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Understanding Organometallic Reaction Mechanisms and Catalysis Experimental and Computational Tools

  • Erscheinungsdatum: 29.08.2014
  • Verlag: Wiley-VCH
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Understanding Organometallic Reaction Mechanisms and Catalysis Experimental and Computational Tools

This handbook and ready reference highlights the latest insights and developments in the studies of important organometallic, homogeneous, and heterogeneous reaction mechanisms. It adopts a unique approach, exemplifying how to use experiments, spectroscopic investigations, and computational methods to reveal reaction pathways and molecular structures of catalysts, rather than concentrating solely on one discipline. The result is a deeper understanding of the underlying reaction mechanisms and correlation between molecular structure and reactivity. The contributions represent a wealth of first-hand information from renowned experts working in all major disciplines, covering such topics as activation of small molecules, palladium catalysis, cross-coupling reactions, and nanoparticle synthesis. With the knowledge gained, the reader will be able to improve existing reaction protocols and rationally design more efficient catalysts or selective reactions. An indispensable source of information for synthetic, analytical, and theoretical chemists in academia and industry alike. Valentin Ananikov received his PhD degree in 1999 and his Habilitation in 2003. He was appointed as Professor and Head of the Laboratory of Transition-Metal and Nanoparticle Catalysis at the Zelinsky Institute of Organic Chemistry (Moscow, Russia) in 2005. In 2008 he was elected as a Member of Russian Academy of Sciences. He was a recipient of the Russian State Prize for Outstanding Achievements in Science and Technology (2004), the Science Support Foundation Award (2005), Medal of the Russian Academy of Sciences (2000), Balandin Prize for outstanding achievements in the field of catalysis (2010), and was awarded Liebig Lecturer by the German Chemical Society in 2010. His research has been supported by grants from the President of Russia (2004, 2007, 2011). He is a member of the International Advisory Boards of Organometallics (ACS Publications) and Chemistry - An Asian Journal (WILEY), and Deputy Editor of Russian Chemical Reviews. His scientific interests are focused on transition metal-catalyzed reactions, development of new structural methods, mechanistic studies of catalytic reactions, and theoretical studies of reaction mechanisms.

Produktinformationen

    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 420
    Erscheinungsdatum: 29.08.2014
    Sprache: Englisch
    ISBN: 9783527678228
    Verlag: Wiley-VCH
    Größe: 15506 kBytes
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Understanding Organometallic Reaction Mechanisms and Catalysis Experimental and Computational Tools

Chapter 1
Mechanisms of Metal-Mediated C–N Coupling Processes: A Synergistic Relationship between Gas-Phase Experiments and Computational Chemistry

Robert Kretschmer, Maria Schlangen, and Helmut Schwarz
1.1 Introduction

As a consequence of the key positions that the elements carbon and nitrogen occupy in nature, C–N bond formation constitutes an important issue in the synthesis of various products ranging from chemical feedstocks to pharmaceuticals. Not surprisingly, over the last few decades, intensive research has been devoted to this timely topic [1], and the use of ammonia as a relatively inexpensive reagent for C–N coupling reactions has been found to be highly desirable [2]. However, despite the impressive progress reported on the development of new synthetic methodologies, there exists a lack of information on the precise, atomistic-level derived mechanisms in particular for the metal-mediated formation of nitrogen-containing organic molecules generated directly from ammonia. One way to gain such insight is to perform gas-phase experiments on "isolated" reactants. These studies provide an ideal arena for probing experimentally the energetics and kinetics of a chemical reaction in an unperturbed environment at a strictly molecular level without being obscured by difficult-to-control or poorly defined solvation, aggregation, counterion, and other effects. Thus, an opportunity is provided to reveal the intrinsic feature(s) of a catalyst, to explore directly the concept of single-site catalysts, or to probe in detail how mechanisms are affected by factors such as cluster size, different ligands, dimensionality, stoichiometry, oxidation state, degree of coordinative saturation, and charge state. In short, from these experiments, one may learn what determines the outcome of a chemical transformation [3]. In addition, thermochemical and kinetic data derived from these experiments provide a means to benchmark the quality of theoretical studies.

While the study of "naked" gas-phase species will, in principal, never account for the precise kinetic and mechanistic details that prevail at a surface, in an enzyme, or in solution, when complemented by appropriate, computationally derived information, these gas-phase experiments prove meaningful on the ground that they permit a systematic approach to address the above-mentioned questions; moreover, they provide a conceptual framework. The DEGUSSA process, which is the rather unique, platinum-mediated, large-scale coupling of CH4 and NH3 to generate HCN [4], serves as a good example. Mass spectrometry-based experiments [5] suggested both the key role of CH2NH as a crucial gas-phase transient and also pointed to the advantage of using a bimetallic system rather than a pure platinum-based catalyst for the C–N coupling step to diminish undesired, catalyst-poisoning "soot" formation [6, 7]. The existence of CH2NH was later confirmed by in situ photoionization studies [8] and catalysts that are currently employed contain silver-platinum alloys rather than pure platinum.

In this chapter, we focus on two types of gas-phase C–N coupling processes, Eqs. ( 1.2 ) and ( 1.2 ), using metal complexes bearing simple carbon- and nitrogen-based ligands and probing their thermal reactions with ammonia and hydrocarbons, respectively. While we will refrain from describing the various experimental techniques and computational methods or the way the reactive species [M(CH x )]+ and [M(NH x )]+ are generated [9], the emphasis will rather be on the elucidation of the often intriguing mechanisms of these metal-mediated coupling reactions.
1.1 1.2 1.2 From Metal-Carbon to Carbon–Nitrogen Bonds

1.2.1 Thermal Reactions of Metal C

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