Polymerization of 3‐ethynylthiophene with homogeneous and heterogeneous Rh catalysts

3‐Ethynylthiophene (3ETh) was polymerized with Rh(I) complexes: [Rh(cod)acac], [Rh(nbd)acac], [Rh(cod)Cl]₂, and [Rh(nbd)Cl]₂ (cod is η²:η²‐cycloocta‐1,5‐diene and nbd η²:η²‐norborna‐2,5‐diene), used as homogeneous catalysts and with the last two complexes anchored on mesoporous polybenzimidazole (PBI) beads: [Rh(cod)Cl]₂/PBI and [Rh(nbd)Cl]₂/PBI used as heterogeneous catalysts. All tested catalyst systems give high‐cis poly(3ETh). In situ NMR study of homogeneous polymerizations induced with [Rh(cod)acac] and [Rh(nbd)acac] complexes has revealed: (i) a transformation of acac ligands into free acetylacetone (Hacac) occurring since the early stage of polymerization, which suggests that this reaction is part of the initiation, (ii) that the initiation is rather slow in both of these polymerization systems, and (iii) a release of cod ligand from [Rh(cod)acac] complex but no release of nbd ligand from [Rh(nbd)acac] complex during the polymerization. The stability of diene ligand binding to Rh‐atom in [Rh(diene)acac] catalysts remarkably affects only the molecular weight but not the yield of poly(3ETh). The heterogeneous catalyst systems also provide high‐cis poly(3ETh), which is of very low contamination with catalyst residues since a leaching of anchored Rh complexes is negligible. The course of heterogeneous polymerizations is somewhat affected by limitations arising from the diffusion of monomer inside catalyst beads. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2776–2787, 2008     

A highly efficient and extensively reusable "dip catalyst" based on a silver-nanoparticle-embedded polymer thin film

Achieving a harmonious combination of the efficiency of homogeneous catalysts with the reusability of heterogeneous catalysts is a fundamental and challenging problem. Metal nanoparticles in a suitable matrix offer a potential solution. However an ideal design is yet to be realized, because the critical requirements of facile access to the catalyst, its durability, and ease of retrieval and reuse are difficult to reconcile. We report herein a multilayer free‐standing thin‐film catalyst based on silver nanoparticles, generated in situ inside poly(vinyl alcohol) by using a facile protocol, which shows excellent efficiency and extensive reusability in the prototypical reaction, the reduction of 4‐nitrophenol by sodium borohydride. The “dip catalyst” film, which can start/stop the reaction instantaneously by mere insertion/removal, is used 30 times leading to a total turnover number (TON) of ≈3390, which is unprecedented for this reaction. The efficiency of the catalyst is reduced only marginally at the end of these runs, promising further extended usage. The unique advantage of convenient catalyst monitoring is illustrated by the periodic spectroscopic and microscopic examinations of the thin film, which revealed the basis of its durability. The demonstrated potential of metal‐nanoparticle‐embedded polymer thin films, coupled with their versatility and ease of fabrication, promises extensive applications in chemical catalysis.     

单原子催化:沟通均相催化与多相催化的桥梁（英文）

催化在现代化学工业中占据着极为重要的地位.催化剂是催化过程的核心.均相催化剂由于具有均一、孤立的活性位点,往往具有高活性与高选择性;但是分离困难限制了其实际应用.多相催化剂由于金属原子利用效率低、活性组分不均匀,活性与选择性相对较低;但其稳定易分离的特点使得目前大多数工业催化过程都是多相催化过程.近年来,单原子催化逐渐成为催化领域新的研究热点与前沿,受到相关研究人员的广泛关注.作为一种多相催化剂,单原子催化剂具有稳定易分离的优势.此外,单原子催化剂具有类似均相催化剂的孤立活性位点,可能具有高活性与高选择.因此单原子催化的概念一经提出,便被认为有望成为架起多相催化与均相催化的桥梁;但几年来并未从实验上得到证实.2016年开始,逐渐有单原子催化剂在经典均相催化反应过程中的应用报道,为该观点提供了实验上的证据.本综述概述了2016至2017年单原子催化剂在典型均相催化反应中的成功应用,包括:1)氢甲酰化反应.以烯烃和合成气为原料合成精细化学品醛类化合物的氢甲酰化反应是目前化工生产中典型的均相催化反应之一.2016年,张涛课题组和曾杰课题组先后报道了Rh/ZnO和Rh/CoO单原子催化剂在该反应中的成功应用.催化剂都表现出优异的催化性能,活性与经典均相Wilkinson’s催化剂相当;2)氢硅加成反应.作为合成有机硅产品的重要反应之一,工业上硅氢加成反应主要由Pt基均相催化剂催化.2016年Beller课题组首次报道了将Pt/Al_2O_3单原子催化剂用于烯烃硅氢加成反应中.该催化剂除表现出良好的催化活性和区域选择性外,还具有较高的稳定性和底物普适性;3)C–H键选择性氧化.烷烃部分氧化反应在学术研究和工业应用方面都有重要意义.刘文刚等将M-N-C单原子催化剂(其中M为Fe,Co等金属)成功应用于C–H键的活化反应中,并对催化剂的结构进行了深入剖析.以上实例表明通过调控金属与载体组合、设计开发合适的单原子催化剂,可以达到结合均相催化高活性、高选择性与多相催化稳定易分离的目的,为均相催化多相化提供了一条新途径,也证明单原子催化可望成为沟通均相催化与多相催化的桥梁.     

