Si₁₀Cu₆N₄Cage Hexacoppersilsesquioxanes Containing N Ligands: Synthesis, Structure, and High Catalytic Activity in Peroxide Oxidations

Abstract

The synthesis, composition, and catalytic properties of a new family of hexanuclear Cu(II)-based phenylsilsesquioxanes are described here. Structural studies of 17 synthesized compounds revealed the general principle underlying their molecular topology: viz., a central metal oxide layer consisting of two Cu trimers is coordinated by two cyclic [PhSiO] siloxanolate ligands to form a skewed sandwich architecture with the composition [(PhSiO)(CuO)]. In addition to this O ligation by the siloxanolate rings, two opposite copper ions are additionally coordinated by the nitrogen atoms of corresponding N ligand(s), such as 2,2'-bipyridine (compounds 1-9), 1,10-phenanthroline (compounds 10-13), mixed 1,10-phenanthroline/2,2'-bipyridine (compound 14), or bathophenanthroline (compounds 15-17). Finally, the charge balance is maintained by two HO (compounds 1-7, 10-13, and 15-17), two HCO (compound 8), or two CHCOO (compounds 9 and 14) anions. Complexes 1 and 10 exhibited a high activity in the oxidative amidation oxidation of alcohols. Compounds 1, 10, and 15 are very efficient homogeneous catalysts in the oxidation of alkanes and alcohols with peroxides.

Palanquin-Like Cu4Na4 Silsesquioxane Synthesis (via Oxidation of 1,1-bis(Diphenylphosphino)methane), Structure and Catalytic Activity in Alkane or Alcohol Oxidation with Peroxides

“…It is important to note that the oxidation of dppm to dppmO2 was previously reported in the literature [40]. Moreover, some examples of oxidations during CLMS synthesis were described [33,34,37,[41][42][43][44][45], but to the best of our knowledge, no single example of CLMS synthesis accompanied by dppm oxidation has been reported to date. An additional and intriguing feature of such oxidation that acted favorably in aiding the formation of 1 is the requirement of mild conditions.…”

“…A modified self-assembly procedure such as this in most cases leads to the "ligand synergy" situation, with different ligands coordinating metal ions of the same cage compound. This feature was observed for several types on N-based ligands: 1,10-phenanthroline [33,34], 2,2′-bipyridine [33][34][35], and bathophenantroline [34][35][36]. Dual behavior was detected for the neocuproine-assisted synthesis of Cu(II)-CLMS: in the case of DMF/dioxane reaction/crystallization media, a similar "ligand synergy product" was formed [37], while DMF media favors the isolation of "ligand antagonism" product with the redistribution of copper centers between silsesquioxane and neocuproine ligands [38], as seen in Figure 1.…”

Selective Oxidation of Simple Aromatics Catalyzed by Nano-Biomimetic Metal Oxide Catalysts: A Mini Review

“…CH 3 CN is a polar solvent that can be miscible with polar H 2 O 2 and H 2 O as well as the non-polar aromatic substrates, leading to oxygenate formation. When the metal salts dissolved in the reaction mixtures of aromatics, the free Cu/Fe/V ions presumably coordinate with CH 3 CN serving as a ligand to form metal complexes (Rach and Kühn, 2009;Kulakova et al, 2017). As V nr catalyst can be directly prepared from H 2 O 2(aq) in CH 3 CN without any additional substrates (Wanna et al, 2019a), we therefore surmise that these CH 3 CN-based metal complexes in the presence of H 2 O 2(aq) can occur and are essential to assist the metal oxide polymerization/formation.…”

“…Multi-copper complexes including cage compounds were employed for selective oxidation of alkanes and aromatics with H 2 O 2(aq) in CH 3 CN (You et al, 2014;Kulakova et al, 2017Kulakova et al, , 2019. Shul'pin and co-workers further reported a double oxidation from benzene to p-BQ with molar ratio of ∼1:1 (PhOH:p-BQ) using Cu(ClO 4 ) 2 (Shul'pina et al, 2008).…”

Recent Advances in Copper Catalyzed Alcohol Oxidation in Homogeneous Medium

“…In 2017, Shul pin and coworkers [14] applied the hexanuclear Cu(II)-based phenylsilsesquioxane complex [(PhSiO 1.5 ) 10 (CuO) 6 (HO 0.5 ) 2 (C 12 H 8 N 2 ) 2 ] (5) as catalyst for the oxidation of 1-phenylethanol with tert-butyl hydroperoxide (TBHP, 70% aq. solution) in acetonitrile, at 50 • C and in presence of HNO 3 , leading to 94% yield of acetophenone (TON = 600) after 14 h. Moreover, the cage-like (6), obtained very recently [15] by self-assembly synthesis, has also shown to be a very good catalyst for the oxidation of alcohols in acetonitrile solution: 1-phenylethanol was oxidized by TBHP to acetophenone in an almost quantitative yield.…”