Organometallic Reaction Mechanisms Research Articles

Automated approaches, reaction parameterisation, and data science in organometallic chemistry and catalysis: towards improving synthetic chemistry and accelerating mechanistic understanding

This review discusses the use of automation for organometallic reactions to generate rich datasets and, with statistical analysis and reaction component parameterisation, how organometallic reaction mechanisms can be probed to gain understanding.

Elucidation of Organometallic Reaction Mechanisms by a China–Germany Team

AbstractThis invited Team Profile was created by Jiaxiang Chu at the University of Chinese Academy of Sciences (China) and Dominik Munz at Saarland University (Germany). They recently reported isocyanide homologation mediated by aluminium(I) as a Fischer–Tropsch model reaction. Up to five molecules were coupled, and the step‐by‐step mechanism was elucidated. Combined mechanistic/computational work provided evidence that carbenes are the key intermediates during this process. “Evidence for Carbene Intermediates in Isocyanide Homologation by Aluminium(I)”, C. J. Zhang, F. Dankert, Z. A. Jiang, B. L. Wang, D. Munz, J. X. Chu, Angew. Chem. Int. Ed. 2023, 62, e202307352.

Elucidation of Organometallic Reaction Mechanisms by a China-Germany Team.

This invited Team Profile was created by Jiaxiang Chu at the University of Chinese Academy of Sciences (China) and Dominik Munz at Saarland University (Germany). They recently reported isocyanide homologation mediated by aluminium(I) as a Fischer-Tropsch model reaction. Up to five molecules were coupled, and the step-by-step mechanism was elucidated. Combined mechanistic/computational work provided evidence that carbenes are the key intermediates during this process. "Evidence for Carbene Intermediates in Isocyanide Homologation by Aluminium(I)", C. J. Zhang, F. Dankert, Z. A. Jiang, B. L. Wang, D. Munz, J. X. Chu, Angew. Chem. Int. Ed. 2023, 62, e202307352.

William H. Nichols Medal to Karen Goldberg

The 2023 William H. Nichols Medal has been awarded to Karen I. Goldberg , the Vagelos Professor of Energy Research at the University of Pennsylvania. This award is presented by the American Chemical Society New York Local Section for outstanding contributions in the field of chemistry. Goldberg is recognized for her leading work in organometallic reaction mechanisms. She received her medal during the William H. Nichols Symposium and Awards Ceremony on April 14. The ceremony was preceded by a symposium titled “Catalysis for a Sustainable Future,” which featured presentations from Goldberg, Melanie Sanford from the University of Michigan, Rachel Narehood Austin from Barnard College, William Jones from the University of Rochester, and Alan Goldman from Rutgers University.

A Look at Real‐World Transition‐Metal Thermochemistry and Kinetics with Local Hybrid Functionals

AbstractLocal hybrid functionals (LHs) use a position‐dependent admixture of exact exchange in real space, which has previously been shown to offer various advantages over global hybrids and the potential to construct functionals with wide applicability. While main‐group thermochemistry and kinetics and other properties have already been studied extensively, no broad and systematic investigation for the energetics of transition‐metal complexes has been reported so far for LHs. To close this gap, we evaluate eight LHs for three previously reported test sets on barrier heights and reaction energies of real‐world transition metal complexes, in comparison with several other rung‐4 hybrid functionals. The recent LH20t‐D4 method emerges as the top‐performing functional for the overall benchmark, comparable to the simpler TPSS0‐D4 and slightly before the more complex range‐separated ωB97M‐V. But LH20t‐D4 and ωB97M‐V perform much better for main‐group energetics, making them overall more reliable tools to study organometallic reaction mechanisms. Given also its previously observed excellent performance for mixed‐valence systems, LH20t‐D4 is thus a widely applicable functional in both main‐group and transition‐metal chemistry, while also providing convincing accuracy for many spectroscopic properties. The earlier LH14t‐calPBE‐D4 local hybrid also performs well, while some first‐generation LHs fall behind.

Quasiclassical Direct Dynamics Trajectory Simulations of Organometallic Reactions.

