液中的反应得到化合物1。当使用1,4 - 二氧六环 - 甲醇混合物时，制备了化合物2。通过X射线研究证实了笼状结构和不寻常的晶体堆积。已经发现，在50℃下，由1催化的苯与H2O2在乙腈溶液中的反应需要加入低浓度的三氟乙酸（TFA），并且在3小时后得到周转数（TON）为250的苯酚。初始反应速率W0线性取决于催化剂2的浓度。在TFA存在下，由配合物1催化的过氧化氢将1 - 苯乙醇氧化为苯乙酮的效率不高。相反，1在没有任何酸的情况下，对叔丁基过氧化氢（TBHP）的氧化表现出优异的活性（苯乙酮的产率接近定量，2小时后TON达到475）。对该反应的动力学研究得出结论，该过程是在铜促进的TBHP分解中产生的叔丁基自由基（tert-BuO˙）参与下发生的。W0对TBHP初始浓度的依赖模式表明在催化剂1和TBHP之间形成了中间加合物（在所进行实验的条件下，平衡常数K1≈2 M(-1)），随后加合物分解（k2≈0.2 s(-1)）以产生诱导醇氧化的中间物种叔丁基自由基（tert-BuO˙）。
