Search

International audience; The development of highly efficient enantioselective olefin metathesis catalysts is a significant challenge. Using optically pure chiral cyclic (alkyl)(amino)carbene (ChiCAAC) ligands combined with preliminary mechanistic insights and density functional theory (DFT) computations, we show that catalytic performances in this field can be impaired by the formation of rotamers before the enantio-determining step. Using DFT, we also demonstrate that these results can help accelerate the process of ligand discovery by providing faster methods to discriminate potential candidates.

International audience; Optically pure oxazolidines were synthesized in nearly quantitative yields from chiral hydroxyalkyl-functionalized imidazolinium salts. Acting as transient chiral diamino N-heterocyclic carbenes (NHCs), these oxazolidines allowed the efficient formation of well-defined copper(i) and gold(i) hydroxyalkyl-NHC complexes, which could be isolated, for the first time, as air stable complexes after silica gel chromatography. Interestingly, X-ray analysis of gold complexes revealed that the hydroxyl-function is not chelated to the metal. Computational studies suggested that both cyclisation to produce oxazolidine and O-H bond elimination to form the transient carbene (prior to coordination) occur through a concerted mechanism. The novel chiral copper-catalysts, as well as oxazolidines alone (copper free), demonstrated excellent performances in asymmetric conjugate addition and allylic alkylation with high regio- and enantio-selectivities (up to 99% ee).

Cyclophane structures can control steric pressure in the otherwise open spaces of square‐planar d8‐metal catalysts. This elegant concept was so far limited to symmetrical coordinated metals. We report how a cyclophane motif can be generated in ligands that chelate via two different donors. An ancillary second imine in the versatile κ2‐N,O‐salicylaldiminato catalyst type enables ring closure via olefin metathesis and selective double bond hydrogenation to yield a 30‐membered ring efficiently. Experimental and theoretical analyses show the ancillary imine is directed away from the active site and inert for catalysis. In ethylene polymerization the cyclophane catalyst is more active and temperature stable vs. an open structure reference, notably also in polar solvents. Increased molecular weights and decreased degrees of branching can be traced to an increased energy of sterically demanding transition states by the encircling cyclophane while chain propagation remains highly efficient., We demonstrate how a cyclophane structure can be generated in square‐planar complexes with two different chelating donors (N,O). An ancillary second imine function in the versatile κ 2‐N,O‐salicylaldiminato catalyst type enables ring closure between two symmetrical 4′,4′′‐diallyl substituted terphenyl motifs.

Polyethylene materials with in-chain-incorporated keto groups were recently enabled by nonalternating copolymerization of ethylene with carbon monoxide in the presence of Ni(II) phosphinephenolate catalysts. We elucidate the mechanism of this long-sought-for reaction by a combined theoretical DFT study of catalytically active species and the experimental study of polymer microstructures formed in pressure-reactor copolymerizations with different catalysts. The pathway leading to the desired nonalternating incorporation proceeds via the cis/trans isomerization of an alkyl-olefin intermediate as the rate-determining step. The formation of alternating motifs is determined by the barrier for the opening of the six-membered C,O-chelate by ethylene binding as the decisive step. An η2-coordination of a P-bound aromatic moiety axially oriented to the metal center is a crucial feature of these Ni(II) catalysts, which also modulates the competition between the two pathways. The conformational constraints imposed in a 2',6'-dimethoxybiphenyl moiety overall result in a desirable combination of disfavoring ethylene coordination along the alternating incorporation pathway, which is primarily governed by electronics, while not overly penalizing the nonalternating chain growth, which is primarily governed by sterics. published

A direct comparison between neutral active sites and their corresponding cationic analogues is enabled by protonation of neutral bis(imino)phenoxy complexes, active for ethylene polymerization. The...