The Co‐Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol–gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co‐entrapped with the ionic liquid [Bmim]NTf₂ inside a silica matrix by a sol–gel method. These catalytic ionogels have been compared to simple catalyst‐doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh‐doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X‐ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.     

One‐Pot Cooperation of Single‐Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization‐Hydrosilylation Process

Realizing the full potential of oxide‐supported single‐atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one‐pot combination of Ru₁/CeO₂ and Rh₁/CeO₂ SACs enables a highly selective olefin isomerization‐hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double‐bond migration and anti‐Markovnikov α‐olefin hydrosilylation, respectively. First‐principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single‐pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio‐selectivity (>95 %) even from industrially‐relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide‐supported single‐atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes.     

Ordered Porous Nitrogen‐Doped Carbon Matrix with Atomically Dispersed Cobalt Sites as an Efficient Catalyst for Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H₂. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H₂, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.     

Towards a Practical Development of Light‐Driven Acceptorless Alkane Dehydrogenation

The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter‐chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom‐efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans‐[Rh(PMe₃)₂(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C₄) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.     

Asymmetric hydrogenation using chiral Rh complexes immobilised with a new ion-exchange strategy

Rh diphosphine complexes using DuPhos and JosiPhos as chiral ligands have been immobilised by ion exchange into the mesoporous material MCM-41. When used as catalysts for the enantioselective hydrogenation of dimethyl itaconate and methyl-2-acetamidoacrylate, these heterogeneous catalysts give catalytic performance in terms of yield and enantioselection that are comparable to the corresponding homogeneous catalysts. Furthermore, the heterogeneous catalysts can be readily recovered and reused without loss of catalyst performance. A second immobilisation strategy is described in which [Rh(COD)2]+BF4- is initially immobilised by ion exchange and subsequently modified by the chiral diphosphine and this give comparable catalyst performance. This immobilisation strategy opens up the possibility of easy ligand-screening for parallel synthesis and libraries.     

Rh/Al_2O_3-Cr_2O_3整体式催化剂的制备和二氯甲烷催化氧化性能

以粉末Al_2O_3为载体,通过浸渍Rh(NO_3)_3制备Rh/Al_2O_3催化剂;再以Rh/Al_2O_3、粉末Cr_2O_3和铝胶经过研磨混合制得催化剂活性浆料;将催化剂活性浆料涂覆到堇青石蜂窝陶瓷载体表面,经烘干,焙烧制得不同Rh含量的Rh/Al_2O_3-Cr_2O_3系列整体式催化剂.研究了该类催化剂的二氯甲烷催化氧化性能,发现Rh负载量为0.4 g/L的Rh/Al_2O_3-Cr_2O_3催化剂活性最佳,且未生成含氯中间产物.结合催化剂的表征结果发现,Rh的添加可增加催化剂的表面酸性和氧化还原性能,二者的协同作用提高了催化剂活性;而Cr_2O_3的存在有利于CH_3Cl中间体的进一步氧化,从而提高了催化剂的选择性.     

Preparation and Characterization of Chiral Oxazaborolidine Complex Immobilized SBA‐15 and Its Application in the Asymmetric Reduction of Prochiral Ketones

The immobilization of chiral oxazaborolidine complex in the well‐ordered mesochannels of SBA‐15 is demonstrated by a postsynthetic approach using 3‐aminopropyltriethoxysilane as a reactive surface modifier. The immobilized catalysts are characterized by various techniques, such as XRD, nitrogen adsorption, HRSEM, UV/Vis diffuse reflectance spectroscopy, and FTIR spectroscopy. The catalysts are used for the enantioselective reduction of aromatic prochiral ketones. The activity of the chiral oxazaborolidine complex immobilized SBA‐15 catalysts is also compared with that of the pure chiral oxazaborolidine complex, which is a homogeneous catalyst. It is found that the activity of the chiral complex immobilized SBA‐15 heterogeneous catalyst is comparable with that of the homogeneous catalyst.     

