Alkoxide Catalyst Research Articles

Recent Advances in the Understanding of Boron-Containing Catalysts for the Selective Oxidation of Alkanes to Olefins

The production of ethylene and propylene through aerobic alkane oxidation without significant coproduction of CO and CO2 (COx) presents a challenge to academic and industrial researchers alike. Recently, boron-containing materials such as hexagonal boron nitride (hBN) have been identified as active and selective catalysts for the oxidative dehydrogenation (ODH) of propane to propylene with minimal COx selectivity. Additionally, high olefin selectivity is also obtained in the oxidation of other alkanes and other materials such as metal borides and supported B/SiO2 have been successfully applied to this transformation. Recent advances in the understanding of these catalysts in the oxidation of light alkanes are presented here providing a framework for further study of this exciting field.

Chitosan supported molybdate nanoclusters as an efficient catalyst for oxidation of alkenes and alcohols

The excellent Lewis acidity and variable oxidation states of molybdate anions for the oxidation reactions was utilized by supporting it on eco-friendly and amply available fishery waste chitosan backbone using a simple “mix and make” methodology. The comprehensive structural analysis was done by FTIR, XRD, FESEM, elemental mapping, TEM and XPS. FESEM and elemental analysis revealed the mono-dispersion of molybdate nanoclusters on the surface of the chitosan. The increase in the molybdate loading increased the size of the clusters without affecting their uniformity over the polymer. This multi-nuclear material showed high catalytic activity towards the liquid phase oxidation of alkenes and alcohols owing to the surface sorption of the molybdate nanoclusters. The oxidation of cycloalkenes gave full conversion with > 90% selectivity towards the corresponding epoxides, while the oxidation of aryl alkenes and alcohols gave good to best results in terms of catalytic activity and selectivity. The catalyst exhibited prominent reusability.

Copper complexes with 1,10-phenanthrolines as efficient catalysts for oxidation of alkanes by hydrogen peroxide

The Copper complexes with 1,10-phenanthrolines and 1,10- phenanthrolines-5,6-diones were synthesized and characterized by elemental analysis and spectra. One complex was characterized by X-ray analysis. The complexes turned out to be active in oxidations of cyclic, branched and linear alkanes. Hydrogen peroxide (50%) was used as an oxidant. The reactions were carried out in solvent acetonitrile at relatively the low temperatures (40–60 °C). Alkyl hydroperoxides are the primary products which partly decompose in the course of the reaction to produce mainly ketones (aldehydes) and alcohols. Treating the reaction mixture with PPh3 leads to the transformation of alkyl hydroperoxides (ROOH) to corresponding alcohols (ROH).

Donor‐Flexible Bis(pyridylidene amide) Ligands for Highly Efficient Ruthenium‐Catalyzed Olefin Oxidation

AbstractAn exceptionally efficient ruthenium‐based catalyst for olefin oxidation has been designed by exploiting N,N′‐bis(pyridylidene)oxalamide (bisPYA) as a donor‐flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson‐type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state‐of‐the‐art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h−1 and turnover numbers of several millions.

Synthesis and characterization of magnetic perovskites La1-xSrxMnO3: Green catalyst for oxidation of olefins in aqueous medium

The main goal of this work is the preparation of magnetic perovskites La1-xSrxMnO3 (x = 0, 0.2 and 0.4) with a modified sol-gel process and the assessment of their catalytic activity in the oxidation of styrene in neat water (aqueous medium). The structural properties of LaMnO3, La0.8Sr0.2MnO3 and La0.6Sr0.4MnO3 were characterized using the X-ray Diffraction and infrared techniques. Microstructural features of the catalyst were confirmed by the Scanning Electron Microscopy. The sample La0.6Sr0.4MnO3 has proven a good catalytic activity in the oxidation of styrene after different optimization steps. The catalyst has shown a good recyclability after four cycles. The optimized parameters of the reaction procedure were applied successfully in the oxidation of other simple olefins.

Amino-Induced 2D Cu-Based Metal-Organic Framework as an Efficient Heterogeneous Catalyst for Aerobic Oxidation of Olefins.

With the assistance of hydrogen bonds of the o-amino group, we have successfully tuned a coordination structure from a metal-organic polyhedron (MOP) to a two-dimensional (2D) metal-organic framework (MOF). The amino group forms hydrogen bonds with the two vicinal carboxylic groups, and induces the ligand to coordinate with copper ions to form the 2D structure. The obtained 2D Cu-based MOF (Cu-AIA) has been applied as an efficient heterogeneous catalyst in the aerobic epoxidation of olefins by using air as oxygen source. Without the aggregation problem of active sites in MOPs, Cu-AIA possesses much higher reactivity than MOP-1. Furthermore, the amino group of the framework has been used as a modifiable site through post-synthetic metalation (PSMet) to prepare a 2D MOF-supported Pd single-site heterogeneous catalyst, which shows excellent catalytic performance for the Suzuki reaction. It indicates that Cu-AIA can also work as a good 2D MOF carrier for the derivation of other heterogeneous catalysts.