Summary Intrinsically recyclable polymers represent a circular economy approach to address plastics problems. However, the design of such circular polymers is challenged by unyielding trade-offs between the monomer’s polymerizability and the polymer’s depolymerizability and performance properties. Here, we introduce a hybrid monomer design strategy that synergistically couples a high ceiling temperature (HCT) sub-structure for high polymerizability and performance properties with a low ceiling temperature (LCT) sub-structure for high depolymerizability and recyclability within the same monomer structure. Thus, structural hybridization between HCT e-caprolactone and LCT γ-butyrolactone led to an offspring [3.2.1]bicyclic lactone, which exhibits both high polymerizability and depolymerizability, otherwise conflicting properties in a typical monomer. The resulting polymer becomes a high-performance material, and thermal transition temperatures are ∼200°C higher and tensile modulus 10× higher than its parent polymers. These results demonstrate that the HCT/LCT hybrid monomer strategy is a powerful approach for designing circular polymers where conflicting properties must be exploited and unified.

International audience; An expedient access to the first optically pure ruthenium complexes containing C(1)-symmetric cyclic (alkyl)(amino)carbene ligands is reported. They demonstrate excellent catalytic performances in asymmetric olefin metathesis with high enantioselectivities (up to 92% ee). Preliminary mechanistic insights provided by density functional theory models highlight the origin of the enantioselectivity.

Bacterial polyhydroxyalkanoates (PHAs) are a unique class of biodegradable polymers because of their biodegradability in ambient environments and structural diversity enabled by side-chain groups. However, the biosynthesis of PHAs is slow and expensive, limiting their broader applications as commodity plastics. To overcome such limitation, the catalyzed chemical synthesis of bacterial PHAs has been developed, using the metal-catalyzed stereoselective ring-opening (co)polymerization of racemic cyclic diolides (rac-8DLR , R=alkyl group). In this combined experimental and computational study, polymerization kinetics, stereocontrol, copolymerization characteristics, and the properties of the resulting PHAs have been examined. Most notably, stereoselective copolymerizations of rac-8DLMe with rac-8DLR (R=Et, Bu) have yielded high-molecular-weight, crystalline isotactic PHA copolymers that are hard, ductile, and tough plastics, and exhibit polyolefin-like thermal and mechanical properties.

The role of sodium acetate in the synthesis of [Au(NHC)Cl] complexes was examined. The use of this base was also investigated for the activation of C-H and S-H bonds by experimental and computational methods. The synthetic use of NaOAc to assemble these complexes is applicable to a wide range of NHCs and proceeds under air, under mild conditions and using technical grade green solvents.

In typical cyclic polymer synthesis via ring-closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.

An efficient and chemoselective methodology deploying gold- N -heterocyclic carbene (NHC) complexes as catalysts in the hydrofluorination of terminal alkynes using aqueous HF has been developed. Mechanistic studies shed light on an in situ generated catalyst, formed by the reaction of Bronsted basic gold pre-catalysts with HF in water, which exhibits the highest reactivity and chemoselectivity. The catalytic system has a wide alkyl substituted-substrate scope, and stoichiometric as well as catalytic reactions with tailor-designed gold pre-catalysts enable the identification of various gold species involved along the catalytic cycle. Computational studies aid in understanding the chemoselectivity observed through examination of key mechanistic steps for phosphine- and NHC-coordinated gold species bearing the triflate counterion and the elusive key complex bearing a bifluoride counterion.

The cis–trans isomerization of (thio)amides was studied by DFT calculations to get the model for the higher preference for the cis conformation by guided predictive chemistry, suggesting how to select the substituents that lead to the trans isomer.

Financial support by the DFG (Me 1388/14-1) is gratefully acknowledged. We thank Steffen Oswald for assistance with the CV measurements and Lars Bolk for DSC and GPC measurements.

