Lawrence Berkeley National Laboratory Recent Work Title Iridium-Catalyzed, Intermolecular Hydroetherification of Unactivated Aliphatic Alkenes with Phenols Permalink https://escholarship.org/uc/item/5xd8s951 Journal Journal of the American Chemical Society, 135(25) ISSN 0002-7863 Authors Sevov, Christo S. Hartwig, John F. Publication Date 2013-06-26 eScholarship.org Powered by the California Digital Library University of California Angewandte. Minireviews J. F. Hartwig and P. S. Hanley DOI: 10.1002/anie.201300134 Organometallic Reactions Migratory Insertion of Alkenes into Metal–Oxygen and Metal–Nitrogen Bonds Patrick S. Hanley and John F. Hartwig* amination · organometallic reactions · palladium · insertion · reaction mechanisms he insertion of an unsaturated ligand into a M C or M H bond T À À proceeds through migratory insertion, a fundamental organometallic reaction. Recent literature documents evidence of the migratory insertion of alkenes into an M O and M N bonds for alkene alkox- À À ylation and alkene amination reactions, respectively. Herein we provide an overview of the literature and a perspective on how these recent experiments relate to classic experiments on C O and C N À À bond formation with alkene complexes of the late transition metals. Introduction tionalization of alkenes,[15–18] and the olefination of aryl halides (commonly termed the Mizoroki–Heck reaction).[19–22] Migratory insertion is a fundamental organometallic In most cases, the unsaturated ligand inserts into a metal– reaction. It is a concerted reaction that combines an carbon (M C) or metal–hydrogen (M H) bond. Related À À unsaturated ligand with an adjacent metal–ligand bond to insertions of alkenes into metal–oxygen (M O) and metal– À form a product containing a new ligand with the unsaturated nitrogen (M N) bonds are much less common (Scheme 1). À group formally inserted into the original covalent metal– Over the past decade, however, several papers have described ligand bond (Scheme 1). A variety of unsaturated ligands palladium-catalyzed alkene alkoxylation and alkene amina- undergo migratory insertion, including carbon monoxide, tion reactions for which stereochemical data implies that carbon dioxide, alkenes, alkynes, ketones, aldehydes, and migratory insertion of an alkene occurs into an M O or M N À À imines, and migratory insertion is a common step in numerous bond. Moreover, the first isolated transition metal amido catalytic reactions, including hydroformylation,[1,2] hydroge- complexes that insert unactivated alkenes have been reported nation,[3–5] polymerization,[6–9] hydroarylation,[10–14] difunc- in the past few years. These recent publications on isolated amido complexes include information on the factors control- ling the rate of insertion. Although the first examples of insertion of an alkene into a metal–heteroatom bond were reported more than two decades ago, experiments on the insertions of alkenes into isolated metal amido complexes are rare. An open coordina- tion site is necessary for alkene coordination prior to insertion, and many alkoxo and amido complexes form stable multinuclear structures if the metal center is coordinatively unsaturated. Thus, preparation of monomeric amido com- plexes containing an open coordination site to bind and Scheme 1. Migratory insertion of an alkene or alkyne into M R and À subsequently insert alkenes is difficult, and the absence of M X bonds. À such complexes has meant that the factors which control insertions of alkenes into metal–heteroatom bonds have been poorly understood. [*] Dr. P. S. Hanley, Prof. J. F. Hartwig Many alkene complexes have been prepared and react Department of Chemistry, University of Illinois Urbana-Champaign Urbana, IL 61801 (USA) with nucleophiles by attack onto the coordinated alkene. As discussed below, the classic Wacker reaction has been Prof. J. F. Hartwig University of California, Department of Chemistry proposed to occur by this elementary reaction, rather than 718 Latimer Hall, Berkeley, CA 94720 (USA) migratory insertion. Although the product of migratory E-mail: [email protected] insertion and nucleophilic attack on a coordinated alkene 8510 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2013, 52, 8510 – 8525 Angewandte Migratory Insertion Chemie the section on this topic is divided into three subsections: 1) The description of catalytic reactions involving insertions of alkenes into bonds between nitrogen and lanthanide, actinide, alkaline earth, and early transition metals, 2) the description of catalytic reactions involving the insertion of alkenes into late-transition-metal–nitrogen bonds, and 3) the description of reactions of discrete amido complexes with alkenes that likely occur by a migratory insertion of