Recent improvements in the alkoxycarbonylation reaction catalyzed by transition metal complexes

Co/SiO2 Catalyst for Methoxycarbonylation of Acetylene: On Catalytic Performance and Active Species

Reppe carbonylation of acetylene is an atom-economic and non-petroleum approach to synthesize acrylic acid and acrylate esters, which are key intermediates in the textile, leather finishing, and polymer industries. In the present work, a noble metal-free Co@SiO2 catalyst was prepared and evaluated in the methoxycarbonylation reaction of acetylene. It was discovered that pretreatment of the catalyst by different reductants (i.e., C2H2, CO, H2, and syngas) greatly improved the catalytic activity, of which Co/SiO2-H2 demonstrated the best performance under conditions of 160 °C, 0.05 MPa C2H2, 4 MPa CO, and 1 h, affording a production rate of 4.38 gMA+MP gcat-1 h-1 for methyl acrylate (MA) and methyl propionate (MP) and 0.91 gDMS gcat-1 h-1 for dimethyl succinate (DMS), respectively. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectra of CO adsorption (CO-DRIFTS) measurements revealed that an H2 reduction decreased the size of the Co nanoparticles and promoted the formation of hollow architectures, leading to an increase in the metal surface area and CO adsorption on the catalyst. The hot filtration experiment confirmed that Co2(CO)8 was generated in situ during the reaction or at the pre-activation stage, which served as the genuine active species. Our work provides a facile and convenient approach to the in situ synthetization of Co2(CO)8 for a Reppe carbonylation reaction.

Identification of a potent palladium-aryldiphosphine catalytic system for high-performance carbonylation of alkenes

The development of stable and efficient ligands is of vital significance to enhance the catalytic performance of carbonylation reactions of alkenes. Herein, an aryldiphosphine ligand (L11) bearing the [Ph2P(ortho-C6H4)]2CH2 skeleton is reported for palladium-catalyzed regioselective carbonylation of alkenes. Compared with the industrially successful Pd/1,2-bis(di-tert-butylphosphinomethyl)benzene catalyst, catalytic efficiency catalyzed by Pd/L11 on methoxycarbonylation of ethylene is obtained, exhibiting better catalytic performance (TON: >2,390,000; TOF: 100,000 h-1; selectivity: >99%) and stronger oxygen-resistance stability. Moreover, a substrate compatibility (122 examples) including chiral and bioactive alkenes or alcohols is achieved with up to 99% yield and 99% regioselectivity. Experimental and computational investigations show that the appropriate bite angle of aryldiphosphine ligand and the favorable interaction of 1,4-dioxane with Pd/L11 synergistically contribute to high activity and selectivity while the electron deficient phosphines originated from electron delocalization endow L11 with excellent oxygen-resistance stability.

Ethylene Methoxycarbonylation over Heterogeneous Pt1/MoS2 Single-Atom Catalyst: Metal-Support Concerted Catalysis

Ethylene methoxycarbonylation (EMC) to methyl propanoate (MP) is an industrially important reaction and commercially uses a homogeneous Pd-phosphine organometallic complex as the catalyst and corrosive strong acid as the promoter. In this work, we develop a Pt1/MoS2 heterogeneous single-atom catalyst (SAC) which exhibits high activity, selectivity, and good recyclability for EMC reaction without need of any liquid acid. The production rate of MP achieves 0.35 gMP gcat-1 h-1 with MP selectivity of 91.1% at 1 MPa CO, 1 MPa C2H4, and 160 °C, which can be doubled at 2 MPa CO and corresponds to 320.1 molMP molPt-1 h-1, at least 1 order of magnitude higher than the earlier reported heterogeneous catalyst and even comparable to some of homogeneous catalyst. Advanced characterizations and DFT calculations reveal that all the Pt single atoms are located at the Mo vacancies along the Mo edge of the MoS2 nanosheets, forming pocket-like Mo-S-Pt1-S-Mo ensembles with uniform and well-defined structure. Methanol is first adsorbed and dissociated on Mo sites, and the produced H spillovers to the adjacent Pt site forming Pt-H species which then activate ethylene, forming Pt-ethyl species. Meanwhile, CO adsorbed on the other Mo site reacts with the Pt-ethyl species, yielding propionyl species, and this carbonylation is the rate-determining step. The final methoxylation step proceeds via the nucleophilic attack of propionyl species by -OCH3 affording the final product MP. Such a metal-support concerted catalysis enabled by the Mo-S-Pt1-S-Mo multisite ensemble opens a new avenue for SACs to promote the multimolecular reactions that prevail in homogeneous catalysis.