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), AstraZeneca (Studenship to C.M.Z) and VLAIO (CO2PERATE) for support of this work. We thank King Saud University (DSF Program) and KAUST (Award No.OSR-2015-CCF-1974-03) for support. A new class of [Au(NHC)(Bpin)] complexes has been synthesized and their unusual reactivity was investigated using computational and experimental methods. The gold-boryl complexes exhibit unexpected high stability and reactivity. Postprint

A series of NHC-gold(i) (NHC = N-heterocyclic carbene) complexes has been studied by DFT calculations, enabling comparison of electronic and NMR behaviour with related protonated and free NHC molecules. Based on calculations, the NMR resonances of the carbenic C2 carbon atom in [Au(NHC)(Cl)] and [NHC(H)][Cl] exhibit increased shielding when compared to the free N-heterocyclic carbenes by an average of 46.6 ± 2.2 and 73.7 ± 4.3 ppm, respectively. A similar trend is observed when analysing the paramagnetic term of the magnetic shielding tensor. Although gold(i) and proton are considered isolobal fragments, imidazolium compounds lack π-backdonation due to the energetic unavailability of d-orbitals in H+. We propose that NHC-gold(i) complexes exhibit important π-backdonation irrespective of the relative amount of σ-donation between the NHC and gold(i)-X (X = anionic ligand) moieties in Au-NHC complexes. Interestingly, a correlation exists between the calculated shielding for gold (197Au) and the π-donation and π-backdonation contributions. We describe that this correlation also exists when analysing the σ-backdonation term, a property generally ignored yet representing a significant energetic contribution to the stability of the C2-Au bond.

We thank the Ghent University (IoF), the Special Research Fund (BOF) starting (SPN, CSJC) and advanced (SPN, KVH) grants and Research Foundation Flanders (FWO) (fellowship to SVB and grant to CSJC and KVH) for funding. Readily-prepared and bench-stable [Au(CF3)(NHC)] compounds were synthesized using new methodologies, starting from [Au(OH)(NHC)], [Au(Cl)(NHC)] or [Au(L)(NHC)]HF2 precursors (NHC = N-heterocyclic carbene). The mechanism of formation of these species was investigated. Consequently, a new and straightforward strategy for the mild and selective cleavage of a single carbon-fluorine bond from [Au(CF3)(NHC)] complexes was attempted and found to be reversible in the presence of an additional nucleophilic fluoride source. This straightforward technique has led to the unprecedented spectroscopic observation of a gold(I)-NHC difluorocarbene species. Postprint

The development of novel and operationally simple synthetic routes to carbene‐metal‐amido (CMA) complexes of copper, silver and gold relevant for photonic applications are reported. A mild base and sustainable solvents allow all reactions to be conducted in air and at room temperature, leading to high yields of the targeted compounds even on multigram scales. The effect of various mild bases on the N−H metallation was studied in silico and experimentally, while a mechanochemical, solvent‐free synthetic approach was also developed. Our photophysical studies on [M(NHC)(Cbz)] (Cbz=carbazolyl) indicate that the occurrence of fluorescent or phosphorescent states is determined primarily by the metal, providing control over the excited state properties. Consequently, we demonstrate the potential of the new CMAs beyond luminescence applications by employing a selected CMA as a photocatalyst. The exemplified synthetic ease is expected to accelerate the applications of CMAs in photocatalysis and materials chemistry., N−H metallation routes: Interest in carbene‐metal‐amido (CMA) complexes of the coinage metals has inspired comprehensive efforts towards simplifying their synthesis. We now showcase simple and sustainable routes to various CMAs, using mild conditions for the N−H metallation of carbazole and other amines. The action of a mild base is studied computationally and the photophysical properties of some new CMA complexes are examined.

In this work permaleic acid (PMA) was investigated as possible disinfecting agent and compared to peracetic acid (PAA) in real tap water and wastewater. Preliminary tests in lysogeny broth (LB) were also performed. PMA was synthesized from maleic anhydride and hydrogen peroxide and, for the first time, its antimicrobial activity was evaluated with respect to the growth inhibition of E. coli. The effect of the pH and bivalent ions, typically occurring in real water matrices (namely, Mg2+ and Ca2+), was also investigated. pKa values for PMA were calculated for the first time by DFT calculations. The concentration of bivalent ions strongly affected disinfection efficiency with PMA (Ca2+=0.33 mgL−1 and Mg2+=0.35 mgL−1: 100% E. coli reduction > log 5; Ca2+=13.3 mg L−1 and Mg2+=25.6 mg L−1: E. coli reduction log 5 E.coli reduction; pH = 9