the alkene into the M N bond. À Scheme 2. Migratory insertion of an alkene into M X bonds versus À nucleophilic attack of X onto a coordinated alkene. Reactions Occurring by Migratory Insertion of Olefins into M O Bonds contain the same connectivity, the stereochemistry of the À products of the two reactions is different. As shown in The oxidative functionalization of alkenes is the one of Scheme 2, the migratory insertion pathway leads to the the most widely used processes catalyzed by soluble transi- opposite relative configurations of the a- and b-carbon atoms tion-metal complexes. The oxidation of ethylene in water with of the resulting alkyl complex. Ongoing work has sought to a palladium catalyst, commonly termed the Wacker process, is reveal what complexes and reaction conditions lead to used to produce 2 106 tons of acetaldehyde annually insertion and what complexes and reaction conditions lead to nucleophilic attack on the coordinated alkene. Recent data that begins to address this issue are included in this Mini- review. To develop new, selective metal-catalyzed olefin alkox- Scheme 3. The Wacker process. ylation and amination reactions, fundamental knowledge of the factors that control the rate and stereoselectivity of the insertion of alkenes into M O and M N bonds is needed. (Scheme 3).[23] The metal-mediated formation of new C O À À À These factors are just beginning to be revealed. Thus, one aim bonds by the addition of an oxygen nucleophile to an olefin of this Minireview is to provide a perspective on how these was thought for many years to occur exclusively by nucleo- recent experiments relate to classic experiments on C O and philic attack of an oxygen nucleophile onto a metal-coordi- À C N bond formation with alkene complexes of the late nated olefin. Well-characterized metal olefin complexes had À transition metals, and to summarize the existing literature on been prepared, and alcohols were shown to add to the alkene chemistry involving migratory insertion of alkenes into the of these complexes at the face opposite the metal center.[24–27] M N and M O bonds of isolated metal amido and metal Thus, metal-catalyzed additions of oxygen nucleophiles to À À alkoxo complexes, respectively. We will also describe mech- olefins were typically assumed to occur by anti addition. anistic studies of catalytic amination and alkoxylation reac- However, alkoxometal olefin complexes that react by migra- tions, that offer insight into the migratory insertion step. tory insertion have recently been identified. In this section, we We have separated this review into two sections. The first describe catalytic reactions, including the Wacker process, for section is divided into two subsections: 1) The description of which mechanistic data implies that the C O bond is formed À catalytic reactions for which evidence of alkene insertion into by insertion of an alkene into an M O bond. Stoichiometric À an M O bond has been gained, and 2) the description of reactions of alkoxo complexes with alkenes will be discussed À stoichiometric reactions of alkoxo complexes with alkenes. in detail. The second section describes chemistry involving migratory insertions of alkenes into M N bonds. Because more data À have been published on alkene insertions into M N bonds, À John Hartwig is the Henry Rapoport Profes- Patrick Hanley received his B.S. from West sor at the University of California, Berkeley. Virginia University in 2008 under the direc- His group seeks to discover new reactions tion of Prof. Jeffrey L. Petersen. He com- catalyzed by transition-metal complexes and pleted his Ph.D. in 2012 at the University to reveal new reaction mechanisms. He of Illinois at Urbana-Champaign under the recently authored the textbook “Organo- direction of Prof. John F. Hartwig, studying transition Metal Chemistry: From Bonding new carbon–nitrogen bond-forming reac- to Catalysis”. He is the 2006 recipient of tions of palladium. Currently, he is a Senior the ACS Award in Organometallic Chemist at The Dow Chemical Company in Chemistry and the 2013 ACS H.C. Brown Michigan. Award in Synthetic Methods. He was elected to the National Academy of Scien- ces in 2012. Angew. Chem. Int. Ed. 2013, 52, 8510 – 8525 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org 8511 . Angewandte J. F. Hartwig and P. S. Hanley Minireviews Catalytic Reactions Involving Alkene Insertion into M O Bonds À The mechanism of the Wacker process has been disputed for the last four decades. Early kinetic data on the Wacker oxidation were consistent with a mechanism involving syn addition of a preformed palladium-hydroxo complex across ethylene.[28] However, experiments conducted by Akermark, Stille, Bäckvall, and co-workers demonstrated that palladium ligated