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Polar Organometallic Reagents


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(ebook) | ISBN 9781119448822 (hardback) | ISBN 9781119448860 (adobe pdf) | ISBN 9781119448846 (epub)

      Subjects: LCSH: Organometallic chemistry.

      Classification: LCC QD411 .P63 2022 (print) | LCC QD411 (ebook) | DDC 547/.05–dc23

      LC record available at https://lccn.loc.gov/2021037022 LC ebook record available at https://lccn.loc.gov/2021037023

      Cover Design: Wiley

      Cover Image: © Piotr Zajc/Shutterstock, ANDREW E. H. WHEATLEY

      Preface

      Just as it has done for many years, organometallic and metalloorganic chemistry continues to play a vital role for synthetic chemists in the twenty‐first century. It offers some of the most effective ways of regiospecifically elaborating organic systems or of harnessing the potential of small molecules. Nevertheless, chemists constantly encounter challenges and target new systems which are not amenable to existing reagents. It is issues such as aggressive nucleophilicity or the implications of temperature instability or solvent sensitivity of many traditional organometallic bases, which have driven much of the research discussed in this volume. A major emergent theme covered is the potential of new, heterobimetallic systems. In particular, the problems of understanding just how reagents predicated on the action of two different metals operate. Synergy vs. cooperativity will be looked at in depth.

      The new and often unique reactivities of these more complex reagents (or reagent mixtures) and their ability to achieve more effective chemical transformations under increasingly mild conditions are discussed. To do this, a broad view of organometallic chemistry is adopted, taking in organooxides, amides and the like as appropriate. Mostly, combinations of main group metals will be looked at but, in particular when considering environmental applications of bimetallic systems, coverage will extend to the d‐block. Divided into nine chapters, the volume broadly covers three main fields; structural chemistry in the solid state, understanding often catalytic processes by monitoring reaction pathways, and synthetic applications.

      Chapter 4 is the first of two chapters dominated by a catalytic emphasis on our consideration of applied chemistry. It does this, though, through the lens of understanding chemical processes. It directs the reader towards the role of computation in understanding how heterobimetallic complexes that now take in d‐block as well as main group elements can work, and also the applications of these systems in environmentally relevant polymerization processes dependent on the activation of small molecules. As is pointed out, proving positive cooperative effects is easily done, though understanding the nature and origin of a cooperative mechanism remains difficult, with concerted or consecutive actions of different metals potentially competing, and then with variance between formal metal–metal bonding or metals tethered by bridging ligands. In all this it is important to bear in mind that limited direct observation of structures will typically be possible on catalytic species in operando. Catalysis remains the dominant theme in Chapter 5, but more through the prism of p‐block chemistry, and of group 13 in particular. Noting that the domain of catalysis has been dominated by d‐block metals, this chapter records that the beginning of the twenty‐first century has seen a shift towards main group element alternatives. This is the context then in which the remarkable reactivity of group 13 compounds have entered the catalytic arena. While tuning of their Lewis acidity and electrophilicity is possible by varying metal coordination number, it is the conversion of covalent complexes into cationic derivatives that will dominate. The chapter provides an overview of recent developments in the synthetic, characterization, computation and reactivity studies and applications in catalysis of cationic complexes. It will cover boron for completeness, but focus on aluminium and the higher group 13 elements.

      Following the introduction of convenient spectroscopic handles in Chapter 5, multinuclear NMR studies allow the interrogation of solution processes and intermediates in Chapter 6. This picks up ideas hinted at but not fully explored in Chapters 13. The chapter revisits early studies in the NMR spectroscopic analysis of recognizably traditional organolithium and lithium amide systems, but then brings that work up‐to‐date, looking at the recent elegant advances in our understanding of the solution dynamics of enolates. The main focus of this chapter, though, relates to recent developments in diffusion‐ordered spectroscopy. Again, this is contextualized though reference to the early work of Williard, but then shifts to modern lithium amide chemistry capable of being done under aerobic conditions. Most particularly, though, modern diffusion methods have allowed us to better understand the real solution chemistries of heterobimetallic formulations. This has been greatly enabled by the work of Stalke, raising the bar where the accuracy of molecular weight determination in solution is concerned. In consequence, diffusion analysis and multinuclear spectroscopy has prompted a much truer understanding of the aggregation and solvation of highly applied systems—for example the turbo reagents of Knochel.