Computational Studies Of Alkane C H Functionalization By Main Group Metals

The most efficient homogeneous catalysts for hydroxylation of light alkanes utilize transition metals in superacid solvent and operate by tandem electrophilic C–H activation/metal–alkyl (M–R) functionalization. An emerging alternative strategy to transition metals is the use of high-oxidation state main-group metals (e.g. TlIII, PbIV, IIII) that hydroxylate light alkanes. This dissertation reports density-functional theory calculations that reveal the mechanisms, reactivity, and selectivity of TlIII promoted alkane C–H functionalization in trifluoroacetic acid and TlIII–dialkyl functionalization in water. Calculations reveal that TlIII oxidizes alkanes via a closed-shell C–H activation and M–R functionalization mechanism that is similar to transition-metal C–H functionalization mechanisms. Comparison of TlIII to similar transition metals reveals that while TlIII and transition metals can have similar activation barriers for C–H activation, TlIII M–R functionalization is significantly faster due to a highly polar Tl–C bond and large TlIII/TlI reduction potential. The combination of a moderate C–H activation barrier combined with a low M–R functionalization barrier is critical to the success for TlIII promoted alkane C–H oxidation. The proposed TlIII C–H activation/M–R functionalization mechanism also provides an explanation for ethane conversion to a mixture of ethyl trifluoroacetate and ethane-1,2-diyl bis(2,2,2-trifluoroacetate). The reactivity of TlIII contrasts the lack of alkane oxidation by HgII. The C–H activation transition state and frontier-orbital interactions provide a straightforward explanation for the higher reactivity of TlIII versus HgII. This frontier-orbital model also provides a rationale for why the electron-withdrawing group in EtTFA provides “protection” against overoxidation. Calculations also reveal that TlIII–dialkyl functionalization by inorganic TlIII in water occurs by alkyl group transfer to form a TlIII–monoalkyl complex that is rapidly functionalized.

In Chapter 3, DFT calculations reveal that arene C-H functionalization by the p-block main-group metal complex TlIII(TFA)3 (TFA = trifluoroacetate) occurs by a C-H activation mechanism akin to transition metal-mediated C-H activation. For benzene, toluene, and xylenes a one-step C-H activation is preferred over electron transfer or proton-coupled electron transfer. The proposed C-H activation mechanism is consistent with calculation and comparison to experiment, of arene thallation rates, regioselectivity, and H/D kinetic isotope effects. For trimethyl and tetramethyl substituted arenes, electron transfer becomes the preferred pathway and thermodynamic and kinetic calculations correctly predict the experimentally reported electron transfer crossover region.

Over the past decade, much research effort has been devoted to the design and synthesis of new reagents and catalysts that can influence carbon-hydrogen bond activation, mainly because of the prospect that C−H activation could enable the conversion of cheap and abundant alkanes into valuable functionalized organic compounds. Alkane C-H Activation by Single-Site Metal Catalysis presents the current state-of-the-art development in the catalytic systems for the catalytic trans-formations of alkanes under homogeneous conditions. Chapter 1 offers a comprehensive summary of the main discoveries realized so far. Chapter 2 reviews the so-called electrophilic activation, initiated by Shulpín in the late 60s, and the base for the Catalytica system. Chapter 3 examines the catalytic borylation of alkanes, discovered by Hartwig, whereas chapter 4 provides an updated vision of the alkane dehydrogenation reaction. Chapter 5 covers the oxygenation of C-H bonds, a field of enormous interest with bioinorganic im-plications, and finally chapter 6 presents the functionalization of alkane C-H bonds by carbene or nitrene insertion. The history of C-H bond activation, and the current research described in this book, highlight the current research and present the reader with an outlook of this field which continues to be explored by an increasingly visionary and enthusiastic group of organic, organometallic, biological and physical chemists.

This thesis presents detailed mechanistic studies on a series of important C-H activation reactions using combined computational methods and mass spectrometry experiments. It also provides guidance on the design and improvement of catalysts and ligands. The reactions investigated include: (i) a nitrile-containing template-assisted meta-selective C-H activation, (ii) Pd/mono-N-protected amino acid (MPAA) catalyzed meta-selective C-H activation, (iii) Pd/MPAA catalyzed asymmetric C-H activation reactions, and (iv) Cu-catalyzed sp3 C-H cross-dehydrogenative-coupling reaction. The book reports on a novel dimeric Pd-M (M = Pd or Ag) model for reaction (i), which successfully explains the meta-selectivity observed experimentally. For reaction (ii), with a combined DFT/MS method, the author successfully reveals the roles of MPAA ligands and a new C-H activation mechanism, which accounts for the improved reactivity and high meta-selectivity and opens new avenues for ligand design. She subsequently applies ion-mobility mass spectrometry to capture and separate the [Pd(MPAA)(substrate)] complex at different stages for the first time, providing support for the internal-base model for reaction (iii). Employing DFT studies, she then establishes a chirality relay model that can be widely applied to MPAA-assisted asymmetric C-H activation reactions. Lastly, for reaction (iv) the author conducts detailed computational studies on several plausible pathways for Cu/O2 and Cu/TBHP systems and finds a reliable method for calculating the single electron transfer (SET) process on the basis of benchmark studies.