Alkoxide-catalyzed ring expansion of 1,3-cyclobutanediones with aldehydes

1,3-Cyclobutanediones (dialkyl ketene dimer) reacted with various aromatic aldehydes to give six-membered cyclic β-keto esters by using a catalytic amount of potassium ethoxide. Effects of alkoxide catalysts and spiro cyclic groups at the 2,4-positions of 1,3-cyclobutanediones were investigated.

Recent Studies on Single Site Metal Alkoxide Complexes as Catalysts for Ring Opening Polymerization of Cyclic Compounds

The selection of the catalyst is central to being able to control features and to better understand microstructures of polymers. New single-site metal alkoxide catalysts allow chemists to prepare regio/stereo regular polymers or copolymers that meet increasingly demanding performance requirements. These catalysts produce high molecular weights polymers with narrow polydispersity indexes or living properties and essentially regular polymers in structures. This review includes the synthesis, activity, and mechanistic aspects of especially single-site metal alkoxide catalysts with examples from my previous studies and recently published similar articles, beginning with an extensive survey on the aluminum, titanium, zirconium, and tin catalysts used to make polyethers, polyesters, and their derivatives. This review also compares the effects of ligands, substituents on ligands, and central metal atoms on ROP reactions. This review will provide the basis for the researchers who seek the new synthesis and application of catalysts in the future.

Efficient alkane hydroxylation catalysis of nickel(ii) complexes with oxazoline donor containing tripodal tetradentate ligands.

Tris(oxazolynylmethyl)amine TOAR (where R denotes the substituent groups on the fourth position of the oxazoline rings) complexes of nickel(ii) have been synthesized as catalyst precursors for alkane oxidation with meta-chloroperoxybenzoic acid (m-CPBA). The molecular structures of acetato, nitrato, meta-chlorobenzoato and chlorido complexes with TOAMe2 have been determined using X-ray crystallography. The bulkiness of the substituent groups R affects the coordination environment of the nickel(ii) centers, as has been demonstrated by comparison of the molecular structures of chlorido complexes with TOAMe2 and TOAtBu. The nickel(ii)-acetato complex with TOAMe2 is an efficient catalyst precursor compared with the tris(pyridylmethyl)amine (TPA) analogue. Oxazolynyl donors' strong σ-electron donating ability will enhance the catalytic activity. Catalytic reaction rates and substrate oxidizing position selectivity are controlled by the structural properties of the R of TOAR. Reaction of the acetato complex with TOAMe2 and m-CPBA yields the corresponding acylperoxido species, which can be detected using spectroscopy. Kinetic studies of the decay process of the acylperoxido species suggest that the acylperoxido species is a precursor of an active species for alkane oxidation.

Keggin heteropolyacid as catalyst for olefin epoxidation: A multiphase approach

Keggin-type heteropolyacids have been used as catalyst for the selective oxidation of olefins to the corresponding epoxides in multiphase conditions (isooctane/Aliquat 336/water). Multiphase system allowed achieving a higher conversion (72%) and selectivity (70%) to epoxide than the corresponding homogeneous or biphasic systems in the presence of the same catalyst. Optimization of the multiphase system has been conducted considering reaction time, temperature, amount of the catalysts and quantity of the oxidant. The best-found reaction conditions were then employed for the selective epoxidation of several substrates. Interestingly, it was shown that, in the multiphase system, only an insignificant decomposition of hydrogen peroxide was observed.Furthermore, an environmental assessment has been conducted comparing green metrics related to the homogenous, biphasic and multiphase systems herein investigated.

Catalytic Aerobic Oxidation of Alkenes by Ag@Metal Organic Framework with High Catalytic Activity and Selectivity

By coupling of Fe2O3@SiO2 particles with metal organic Framework (MOF) the magnetic MOF structure was fabricated. Precipitation and hydrothermal methods were applied for synthesis of core and MOF. Silver nanoparticles were deposited on nickel based metal organic framework surface and magnetic Fe2O3@SiO2@MOF@Ag was obtained. Because of strong coupling between silver nanoparticles and metal organic framework, the catalyst demonstrated high catalytic activity and selectivity in aerobic oxidation of alkenes under mild conditions. The nanostructure, exhibited high catalytic activity. Alkenes oxides (epoxy alkanes) were the main products with more than 89.9 % selectivity. Composite system of silver nanoparticles supported on Fe2O3@SiO2@Metal Organic Framework has potential to be an active catalysts for aerobic oxidation of alkenes under mild conditions.

