Non-Oxidative Coupling Reaction of Methane to Ethane and Hydrogen Catalyzed by the Silica-Supported Tantalum Hydride: (≡SiO)2Ta−H

A Vanadium Methylidene

Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH2)] (PNP = N[2-PiPr2-4-methylphenyl]-, Ar = 2,6-iPr2C6H3), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH3)] or [(PNP)V(=NAr)(CH3)] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, H2CPPh3. Structural and spectroscopic analysis, including 13C enriched labeling of the methylidene ligand, unequivocally confirmed the terminal nature of a rare 3d methylidene complex, featuring a V=CH2 bond distance of 1.908(2) Å and a highly downfield 13C NMR spectral shift at 298 ppm. In the absence of the ylide, intermediate [(PNP)V=NAr] activates dinitrogen to form an end-on bridging N2 complex, [(PNP)V(=NAr)]2(μ2-η1:η1-N2), having a singlet ground state. Complex [(PNP)V(=NAr)(=CH2)] reacts with H3COTf to form [(PNP)V(=NAr)(OTf)], accompanied by the release of ethylene as evidenced by 1H NMR spectroscopy, and reactivity studies suggest a β-hydride elimination pathway.

Single-Site Ni-Grafted TiO2 with Diverse Coordination Environments for Visible-Light Hydrogen Production

Solar hydrogen production at a high efficiency holds the significant importance in the age of energy crisis, while the micro-environment manipulation of active sites on photocatalysts plays a profound role in enhancing the catalytic performance. In this work, a series of well-defined single-site Ni-grafted TiO2 photocatalysts with unique and specific coordination environments, 2,2'-bipyridine-Ni-O-TiO2 (T-Ni Bpy) and 2-Phenylpyridine-Ni-O-TiO2 (T-Ni Phpy), were constructed with the methods of surface organometallic chemistry combined with surface ligand exchange for visible-light-induced photocatalytic hydrogen evolution reaction (HER). A prominent rate of 33.82 μmol ⋅ g-1  ⋅ h-1 and a turnover frequency of 0.451 h-1 for Ni are achieved over the optimal catalyst T-Ni Bpy for HER, 260-fold higher than those of Ni-O-TiO2 . Fewer electrons trapped oxygen vacancies and a larger portion of long-lived photogenerated electrons (>3 ns, ~52.9 %), which were demonstrated by the electron paramagnetic resonance and femtosecond transient IR absorption, correspond to the photocatalytic HER activity over the T-Ni Bpy. The number of long-lived free electrons injected from the Ni photoabsorber to the conduction band of TiO2 is one of the determining factors for achieving the excellent HER activity.

Rapid Polyolefin Hydrogenolysis by a Single-Site Organo-Tantalum Catalyst on a Super-Acidic Support: Structure and Mechanism

The novel electrophilic organo-tantalum catalyst AlS/TaNpx (1) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np3 Ta=CHt Bu onto highly Brønsted acidic sulfated alumina (AlS). The proposed catalyst structure is supported by EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements and is in good agreement with DFT analysis. Catalyst 1 is highly effective for the hydrogenolysis of diverse linear and branched hydrocarbons, ranging from C2 to polyolefins. To the best of our knowledge, 1 exhibits one of the highest polyolefin hydrogenolysis activities (9,800 (CH2 units) ⋅ mol(Ta)-1  ⋅ h-1 at 200 °C/17 atm H2 ) reported to date in the peer-reviewed literature. Unlike the AlS/ZrNp2 analog, the Ta catalyst is more thermally stable and offers multiple potential C-C bond activation pathways. For hydrogenolysis, AlS/TaNpx is effective for a wide variety of pre- and post-consumer polyolefin plastics and is not significantly deactivated by standard polyolefin additives at typical industrial concentrations.