Presents state-of-the-art information concerning the syntheses of valuable functionalized organic compounds from alkanes, with a focus on simple, mild, and green catalytic processes Alkane Functionalization offers a comprehensive review of the state-of-the-art of catalytic functionalization of alkanes under mild and green conditions. Written by a team of leading experts on the topic, the book examines the latest research developments in the synthesis of valuable functionalized organic compounds from alkanes. The authors describe the various modes of interaction of alkanes with metal centres and examine theoxidative alkane functionalization upon C-O bond formation. They address the many types of mechanisms, discuss typical catalytic systems and highlight the strategies inspired by biological catalytic systems. The book also describes alkane functionalization upon C-heteroatom bond formation as well as oxidative and non-oxidative approaches. In addition, the book explores non-transition metal catalysts and metal-free catalytic systems and presents selected types of functionalization of sp3 C-H bonds pertaining to substrates other than alkanes. This important resource: Presents a guide to the most recent advances concerning the syntheses of valuable functionalized organic compounds from alkanes Contains information from leading experts on the topic Offers information on the catalytic functionalization of alkanes that allows for improved simplicity and sustainability compared to current multi-stage industrial processes Explores the challenges inherent with the application of alkanes as starting materials for syntheses of added value functionalized organic compounds Written for academic researchers and industrial scientists working in the fields of coordination chemistry, organometallic chemistry, catalysis, organic synthesis and green chemistry, Alkane Functionalization is an important resource for accessing the most up-to-date information available in the field of catalytic functionalization of alkanes.

The series Structure and Bonding publishes critical Reviews on Topics of Research concerned with chemical structure and bonding. The scope of the series spans the entire Periodic Table and addresses structure and bonding issues associated with all of the elements. It also focuses attention on new and developing areas of modern structural and theoretical chemistry such as nanostructures, molecular electronics, designed molecular solids, surfaces, metal clusters and supramolecular structures. Physical and spectroscopic techniques used to determine, examine and model structures fall within the purview of Structure and Bonding to the extent that the focus is on the scientific results obtained and not on specialist information concerning the techniques themselves. Issues associated with the development of bonding models and generalizations that illuminate the reactivity pathways and rates of chemical processes are also relevant. The individual volumes in the series are thematic. The goal of each volume is to give the reader, whether at a university or in industry, a comprehensive overview of an area where new insights are emerging that are of interest to a larger scientific audience. Thus each review within the volume critically surveys one aspect of that topic and places it within the context of the volume as a whole. The most significant developments of the last 5 to 10 years should be presented using selected examples to illustrate the principles discussed. A description of the physical basis of the experimental techniques that have been used to provide the primary data may also be appropriate, if it has not been covered in detail elsewhere. The coverage need not be exhaustive in data, but should rather be conceptual, concentrating on the new principles being developed that will allow the reader, who is not a specialist in the area covered, to understand the data presented. Discussion of possible future research directions in the area is welcomed.

This book offers a comprehensive overview of recent theoretical studies on rhodium-catalyzed C-H functionalization, a topic that has attracted considerable attention over the years. It includes a brief experimental history, elementary reactions, and theoretical perspectives and describes in detail recent advanced computational studies on different types of Rh-catalyzed C-H functionalization, the underlying mechanisms, and the origin of regioselectivity in a series of such reactions. Providing examples shows readers how to use theoretical tools to solve problems related to mechanisms of organometallic reactions. As such, the book is an interesting and useful resource for a wide readership in various fields involving synthetic organic, organometallic, and catalysis reactions.

Activation and Functionalization of C-H Bonds explores recent developments in the reaction chemistry of solution-phase transition-metal based systems with simple hydrocarbons and with more complex organic molecules. More than 20 internationally leading research groups contributed to this volume, and their chapters cover such topics as fundamental theoretical and mechanistic studies of C-H bond activation by metal complexes, catalytic systems for alkane functionalization, and new applications in synthetic organic chemistry. An introductory chapter offers an overview of stoichiometric and catalytic reactions of C-H bonds with transition metal complexes. The C-H bond is the most widespread linkage in organic chemistry, present in virtually every organic molecule. Unfortunately, C-H bonds are famously resistant to selective chemical transformations. The development of methods for their selective transformations has enormous potential value in fields ranging from the chemistry of fuels (for example, the conversion of methane to methanol) to the synthesis of the most complex organic molecules.

Provides, in one handbook, comprehensive coverage of one of the hottest topics in stereoselective chemistry Written by leading international authors in the field, this book introduces readers to C-H activation in asymmetric synthesis along with all of its facets. It presents stereoselective C-H functionalization with a broad coverage, from outer-sphere to inner-sphere C-H bond activation, and from the control of olefin geometry to the induction of point, planar and axial chirality. Moreover, methods wherein asymmetry is introduced either during the C-H activation or in a different elementary step are discussed. Presented in two parts?asymmetric activation of C(sp3)-H bonds and stereoselective synthesis implying activation of C(sp2)-H bonds?CH-Activation for Asymmetric Synthesis showcases the diversity of stereogenic elements, which can now be constructed by C-H activation methods. Chapters in Part 1 cover: C(sp3)-H bond insertion by metal carbenoids and nitrenoids; stereoselective C-C bond and C-N bond forming reactions through C(sp3)?H bond insertion of metal nitrenoids; enantioselective intra- and intermolecular couplings; and more. Part 2 looks at: C-H activation involved in stereodiscriminant step; planar chirality; diastereoselective formation of alkenes through C(sp2)?H bond activation; amongst other methods. -Covers one of the most rapidly developing fields in organic synthesis and catalysis -Clearly structured in two parts (activation of sp3- and activation of sp2-H bonds) -Edited by two leading experts in C-H activation in asymmetric synthesis CH-Activation for Asymmetric Synthesis will be of high interest to chemists in academia, as well as those in the pharmaceutical and agrochemical industry.