Synthesis of ester-functionalized indolo[2,1-a]isoquinolines via iron-catalyzed radical cascade cyclization of 2-aryl-N-acryloyl indoles with carbazates

An FeCl₂·4H₂O-catalyzed oxidative alkoxycarbonylation/cyclization reaction of 2-aryl-N-acryloyl indoles with carbazates leading to ester-functionalized indolo[2,1-a]isoquinoline derivatives has been developed. The reaction features mild reaction conditions and broad functional group tolerance. Moreover, the ester group could be easily converted to the corresponding free acid and alcohol, and has high potential applications in organic and pharmaceutical synthesis. A radical pathway was proposed to explain this experiment.

Palladium-catalyzed enantioselective carbonylation reactions

Carbonylation, one of the most powerful approaches to the preparation of carbonylated compounds, has received significant attention from researchers active in various fields. Indeed, impressive progress has been made on this subject over the past few decades. Among the various types of carbonylation reactions, asymmetric carbonylation is a straightforward methodology for constructing chiral compounds. Although rhodium-catalyzed enantioselective hydroformylations have been discussed in several elegant reviews, a general review on palladium-catalyzed asymmetric carbonylations is still missing. In this review, we summarize and discuss recent achievements in palladium-catalyzed asymmetric carbonylation reactions. Notably, this review’s contents are categorized by reaction type.

(In situ) spectroscopic studies on state-of-the-art Pd(ii) catalysts in solution for the alkoxycarbonylation of alkenes

(In situ) liquid-phase spectroscopic investigations on state-of-the-art Pd catalysts modified with pyridyl-substituted diphosphine ligands for alkene alkoxycarbonylations have been performed for characterizing resting state complexes in solution.

Palladium-catalyzed regioselective direct C–H bond alkoxycarbonylation of 2-arylimidazo[1,2-a]pyridines

A palladium catalyzed method for regioselective alkoxycarbonylation of imidazo[1,2-a]pyridines using W(CO)₆, as the CO source, and alcohols has been reported.

Pd-Catalyzed Cyclocarbonylation of Allylic Alcohol under Benign Conditions with Ionic Liquid as Stabilizer

Homogeneous palladium-catalyzed (Pd-catalyzed) cyclocarbonylation of unsaturated allylic alcohols and alkynols in the presence of hydrogen forms lactone products with important applications in the food, perfume, and polymer industry. In this work, the cyclocarbonylation of 2-methyl-3-buten-2-ol was studied for the first time using a very active Pd-DPEphos (bis[(2-diphenylphosphino)phenyl]ether) catalyst in the presence of the ionic liquid (IL) [BMIM]Cl (1-butyl-3-methylimidazolium chloride) in dichloromethane to selectively produce 4,4-dimethyl-γ-butyrolactone. The effect of different parameters such as temperature, gas partial pressures, time of reaction, substrate and ligand concentrations were investigated and found to provide optimal conditions for lactonization (95 °C, 28 bar (CO/H₂/N₂: 20/5/3)), 18 h, 0.1 M substrate, and 16 mol% DPEphos), which were significantly milder than previously reported systems for cyclocarbonylation. Importantly, the study further showed that presence of the IL in the reaction mixture provided stabilization of the catalyst system and prevented formation of Pd-black, which allowed reuse of the catalytic system in consecutive reactions after intermediate extraction of the lactone product.

Site-Selective Double and Tetracyclization Routes to Fused Polyheterocyclic Structures by Pd-Catalyzed Carbonylation Reactions

In this contribution, we report novel palladium-catalyzed carbonylative cascade approaches to highly functionalized polyheterocyclic structures. The Pd-catalyzed carbonylative process involves the regioselective insertion of one to three CO molecules and the sequential ordered formation of up to eight new bonds (one C–O, two C–C, five C–N). The exclusive formation of six-membered heterocycles is elucidated by detailed modeling studies.