Direct Conversion of Methane to Propylene

Nonoxidative coupling of methane exhibits promising prospect in that it affords value-added hydrocarbons and hydrogen with high atom economy. However, challenge remains in direct, selective conversion of methane to more valuable hydrocarbons like olefins. The current work presents a catalyst with well-dispersed Ta atoms anchored by graphitic C3N4-supported phthalocyanine. Such a catalyst is able to convert methane selectively to ethylene and propylene at a relatively low temperature (350 °C). The conception of the active center and construction of the catalyst have been described, and the origins of the catalytic performance are discussed.

Activity Origin of the Nickel Cluster on TiC Support for Nonoxidative Methane Conversion

Designing an active and selective catalyst for nonoxidative conversion of methane under mild conditions is critical for natural gas utilization as a chemical feedstock. Here, we demonstrate that the origin of the selective nonoxidative conversion of methane by the titanium carbide supported nickel cluster arises from the formation of a nickel carbide site under the reaction conditions, which could stabilize the CH_x intermediate to facilitate the C-C coupling, but further coking is rather limited. The reaction mechanism reveals that the C₂ products can be formed via a key -CH_x-CH₃ intermediate. In addition, we demonstrate that boration of the nickel cluster site can improve the methane conversion toward C₂ products. That higher activity and selectivity from the moderate rise in d orbital energy levels can therefore be considered as a descriptor of the catalyst effectiveness. These findings provide an understanding of the dynamic behavior of the single nickel cluster toward methane conversion to C₂ products and guidance for their future rational design.

Direct Coupling of Methane and Carbon Dioxide on Tantalum Cluster Cations

Understanding molecular-scale reaction mechanisms is crucial for the design of modern catalysts with industrial prospect. Through joint experimental and computational studies, we investigate the direct coupling reaction of CH₄ and CO₂ , two abundant greenhouse gases, mediated by Ta_1,4 ⁺ ions to form larger oxygenated hydrocarbons. Coherent with proposed elementary steps, we expose products of CH₄ dehydrogenation [Ta_1,4 CH₂ ]⁺ to CO₂ in a ring electrode ion trap. Product analysis and reaction kinetics indicate a predisposition of the tetramers for C-O coupling with a conversion to products of CH₂ O, whereas atomic cations enable C-C coupling yielding CH₂ CO. Selected experimental findings are supported by thermodynamic computations, connecting structure, electronic properties, and catalyst function. Moreover, the study of bare Ta_1,4 ⁺ compounds indicates that methane dehydrogenation is a significant initial step in the direct coupling reaction, enabling new, yet unknown reaction pathways.

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Zeolite chemistry and catalysis are expected to play a decisive role in the next decade(s) to build a more decentralized renewable feedstock-dependent sustainable society owing to the increased scrutiny over carbon emissions. Therefore, the lack of fundamental and mechanistic understanding of these processes is a critical "technical bottleneck" that must be eliminated to maximize economic value and minimize waste. We have identified, considering this objective, that the chemistry related to the first-generation reaction intermediates (i.e., carbocations, radicals, carbenes, ketenes, and carbanions) in zeolite chemistry and catalysis is highly underdeveloped or undervalued compared to other catalysis streams (e.g., homogeneous catalysis). This limitation can often be attributed to the technological restrictions to detect such "short-lived and highly reactive" intermediates at the interface (gas-solid/solid-liquid); however, the recent rise of sophisticated spectroscopic/analytical techniques (including under in situ/operando conditions) and modern data analysis methods collectively compete to unravel the impact of these organic intermediates. This comprehensive review summarizes the state-of-the-art first-generation organic reaction intermediates in zeolite chemistry and catalysis and evaluates their existing challenges and future prospects, to contribute significantly to the "circular carbon economy" initiatives.

High-performance photocatalytic nonoxidative conversion of methane to ethane and hydrogen by heteroatoms-engineered TiO2

Nonoxidative coupling of methane (NOCM) is a highly important process to simultaneously produce multicarbons and hydrogen. Although oxide-based photocatalysis opens opportunities for NOCM at mild condition, it suffers from unsatisfying selectivity and durability, due to overoxidation of CH4 with lattice oxygen. Here, we propose a heteroatom engineering strategy for highly active, selective and durable photocatalytic NOCM. Demonstrated by commonly used TiO2 photocatalyst, construction of Pd-O4 in surface reduces contribution of O sites to valence band, overcoming the limitations. In contrast to state of the art, 94.3% selectivity is achieved for C2H6 production at 0.91 mmol g-1 h-1 along with stoichiometric H2 production, approaching the level of thermocatalysis at relatively mild condition. As a benchmark, apparent quantum efficiency reaches 3.05% at 350 nm. Further elemental doping can elevate durability over 24 h by stabilizing lattice oxygen. This work provides new insights for high-performance photocatalytic NOCM by atomic engineering.