Directly Knitted Hierarchical Porous Organometallic Polymer-Based Self-Supported Single-Site Catalyst for CO2 Hydrogenation in Water

In recent times, heterogenization of homogeneous molecular catalysts onto various porous solid support structures has attracted significant research focus as a method for combining the advantages of both homogeneous as well as heterogeneous catalysis. The design of highly efficient, structurally robust and reusable heterogenized single-site catalysts for the CO₂ hydrogenation reaction is a critical challenge that needs to be accomplished to implement a sustainable and practical CO₂-looped renewable energy cycle. This study demonstrated a heterogenized catalyst [Ir-HCP-(B/TPM)] containing a molecular Ir-abnormal N-heterocyclic carbene (Ir-aNHC) catalyst self-supported by hierarchical porous hyper-crosslinked polymer (HCP), in catalytic hydrogenation of CO₂ to inorganic formate (HCO₂⁻) salt that is a prospective candidate for direct formate fuel cells (DFFC). By employing this unique and first approach of utilizing a directly knitted HCP-based organometallic single-site catalyst for CO₂-to-HCO₂⁻ in aqueous medium, extremely high activity with a single-run turnover number (TON) up to 50816 was achieved which is the highest so far considering all the heterogeneous catalysts for this reaction in water. Additionally, the catalyst featured excellent reusability furnishing a cumulative TON of 285400 in 10 cycles with just 1.6 % loss in activity per cycle. Overall, the new catalyst displayed attributes that are important for developing tangible catalysts for practical applications.     

Pd/ZnO在乙炔选择加氢反应中的不同催化机制研究(英文)

化学选择性是评价催化剂性能最重要的参数之一,它直接决定了产物的经济价值及后续的分离成本.传统的负载型金属催化剂由于其金属粒径分布不均,且不同原子数组成的粒子通常具有特征产物选择性,从而限制化学选择性的提高;另一方面,对于金属多原子活性中心,反应物在催化剂表面可以存在多种吸附构型进而衍化为不同产物,产物可控性差.因此,获得金属尺寸均一,且具有原子分散的活性中心,即单原子催化剂,成为官能团多相催化转化高选择性的迫切需求.本课题组通过400 oC还原1%-Pd/ZnO得到PdZn金属间化合物,依据其规律排布的Pd-Zn-Pd单元获得Pd基单原子催化剂.该催化剂在乙烯化工中少量乙炔的加氢转化反应中获得令人欣喜的催化性能——兼具有乙炔的高转化率和乙烯的高选择性.结合微量吸附量热、理论计算等表征,Pd活性中心在PdZn金属间化合物中的特殊空间排布是其优异催化性能的根源,即乙炔以较强的σ键吸附在两个相邻的单Pd金属中心,易吸附活化加氢生成乙烯,而乙烯则吸附于单Pd金属中心,较弱的π键形式吸附有利于其脱附避免过渡加氢.基于前期研究,构筑具有均一单金属中心的负载型单原子催化剂是获得高选择性的另一有效方法,且较之于PdZn金属间化合物催化剂,该类单原子催化剂兼具有原子利用率最大化的优点.本文采用等体积浸渍法制备Pd/ZnO催化剂,通过降低Pd金属含量(1 wt%→0.1 wt%→0.01 wt%)并在较低的温度下(100 oC)还原(H2-TPR表明高温还原形成PdZn金属间化合物型合金)得到负载型单原子催化剂(Pd1/ZnO SAC).高分辨电镜结果表明,当Pd负载量由1%降至0.1%,金属纳米颗粒的粒径尺寸显著降低,而在0.01%-Pd/ZnO催化剂表面,Pd活性中心则以单原子状态分散于载体ZnO表面.X-射线吸收光谱及电子能谱表明,随着负载量的降低,Pd活性物种具有更高的正电性.该催化剂在乙炔选择性加氢反应中表现出更加优越的催化性能,具有与PdZn催化剂相当的高选择性,而更优的比活性.这归结于Pd1/ZnO单原子催化剂的Pdδ+单原子活性中心有助于其与乙炔的静电相互作用并吸附活化加氢生成乙烯,并促使乙烯以较弱的π键吸附,从而易于从催化剂表面脱附获得高选择性.     