Palladium-Catalyzed Enantioselective Thiocarbonylation of Styrenes

A highly enantioselective thiocarbonylation of styrenes with CO and thiols has been achieved by Pd catalysis, providing highly enantioenriched thioesters in good to excellent yields. Key to the successful execution of this reaction is the use of a chiral sulfoxide-(P-dialkyl)-phosphine (SOP) ligands. This thiocarbonylation proceeds smoothly under mild reaction conditions (1 atm CO and 0 °C) and displays broad substrate scope. Also demonstrated is that this transformation can be conducted using surrogates of CO, greatly increasing the safety aspects of running the reaction. The generality and utility of the method is manifested by its application to the synthetic transformations of thioester products and the direct acylation of cysteine-containing dipeptides. A primary mechanism was investigated and a plausible catalytic cycle was proposed.

PdI2-Based Catalysis for Carbonylation Reactions: A Personal Account

In this account, we review our efforts in the field of carbonylation reactions promoted by palladium iodide-based catalysts, which have proven to be particularly efficient in diverse kinds of carbonylation processes (oxidative carbonylations as well as additive and substitutive carbonylations). Particularly in the case of oxidative carbonylations, more emphasis has been given to the most recent results and applications.

Efficient and Recyclable RuCl3 ⋅ 3H2O Catalyst Modified with Ionic Diphosphine for the Alkoxycarbonylation of Aryl Halides

A series of ionic (mono-/di-)phosphines (L2, L4, and L6) with structural similarity and their corresponding neutral counterparts (L1, L3, and L5) were applied to modulate the catalytic performance of RuCl3 ⋅ 3H2O. With the involvement of the ionic diphosphine (L4), in which the two phosphino-fragments were linked by butylene group, RuCl3 ⋅ 3H2O with advantages of low cost, robustness, and good availability was found to be an efficient and recyclable catalyst for the alkoxycarbonylation of aryl halides. The L4-based RuCl3 ⋅ 3H2O system corresponded to the best conversion of PhI (96 %) along with 99 % selectivity to the target product of methyl benzoate as well as the good generality to alkoxycarbonylation of different aryl halides (ArX, X=I and Br) with alcohols MeOH, EtOH, i-PrOH and n-BuOH. The electronic and steric effects of the applied phosphines, which were analyzed by the 31P NMR for 1 J 31 P- 77 Se 1 J measurement and single-crystal X-ray diffraction, were carefully co-related to the performance RuCl3 ⋅ 3H2O catalyst. In addition, the L4-based RuCl3 ⋅ 3H2O system could be recycled successfully for at least eight runs in the ionic liquid [Bmim]PF6.

The Palladium-Catalyzed Carbonylative Telomerization Reaction with Phenols, Polyphenols and Kraft Lignin

An efficient carbonylative coupling reaction of two equivalents of 1,3-butadiene, yielding aryl nona-3,8-dienoate esters, is performed with phenols as nucleophile, and promoted by palladium-based catalysts. Optimization study reveals the key role of benzoic acid as a cocatalyst. The suggested catalyst combination enables the conversion of a wide scope of variously substituted phenols into corresponding esters with a high yield. Further tests were performed with diphenols, naturally-occurring phenols and an industrial grade Kraft lignin, thus, indicating the scope of this reaction for transforming industrially relevant polyphenolic structures.

A New Tool in the Quest for Biocompatible Phthalocyanines: Palladium Catalyzed Aminocarbonylation for Amide Substituted Phthalonitriles and Illustrative Phthalocyanines Thereof

The amide peptide bond type linkage is one of the most natural conjugations available, present in many biological synthons and pharmaceutical drugs. Hence, aiming the direct conjugation of potentially biologically active compounds to phthalocyanines, herein we disclose a new strategy for direct modulation of phthalonitriles, inspired by an attractive synthetic strategy for the preparation of carboxamides based on palladium-catalyzed aminocarbonylation of aryl halides in the presence of carbon monoxide (CO) which, to our knowledge, has never been used to prepare amide-substituted phthalonitriles, the natural precursors for the synthesis of phthalocyanines. Some examples of phthalocyanines prepared thereof are also reported, along with their full spectroscopic characterization and photophysical properties initial assessment.

