Science of Synthesis Knowledge Updates 2012 Vol. 4 E-Book

• Herausgeber: Thieme
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 942

Veröffentlichungsjahr: 2014

Beschreibung

Science of Synthesis is a reference work for preparative methods in synthetic chemistry. Its product-based classification system enables chemists to easily find solutions to their synthetic problems.

Key Features:

• Critical selection of reliable synthetic methods, saving the researcher the time required to find procedures in the primary literature.
• Expertise provided by leading chemists.
• Detailed experimental procedures.
• The information is highly organized in a logical format to allow easy access to the relevant information.

The Science of Synthesis Editorial Board, together with the volume editors and authors, is constantly reviewing the whole field of synthetic organic chemistry as presented in Science of Synthesis and evaluating significant developments in synthetic methodology. Four annual volumes updating content across all categories ensure that you always have access to state-of-the-art synthetic methodology.

Leseprobe

Science of Synthesis

Science of Synthesis is the authoritative and comprehensive reference work for the entire field of organic and organometallic synthesis.

Science of Synthesis presents the important synthetic methods for all classes of compounds and includes:

Methods critically evaluated by leading scientists

Background information and detailed experimental procedures

Schemes and tables which illustrate the reaction scope

Preface

As the pace and breadth of research intensifies, organic synthesis is playing an increasingly central role in the discovery process within all imaginable areas of science: from pharmaceuticals, agrochemicals, and materials science to areas of biology and physics, the most impactful investigations are becoming more and more molecular. As an enabling science, synthetic organic chemistry is uniquely poised to provide access to compounds with exciting and valuable new properties. Organic molecules of extreme complexity can, given expert knowledge, be prepared with exquisite efficiency and selectivity, allowing virtually any phenomenon to be probed at levels never before imagined. With ready access to materials of remarkable structural diversity, critical studies can be conducted that reveal the intimate workings of chemical, biological, or physical processes with stunning detail.

The sheer variety of chemical structural space required for these investigations and the design elements necessary to assemble molecular targets of increasing intricacy place extraordinary demands on the individual synthetic methods used. They must be robust and provide reliably high yields on both small and large scales, have broad applicability, and exhibit high selectivity. Increasingly, synthetic approaches to organic molecules must take into account environmental sustainability. Thus, atom economy and the overall environmental impact of the transformations are taking on increased importance.

The need to provide a dependable source of information on evaluated synthetic methods in organic chemistry embracing these characteristics was first acknowledged over 100 years ago, when the highly regarded reference source Houben–Weyl Methoden der Organischen Chemie was first introduced. Recognizing the necessity to provide a modernized, comprehensive, and critical assessment of synthetic organic chemistry, in 2000 Thieme launched Science of Synthesis, Houben–Weyl Methods of Molecular Transformations. This effort, assembled by almost 1000 leading experts from both industry and academia, provides a balanced and critical analysis of the entire literature from the early 1800s until the year of publication. The accompanying online version of Science of Synthesis provides text, structure, substructure, and reaction searching capabilities by a powerful, yet easy-to-use, intuitive interface.

From 2010 onward, Science of Synthesis is being updated quarterly with high-quality content via Science of Synthesis Knowledge Updates. The goal of the Science of Synthesis Knowledge Updates is to provide a continuous review of the field of synthetic organic chemistry, with an eye toward evaluating and analyzing significant new developments in synthetic methods. A list of stringent criteria for inclusion of each synthetic transformation ensures that only the best and most reliable synthetic methods are incorporated. These efforts guarantee that Science of Synthesis will continue to be the most up-to-date electronic database available for the documentation of validated synthetic methods.

Also from 2010, Science of Synthesis includes the Science of Synthesis Reference Library, comprising volumes covering special topics of organic chemistry in a modular fashion, with six main classifications: (1) Classical, (2) Advances, (3) Transformations, (4) Applications, (5) Structures, and (6) Techniques. Titles will include Stereoselective Synthesis, Water in Organic Synthesis, and Asymmetric Organocatalysis, among others. With expert-evaluated content focusing on subjects of particular current interest, the Science of Synthesis Reference Library complements the Science of Synthesis Knowledge Updates, to make Science of Synthesis the complete information source for the modern synthetic chemist.

The overarching goal of the Science of Synthesis Editorial Board is to make the suite of Science of Synthesis resources the first and foremost focal point for critically evaluated information on chemical transformations for those individuals involved in the design and construction of organic molecules.