Manganese(III) porphyrin anchored onto magnetic nanoparticles via “Click” reaction: An efficient and reusable catalyst for the heterogeneous oxidation of alkenes and sulfides

Oxidation of a variety of organic compounds, using Mn-porphyrin, mesotetrakis(4-hydroxyphenyl)porphyrinatomanganese(III), supported onto functionalized silica-coated magnetic nanoparticles via “Click” reaction has been investigated. The heterogeneous catalyst was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP/OES) and energy-dispersive X-ray spectroscopy (EDX). Thermogravimetric analysis (TGA) demonstrated that the prepared catalyst was thermally stable to almost 300 °C, exhibiting high thermostability of the nanocatalyst over a broad range of temperatures. This heterogeneous catalyst proved to be an efficient and retrievable nanocatalyst in oxidation of alkenes and sulfides.

A Comparative Study of the Catalytic Behaviour of Alkoxy-1,3,5-Triazapentadiene Copper(II) Complexes in Cyclohexane Oxidation

The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) were prepared, characterized (including the single crystal X-ray analysis of 3) and studied as catalysts in the mild oxidation of alkanes with H2O2 as an oxidant, pyridine as a promoting agent and cyclohexane as a main model substrate. The complex 4 showed the highest activity with a yield of products up to 18.5% and turnover frequency (TOF) up to 41 h−1. Cyclohexyl hydroperoxide was the main reaction product in all cases. Selectivity parameters in the oxidation of substituted cyclohexanes and adamantane disclosed a dominant free radical reaction mechanism with hydroxyl radicals as C–H-attacking species. The main overoxidation product was 6-hydroxyhexanoic acid, suggesting the presence of a secondary reaction mechanism of a different type. All complexes undergo gradual alteration of their structures in acetonitrile solutions to produce catalytically-active intermediates, as evidenced by UV/Vis spectroscopy and kinetic studies. Complex 4, having tertiary C–H bonds in its iPr substituents, showed the fastest alteration rate, which can be significantly suppressed by using the CD3CN solvent instead of CH3CN one. The observed process was associated to an autocatalytic oxidation of the alkoxy-1,3,5-triazapentadiene ligand. The deuterated complex 4-d32 was prepared and showed higher stability under the same conditions. The complexes 1 and 4 showed different reactivity in the formation of H218O from 18O2 in acetonitrile solutions.

Single-Site Vanadyl Species Isolated within Molybdenum Oxide Monolayers in Propane Oxidation

The cooperation of metal oxide subunits in complex mixed metal oxide catalysts for selective oxidation of alkanes still needs deeper understanding to allow for a rational tuning of catalyst perform...

The Unanticipated Catalytic Activity of Lithium tert-Butoxide/THF in the Interesterification of Rapeseed Oil with Methyl Acetate

Conventionally, the biodiesel (mixture of fatty acid methyl esters, FAME) production proceeds by transesterification of triglycerides with methanol accordingly by the formation of glycerol as a by-product, which cannot be included in biofuel composition. Biodiesel could also be produced via interesterification ensuring full conversion of oil to biofuel, consisting of FAME and triacetin. The most effective catalysts for interesterification reactions are alkali metal alkoxides. The effectivity of alkoxide catalyst depends on its solubility determined by the structure of the alkyl chain. In our previous studies, we have shown that the branched chain catalyst tert-BuOK/THF is highly suitable for the realisation of interesterification reactions. Till now, in the scientific literature, very little is known about the influence of metal ions. In order to investigate the influence of counterion on the activity of alkoxide catalysts, in this work, we have investigated the proceeding of interesterification reactions of rapeseed oil with methyl acetate in the presence of lithium, sodium, and potassium tert-butoxides in THF. Experimentally obtained relationships for catalyst-to-oil molar ratio (COMR) influence rapeseed oil interesterifications with methyl acetate at 55°C for 1 h, with methyl acetate-to-oil molar ratio (MAOMR) 18 showing that the tert-BuONa/THF and tert-BuOK/THF have high and similar activity, but the tert-BuOLi/THF is fundamentally different. The low and diverse activity of lithium tert-butoxide can be explained by the association of ions and very low catalytic activity of ion pairs. Simulation of the influence of association on the FAME formation shows that at COMR 0.1 (sufficient for fast reaction proceeding in the presence of tert-BuONa/THF and tert-BuOK/THF), the concentration of tert-butoxide ions in the presence of tert-BuOLi/THF because of associations lowers from 28 mmol/L to 13 mmol/L, whcih is not sufficient for effective proceeding of reaction. Activity of alkoxides in this reaction is solely determined by the counterion.