Exploring the slow-light effect of Pt/TiO2-SiO2 inverse opal on photocatalytic nonoxidative coupling of methane

The slow-photon effect of Pt/TiO₂-SiO₂ inverse opal on photocatalytic nonoxidative coupling of methane was explored regarding the cavity size and filming treatment. The ethane production rate was maximized to 72 μmol g^-1 h^-1 on a filmed microarray with a macroporous diameter of 170 nm, demonstrating the significance of enhancing light-matter interaction for methane conversion.

Recent advances in heterogeneous catalysis for the nonoxidative conversion of methane

The direct conversion of methane to high-value chemicals is an attractive process that efficiently uses abundant natural/shale gas to provide an energy supply. The direct conversion of methane to high-value chemicals is an attractive process that efficiently uses abundant natural/shale gas to provide an energy supply. Among all the routes used for methane transformation, nonoxidative conversion of methane is noteworthy owing to its highly economic selectivity to bulk chemicals such as aromatics and olefins. Innovations in catalysts for selective C-H activation and controllable C-C coupling thus play a key role in this process and have been intensively investigated in recent years. In this review, we briefly summarize the recent advances in conventional metal/zeolite catalysts in the nonoxidative coupling of methane to aromatics, as well as the newly emerging single-atom based catalysts for the conversion of methane to olefins. The emphasis is primarily the experimental findings and the theoretical understanding of the active sites and reaction mechanisms. We also present our perspectives on the design of catalysts for C-H activation and C-C coupling of methane, to shed some light on improving the potential industrial applications of the nonoxidative conversion of methane into chemicals.

Versatile and high temperature spectroscopic cell for operando fluorescence and transmission x-ray absorption spectroscopic studies of heterogeneous catalysts

A modular high-temperature cell consisting of a plug-flow microreactor with a fixed catalyst bed and long heating zone has been established for operando x-ray absorption/fluorescence spectroscopic and diffraction studies. The functionality of the cell is demonstrated for two important areas: emission control using 2 wt. % Pd/Al₂O₃ acting as a three-way catalyst and direct conversion of methane to olefins and aromatics on a 0.5% Fe/SiO₂ catalyst. The performance has been determined by online infrared spectroscopy and mass spectrometry, respectively. In addition, the cell can be combined with optical spectroscopy, such as Raman spectroscopy. The catalyst, present as powdered/sieved samples, can be measured under reaction conditions at temperatures of up to 1050 °C. Another key aspect is a long isothermal heating zone with a small temperature gradient (<3 °C/mm at 1000 °C without reaction) including an inert zone for pre-heating of the reactant gas. Due to the small size of the microreactor and the heating system including a water cooling system, heating/cooling rates of up to 100 °C/min can be achieved. Moreover, due to the compact design and the autonomous control system, the high temperature operando setup fits to the space at the majority of synchrotron beamlines. In many cases, the concentration of the element of interest in the catalysts is low requiring x-ray absorption spectroscopy measurements in the fluorescence measurement mode. Hence, the microreactor was designed to fit such needs as well. More specifically, the case of Fe-containing catalysts was particularly considered by using iron-free materials for the reactor housing.

Silica-supported Nb(iii)–CH3 species can act as an efficient catalyst for the non-oxidative coupling of methane

The Nb(iii)–CH₃ catalyst lowers the energetic span of the whole catalytic cycle over its Ta and V analogues.