Throughout the years, the chemical community has benefited tremendously from the outstanding contribution of hundreds of highly dedicated expert authors who have devoted their energies and intellectual capital to these projects. We thank all of these individuals for the heroic efforts they have made throughout the entire publication process to make Science of Synthesis a reference work of the highest integrity and quality.

July 2010

The Editorial Board

E. M. Carreira (Zurich, Switzerland)

C. P. Decicco (Princeton, USA)

A. Fuerstner (Muelheim, Germany)

G. A. Molander (Philadelphia, USA)

P. J. Reider (Princeton, USA)

E. Schaumann (Clausthal-Zellerfeld, Germany)

M. Shibasaki (Tokyo, Japan)

E. J. Thomas (Manchester, UK)

B. M. Trost (Stanford, USA)

Abstracts

1.2.5 Product Subclass 5: Palladium(III)-Containing Complexes

D. C. Powers and T. Ritter

Compared with the chemistry of palladium in the 0, I, II, and IV oxidation states, organopalladium(III) chemistry is in its infancy, and complexes containing palladium in the III oxidation state are rare. Despite the scarcity of isolated palladium(III) complexes, recent studies have suggested palladium(III) intermediates may participate in a variety of palladium-catalyzed reactions, including oxidative C—H functionalization and aerobic oxidation reactions. In addition, several new preparative methods toward isolable palladium(III) complexes have been developed, which has allowed direct interrogation of the fundamental organometallic chemistry of organopalladium(III) complexes. Herein, preparative methods for the synthesis of palladium(III) complexes are reviewed and reactions in which palladium(III) intermediates are proposed are discussed.

Keywords: C—H functionalization · organopalladium chemistry · palladium(III) · aerobic oxidation · metal—metal bonds · radical chain reactions

2.10.20 Organometallic Complexes of Titanium (Update 2)

G. C. Micalizio

This chapter is an update of the earlier Science of Synthesis contribution on organometallic complexes of titanium, specifically on titanium alkoxide mediated methods for C—C bond formation. Distinct from the previous contribution, the current work describes developments that enable the realization and control of a broad class of intermolecular reductive cross-coupling reactions between a variety of unsymmetrically substituted π-systems (alkenes, alkynes, allenes, imines, and aldehydes). General principles of reaction design are discussed, successful demonstrations of these reactions are then described for a variety of metallacycle-mediated cross-coupling reactions, and selected applications of these reactions in natural product synthesis are presented. The bulk of the science described is extracted from literature published in the period of 2006 to early 2012.

Keywords: alicyclic compounds · alkaloids · alkenes · alkyne complexes · alkynes · allenes · allylic alcohols · carbocyclic compounds · carbometalation · C—C bonds · C—C coupling · carbon—metal bonds · chemoselectivity · chiral compounds · complexation · cross-coupling reactions · diastereoselectivity · dienes · enantioselectivity · enynes · fatty acids · Grignard reagents · heterocycles · homoallylic alcohols · homopropargylic alcohols · imines · metallacycles · natural products · polyols · pyridines · reductive coupling · regio-selectivity · stereoselective synthesis · titanium complexes · total synthesis · trienes · umpolung · unsaturated compounds · vinylsilanes

2.13 Product Class 13: Organometallic Complexes of the Actinides

R. J. Batrice, I.-S. R. Karmel, and M. S. Eisen

This manuscript is a revision of the earlier Science of Synthesis contribution describing the methods of synthesis and applications of organoactinide complexes. The preparation of a broad variety of such complexes, along with their catalytic and stoichiometric reactivities, are provided herein. The main focus of this work lies on developments of the past decade; however, earlier works are included for completeness and to provide an adequate background detailing the advances in actinide chemistry.

Keywords: organometallics · actinides · cyclopentadienyl ligands · arenes · carbenes · amido ligands · imido ligands · bridged ligands · homobimetallic complexes · heterobimetallic complexes · catalysis

4.4.3 Product Subclass 3: Silylenes

S. Inoue and M. Driess

Silylenes are the heavier analogues of carbenes, bearing divalent silicon atoms. They are far more electron-donating and reactive species than carbenes and thus represent a novel and promising class of steering ligands suitable for the activation of small molecules and for catalysis. Various novel and differently substituted cyclic silylenes have been successfully isolated and characterized, which provide a better understanding of structure–reactivity relationships of stable divalent silicon compounds. This chapter essentially covers the tremendous progress in the chemistry of carbocyclic and heterocyclic silylenes. Their utility as building blocks for the synthesis of novel functional silicon compounds and their role as strikingly versatile coordination ligands toward transition metals is highlighted.