New Oxidovanadium(IV) Complexes with 2,2′-bipyridine and 1,10-phenathroline Ligands: Synthesis, Structure and High Catalytic Activity in Oxidations of Alkanes and Alcohols with Peroxides

Reactions of [VCl3(thf)3] or VBr3 with 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) in a 1:1 molar ratio in air under solventothermal conditions has afforded polymeric oxidovanadium(IV) four complexes 1–4 of a general formula [VO(L)X2]n (L = bpy, phen and X = Cl, Br). Monomeric complex [VO(DMF)(phen)Br2] (4a) has been obtained by the treatment of compound 4 with DMF. The complexes were characterized by IR spectroscopy and elemental analysis. The crystal structures of 3 and 4a were determined by an X-ray diffraction (XRD) analysis. The {VOBr2(bpy)} fragments in 3 form infinite chains due to the V = O…V interactions. The vanadium atom has a distorted octahedral coordination environment. Complexes 1–4 have been tested as catalysts in the homogeneous oxidation of alkanes (to produce corresponding alkyl hydroperoxides which can be easily reduced to alcohols by PPh3) and alcohols (to corresponding ketones) with H2O2 or tert-butyl hydroperoxide in MeCN. Compound 1 exhibited the highest activity. The mechanism of alkane oxidation was established using experimental selectivity and kinetic data and theoretical DFT calculations. The mechanism is of the Fenton type involving the generation of HO• radicals.

Lower Temperature Synthesis of Polymer Network from Liquid-Crystalline Polyesters with Titanium Alkoxide Catalysts

Lower Temperature Synthesis of Polymer Network from Liquid-Crystalline Polyesters with Titanium Alkoxide Catalysts

Polymer immobilized tantalum(v)–amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

Polymer supported peroxotantalate based heterogeneous catalysts served as highly efficient, selective and recyclable catalysts for alkene epoxidation and sulfide oxidation with green oxidant aqueous H2O2under mild reaction conditions.

Synthesis and characterization of a Mn‐Schiff base complex anchored on modified MCM‐41 as a novel and recyclable catalyst for oxidation of olefins

Mn‐Schiff base complex has been covalently attached to the surface of Mobil Composite Material No. 41 (MCM‐41) using a 1,4‐diisocyanatobutane (DIC‐4) as a binder. The prepared heterogeneous catalyst was characterized by X‐ray diffraction pattern (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared (FT‐IR) spectroscopy, X‐ray fluorescence analysis (XRF), inductively coupled plasma (ICP) spectrometry and Transmission Electron Microscopy (TEM). The BET results indicated that the surface area and pore size of MCM‐41 were decreased after modification. The obtained catalyst was used as a highly efficient, heterogeneous and recyclable catalyst for the oxidation of a wide range of alkenes with hydrogen peroxide (H2O2) as a green oxidant. The effect of various parameters such as catalyst and imidazole (co‐catalyst) concentration, tempreture, and reaction time on the conversion effecincy and selectivity of the reaction have been studied. The catalyst was used in five consecutive experiment without any loss of activity, confirming the success of the anchoring process and the catalyst stability.

Synthesis of Highly Functionalized 2-Pyranone from Silyl Ketene.

We report a highly functionalized 2-pyranone small molecule prepared from tert-butyl diphenyl silyl ketene using an alkoxide catalyst and thermally induced rearrangement. Treatment of the silyl ketene with a substoichiometric amount of alkoxide led to the formation of a trimer which was isolated and fully characterized; heating this trimer in a 1,4-dioxane solution induced a thermal rearrangement, yielding the product 2-pyranone. The isolated intermediate and product are characterized by 1D and 2D nuclear magnetic resonance (NMR) spectroscopies, mass spectrometry, and single crystal X-ray diffraction. A mechanism for the thermally induced rearrangement is proposed based on 1H NMR studies, and a rate law is derived from the proposed mechanism with steady-state approximation. This work illustrates a route for the formation of highly functionalized and modifiable 2-pyranone motifs with potential biological activity. The formation of the trimer, and thus the functionalized 2-pyranone, is highly dependent on the silyl substituents and alkoxide counterion and thus indicates the intriguing reactivity of highly functionalized small molecules.