Catalytic Double Cyclization Process for Antitumor Agents against Breast Cancer Cell Lines

The development of efficient synthetic strategies for the discovery of novel antitumor molecules is a major goal in current research. In this context, we report here a catalytic double cyclization process leading to bicyclic heterocycles with significant antitumor activity on different human breast cancer (BC) cell lines. The products, 6,6a-dihydrofuro[3,2-b]furan-2(5H)-ones, were obtained in one step, starting from simple substrates (4-yne-1,3-diols, CO, and O2), under the catalytic action of PdI2 in conjunction with KI. These compounds have significant antiproliferative activity in vitro on human BC cell lines, both hormone receptor positive (MCF-7) and triple negative (triple-negative breast cancer [TNBC]; MDA-MB-231 and MDAMB-468), while exhibiting practically no effects on normal MCF-10A (human mammary epithelial) and 3T3-L1 (murine fibroblasts) cells. Thus, these compounds have the potential to expand the therapeutic options against BC, and in particular, against its most aggressive forms (TNBCs). Moreover, the present synthetic approach may provide an economic benefit for their production.

2-Pyridyl substituents enhance the activity of palladium-phospha-adamantane catalysts for the methoxycarbonylation of phenylacetylene

The synthesis of a series of CgPAr ligands is reported, where CgP is the 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-6-yl moiety and Ar = 2-pyridyl (L2), 3-pyridyl (L3), 2-pyrimidyl (L4), 4-R-2-pyridyl [R = Me (L5a), CF₃ (L6a), SiMe₃ (L7a)] or 6-R-2-pyridyl [R = Me (L5b), CF₃ (L6b), SiMe₃ (L7b). Testing of these ligands in the Pd-catalysed methoxycarbonylation of phenylacetylene reveals that the activity and branched selectivity of the catalysts derived from these ligands varies as a function of the N-heterocycle, with the catalyst derived from L5b being the most active of those tested. This, together with the poor performance of catalysts derived from L3 supports the hypothesis that the catalysis proceeds by a "proton shuttling" mechanism, an idea that previously had only been applied to arylphosphines. Reaction of [PtCl₂(cod)] with L where L = L2 or L4-7 yields a rac/meso mixture of the trans-[PtCl₂(L)₂] (1a-h) complexes, three of which are structurally characterised. ³¹P NMR spectroscopy shows that reaction of L3 with [PtCl₂(cod)] gives a mixture of mononuclear and binuclear metal complexes in solution. The complex trans-[PdCl₂(L2)₂] (4) reacts with AgBF₄ to give the [PdCl(κ¹-L2)(κ²-L2)]BF₄ (5) with spectroscopic and structural characterisation confirming the presence of a P,N-chelate. ¹H and ³¹P NMR evidence supports the assignment of a pyridyl-protonated species being formed upon treatment of 4 with TsOH·H₂O in CD₂Cl₂; both the protonated species and chelate 5 are observed when the reaction is carried out in MeOH.

The Beneficial Sinergy of MW Irradiation and Ionic Liquids in Catalysis of Organic Reactions

The quest for sustainable processes is becoming more and more important, with catalysis playing a major role in improving atom economy and reducing waste. Organic syntheses with less need of protecting/de-protecting steps are highly desirable. The combination of microwave irradiation, as energy source, with ionic liquids, as both solvents and catalysts, offered interesting solutions in recent years. The literature data of the last 15 years concerning selected reactions are presented, highlighting the importance of microwave (MW) technology coupled with ionic liquids.

Isomerisation versus carbonylative pathways in the hydroxy-carbonylation, methoxy-carbonylation, and amino-carbonylation of N-tosyl-3-pyrroline

DFT calculations show that the competition between carbonylation and isomerisation pathways using Pd/phosphine catalysts can be steered toward the desired carbonylation using less bulky ligands. Thus, the normally less effective phanephos family forms carbonylation products with good ee.

A recyclable CO surrogate in regioselective alkoxycarbonylation of alkenes: indirect use of carbon dioxide

Herein, we report a Pd-catalysed alkoxycarbonylation of alkenes based on the use of a recyclable CO₂reduction product, the crystalline and air-stableN-formylsaccharin, as a CO surrogate.