Homogeneous metal-mediated organometallic reactions represent a very large and diverse reaction class. Density functional theory calculations are now routinely carried out and reported for analyzing organometallic mechanisms and reaction pathways. While density functional theory calculations are extremely powerful to understand the energy and structure of organometallic reactions, there are several assumptions in their use and interpretation to define reaction mechanisms and to analyze reaction selectivity. Almost always it is assumed that potential energy structures calculated with density functional theory adequately describe mechanisms and selectivity within the framework of statistical theories, for example, transition state theory and RRKM theory. However, these static structures and corresponding energy landscapes do not provide atomic motion information during reactions that could reveal nonstatistical intermediates without complete intramolecular vibrational redistribution and nonintrinsic reaction coordinate (non-IRC) pathways. While nonstatistical intermediates and non-IRC reaction pathways are now relatively well established for organic reactions, these dynamic effects have heretofore been highly underexplored in organometallic reactions. Through a series of quasiclassical density functional theory direct dynamics trajectory studies, my group has recently demonstrated that dynamic effects occur in a variety of fundamental organometallic reactions, especially bond activation reactions. For example, in the C-H activation reaction between methane and [Cp*(PMe3)IrIII(CH3)]+, while the density functional theory energy landscape showed a two-step oxidative cleavage and reductive coupling mechanism, trajectories revealed a mixture of this two-step mechanism and a dynamic one-step mechanism that skipped the [Cp*(PMe3)IrV(H)(CH3)2]+ intermediate. This study also showed that despite a methane σ-complex being located on the density functional theory surface before oxidative cleavage and after reductive coupling, this intermediate is always skipped and should not be considered an intermediate during reactive trajectories. For non-IRC reaction pathways, quasiclassical direct dynamics trajectories showed that for the isomerization of [Tp(NO)(PMe3)W(η2-benzene)] to [Tp(NO)(PMe3)W(H)(Ph)], there are many dynamic reaction pathway connections due to a relatively flat energy landscape and π coordination is not necessary for C-H bond activation through oxidative cleavage. Trajectories also showed that dynamic effects are important in selectivity for ethylene C-H activation versus π coordination in reaction with Cp(PMe3)2Re, and trajectories provide a more quantitative model of selectivity than transition state theory. Quasiclassical trajectories examining Au-catalyzed monoallylic diol cyclizations showed dynamic coupling of several reaction steps that include alkoxylation π bond addition, proton shuttling, and water elimination reaction steps. Overall, these studies highlight the need to use direct dynamics trajectory simulations to consider atomic motion during reactions to understand organometallic reaction mechanisms and selectivity.

Unveiling the full reaction path of the Suzuki-Miyaura cross-coupling in a single-molecule junction.

Conventional analytic techniques that measure ensemble averages and static disorder provide essential knowledge of the reaction mechanisms of organic and organometallic reactions. However, single-molecule junctions enable the in situ, label-free and non-destructive sensing of molecular reaction processes at the single-event level with an excellent temporal resolution. Here we deciphered the mechanism of Pd-catalysed Suzuki-Miyaura coupling by means of a high-resolution single-molecule platform. Through molecular engineering, we covalently integrated a single molecule Pd catalyst into nanogapped graphene point electrodes. We detected sequential electrical signals that originated from oxidative addition/ligand exchange, pretransmetallation, transmetallation and reductive elimination in a periodic pattern. Our analysis shows that the transmetallation is the rate-determining step of the catalytic cycle and clarifies the controversial transmetallation mechanism. Furthermore, we determined the kinetic and thermodynamic constants of each elementary step and the overall catalytic timescale of this Suzuki-Miyaura coupling. Our work establishes the single-molecule platform as a detection technology for catalytic organochemistry that can monitor transition-metal-catalysed reactions in real time.

Relationship Between Energy Landscape Shape and Dynamics Trajectory Outcomes for Methane C–H Activation by Cationic Cp*(PMe3)Ir/Rh/Co(CH3)

Density functional theory (DFT) calculations are routinely used to determine organometallic reaction mechanisms. However, these calculations only represent an average structure and lack mechanistic...

New insights into the dihydrogen bonds (MHδ−···Hδ+X) in CpM(PMe3)(L)2H···HX (M=Cr, Mo, W; L=PMe3, CO; X=F, OH, NH2)