Carbide Dihydrides: Carbonaceous Species Identified in Ta4 + -Mediated Methane Dehydrogenation

The products of methane dehydrogenation by gas‐phase Ta₄⁺ clusters are structurally characterized using infrared multiple photon dissociation (IRMPD) spectroscopy in conjunction with quantum chemical calculations. The obtained spectra of [4Ta,C,2H]⁺ reveal a dominance of vibrational bands of a H₂Ta₄C⁺ carbide dihydride structure over those indicative for a HTa₄CH⁺ carbyne hydride one, as is unambiguously verified by studies employing various methane isotopologues. Because methane dehydrogenation by metal cations M⁺ typically leads to the formation of either MCH₂⁺ carbene or HMCH⁺ carbyne hydride structures, the observation of a H₂MC⁺ carbide dihydride structure implies that it is imperative to consider this often‐neglected class of carbonaceous intermediates in the reaction of metals with hydrocarbons.

Catalytic Mechanism of Liquid-Metal Indium for Direct Dehydrogenative Conversion of Methane to Higher Hydrocarbons

There is a great interest in direct conversion of methane to valuable chemicals. Recently, we reported that silica-supported liquid-metal indium catalysts (In/SiO2) were effective for direct dehydrogenative conversion of methane to higher hydrocarbons. However, the catalytic mechanism of liquid-metal indium has not been clear. Here, we show the catalytic mechanism of the In/SiO2 catalyst in terms of both experiments and calculations in detail. Kinetic studies clearly show that liquid-metal indium activates a C-H bond of methane and converts methane to ethane. The apparent activation energy of the In/SiO2 catalyst is 170 kJ mol-1, which is much lower than that of SiO2, 365 kJ mol-1. Temperature-programmed reactions in CH4, C2H6, and C2H4 and reactivity of C2H6 for the In/SiO2 catalyst indicate that indium selectively activates methane among hydrocarbons. In addition, density functional theory calculations and first-principles molecular dynamics calculations were performed to evaluate activation free energy for methane activation, its reverse reaction, CH3-CH3 coupling via Langmuir-Hinshelwood (LH) and Eley-Rideal mechanisms, and other side reactions. A qualitative level of interpretation is as follows. CH3-In and H-In species form after the activation of methane. The CH3-In species wander on liquid-metal indium surfaces and couple each other with ethane via the LH mechanism. The solubility of H species into the bulk phase of In is important to enhance the coupling of CH3-In species to C2H6 by decreasing the formation of CH4 though the coupling of CH3-In species and H-In species. Results of isotope experiments by combinations of CD4, CH4, D2, and H2 corresponded to the LH mechanism.

Single-Atom Catalysts across the Periodic Table

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Catalytic Non-Oxidative Coupling of Methane on Ta8O2

Mass-selected Ta₈O₂⁺ cluster ions catalyze the transformation of methane in a gas-phase ion trap experiment via nonoxidative coupling into ethane and H₂, which is a prospective reaction for the generation of valuable chemicals on an industrial scale. Systematic variation of the reaction conditions and the isotopic labeling of methane by deuterium allow for an unambiguous identification of a catalytic cycle. Comparison with the proposed catalytic cycle for tantalum-doped silica catalysts reveals surprising similarities as the mechanism of the C-C coupling step, but also peculiar differences like the mechanism of the eventual formation of molecular hydrogen and ethane. Therefore, this work not only supplies insights into the mechanisms of methane coupling reactions but also illustrates how the study of trapped ionic catalysts can contribute to the understanding of reactions, which are otherwise difficult to study.

Oxidative Methane Conversion to Ethane on Highly Oxidized Pd/CeO2 Catalysts Below 400 °C

Methane upgrading into more valuable chemicals has received much attention. Herein, we report oxidative methane conversion to ethane using gaseous O₂ at low temperatures (<400 °C) and atmospheric pressure in a continuous reactor. A highly oxidized Pd deposited on ceria could produce ethane with a productivity as high as 0.84 mmol g_cat ^-1  h^-1 . The Pd-O-Pd sites, not Pd-O-Ce, were the active sites for the selective ethane production at low temperatures. Density functional theory calculations confirmed that the Pd-O-Pd site is energetically more advantageous for C-C coupling, whereas Pd-O-Ce promotes CH₄ dehydrogenation. The ceria helped Pd maintain a highly oxidic state despite reductive CH₄ flow. This work can provide new insight for methane upgrading into C₂ species.

