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• 96-76-4 2,4-di-tert-Butylphenol 
• 6390-69-8 3,3',5,5'-tetra(tert-butyl)biphenyl-2,2'-diol 

Relevant academic research and scientific papers

Catalytic Aerobic Phenol Homo- and Cross-Coupling Reactions with Copper Complexes Bearing Redox-Active Guanidine Ligands

Due to their large importance in synthetic chemistry, catalytic C?C coupling reactions of phenols are currently intensively studied. Herein, new copper catalysts for the C?C coupling reaction of phenols using dioxygen as a green oxidizing reagent are reported. By using redox-active guanidine ligands, the activity as well as chemoselectivity in the cross-coupling reaction of non-complementary phenols (between an electron-rich phenol and a less nucleophilic second phenol) is significantly improved. Based on the collected data for several test reactions, a reaction mechanism is proposed.

Synthesis and Catalytic Reactivity of a Dicopper(II) μ-η2:η2-Peroxo Species Supported by 1,4,7-Tri-tert-butyl-1,4,7-triazacyclononane

O2-derived CunO2 adducts are attractive targets for aerobic oxidation catalysis because of their remarkable reactivity, but oxidation of the supporting ligand limits catalytic turnover. We report that tBu3tacn (1,4,7-tri-tert-butyl-1,4,7-triazacyclononane) supports a dicopper(II) μ-η2:η2-peroxo species with the highest solution stability outside of an enzyme. Decomposition of this species proceeds without oxidation of the tBu3tacn ligand. Additive-free catalytic aerobic oxidation reactions at or above room temperature are described, highlighting the potential of oxidatively robust ligands in aerobic copper catalysis.

Controlling the catalytic aerobic oxidation of phenols

The oxidation of phenols is the subject of extensive investigation, but there are few catalytic aerobic examples that are chemo- and regioselective. Here we describe conditions for the ortho-oxygenation or oxidative coupling of phenols under copper (Cu)-catalyzed aerobic conditions that give rise to ortho-quinones, biphenols or benzoxepines. We demonstrate that each product class can be accessed selectively by the appropriate choice of Cu(I) salt, amine ligand, desiccant and reaction temperature. In addition, we evaluate the effects of substituents on the phenol and demonstrate their influence on selectivity between ortho-oxygenation and oxidative coupling pathways. These results create an important precedent of catalyst control in the catalytic aerobic oxidation of phenols and set the stage for future development of catalytic systems and mechanistic investigations.

Access to a CuII-O-CuII motif: Spectroscopic properties, solution structure, and reactivity

We report a complex with a rare CuII-O-CuII structural motif that is stable at room temperature, which allows its in-depth characterization by a variety of spectroscopic methods. Interest in such compounds is fueled by the recent discovery that a CuII-O-Cu II species on the surface of Cu-ZSM-5 is capable of oxidizing methane to methanol, and this in turn ties into mechanistic discussions on the methane oxidation at the dicopper site within the particulate methane monooxygenase. For the synthesis of our Cu2O complex we have developed a novel, neutral ligand system, FurNeu, exhibiting two N-(N′,N′-dimethylaminoethyl) (2-pyridylmethyl)amino binding pockets connected by a dibenzofuran spacer. The reaction of FurNeu with CuCl yielded [FurNeu](Cu2(μ-Cl))(CuCl 2), 1, demonstrating the geometric potential of the ligand to stabilize Cu-X-Cu moieties. A CuI precursor with weakly coordinating anions was chosen in the next step, namely [Cu(NCCH3) 4]OTf, which led to the formation of [FurNeu](Cu(NCCH 3))2(OTf)2, 3. Treatment of 3 with O 2 or PhIO led to identical green solutions, whose UV-vis spectra were markedly different from the one displayed by [FurNeu](Cu)2(OTf) 4, 4, prepared independently from FurNeu and Cu(OTf)2. Further investigations including PhIO consumption experiments, NMR and UV-vis spectroscopy, HR-ESI mass spectrometry, and protonation studies led to the identification of the green product as [FurNeu](Cu2(μ-O))(OTf) 2, 5. DOSY NMR spectroscopy confirmed its monomeric character. Over longer periods of time 5 decomposes to give [Cu(picoloyl)2], formed through an oxidative N-dealkylation reaction followed by further oxidation of the ligand. Due to its slow decomposition reaction, all attempts to crystallize 5 failed. However, its structure in solution could be determined by EXAFS analysis in combination with DFT calculations, which revealed a Cu-O-Cu angle that amounts to 105.17. Moreover, TDDFT calculations helped to rationalize the UV-vis absorptions of 5. The reactivity of complex 5 with 2,4-di-tert- butylphenol, DTBP, was also investigated; the initially formed biphenol product, TBBP, was found to further react in the presence of excessive O2 to yield 2,4,7,9-tetra-tert-butyloxepino[2,3-b]benzofuran, TBOBF, via an intermediate diphenoquinone. It turned out that 5, or its precursor 3, can even be employed as a catalyst for the oxidation of DTBP to TBBP or for the oxidation of TBBP to TBOBF.