Dihydrogen bonds (DHBs) play a fundamental role in catalytic processes, organometallic reaction mechanisms, and potential hydrogen storage materials. In this work, we analyzed the interactions of transition metal (TM) hydrides CpM(PMe3)(L)2H (M=Cr, Mo, W; L=PMe3, CO) with poor, moderate, and strong proton donors HX (NH3, H2O, and HF), and focus on the DHBs in these complexes. All important factors that can affect the DHBs have been considered: transition metal, proton donor, and substituent group. Electrostatic potential (ESP) analysis, topological (atoms in molecules) analysis and noncovalent interactions index (NCI) analysis of the electron density, energy decomposition analysis (EDA) and the effect of electric field were applied to better understand the nature of the DHBs (MHδ−···Hδ+X) in CpM(PMe3)(L)2H···HX (M=Cr, Mo, W; L=PMe3, CO; X=F, OH, NH2). The calculated results showed that both the MHδ−···Hδ+X bonds and M···Hδ+X bonds can form in CpM(PMe3)(L)2H···HX complexes. Electron-rich 5d metal (W in this case) hydrides have a greater chance of forming M···Hδ+X bonds rather than MHδ−···Hδ+X bonds. Cr is more likely to form DHBs than Mo and W. This is a very inspiring finding because this may indicate that the first-row transition metal, which shows low cost, low toxicity, and exceptional synthetic versatility, is more suitable for catalytic hydrogenation. The type of proton donor and the substituting of PMe3 by CO can alter the strength of DHBs. The stronger proton donor involves the stronger DHBs form. The substitution of CO decreases the strength of the dihydrogen bond. Both the electrostatic interaction and the orbital interaction play important roles in DHBs, R (Hδ−···Hδ+) = 1.6 A seems to be the boundary between these two kinds of interactions. The addition of electric field is conducive to H2 formation for strong DHB complexes, while it has no effect on the weak DHB complexes.

Hard X-ray spectroscopy: an exhaustive toolbox for mechanistic studies (?).

Established and recent hard X-ray spectroscopic methods in the form of conventional X-ray absorption near edge structure spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS), and the photon-in/photon-out techniques high energy resolution fluorescence detection XANES and valence-to-core X-ray emission spectroscopy (VtC-XES) provide unique opportunities to study mechanisms in metal-organic reactions. The combination of these techniques allows the determination of the local geometric and electronic structures in the form of the numbers of nearest neighbours, their types and distances around an X-ray absorbing atom and the highest occupied and lowest unoccupied molecular levels. Different sample cells for this purpose, which allow high pressure, electrochemical or multi-spectroscopic measurements under inert conditions, are presented and discussed. The potential of HERFD-XANES and VtC-XES to eliminate limitations of conventional EXAFS spectroscopy is established with case studies on the Hieber anion [Fe(CO)3(NO)]- and the iron hydride complex [Fe(CO)H(NO)(PPh3)2]. With VtC-XES the formation of an allyl complex by reaction of [Fe(CO)3(NO)]- in a catalytic nucleophilic substitution reaction can be followed. Combination of HERFD-XANES and VtC-XES allows the identification and investigation of hydride species, as well as their fate in chemical reactions. On the other hand, in order to investigate the active species formation in iron-catalysed cross coupling reactions, conventional XANES and EXAFS are the method of choice for the moment. For all examples, the advantages and limitations of the hard X-ray toolbox are commented on and the value of the individual methods are compared.

Dynamical Mechanism May Avoid High-Oxidation State Ir(V)-H Intermediate and Coordination Complex in Alkane and Arene C-H Activation by Cationic Ir(III) Phosphine.

Organometallic reaction mechanisms are assumed to be appropriately described by minimum energy pathways mapped out by density functional theory calculations. For the two-step oxidative addition/reductive elimination mechanism for C-H activation of methane and benzene by cationic Cp*(PMe3)IrIII(CH3), we report quasiclassical direct dynamics simulations that demonstrate the IrV-H intermediate is bypassed in a significant amount of productive trajectories initiated from vibrationally averaged velocity distributions of oxidative addition transition states. This organometallic dynamical mechanism is akin to the σ-bond metathesis pathway but occurs on the oxidative addition/reductive elimination energy surface and blurs the line between two- and one-step mechanisms. Quasiclassical trajectories also reveal that the momentum of crossing the reductive elimination structure always induces complete alkane and arene dissociation from the Ir metal center, skipping weak C-H σ and π coordination complexes. This suggests that these weak coordination complexes after reductive elimination are not necessarily on the reaction pathway and likely result from a solvent cage.