Entrapment of an organometallic complex within a metal: a concept for heterogeneous catalysis

A novel family of composite materials, organically doped metals, has been recently introduced. Here, we demonstrate their use as a new platform for heterogeneous catalysis, namely the doping of a metal with a catalytic organometallic complex. Specifically, a rhodium(I) catalyst, (RhCl(COD)(Ph2P(C6H4SO3Na))), ([Rh]), was physically entrapped within silver, thus creating a new type of catalytic material: [Rh]@Ag. Several aspects were demonstrated with the development of this heterogeneous catalyst: a metal can be used as a support for heterogenizing a homogeneous catalyst; the homogeneous catalyst is stabilized by the entrapment within the metal; the products of the composite catalyst are different compared to those obtained from the homogeneous one; and the adsorption of [Rh] on the surface of Ag and its entrapment are very different processes only the latter provided appreciable catalytic activity. Thus, while homogeneous [Rh] was entirely destroyed after converting styrene to ethylbenzne at 50%, [Rh]@Ag remained active after effecting the same reaction to a yield of 85% (compared to only 7% for [Rh] adsorbed on Ag), and while homogeneous [Rh] hydrogenated diphenylacetylene to bibenzyl (and was completely deactivated after one cycle) with no trace of cis-stilbene, [Rh]@Ag afforded that compound as the main product and could be reused.     

Is it homogeneous or heterogeneous catalysis? Compelling evidence for both types of catalysts derived from [Rh(eta5-C5Me5)Cl2]2 as a function of temperature and hydrogen pressure

Addressed herein is the 20+ year-old question of whether the true benzene and cyclohexene hydrogenation catalysts derived from the organometallic precursor [Rh(eta5-C5Me5)Cl2]2, 1, are homogeneous or heterogeneous. The methodology employed is that developed earlier (Lin, Y.; Finke, R. G. Inorg Chem. 1994, 33, 4891, "A More General Approach to Distinguishing Homogeneous from Heterogeneous Catalysis..."). The kinetic evidence especially, but also the metal product (nanoclusters plus bulk metal), Hg0 poisoning and other experiments, provide compelling evidence that Rh0 nanoclusters are the true benzene hydrogenation heterogeneous catalyst derived from [Rh(eta5-C5Me5)Cl2]2, 1, at the required more vigorous conditions of 50-100 degrees C and 50 atm H2. However, the same methods reveal that the cyclohexene hydrogenation catalyst derived from 1 at the milder conditions of 22 degrees C and 3.7 atm H2 is a nonnanocluster, homogeneous catalyst, most likely the previously identified complex, [Rh(eta5-C5Me5)(H)2(solvent)] (Gill, D. S.; White, C.; Maitlis, P. M J. C. S. Dalton Trans. 1978, 617). In short, the present results solve the two-decade-old problem of identifying the true benzene and cyclohexene hydrogenation catalysts derived from [Rh(eta5-C5Me5)Cl2]2. Perhaps most significant is the demonstration that the methodology employed has the ability to identify both heterogeneous and homogeneous catalysts from the same catalyst precursor.     

Zeolite‐Encaged Single‐Atom Rhodium Catalysts: Highly‐Efficient Hydrogen Generation and Shape‐Selective Tandem Hydrogenation of Nitroarenes

Single‐atom catalysts are emerging as a new frontier in heterogeneous catalysis because of their maximum atom utilization efficiency, but they usually suffer from inferior stability. Herein, we synthesized single‐atom Rh catalysts embedded in MFI ‐type zeolites under hydrothermal conditions and subsequent ligand‐protected direct H₂ reduction. C_s‐corrected scanning transmission electron microscopy and extended X‐ray absorption analyses revealed that single Rh atoms were encapsulated within 5‐membered rings and stabilized by zeolite framework oxygen atoms. The resultant catalysts exhibited excellent H₂ generation rates from ammonia borane (AB) hydrolysis, up to 699 min^?1 at 298 K, representing the top level among heterogeneous catalysts for AB hydrolysis. The catalysts also showed superior catalytic performance in shape‐selective tandem hydrogenation of various nitroarenes by coupling with AB hydrolysis, giving >99 % yield of corresponding amine products.     