Keywords: catalysis · reduction · silyl halides · cations · insertion reactions · addition reactions · dienes · aldehydes · ketones · imines · alkynes · cyanides · isocyanides · azides · alkenes · silicon · silenes · carbenes · pyridines · oxygen compounds · phosphorus compounds · transition metals

6.1.28.24 Vinylboranes

M. Vaultier and M. Pucheault

Vinylboranes have numerous applications in organic synthesis. This chapter provides an update to the original Science of Synthesis contribution on synthesis and applications of this scaffold. New and modified routes to vinylboranes are detailed and further transformations of vinylborane synthons, exploiting the reactivity of the C—B bond or the C=C bond, are also described.

Keywords: vinylboranes · catalysis · C=C bonds · borylation · hydroboration · silaboration · transmetalation

9.14.4 Phospholes

F. Mathey

This chapter is an update to the earlier Science of Synthesis contribution describing methods for the synthesis of phospholes, phospholide ions, and phosphametallocenes. It focuses on the literature published in the period 2001–2012.

Keywords: phospholes · phospholide ions · phosphametallocenes · phosphaferrocenes · aromaticity · [1,5]-sigmatropic shifts

40.1.1.5.6 Transition-Metal-Catalyzed Functionalization of C(sp3)—H Bonds of Amines

J. Ipaktschi and M. R. Saidi

This chapter describes the recent literature dealing with the selective functionalization of C(sp3)—H bonds adjacent to the nitrogen atom of amines or amides. The transition-metal-catalyzed transformation of a C—H bond into a C—C or carbon—heteroatom bond enables strategically new approaches to complex organic compounds including biologically active agents and functional organic materials. Straightforward and operationally economical solutions for target-oriented synthesis of complex structures are presented.

Particularly useful methods discussed are the transition-metal-catalyzed oxidation of α-C(sp3)—H bonds of tertiary N-methylamines and amides, transition-metal-catalyzed cross-dehydrogenative coupling (CDC) reaction of C(sp3)—H bonds at the α position of amines, transition-metal-catalyzed hydroaminoalkylation, functionalization of amines via transition-metal-catalyzed hydride transfer cyclization, and the synthesis of non-natural amino acids via functionalization of α-C(sp3)—H bonds of tertiary amines. Further methods discussed are the C—C bond formation at the γ-position of amines and the application of cooperative metal and organocatalysis for the C(sp3)—H bond activation of amines, which is otherwise impossible with a metal catalyst or an organocatalyst alone. An example is the cross-dehydrogenative coupling reaction of glycine esters with unmodified ketones cooperatively catalyzed by copper(II) acetate and pyrrolidine.

Keywords: C—H activation · transition-metal catalysis · oxidation · cross-dehydrogenative coupling · organocatalysts · Mannich reaction · aza-Henry reaction · aerobic oxidative coupling · Petasis–Mannich reaction · photoredox reaction · phosphonation · amino acids · hydroaminoalkylation

Table of Contents

Volume 1: Compounds with Transition Metal—Carbon π-Bonds and Compounds of Groups 10–8 (Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os)