Poly (vinyl ethers) are compounds with great value in the coating industry due to exhibiting properties such as high viscosity, soft adhesiveness, resistance to saponification and solubility in water and organic solvents. However, the main challenge in this field is the synthesis of vinyl ether monomers that can be synthetized by methodologies such as vinyl transfer, reduction of vinyl phosphate ether, isomerization, hydrogenation of acetylenic ethers, elimination, addition of alcohols to alkyne species etc. Nevertheless, the most successful strategy to access to vinyl ether derivatives is the addition of alcohols to alkynes catalyzed by transition metals such as molybdenum, tungsten, ruthenium, palladium, platinum, gold, silver, iridium and rhodium, where gold-NHC catalysts have shown the best results in vinyl ether synthesis. Recently, the hydrophenoxylation reaction was found to proceed through a digold-assisted process where the species that determine the rate of the reaction are PhO-[Au(IPr)] and alkyne-[Au(IPr)]. Later, the improvement of the hydrophenoxylation reaction by using a mixed combination of Cu-NHC and Au-NHC catalysts was also reported. DFT studies confirmed a cost-effective method for the hydrophenoxylation reaction and located the rate-determining step, which turned out to be quite sensitive to the sterical hindrance due to the NHC ligands This research was funded by the Ministerio de Economía y Competitividad (MINECO) of Spain for project PGC2018-097722-B-I00, the Generalitat de Catalunya for project 2017SGR39 and Xarxa de Referència en Química Teórica i Computacional

Chiral, cationic NHC–iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes. The catalysts show high activity in the construction of a range of 5- and 6-membered N-heterocycles, which are accessed in excellent optical purity, with various functional groups being tolerated with this system. A major deactivation pathway is presented and eliminated by using alternative reaction conditions. A detailed experimental and computational study on the reaction mechanism is performed providing valuable insights into the mode of action of the catalytic system and pointing to future modifications to be made for this catalytic platform., Chiral, cationic NHC–iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes.

Funding sources from the King Abdulaziz University and the King Abdullah University of Science and Technology, Thuwal, Saudi Arabia. Computation for the work presented in this paper was supported by KAU's High Performance Computing Center (Aziz Supercomputer) (http://hpc.kau.edu.sa) and by the KAUST Super-computing Laboratory (KSL) at KAUST.

An expedient access to the first optically pure ruthenium complexes containing

Invited for the cover of this issue are the groups of Yann Sarazin at the University of Rennes and Laura Falivene at the King Abdullah University of Science and Technology. The image depicts two barium figures working in tandem to mimic the dinuclear nature of the active species in the catalytic cycle described in the manuscript. Read the full text of the article at 10.1002/chem.201904933.

We thank Prof. Anthony Linden (University of Zurich) for solving the crystal structure of 8 and Ms. Christina Wronna for carrying out the elemental analyses. Financial support by Friedrich–Alexander University and King Abdullah University of Science and Technology (KAUST) is acknowledged. For computer time, this research used the resources of the Supercomputing Laboratory (KSL) at KAUST.

The noncovalent interactions and remote ligand effects in catalysis have attracted a large attention in the last years. The rationalization of such interactions is tricky and often their role can be elucidated only with a detailed mechanistic study. Here we report the case of fluorinated ligand systems showing a very peculiar behavior in the catalysis of olefin polymerization. The results reported aim to clarify the origin of such behavior underlying the nature of the control of the fluorinated groups on the key steps of the polymerization. These insights can offer new cues to rationalize similar evidences in other reaction fields.

Circular plastics defy traditional trade-offs in recyclability-performance and structure-property relationships., Three types of seemingly unyielding trade-offs have continued to challenge the rational design for circular polymers with both high chemical recyclability and high-performance properties: depolymerizability/performance, crystallinity/ductility, and stereo-disorder/crystallinity. Here, we introduce a monomer design strategy based on a bridged bicyclic thiolactone that produces stereo-disordered to perfectly stereo-ordered polythiolactones, all exhibiting high crystallinity and full chemical recyclability. These polythioesters defy aforementioned trade-offs by having an unusual set of desired properties, including intrinsic tacticity-independent crystallinity and chemical recyclability, tunable tacticities from stereo-disorder to perfect stereoregularity, as well as combined high-performance properties such as high thermal stability and crystallinity, and high mechanical strength, ductility, and toughness.