Gabor A. Somorjai Award for Creative Research in Catalysis: John E. Bercaw

NATIONAL AWARDS Gabor A. Somorjai Award for Creative Research in Catalysis: John E. Bercaw ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2017, 95 (1), pp 36–50January 2, 2017Cite this:C&EN 95, 1, 36-50John E. Bercaw (Credit: Bob Paz )Figure1of1Sponsor: Gabor A. & Judith K. Somorjai Endowment Fund Citation: For the elucidation of detailed mechanisms of organometallic reactions that comprise catalytic cycles. Current position: Centennial Professor Emeritus of Chemistry, California Institute of Technology Education: B.S., chemistry, North Carolina State University; Ph.D., chemistry, University of Michigan, Ann Arbor Bercaw on his scientific role model: “Harry Gray is one of my scientific role models. In addition to watching with amazement his scientific accomplishments, I have marveled at his enthusiasm, modesty, generosity, and love of interacting with students. He is truly a great man.” What his colleagues say: “Bercaw has made path-breaking contributions to developing and elucidating new homogenous catalytic reactions. His fundamental work in olefin polymerization catalysis and catalytic alkane oxidation is without equal.”—Maurice Brookhart, University of North Carolina, Chapel Hill

“Understanding Organometallic Reaction Mechanisms and Catalysis: Computational and Experimental Tools”

“Understanding Organometallic Reaction Mechanisms and Catalysis: Computational and Experimental Tools”

Understanding Organometallic Reaction Mechanisms and Catalysis: Computational and Experimental Tools. Edited by Valentin P. Ananikov

<b>Understanding Organometallic Reaction Mechanisms and Catalysis: Computational and Experimental Tools</b>. Edited by Valentin P. Ananikov

Reactivity of organometallic compounds and polarizability effect

An elucidation of the factors determining the magnitude of the rate constants, k, is of primary importance in understanding organometallic reactivity. Nevertheless, the influence of substituents bound to the reaction centre on the k is poorly understood. In this work, the literature data on substituent influence on the log k values of reactions involving derivatives of Groups 5–10, 12–14, 16 elements (there are 25 series, in each of them the reaction centre being fixed, and the substituents varying in properties) have been analyzed, using the correlation analysis. Generally not only classic inductive, resonance, and steric effects, as well as the polarizability one have been first established to operate. The presence or absence of certain effects are dictated by the type of series. The polarizability effect is caused by a partial charge appearing on the reaction centre of the activated complex. The contribution of this effect ranges up to 50%. A knowledge of the substituent effects may give a better insight into organometallic reaction mechanisms.

Synthesis and Migratory-Insertion Reactivity of CpMo(CO)3(CH3): Small-Scale Organometallic Preparations Utilizing Modern Glovebox Techniques

Experiments are described for the reliable small-scale glovebox preparation of CpMo(CO)3(CH3) and acetyl derivatives thereof through phosphine-induced migratory insertion. The robust syntheses introduce students to a variety of organometallic reaction mechanisms and glovebox techniques, and they are easily carried out during three laboratory meetings. Furthermore, the series of complexes offers several interesting case studies for symmetry analysis of IR and NMR spectra.

Heterogeneous Catalysis: The Horiuti–Polanyi Mechanism and Alkene Hydrogenation

The hydrogenation of alkenes by heterogeneous catalysts has been studied for 80 years. The foundational mechanism was proposed by Horiuti and Polanyi in 1934 and consists of three steps: (i) alkene adsorption on the surface of the hydrogenated metal catalyst, (ii) hydrogen migration to the β-carbon of the alkene with formation of a σ-bond between the metal and α-C, and finally (iii) reductive elimination of the free alkane. Hundreds of papers have appeared on the topic, along with a number of variations on the Horiuti–Polanyi mechanism. The second step is highly reversible, leading to extensive deuterium–hydrogen exchange when D2(g) is used. This paper describes the investigation of gas-phase reactions between deuterium and 1-butene using a supported palladium catalyst under ambient laboratory conditions and how the results are consistent with the Horiuti–Polanyi mechanism. An Excel spreadsheet for modeling the extent and distribution of deuteration within butane-dx is described. Interested readers could develop a laboratory or research experience based on results presented here. The results are also suitable for inclusion in an upper-division chemistry course in which organometallic chemistry or reaction mechanisms involving heterogeneous catalysts are discussed. The catalyst tubes are inexpensive and easy to construct. Analysis of the butane produced by 1H NMR and GC–MS leads to numerous conclusions in support of the Horiuti–Polanyi mechanism.

Defragmenting Catalysis

Defragmenting Catalysis

Kinetic Isotope Effects in the Study of Organometallic Reaction Mechanisms

Kinetic Isotope Effects in the Study of Organometallic Reaction Mechanisms

ChemInform Abstract: Theoretical Treatment of Organometallic Reaction Mechanisms and Catalysis

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