Evoked Methane Photocatalytic Conversion to C2 Oxygenates over Ceria with Oxygen Vacancy

Direct conversion of methane to its oxygenate derivatives remains highly attractive while challenging owing to the intrinsic chemical inertness of CH4. Photocatalysis arises as a promising green strategy which could stimulate water splitting to produce oxidative radicals for methane C–H activation and subsequent C–C coupling. However, synthesis of a photocatalyst with an appropriate capability of methane oxidation by water remains a challenge using an effective and viable approach. Herein, ceria nanoparticles with abundant oxygen vacancies prepared by calcinating commercial CeO2 powder at high temperatures in argon are reported to capably produce ethanol and aldehyde from CH4 photocatalytic oxidation under ambient conditions. Although high-temperature calcinations lead to lower light adsorptions and increased band gaps to some extent, deficient CeO2 nanoparticles with oxygen vacancies and surface CeIII species are formed, which are crucial for methane photocatalytic conversion. The ceria catalyst as-calcinated at 1100 °C had the highest oxygen vacancy concentration and CeIII content, achieving an ethanol production rate of 11.4 µmol·gcat−1·h−1 with a selectivity of 91.5%. Additional experimental results suggested that the product aldehyde was from the oxidation of ethanol during the photocatalytic conversion of CH4.

Theoretical Study on the C-H Activation of Methane by Liquid Metal Indium: Catalytic Activity of Small Indium Clusters

The mechanism of C-H activation of methane by liquid indium, which is the first step of the dehydrogenative conversion of methane to higher hydrocarbons, was investigated using density functional theory calculations. In the first-principle molecular dynamics trajectory at the experimental temperature (1200 K), low-coordinated indium atoms continuously appear on the disordered liquid surface. The C-H cleavage is endothermic on clean surfaces, while the low-coordinated indium atoms reduce the endothermicity significantly. In small indium clusters, which are models of low-coordinated atoms on a surface, the calculated activation energy is much smaller than that on the clean surface. The energy level of the methane C-H σ* orbital is reduced by the interaction with the indium 5pσ orbitals. In₂ shows the lowest activation energy and exothermicity in the C-H bond cleavage.

The Comparison between Single Atom Catalysis and Surface Organometallic Catalysis

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.

Thermal C–O coupling reactions of Ta methylene clusters [TanCH2]+ (n = 1, 4) with O2

Cationic tantalum carbenes [TaCH₂]⁺ and [Ta₄CH₂]⁺, products of methane dehydrogenation, are reacted with dioxygen in an ion trap. Detected products suggest a formation of value-added molecules originating from C–O coupling reactions.

A review of plasma-assisted catalytic conversion of gaseous carbon dioxide and methane into value-added platform chemicals and fuels

CO2 and CH4 contribute to greenhouse gas emissions, while the production of industrial base chemicals from natural gas resources is emerging as well. Such conversion processes, however, are energy-intensive and introducing a renewable and sustainable electric activation seems optimal, at least for intermediate-scale modular operation. The review thus analyses such valorisation by plasma reactor technologies and heterogeneous catalysis application, largely into higher hydrocarbon molecules, that is ethane, ethylene, acetylene, propane, etc., and organic oxygenated compounds, i.e. methanol, formaldehyde, formic acid and dimethyl ether. Focus is given to reaction pathway mechanisms, related to the partial oxidation steps of CH4 with O2, H2O and CO2, CO2 reduction with H2, CH4 or other paraffin species, and to a lesser extent, to mixtures' dry reforming to syngas. Dielectric barrier discharge, corona, spark and gliding arc sources are considered, combined with (noble) metal materials. Carbon (C), silica (SiO2) and alumina (Al2O3) as well as various catalytic supports are examined as precious critical raw materials (e.g. platinum, palladium and rhodium) or transition metal (e.g. manganese, iron, cobalt, nickel and copper) substrates. These are applied for turnover, such as that pertinent to reformer, (reverse) water-gas shift (WGS or RWGS) and CH3OH synthesis. Time-on-stream catalyst deactivation or reactivation is also overviewed from the viewpoint of individual transient moieties and their adsorption or desorption characteristics, as well as reactivity.