We gratefully acknowledge VLAIO (SBO project CO2PERATE), King Saud University (Distinguished Scientist Fellowship Program) and King Abdullah University of Science and Technology for support. The Special Research Fund (BOF) of Ghent University is also acknowledged (Doctoral Scholarship to N.V.T.). COST action (CA15106-CHAOS) is thanked for mobility support to N.V.T. Umicore AG is acknowledged for generous gifts of materials. We have been puzzled by the involvement of weak organic and inorganic bases in the synthesis of metal‐N‐heterocyclic carbene (NHC) complexes. Such bases are insufficiently strong to permit the presumed required deprotonation of the azolium salt (the carbene precursor) prior to metal binding. Experimental and computational studies provide support for a base‐assisted concerted process that does not require free NHC formation. The synthetic protocol was found applicable to a number of Transition Metal‐ and Main Group‐centered NHC compounds and could become the synthetic route of choice to form M‐NHC bonds. Postprint

The copolymerization of ethylene (E) with allyl ethyl ether (AEE) by [di(2-dianisyl)phosphine-2-yl]benzenesulfonato Pd(II) as a catalyst is investigated by DFT calculations and compared with the copolymerization of E with diallyl ether (DAE). For AEE, both 1,2- and 2,1-monomer insertions lead to a very stable O-Chelate product (a five-membered and a four-membered ring, respectively) that hinders any further ethylene insertion. As for DAE, a first 2,1-insertion (favored by 1.8 kcal mol–1 vs the 1,2-insertion) leads to the four-membered O-Chelate product that easily evolves to the most stable intermediate with the second DAE C═C bond coordinated to the metal promoting the following 1,2-insertion. The 2,1 + 1,2 DAE insertion product, bearing a five-membered cyclic unit, is stabilized by a β-agostic interaction that easily opens in favor of E coordination and insertion. Based on the proposed copolymerization mechanism, the stereochemistry of the E/DAE copolymer is studied and the experimental microstructure e...

Better catalysts are needed to address numerous challenges faced by humanity. In this Perspective, we review concepts and tools in theoretical and computational chemistry that can help to accelerate the rational design of homogeneous and heterogeneous catalysts. In particular, we focus on the following three topics: (1) identification of key intermediates and transition states in a reaction using the energetic span model, (2) disentanglement of factors influencing the relative stability of the key species using energy decomposition analysis and the activation strain model, and (3) discovery of new catalysts using volcano relationships. To facilitate wider use of these techniques across different areas, we illustrate their potentials and pitfalls when applied to the study of homogeneous and heterogeneous catalysts.

A chiral iodoarene organocatalyst for the catalytic asymmetric fluorination has been developed. The catalyst was used in the asymmetric fluorination of carbonyl compounds, providing the products with a quaternary stereocenter with high enantioselectivities. Chiral hypervalent iodine difluoride intermediates were generated in situ by treatment of the catalyst with an oxidant and hydrogen fluoride as fluoride source. As such, the α-fluorination of a carbonyl compound was achieved with a nucleophilic fluorine source. A combined computational and experimental approach provided insight into the reaction mechanism and the origin of enantioselectivity.

A simple and efficient catalyst, benzimidazole (BIMH)-modified copper foil, is developed to enhance the selective conversion of CO2 to C2/C3 products. The overall faradaic efficiency (FE) for CO2 reduction reaches 92.1% and the undesired hydrogen evolution reaction (HER) is lowered to a FE of 7% at −1.07 VRHE.

Recent theoretical analysis of the NMR properties of free N-heterocyclic carbenes (NHC) and metal-NHC complexes has complemented experiments, allowing the establishment of structure/property relationships and the rationalization of otherwise surprising experimental results. In this review, the main conclusions from recent literature are discussed, with the aim to offer a vision of the potential of theoretical analyses of NMR properties.