1.2 Product Class 2: Organometallic Complexes of Palladium

1.2.5 Product Subclass 5: Palladium(III)-Containing Complexes

D. C. Powers and T. Ritter

1.2.5 Product Subclass 5: Palladium(III)-Containing Complexes

1.2.5.1 Synthesis of Palladium(III)-Containing Complexes

1.2.5.1.1 Mononuclear Palladium(III) Complexes

1.2.5.1.1.1 Method 1: Disproportionation of Palladium(II) Complexes

1.2.5.1.1.2 Method 2: Oxidation of Palladium(II) Complexes with Perchloric Acid

1.2.5.1.1.3 Method 3: Electrochemical Oxidation of Palladium(II) Complexes

1.2.5.1.1.4 Method 4: Oxidation of Palladium(II) with Single-Electron Oxidants

1.2.5.1.1.5 Method 5: Oxidation of Palladium(II) Complexes with Oxygen

1.2.5.1.2 Binuclear Palladium(III) Complexes without a Pd—Pd Bond

1.2.5.1.2.1 Method 1: Electrochemical Oxidation

1.2.5.1.2.2 Method 2: Comproportionation of Palladium(II) and Palladium(IV) Complexes

1.2.5.1.3 Binuclear Palladium(2.5) Complexes with a Pd—Pd Bond Order of 0.5

1.2.5.1.3.1 Method 1: Binuclear Palladium(2.5) Complexes by Electrochemical Oxidation

1.2.5.1.3.2 Method 2: Binuclear Palladium(2.5) Complexes Using Single-Electron Oxidants

1.2.5.1.4 Tetrabridged Binuclear Palladium(III) Complexes with a Pd—Pd Bond

1.2.5.1.4.1 Method 1: Binuclear Palladium(III) Complexes by Oxidation with Hypervalent Iodine

1.2.5.1.4.2 Method 2: Inorganic Binuclear Palladium(III) Complexes via Ligand Metathesis

1.2.5.1.4.3 Method 3: Organometallic Tetrabridged Binuclear Palladium(III) Complexes

1.2.5.1.5 Binuclear Palladium(III) Complexes Supported by Two Bridging Ligands

1.2.5.1.5.1 Method 1: Oxidation with Hypervalent Iodine Reagents

1.2.5.1.5.2 Method 2: Oxidation with Peroxides

1.2.5.1.5.3 Method 3: Oxidation with Halogens

1.2.5.1.6 Unbridged Pd(III)—Pd(III) Bonds

1.2.5.1.6.1 Method 1: Oxidation of Acetate-Bridged Binuclear Palladium(III) Complexes with Xenon Difluoride

1.2.5.2 Stoichiometric Organometallic Chemistry of Isolated Palladium(III) Complexes

1.2.5.2.1 Organometallic Chemistry of Mononuclear Palladium(III) Complexes

1.2.5.2.1.1 Method 1: C—C Bond-Forming Reactions of Mononuclear Palladium(III) Complexes

1.2.5.2.1.2 Method 2: C—C Bond-Forming Reactions Initiated by Ligation of Anionic Donors

1.2.5.2.2 Organometallic Chemistry of Binuclear Palladium(III) Complexes

1.2.5.2.2.1 Method 1: C—X Bimetallic Reductive Elimination from Binuclear Palladium(III) Complexes

1.2.5.3 Organometallic Reactions Proposed To Proceed via Unobserved Mononuclear Palladium(III) Intermediates

1.2.5.3.1 Method 1: C—C Bond-Forming Reactions Initiated by One-Electron Oxidation of Mononuclear Palladium(II) Complexes

1.2.5.3.2 Method 2: Oxygen-Insertion Reactions

1.2.5.4 Binuclear Palladium(III) in the Synthesis of Mononuclear Palladium(IV) Complexes

1.2.5.4.1 Method 1: Pd—Pd Heterolysis in Trifluoromethylation

1.2.5.4.2 Method 2: Heterolysis of Unbridged Pd(III)—Pd(III) Bonds

1.2.5.5 Proposed Catalysis via Mononuclear Palladium(III) Intermediates

1.2.5.5.1 Method 1: Kharasch Reaction

1.2.5.6 Catalysis via Proposed Binuclear Palladium(III) Intermediates

1.2.5.6.1 Method 1: Binuclear Palladium(III) Intermediates in C—H Arylation

1.2.5.6.2 Method 2: Binuclear Palladium(III) Intermediates in C—H Chlorination

1.2.5.6.3 Method 3: Binuclear Palladium(III) Complexes in C—H Acetoxylation

1.2.5.6.4 Method 4: C—N Bond-Forming Reactions Initiated by One-Electron Oxidants

1.2.5.6.5 Method 5: Binuclear Catalysts for C—H Hydroxylation Chemistry

1.2.5.7 Binuclear Palladium(III) Precatalysts

1.2.5.7.1 Method 1: Alkene Diboration

Volume 2: Compounds of Groups 7–3 (Mn…, Cr…, V…, Ti…, Sc…, La…, Ac…)

