Acetone Factor in the Design of Cu 4 -, Cu 6 -, and Cu 9 -Based Cage Coppersilsesquioxanes: Synthesis, Structural Features, and Catalytic Functionalization of Alkanes.

The present study describes a new feature in the self-assembly of cagelike copperphenylsilsesquioxanes: the strong influence of acetone solvates on cage structure formation. By this simple approach, a series of novel tetra-, hexa-, or nonacoppersilsesquioxanes were isolated and characterized. In addition, several new complexes of Cu 4 or Cu 6 nuclearity bearing additional nitrogen-based ligands (ethylenediamine, 2,2'-bipyridine, phenanthroline, bathophenanthroline, or neocuproine) were produced. Single-crystal X-ray diffraction studies established molecular architectures of all of the synthesized products. Several coppersilsesquioxanes represent a novel feature of cagelike metallasilsesquioxane (CLMS) in terms of molecular topology. A Cu 4 -silsesquioxane complex with ethylenediamine (En) ligands was isolated via the unprecedented self-assembly of a partly condensed framework of silsesquioxane ligands, followed by the formation of a sandwich-like cage. Two prismatic Cu 6 complexes represent the different conformers─regular and elliptical hexagonal prisms, "cylinders", determined by the different orientations of the coordinated acetone ligands (" shape-switch effect"). A heterometallic Cu 4 Na 4 -sandwich-like derivative represents the first example of a metallasilsesquioxane complex with diacetone alcohol ligands formed in situ due to acetone condensation reaction. As a selected example, the compound [(Ph 6 Si 6 O 11 ) 2 Cu 4 En 2 ]·(acetone) 2 was explored in homogeneous oxidation catalysis. It catalyzes the oxidation of alkanes to alkyl hydroperoxides with hydrogen peroxide and the oxidation of alcohols to ketones with tert -butyl hydroperoxide. Radical species take part in the oxidation of alkanes. Besides, [(Ph 6 Si 6 O 11 ) 2 Cu 4 En 2 ]·(acetone) 2 catalyzes the mild oxidative functionalization of gaseous alkanes (ethane, propane, n -butane, and i -butane). Two different model reactions were investigated: (1) the oxidation of gaseous alkanes with hydrogen peroxide to give a mixture of oxygenates (alcohols, ketones, or aldehydes) and (2) the carboxylation of C n gaseous alkanes with carbon monoxide, water, and potassium peroxodisulfate to give C n +1 carboxylic acids (main products), along with the corresponding C n oxygenates. For these reactions, the effects of acid promoter, reaction time, and substrate scope were explored. As expected for free-radical-type reactions, the alkane reactivity follows the trend C 2 H 6 < C 3 H 8 < n -C 4 H 10 < i -C 4 H 10 . The highest total product yields were observed in the carboxylation of i -butane (up to 61% based on i -C 4 H 10 ). The product yields and catalyst turnover numbers (TONs) are remarkable, given an inertness of gaseous alkanes and very mild reaction conditions applied (low pressures, 50-60 °C temperatures).