Density functional theory calculations have been used to investigate competition between inner- and outer-sphere reaction pathways in the oxidative coupling of CO2 and ethylene for a set of 12 Ni–bisphosphine complexes, in order to build a QSAR approach correlating catalyst structure to calculated energy barriers for CO2 activation. The ligands were selected to explore different substituents on the P atoms (cyclohexyl, phenyl, and tert-butyl) and different lengths of the tether connecting the P atoms, −(CH2)n– with n = 1–3. As expected, the conclusion is that the inner-sphere reaction pathway is favored with unhindered ligands, while the outer-sphere reaction pathway is favored with hindered ligands. To find a possible correlation with molecular descriptors, we started using the buried volume as a steric descriptor. A reasonable correlation could be found for the energy barrier along the inner-sphere pathway, while scarce correlation was found for the energy barrier along the outer-sphere pathway, indicat...

We report on the DFT stability of zwitterion and spirocycle adducts of five polar monomers with nine N-heterocyclic carbenes (NHC), covering the most typical classes of monomers and NHCs used in organopolymerization. Results indicate that the relative stability of the two adducts is dominated by the singlet–triplet energy gap of the free NHC, with low energy gaps favoring the spirocycle adduct, while high energy gaps favor the zwitterionic adduct. This basic structure/property relationship can be tuned by the hindrance of the NHC and the nature of the monomer. In addition to rationalize existing systems, the 45 NHC/monomer combinations we examined can be used as a guideline to predict the behavior of a new NHC/monomer combination.

We report a mechanistic DFT investigation of the organopolymerization of propylene oxide (PO) promoted by N-heterocyclic olefins (NHOs) in combination with benzylic alcohol (BnOH). Calculations support the experimentally based hypothesis of two competing pathways, namely, the anionic and zwitterionic pathways. The former is based on an acid–base cooperativity between BnOH and the NHO, promoting ring opening of PO by BnO–. The latter occurs through the formation of a zwitterionic adduct by nucleophilic attack of the exocyclic carbon atom of the NHO on the PO, with the concerted ring opening of PO. The two initiating species cannot interconvert, and chain elongation can proceed from both initiation adducts. Potential energy surfaces were computed for a set of NHOs to clarify the effects of the steric and electronic properties of the NHO on the system reactivity. The results achieved represent useful insight toward the synthesis of PPO with better properties with respect to the polymer obtained with the expe...

The zwitterionic organopolymerization of four different acrylic monomers (N,N-dimethylacrylamide, methyl acrylate, methyl methacrylate and tert-butyl methacrylate) based on neutral initiators, so-called N-heterocyclic olefins (NHOs), is presented. The scope and underlying (deactivation-)mechanisms were studied in a combined experimental and computational effort. From a range of differently structured NHOs it was shown that imidazole-derivatives, in contrast to imidazoline- and benzimidazole-derivatives, readily polymerize the selected monomers. While the additive-free reactions proceed with a relatively low degree of control to yield a largely atactic material, for the acrylamide the addition of LiCl as a μ-type ligand has been shown to result in a rapid and quantitative monomer consumption. The thus generated poly(N,N-dimethyl acrylamide) was found to be highly isotactic (>90% isotactic dyads) with high molecular weight (Mn = 250 000–650 000 g mol−1, ĐM = 1.3–1.6). Complementing DFT calculations considered the zwitterionic chain growth with respect to competing side reactions, namely spirocycles and enamine formation. It was found that NHOs with an unsaturated backbone better support the zwitterionic chain growth, with the spirocycles acting as dormant species that slow down but do not quench the polymerization process. Contrasting this, enamine formation irreversibly terminates the polymerization and is found to be energetically favored. This pathway can be blocked by the introduction of substituents on the exocyclic carbon of the NHO, resulting in structures like 2-isopropylidene-1,3,4,5-tetramethylimidazoline (4) which consequently deliver the most controlled polymerizations. Finally, a good correlation of the initiation energy barrier with the buried volume (%VBur) and the Parr electrophilicity index is described, allowing for a quick and reliable screening of potential monomers based on these two readily accessible parameters.