2.10 Product Class 10: Organometallic Complexes of Titanium

2.10.20 Organometallic Complexes of Titanium (Update 2)

G. C. Micalizio

2.10.20 Organometallic Complexes of Titanium (Update 2)

2.10.20.1 Titanium-Mediated Reductive Cross-Coupling Reactions (Intermolecular Metallacycle-Mediated C—C Bond Formation)

2.10.20.1.1 Method 1: Synthesis of Allylic Alcohols by Alkoxide-Directed Regioselective Coupling of Internal Alkynes with Aldehydes (Class I)

2.10.20.1.2 Method 2: Synthesis of Trisubstituted E-1,3-Dienes by Alkoxide-Directed Regioselective Coupling of Internal Alkynes with Terminal Alkynes (Class I)

2.10.20.1.3 Method 3: Synthesis of Tetrasubstituted 1,3-Dienes by Alkoxide-Directed Regioselective Cross-Coupling Reactions of Internal Alkynes (Class II)

2.10.20.1.4 Method 4: Titanium Alkoxide Mediated Alkene–Alkyne Cross Coupling (Class II)

2.10.20.1.5 Method 5: Titanium Alkoxide Mediated Allylic Alcohol–Alkyne Cross Coupling (Class II)

2.10.20.1.6 Method 6: Alkoxide-Directed Coupling of Allylic Alcohols with Vinylsilanes (Class II)

2.10.20.1.7 Method 7: Alkoxide-Directed Coupling of Imines with Internal Alkynes (Class II)

2.10.20.1.8 Method 8: Alkoxide-Directed Coupling of Imines with Alkenes (Class II)

2.10.20.1.9 Method 9: Alkoxide-Directed Coupling of Imines with Allylic Alcohols (Class II)

2.10.20.1.10 Method 10: Allenes in Alkoxide-Directed Titanium-Mediated Reductive Cross Coupling (Class II)

2.10.20.1.11 Method 11: Alkoxide-Directed Coupling of Vinylcyclopropanes with Silyl-Substituted Ethene and Alkynes (Class II)

2.10.20.1.12 Method 12: Titanium-Mediated Cyclopropanation of Vinylogous Esters (Class I Alkoxide-Directed Reductive Cross Coupling)

