Modern Organoaluminum Reagents

Table of Contents

1. Frontmatter

2. Simple Trivalent Organoaluminum Species: Perspectives on Structure, Bonding, and Reactivity

   Janusz Lewiński, Andrew E. H. Wheatley

   Abstract

   This chapter deals with the most significant developments in Al(III) organoaluminum chemistry since 2000. The most prominent synthetic and structural features along with reactivity trends are discussed for organoaluminum compounds featuring simple σ-bonded substituents and the corresponding 4- and 5-coordinate complexes formed in the presence of Lewis base. The structural effects of including ligands with group 15 and 16 donors are discussed in terms of the formation of heteroatom bridges and the ubiquitous formation of cyclic motifs. The structural implications of using bidentate, chelating ligands are also introduced, including the propensity of these for stabilizing cationic Al(III) species. The current and potential utility of such species in areas such as catalysis and material science is also highlighted with, whenever appropriate, structure/reactivity correlations.

3. Organoaluminum Complexes with Bonds to s-Block, p-Block, d-Block, and f-Block Metal Centers

   Stephan Schulz

   Abstract

   This chapter summarizes the recent developments in organoaluminum compounds containing at least one direct bond between aluminum and a s-block, p-block, d-block, or f-block metal center. General synthetic pathways to access such species are described along with their structural and bonding properties.

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4. Low Valent Organoaluminum (+I, +II) Species

   Rudolf J. Wehmschulte

   Abstract

   Since the isolation of the first stable molecular aluminum(II) compound {(Me₃Si)₂CH}₂Al–Al{CH(SiMe₃)₂}₂, the field of low oxidation state aluminum species has burgeoned tremendously. Organoaluminum(I) species (RAl) _n stabilized with bulky substituents have been isolated and used as reducing agents, precursors to aluminum(III) compounds, ligands toward transition group metal complexes, and main group Lewis acids. Mixed valent aluminum compounds and numerous clusters such as the large aluminum anion [Al₇₇{N(SiMe₃)₂}₂₀]²⁻ have provided insight into the stepwise formation of metallic aluminum from molecular precursors. It now appears likely that low oxidation state organoaluminum compounds will find their way into the organic and organometallic synthetic toolbox.

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5. Organoaluminum Species in Homogeneous Polymerization Catalysis

   Samuel Dagorne, Christophe Fliedel

   Abstract

   This chapter highlights the most recent and representative results on the use of organoaluminum compounds in polymerization catalysis with a special emphasis on discrete Al-incorporating catalysts. The first part of this contribution summarizes recent and noteworthy developments on well-defined Al-based initiators for the controlled (and stereocontrolled) polymerization of various monomers including isobutene, styrene, epoxides, methyl methacrylate, cyclic esters, and cyclic carbonates. The second part discusses the latest significant advances on the synthesis and structural characterization of polynuclear organoaluminum/transition (and f-block) metal complexes relevant to Ziegler–Natta-type catalysis.

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6. Preparation of Organoalanes for Organic Synthesis

   Paul Knochel, Tobias Blümke, Klaus Groll, Yi-Hung Chen

   Abstract

   Organoaluminums have become more and more important in organic synthesis due to their excellent reactivity and chemoselectivity. Several methods are available for the preparation of various organoaluminums: transmetalation of organomagnesium or lithium reagents, direct insertion of aluminum powder, deprotonation reactions using aluminate bases (metalation), hydro- and carboalumination of unsaturated compounds, and cycloaddition reactions. These methods provide access to aryl, alkynyl, alkenyl, alkyl, allylic, benzylic, and propargylic organoaluminums which all have interesting properties, and can be readily used in organic synthesis.

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7. Reactions Triggered by Lewis Acidic Organoaluminum Species

   Yuki Naganawa, Keiji Maruoka

   Abstract

   The use of organoaluminum-based Lewis acids (AlR _n X_3–n ; R = alkyl, alkynyl, X = halide or pseudohalide) in the period 2000 to mid-2011 is overviewed with a focus on: (1) stoichiometric reactions in which one of the organoaluminum substituents is transferred to the substrate (e.g., the opening of epoxides, 1,2-additions to carbonyl compounds, coupling with C–X, and Reissert chemistry) and (2) asymmetric, often catalytic, reactions promoted by Lewis acid catalysts derived from organoaluminum species (e.g., use of auxiliaries with alanes, Diels–Alder, and related cycloaddition reactions, additions to aldehydes and ketones, and skeletal rearrangement reactions).

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8. Hydro-, Carbo-, and Cycloalumination of Unsaturated Compounds

   Usein M. Dzhemilev, Vladimir A. D’yakonov

   Abstract

   This chapter gives a survey and a systematic account of modern achievements in the synthesis of acyclic and cyclic organoaluminum compounds using thermal and catalytic hydro- and carboalumination of unsaturated compounds. Here we consider a new, versatile catalytic cycloalumination reaction of olefins, acetylenes, and 1,2-dienes of various structures with alkyl and halogen alkyl Al catalyzed by Zr and Ti complexes to give previously unknown classes of OACs: aluminacyclopropanes, aluminacyclopropenes, aluminacyclopentanes, aluminacyclopentenes, aluminacyclopentadienes, and aluminamacrocarbocycles. Much attention is given to applications of hydro-, carbo-, and cycloalumination reactions for the synthesis of practically important natural carbo- and heterocyclic compounds.

9. Organoaluminum Couplings to Carbonyls, Imines, and Halides

   Andreas Kolb, Paultheo von Zezschwitz

   Abstract

   While the stereoselective addition of zinc organyls to carbonyl compounds is nowadays an established synthetic method, the use of aluminum reagents is less common, even though they offer distinct advantages. This chapter presents an overview of the current status of catalytic asymmetric additions to aldehydes, ketones, and imines, as well as the difficulties and the limitations of such transformations, respectively. Certain combinations of substrate types and carbon nucleophiles were so far only achieved using stoichiometric systems under substrate or auxiliary control. These examples are also included, as well as aspects of cross-coupling reactions of aluminum organyls with organic halides.

10. Conjugate Addition of Organoaluminum Species to Michael Acceptors and Related Processes

    Oscar Pàmies, Montserrat Diéguez

    Abstract

    Over the last decade much effort has been devoted to develop new methodologies to expand the conjugate addition and related processes to the use of triorganoaluminum reagents. This chapter covers the recent literature reports (ca. 2003 onward) on asymmetric conjugate addition of triorganoaluminum reagents to a range of Michael acceptors and also mechanistically closely related allylic alkylation of allylic substrates. It also includes cascade processes where the intermediate enolates (conjugate addition) and alkenes (allylic alkylation) are used for the synthesis of more complex molecules (including natural products and pharmaceutical targets).

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11. Backmatter