Single atom catalysis (SAC) is a recent discipline of heterogeneous catalysis for which a single atom on a surface is able to carry out various catalytic reactions. A kind of revolution in heterogeneous catalysis by metals for which it was assumed that specific sites or defects of a nanoparticle were necessary to activate substrates in catalytic reactions. In another extreme of the spectrum, surface organometallic chemistry (SOMC), and, by extension, surface organometallic catalysis (SOMCat), have demonstrated that single atoms on a surface, but this time with specific ligands, could lead to a more predictive approach in heterogeneous catalysis. The predictive character of SOMCat was just the result of intuitive mechanisms derived from the elementary steps of molecular chemistry. This review article will compare the aspects of single atom catalysis and surface organometallic catalysis by considering several specific catalytic reactions, some of which exist for both fields, whereas others might see mutual overlap in the future. After a definition of both domains, a detailed approach of the methods, mostly modeling and spectroscopy, will be followed by a detailed analysis of catalytic reactions: hydrogenation, dehydrogenation, hydrogenolysis, oxidative dehydrogenation, alkane and cycloalkane metathesis, methane activation, metathetic oxidation, CO2 activation to cyclic carbonates, imine metathesis, and selective catalytic reduction (SCR) reactions. A prospective resulting from present knowledge is showing the emergence of a new discipline from the overlap between the two areas.

The concept of upcycling postconsumer plastics into higher-value products is attractive, but the challenges remain to develop a cost-effective upcycling scheme, discover property-enhancing structur...

The use of palladium(II) catalysts for the synthesis of aryl alkenes by addition of aromatic C–H bonds to alkynes has received a great interest in the literature. The mechanistic features of the re...

The influence of the labile ligand on the rate of β-hydride elimination (BHE) for salicylaldiminato Ni(II) complexes is shown using a series of precatalysts which differ only in the labile ligand but produce polyethylenes with a range of molecular weights (Mn = 466 to 100 kg mol–1), degrees of branching (1.7 to 7.3 branches/1000 C), and melting temperatures (from 132 to 123 °C) under the same conditions. The use of a weakly coordinating solvent (diethyl ether) was able to suppress this increase in BHE. DFT studies on a related salicylaldiminato Ni(II) complex show that BHE can feasibly occur following recombination of the labile ligand with the catalyst.

α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL)VAP. Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL)ROP with Mn up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL)CLP. The formation of the three types of polymers, P(MBL)VAP, P(MBL)CLP, and P(MBL)ROP, can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La–X (X = OR, NR2,...

A single-step route to telechelic polyethylene (PE) is enabled by selective insertion polymerization. Pd(II) -catalyzed copolymerization of ethylene and 2-vinylfuran (VF) generates α,ω-di-furan telechelic polyethylene. Orthogonally reactive exclusively in-chain anhydride groups are formed by terpolymerization with carbic anhydride. Combined experimental and theoretical DFT studies reveal the key for this direct approach to telechelics to be a match of the comonomers' different electronics and bulk. Identified essential features of the comonomer are that it is an electron-rich olefin that forms an insertion product stabilized by an additional interaction, namely a π-η3 interaction for the case of VF. published

We report on a DFT investigation of initiation, propagation, and termination in the organopolymerization of N-methyl N-carboxyanhydrides toward cyclic poly(N-substituted glycine)s, promoted by N-heterocyclic carbenes (NHC). Calculations support the experimentally based hypothesis of two competing initiation pathways. The first leading to formation of a zwitterionic adduct by nucleophilic addition of the NHC to one of the carbonyl groups of monomer. The second via acid–base reactivity, starting with the NHC promoted abstraction of a proton from the methylene group of the monomer, leading to an ion-pair-type adduct, followed by nucleophilic attack of the adduct to a new monomer molecule. Chain elongation can proceed from both the initiation adducts via nucleophilic attack of the carbamate chain-end to a new monomer molecule via concerted elimination of CO2 from the carbamate chain-end. Energy barriers along all the considered termination pathways are remarkably higher that the energy barrier along the chain...