2.13 Product Class 13: Organometallic Complexes of the Actinides

R. J. Batrice, I.-S. R. Karmel, and M. S. Eisen

2.13 Product Class 13: Organometallic Complexes of the Actinides

2.13.1 Product Subclass 1: Actinide–Cyclooctatetraene Complexes

Synthesis of Product Subclass 1

2.13.1.1 Method 1: Metathesis with Alkali Metal Salts

2.13.1.2 Method 2: Transmetalation with Magnesium Salts

2.13.1.3 Method 3: Electrolytic Amalgamation

2.13.1.4 Method 4: Reduction with Lithium Naphthalenide

2.13.1.5 Method 5: Redistribution

2.13.1.6 Method 6: Cyclooctatetraene-Bridged Actinide Complexes

Applications of Product Subclass 1 in Organic Synthesis

2.13.1.7 Method 7: Binding of Carbon Monoxide

2.13.2 Product Subclass 2: Actinide–Arene Complexes

Synthesis of Product Subclass 2

2.13.2.1 Method 1: Friedel–Crafts Route

2.13.2.2 Method 2: Synthesis of Bimetallic Species

2.13.2.3 Method 3: Thermolysis of Uranium(IV) Borohydride

2.13.2.4 Method 4: Synthesis of Bridged Uranium–Arene Complexes by Salt Metathesis

2.13.3 Product Subclass 3: Actinide–Cyclopentadienyl Complexes

Synthesis of Product Subclass 3

2.13.3.1 Method 1: Metathesis with Alkali Metal Salts

2.13.3.2 Method 2: Transmetalation

2.13.3.3 Method 3: Reduction of Tetravalent Actinide Precursors

2.13.3.3.1 Variation 1: Reduction with Sodium Hydride

2.13.3.3.2 Variation 2: Reduction with Alkali Metals

2.13.3.4 Method 4: Reaction with Tetramethylfulvene

Applications of Product Subclass 3 in Organic Synthesis

2.13.3.5 Method 5: Catalytic Reduction of Azides and Hydrazines

2.13.3.6 Method 6: Intermolecular Hydroamination of Terminal Alkynes

2.13.3.7 Method 7: Hydrosilylation of Terminal Alkynes

2.13.3.8 Method 8: Polymerization of α-Alkenes

2.13.3.9 Method 9: C—H Bond Activation

2.13.4 Product Subclass 4: Allyl- and Pentadienylactinide Complexes

Synthesis of Product Subclass 4

2.13.4.1 Method 1: Transmetalation with Grignard Reagents

2.13.4.2 Method 2: Metathesis with Alkali Metal Salts

2.13.5 Product Subclass 5: Alkylactinide Complexes

Synthesis of Product Subclass 5

2.13.5.1 Method 1: Metathesis with Alkali Metal Salts

2.13.5.2 Method 2: Application of Stabilizing Phosphine Ancillary Ligands

2.13.6 Product Subclass 6: Actinide–Carbene Complexes

Synthesis of Product Subclass 6

2.13.6.1 Method 1: Metathesis with Alkali Metal Salts

2.13.6.2 Method 2: Ligand Redistribution

2.13.7 Product Subclass 7: Oxygen-Ligand Complexes of Actinide Systems

Synthesis of Product Subclass 7

2.13.7.1 Method 1: Ligand Substitution

2.13.7.1.1 Variation 1: Nucleophilic Displacement of Halides

2.13.7.1.2 Variation 2: By Ligand Redistribution

Applications of Product Subclass 7 in Organic Synthesis

2.13.7.2 Method 2: Molecular Nitrogen Reduction

2.13.8 Product Subclass 8: Nitrogen-Ligand Complexes of Actinide Systems

Synthesis of Product Subclass 8

2.13.8.1 Method 1: Formation of Actinide Amide Complexes

2.13.8.1.1 Variation 1: Homoleptic Actinide Amide Formation by Nucleophilic Halide Displacement

2.13.8.1.2 Variation 2: Heteroleptic Actinide Amide Synthesis by Nucleophilic Halide Displacement

2.13.8.1.3 Variation 3: Reaction of Organoactinide Species with Nitriles and Thiocyanates

2.13.8.2 Method 2: Formation of Actinide Imides

2.13.8.2.1 Variation 1: By Oxidation of the Actinide Center

2.13.8.2.2 Variation 2: By Reductive Cleavage with Amines and Hydrazines

2.13.8.2.3 Variation 3: By Reductive Cleavage with Azides and Diazenes

2.13.8.3 Method 3: Synthesis of Actinide Amidinate Complexes

2.13.8.3.1 Variation 1: By Reaction of Actinide Halides with Lithium Amidinates

2.13.8.3.2 Variation 2: By Carbodiimide Insertion

2.13.8.4 Method 4: Synthesis of Actinide Complexes Bearing N-Heterocyclic Ligands

2.13.8.4.1 Variation 1: Actinide Complexes Bearing Pyrrolyl Ligands and Polypyrrole Macrocycles

2.13.8.4.2 Variation 2: Organoactinide Complexes Bearing Pyrazole and Imidazole Functionality

2.13.8.4.3 Variation 3: Pyridine-Stabilized Organoactinide Systems

2.13.8.5 Method 5: Actinide Complexes Bearing Ketimide Ligands

Applications of Product Subclass 8 in Organic Synthesis

2.13.8.6 Method 6: Binding of Carbon Dioxide

2.13.8.7 Method 7: Oligomerization of ɛ-Caprolactone

