Higher Oxidation State Organopalladium and Platinum Chemistry

Table of Contents

1. Frontmatter

2. Five-Coordinate Platinum(IV) Complexes

   Kyle A. Grice, Margaret L. Scheuermann, Karen I. Goldberg

   Abstract

   Octahedral organometallic platinum(IV) complexes have been known for more than a century. Mechanistic studies suggest that many reactions of these six-coordinate platinum(IV) complexes proceed through unobservable five-coordinate platinum(IV) intermediates. Only recently have five-coordinate platinum(IV) complexes been isolated and characterized. These novel complexes serve as models for unobserved intermediates in stoichiometric and catalytic reactions involving high oxidation state platinum. The isolation of five-coordinate complexes allows the unique reactivity of these unsaturated species to be investigated directly. This contribution describes the development of five-coordinate platinum(IV) from proposed intermediates to isolable complexes. The syntheses, characterization, and reactivity studies of complexes with this new coordination geometry of platinum(IV) are also presented.

3. The Role of Higher Oxidation State Species in Platinum-Mediated C–H Bond Activation and Functionalization

   Jay A. Labinger, John E. Bercaw

   Abstract

   The Shilov system, a mixture of di- and tetravalent chloroplatinate salts in aqueous solution, provided the first indication of the potential of organotransition metal complexes for activating and functionalizing alkanes under mild conditions; the participation of higher-valent species plays a crucial role. In this chapter, we discuss the experimental and computational studies that have led to detailed mechanistic understanding of C–H activation and functionalization by both the original Shilov system and the many subsequent modifications that have been developed, and assess the prospects for practical, selective catalytic oxidation of alkanes using this chemistry.

4. Carbon–Heteroatom Bond-Forming Reductive Elimination from Palladium(IV) Complexes

   Joy M. Racowski, Melanie S. Sanford

   Abstract

   This work provides a comprehensive review (1986–2010) of the synthesis, characterization, and reactivity of palladium(IV) complexes that undergo carbon–heteroatom bond-forming reductive elimination reactions. In cases where mechanistic information is available, the molecular pathway for C–X bond formation is described in detail. Examples of catalytic transformations that may involve this mechanistic manifold are also presented.

5. Palladium(IV) Complexes as Intermediates in Catalytic and Stoichiometric Cascade Sequences Providing Complex Carbocycles and Heterocycles

   Helena C. Malinakova

   Abstract

   Palladium-catalyzed multicomponent coupling and annulation reactions have become important tools in organic synthesis. Recently, palladium(IV) complexes have been proposed as intermediates in catalytic cycles of these transformations, although experimental evidence for their involvement is frequently lacking. Examples of such catalytic annulation reactions are discussed, followed by a review of studies performed with stoichiometric isolable or semistable palladium(IV) complexes seeking experimental evidence for feasibility of the participation of palladium(IV) intermediates in cascade carbon–carbon and carbon–heteroatom bond-forming sequences.

6. η1-Alkynyl Chemistry for the Higher Oxidation States of Palladium and Platinum

   Allan J. Canty, Manab Sharma

   Abstract

   This chapter reviews the organometallic chemistry of palladium and platinum, in which the metal atom is bonded to alkynyl ligands and the formal oxidation state of the metal atom is greater than two. Several synthetic methods have been reported, where the most generally applicable involve oxidation of alkynylmetal(II) complexes and reactions of organometal(II) complexes with alkynyl(aryl)iodine(III) reagents. Metal(IV) complexes obtained have octahedral geometry and some have been shown to decompose via reductive elimination processes to generate carbon–carbon bonds. Unsymmetrical metal–metal bonded species formally represented as Pt^III–Pt^III ↔ Pt^IV–Pt^II have been characterised as intermediates in oxidation of Pt^II to Pt^IV. Potential implications for mechanisms of organic reactions mediated by higher oxidation state metal centres are discussed.

7. Palladium(III) in Synthesis and Catalysis

   David C. Powers, Tobias Ritter

   Abstract

   While the organometallic chemistry of Pd in its (0), (+II), and (+IV) oxidation states is well established, organometallic Pd(III) chemistry remains widely unexplored. Few characterized Pd(III) complexes are known, which has inhibited detailed study of the organometallic chemistry of Pd(III). In this review, the potential roles of both mono- and dinuclear Pd(III) complexes in organometallic chemistry are discussed. While not widely recognized, Pd in the (+III) oxidation state may play a significant role in a variety of known Pd-catalyzed reactions.

8. Organometallic Platinum(II) and Palladium(II) Complexes as Donor Ligands for Lewis-Acidic d10 and s2 Centers

   Marc-Etienne Moret

   Abstract

   Square-planar palladium(II) and platinum(II) complexes with a high-lying filled d_z² orbital can act as metalloligands for Lewis-acidic metal centers such as d¹⁰ and s² cations. This behavior is promoted by hard ligands such as σ-bound hydrocarbyl ligands. A wide diversity of structural motifs based on this kind of donor–acceptor metal–metal bonds has been discovered in the last decades. This chapter reviews the coordination chemistry of metalloligands derived from alkyl, aryl, alkynyl, and carbene complexes of palladium(II) and platinum(II). The specific reactivity of the resulting bimetallic complexes is also addressed.

9. Backmatter