Single-atom catalysis: a new field that learns from tradition

Much of industrial chemical processing (in the petrochemicals industry, for example), and a great deal of laboratory chemical synthesis, involves catalysts that both lower the energy barrier to reaction and may help steer a reaction along a particular path. Traditionally, catalysts have come in two classes: heterogeneous, typically meaning that the catalyst is an extended solid; and homogeneous, where the catalyst is a small molecule that shares a solvent with the reactants. In heterogeneous catalysis, the reaction generally takes place on a surface, involving molecules attached there by covalent bonds. Homogeneous catalysts are often organometallic compounds, in which a metal atom or small cluster of atoms supplies the active site for reaction.

 In recent years, these distinctions have become somewhat blurred thanks to the advent of single-atom catalysis, where the catalytic site consists of a single atom (as in many homogeneous catalysts) attached to or embedded in a surface. The emergence of this field might be regarded as the logical conclusion of the use of ‘supported metal clusters’—small metal particles of nanometer scale and below, containing perhaps hundreds, tens or just a few atoms. It has became clear that such clusters can sometimes provide greater product selectivity and activity than macro-sized particles or powders of the same metal, partly because the active sites might be atoms at particular locations (such as edges and corners) in the nanoscale particles. By reducing their scale down to the level of single atoms, one can optimize these properties. At the same time, the potential uniformity of the atoms’ environments makes such catalysts more amenable to rational design and modeling to understand mechanism.

 This field represents an appealing blend of fundamental chemistry and physics—from the quantum-mechanical level upwards—and applied research aimed at producing many of the products vital to society, such as fuels and materials. Researchers in China have been strongly active in this field in recent years (see, for example, refs [1–5]). Jean Marie Basset of the King Abdullah University of Science and Technology in Thuwal, Saudi Arabia, is one of the leading practitioners in the area, and National Science Review spoke to him about the development and prospects of the field.

Room temperature olefination of methane with titanium-carbon multiple bonds

C–H activation of methane followed by dehydrocoupling at room temperature led ultimately to the formation of the olefin H₂C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH^tBu via the addition of redox-active ligands (L) such as thioxanthone or 2,2′-bipyridine (bipy) to (PNP)Ti Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH^tBu(CH₃) (1).

C–H activation of methane followed by dehydrocoupling at room temperature led ultimately to the formation of the olefin H₂C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH^tBu via the addition of redox-active ligands (L) such as thioxanthone or 2,2′-bipyridine (bipy) to (PNP)Ti Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH^tBu(CH₃) (1). Using both of these exogenous ligand systems, we could trap the titanium fragment via an insertion reaction with these two substrates to afford species of the type (PNP)Ti(L)(LH). A combination of computational and isotopic labeling studies reveals that the L ligand promotes the C–C bond forming step by migration of the methyl moiety in 1 to the α-alkylidene carbon by producing a Ti(iii) species (PNP)Ti{CH(CH₃)^tBu}(L). In the case of L = thioxanthone, β-hydrogen abstraction gives an olefin, whereas with 2,2′-bipyridine β-hydride elimination and migratory insertion lead to (PNP)Ti(L)(LH). These redox-active ligands play two important roles: (i) they accept an electron from the Ti-alkylidene fragment to allow the methyl to approach the alkylidene and (ii) they serve as traps of a hydrogen atom resulting from olefin elimination. These systems represent the first homogeneous models that can activate methane and selectively dehydrocouple it with a carbene to produce an olefin at room temperature.

Surface organometallic chemistry in heterogeneous catalysis

Surface organometallic chemistry has been reviewed with a special focus on environmentally relevant transformations (C–H activation, CO₂conversion, oxidation).