Oxidation of 2,4-Di-t-butylphenol with t-Butyl Hydroperoxide Catalysed by Copper(II)-Ethylenediamine Complexes

In the oxidation of 2,4-di-t-butylphenol (1) with ButO2H in alcohols in the presence of CuII-ethylenediamine (including N,N'-dialkylethylenediamines) (abbreviated to EDA) (1:2) complexes, the solvents are partly oxidized to the corresponding aldehydes or ketones in a competitive manner with phenol (1), while ButO2H is quantitatively reduced to ButOH.Suitable solvents, e.g., chlorobenzene, used in the oxidation of (1) are found to be inert.Activity of the copper(II) complexes in the oxidation of phenol (1) is strongly dependent on the structure of the EDA ligands, as in the case of the oxidation of the phenol (1) by O2 or H2O2.In the ButO2H oxidation of (1), the greatest degree of efficiency is brought about by the combination of copper(II) and N,N'-di-t-butyl-EDA.The initial stage of the oxidation of the phenol (1) has been kinetically investigated.The reaction velocity can be summarized by the equation: v=ktO2H>II-EDA>.Taking into account the results of the product analyses and kinetics, a mechanism for the oxidation of the phenol (1) with ButO2H catalysed by CuII-EDA complexes is proposed.

Autoxidation of Phenols Catalyzed by Copper(II)-Ethylenediamine Complexes: The Reaction Mechanism

The mechanism of the autoxidation of phenols with molecular oxygen catalyzed by Cu(II)-ethylenediamine complexes is elucidated.The kinetics are of first order in both and and of one-half order in .Those results imply the formation of a oxygen-bridged complex in the course of the reaction.The C-C coupling of two phenoxy radicals is facilitated within the coordination sphere of Cu(II) and affords the primary oxidation products, i. e. 2,2'-biphenyldiols.The bulkiness of substituents determines the type of the secondary products and either benzofuran or dioxepin is produced.Taking into account the results of oxidation of 2,2'-biphenyldiols, the mechanism of the production of benzofuran and dioxepin is also clarified.In the Cu(II) complex with sterically crowded biphenyldiolate, the oxidation activity of Cu(II) has been enhanced and the coordinating biphenyldiolate is immediately oxidized to benzofuran.On the contrary, the biphenyldiolate-Cu(II) complex with square-planar geometry could not produce benzofuran.After the complex is forced into the active tetrahedral configuration by the access of phenoxy radical-Cu(II) complex, the biphenyldiolate is oxidized to biphenyloxy radical and suffers C-O coupling with the phenoxy radical to afford dioxepin.

Oxidation of Phenols with Iodine in Alkaline Methanol

The use of iodine as an oxidizing agent for phenolic compounds has been explored.The reaction has been conducted in methanol containing such alkali as potassium hydroxide and, depending on the nature of the substituents and on the amount of iodine employed, leads to iodination, oxidation to give a stable phenoxy radical, oxidative dimerization, or benzylic oxidation.In general the reaction proceeds smoothly at room temperature, and under appropriate conditions yields of products are good to excellent.Oxidative dimerization of 2,4- and 2,6-di-tert-butylphenols invol-ves iodination followed by iodine-catalyzed dimerization.The oxidation of 4-methylphenols with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in methanol has been carried out for comparison.

Catalytic Activity of Copper(II)-Ethylenediamine Complexes in Autoxidation of Phenols

Studies of the autoxidation of tert-butylphenols 1-4 with molecular oxygen in the presence of Cu(II) complexes of N-substituted ethylenediamines indicate that the most catalytically active complexes are sterically crowded around the nitrogen atoms.The principal primary oxidation products formed in the presence of these complexes are substituted biphenyls 5, 7, 10, and 14, the first three of which are converted into secondary products on prolonged oxidation.Only in the oxidation of 2 is a diphenyl ether (9) formed, in quantities that increase little after the first 5 min of oxidation.