title: Solvent-controlled synthesis of tetranuclear cage-like copper(II) silsesquioxanes. Remarkable features of the cage structures and their high catalytic activity in oxidation with peroxides.
abstract: 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.
authors.affiliation: Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Ulitsa Vavilova, dom 28, Moscow 119991, Russia. bilyachenko@ineos.ac.ru levitsk@ineos.ac.ru.
authors.forename: Marina S
authors.initials: MS
authors.lastname: Dronova
authors.forename: Alexey N
authors.initials: AN
authors.lastname: Bilyachenko
authors.forename: Alexey I
authors.initials: AI
authors.lastname: Yalymov
authors.forename: Yuriy N
authors.initials: YN
authors.lastname: Kozlov
authors.forename: Lidia S
authors.initials: LS
authors.lastname: Shul'pina
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Korlyukov
authors.forename: Dmitry E
authors.initials: DE
authors.lastname: Arkhipov
authors.forename: Mikhail M
authors.initials: MM
authors.lastname: Levitsky
authors.forename: Elena S
authors.initials: ES
authors.lastname: Shubina
authors.forename: Georgiy B
authors.initials: GB
authors.lastname: Shul'pin
mesh_terms: D001554:Benzene / Q000737:chemistry; D002384:Catalysis; D060326:Chemistry Techniques, Synthetic; D003300:Copper / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D010626:Phenylethyl Alcohol / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D020122:tert-Butylhydroperoxide / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D012997:Solvents; D003300:Copper; D020122:tert-Butylhydroperoxide; D006861:Hydrogen Peroxide; D001554:Benzene; D010626:Phenylethyl Alcohol