Unusual Tri-, Hexa-, and Nonanuclear Cu(II) Cage Methylsilsesquioxanes: Synthesis, Structures, and Catalytic Activity in Oxidations with Peroxides

Three types of unusual cagelike copper(II) methylsilsesquioxanes, namely, nona- [(MeSiO_1.5)₁₈(CuO)₉] 1, hexa- [(MeSiO_1.5)₁₀(HO_0.5)₂(CuO)₆(C₁₂H₈N₂)₂(MeSiO_1.5)₁₀(HO_0.5)_1.33(CH₃COO_0.5)_0.67(CuO)₆(C₁₂H₈N₂)₂] 2, [(MeSiO_1.5)₁₀(CuO)₆(MeO_0.5)₂(C₁₀H₈N₂)₂] 3, and trinuclear [(MeSiO_1.5)₈(CuO)₃(C₁₀H₈N₂)₂] 4, were obtained in 44%, 27%, 20%, and 16% yields, respectively. Nuclearity and structural fashion of products was controlled by the choice of solvent system and ligand, specifically assisting the assembling of cage. Structures of 1-4 were determined by single-crystal X-ray diffraction analysis. Compounds 1 and 4 are the first cage metallasilsesquioxanes, containing nine and three Cu ions, respectively. Product 1 is the first observation of nonanuclear metallasilsesquioxane ever. Unique architecture of 4 represents early unknown type of molecular geometry, based on two condensed pentamembered siloxane cycles. Topological analysis of metal clusters in products 1-4 is provided. Complex 1 efficiently catalyzes oxidation of alcohols with tert-butylhydroperoxide TBHP to ketones or alkanes with H₂O₂ to alkyl hydroperoxides in acetonitrile.