Toward Continuous-Flow Hyperpolarisation of Metabolites via Heterogenous Catalysis,Side-Arm-Hydrogenation,and Membrane Dissolution of Parahydrogen

Side-arm hydrogenation (SAH) by homogeneous catalysis has extended the reach of the parahydrogen enhanced NMR technique to key metabolites such as pyruvate. However, homogeneous hydrogenation requires rapid separation of the dissolved catalyst and purification of the hyperpolarised species with a purity sufficient for safe in-vivo use. An alternate approach is to employ heterogeneous hydrogenation in a continuous-flow reactor, where separation from the solid catalysts is straightforward. Using a TiO₂-nanorod supported Rh catalyst, we demonstrate continuous-flow parahydrogen enhanced NMR by heterogeneous hydrogenation of a model SAH precursor, propargyl acetate, at a flow rate of 1.5 mL/min. Parahydrogen gas was introduced into the flowing solution phase using a novel tube-in-tube membrane dissolution device. Without much optimization, proton NMR signal enhancements of up to 297 (relative to the thermal equilibrium signals) at 9.4 Tesla were shown to be feasible on allyl-acetate at a continuous total yield of 33 %. The results are compared to those obtained with the standard batch-mode technique of parahydrogen bubbling through a suspension of the same catalyst.     

Efficient Batch‐Mode Parahydrogen‐Induced Polarization of Propane

We report on a simple approach for efficient NMR proton hyperpolarization of propane using the parahydrogen‐induced polarization (PHIP) technique, which yielded ≈6.2 % proton polarization using ≈80 % parahydrogen, a record level achieved with any hyperpolarization technique for propane. Unlike in previously developed approaches designed for continuous‐flow operation, where reactants (propene and parahydrogen) are simultaneously loaded for homogeneous or heterogeneous pairwise addition of parahydrogen, here a batch‐mode method is applied: propene is first loaded into the catalyst‐containing solution, which is followed by homogeneous hydrogenation via parahydrogen bubbling delivered at ≈7.1 atm. The achieved nuclear spin polarization of this contrast agent potentially useful for pulmonary imaging is approximately two orders of magnitude greater than that achieved in the continuous‐flow homogeneous catalytic hydrogenation, and a factor of 3–10 more efficient compared to the typical results of heterogeneous continuous‐flow hydrogenations.     

MCM‐41‐Immobilized [Rh(cod)OCH3]2 Complex – A Hybrid Catalyst for the Polymerization of Phenylacetylene and Its Ring‐Substituted Derivatives

The immobilization of [Rh(cod)OCH₃]₂ (cod = cycloocta‐1,5‐diene) on mesoporous molecular sieves MCM‐41 provides the first inorganic‐type hybrid catalyst, which affords heterogeneous polymerization of phenylacetylene and its ring‐substituted derivatives, – 2‐fluorophenylacetylene, 4‐fluorophenylacetylene, and 4‐pentylphenylacetylene – into readily isolable high‐molecular‐weight (M̄_w from 50 000 to 180 000) substituted polyvinylenes of high cis‐transoid structure. The activity of this catalyst is compared with that of homogeneous catalyst [Rh(cod)OCH₃]₂.     

Isolated Diatomic Ni‐Fe Metal–Nitrogen Sites for Synergistic Electroreduction of CO2

Polynary single‐atom structures can combine the advantages of homogeneous and heterogeneous catalysts while providing synergistic functions based on different molecules and their interfaces. However, the fabrication and identification of such an active‐site prototype remain elusive. Here we report isolated diatomic Ni‐Fe sites anchored on nitrogenated carbon as an efficient electrocatalyst for CO₂ reduction. The catalyst exhibits high selectivity with CO Faradaic efficiency above 90 % over a wide potential range from ?0.5 to ?0.9 V (98 % at ?0.7 V), and robust durability, retaining 99 % of its initial selectivity after 30 hours of electrolysis. Density functional theory studies reveal that the neighboring Ni‐Fe centers not only function in synergy to decrease the reaction barrier for the formation of COOH* and desorption of CO, but also undergo distinct structural evolution into a CO‐adsorbed moiety upon CO₂ uptake.     

The effect of molecular weight and catalyst concentration on catalytic activity in mechanochemically activated transesterification using silver(I)‐N‐heterocyclic carbene latent catalysts

We have investigated the effect of the concentration and molecular weight on the activity of polymeric silver(I)‐NHC (NHC = N‐heterocyclic carbene) catalyst complexes in ultrasound‐induced mechanochemical catalyst activation. A strong dependence of the turnover number (TON) on initial catalyst concentration was observed in the transesterification of vinyl acetate with benzyl alcohol. The main findings of this study are that the concentration and molecular weight effects on TON are caused by competition between mechanochemical catalyst activation and deactivation, most likely by reactive species produced during the sonication process. Performing the transesterification reaction under radical‐suppressing conditions resulted in a significant increase of TON. This result clearly demonstrates the increased catalyst lifetime when reducing the amount of sonochemical impurities, and it highlights the importance of controlling and suppressing secondary, sonochemical processes when using ultrasound‐induced mechanochemical generation of reactive species such as catalysts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012