2.13.8.8 Method 8: Dehydrogenative Coupling of Amines with Silanes

2.13.8.9 Method 9: Catalytic Hydrosilylation of Alkynes

2.13.8.10 Method 10: Binding of Molecular Nitrogen

2.13.8.11 Method 11: Alkene Polymerization

2.13.9 Product Subclass 9: Sulfur- and Phosphorus-Ligand Complexes of Actinide Systems

Synthesis of Product Subclass 9

2.13.9.1 Method 1: Synthesis of Organoactinide Complexes Bearing Sulfur Ligands

2.13.9.1.1 Variation 1: Formation of Actinide Thiolate Complexes by Coordinative Insertion

2.13.9.1.2 Variation 2: Formation of Actinide Thiolate Complexes by Nucleophilic Halide Displacement

2.13.9.2 Method 2: Synthesis of Organoactinide Complexes Bearing Phosphorus Ligands

2.13.9.2.1 Variation 1: Formation of Actinide–Phospholyl Complexes

2.13.9.2.2 Variation 2: Reactions Forming Actinide–Phosphine Complexes

2.13.9.2.3 Variation 3: Reactions Forming Actinide–Phosphine Oxide Complexes

2.13.9.2.4 Variation 4: Reactions Forming Actinide–Phosphoranimide Complexes

2.13.10 Product Subclass 10: Organoactinide Complexes Bearing Bridged Ligands

Synthesis of Product Subclass 10

2.13.10.1 Method 1: Organoactinide Complexes Bearing Bridged Ligands

2.13.10.1.1 Variation 1: Carbon-Bridged Ancillary Ligand Complexes of the Actinides

2.13.10.1.2 Variation 2: Nitrogen-Bridged Ancillary Ligand Complexes of the Actinides

2.13.10.1.3 Variation 3: Oxygen-Bridged Ancillary Ligand Complexes of the Actinides

2.13.10.1.4 Variation 4: Silicon-Bridged Ancillary Ligand Complexes of the Actinides

Applications of Product Subclass 10 in Organic Synthesis

2.13.10.2 Method 2: Catalytic Intramolecular Hydroamination/Cyclization Mediated by Constrained-Geometry Actinide Complexes

2.13.10.3 Method 3: Intermolecular Hydrosilylation with Phenylsilane Mediated by Constrained-Geometry Thorium Complexes

2.13.10.4 Method 4: Intermolecular Hydrothiolation

2.13.11 Product Subclass 11: Multimetallic Actinide Complexes

Synthesis of Product Subclass 11

2.13.11.1 Method 1: Homobimetallic Actinide Complexes

2.13.11.1.1 Variation 1: Nitrogen-Bridged Homobimetallic Actinide Complexes

2.13.11.1.2 Variation 2: Halogen-Bridged Homobimetallic Actinide Complexes

2.13.11.1.3 Variation 3: Oxygen-Bridged Homobimetallic Complexes

2.13.11.1.4 Variation 4: Carbide-Bridged Homobimetallic Actinide Complexes

2.13.11.2 Method 2: Heterobimetallic Complexes

2.13.11.2.1 Variation 1: Hydride-Bridged Heterobimetallic Complexes

2.13.11.2.2 Variation 2: Phosphorus-Bridged Heterobimetallic Actinide Complexes

2.13.11.2.3 Variation 3: Heterobimetallic Actinide–Ferrocenyl Complexes

2.13.11.2.4 Variation 4: Heterobimetallic Actinide Complexes with Unsupported Metal—Metal Bonds

2.13.11.2.5 Variation 5: Heterobimetallic Nitrogen-Bridged Actinide Complexes

Applications of Product Subclass 11 in Organic Synthesis

2.13.11.3 Method 3: Reversible Carbon—Carbon Coupling

2.13.11.4 Method 4: Inter-and Intramolecular Hydroamination

2.13.11.5 Method 5: σ-Bond Metathesis of Silylalkynes

Volume 4: Compounds of Group 15 (As, Sb, Bi) and Silicon Compounds

4.4 Product Class 4: Silicon Compounds

4.4.3 Product Subclass 3: Silylenes

S. Inoue and M. Driess

4.4.3 Product Subclass 3: Silylenes

Synthesis of Product Subclass 3

4.4.3.1 Method 1: Reduction of Dihalosilanes

4.4.3.2 Method 2: Reduction of Trichlorosilanes or Silicon Tetrachloride

4.4.3.3 Method 3: Reaction of a Silyliumylidene Cation

4.4.3.4 Method 4: Dehydrochlorination of Hydrochlorosilanes

Applications of Product Subclass 3 in Organic Synthesis

4.4.3.5 Method 5: Insertion Reactions

4.4.3.6 Method 6: Addition Reactions to 1,3-Dienes

4.4.3.7 Method 7: Addition Reactions to Aldehydes, Ketones, and Imines

4.4.3.8 Method 8: Addition Reactions to Alkynes and Cyanides

4.4.3.9 Method 9: Addition Reactions to Isocyanides and Azides

4.4.3.10 Method 10: Addition Reactions to Alkenes and Silenes

4.4.3.11 Method 11: Reactions with Carbenes and 4-(Dimethylamino)pyridine

4.4.3.12 Method 12: Reactions with Elemental Chalcogens or Phosphorus

4.4.3.13 Method 13: Reactions with Transition Metals

Volume 6: Boron Compounds

6.1 Product Class 1: Boron Compounds

6.1.28.24 Vinylboranes

M. Vaultier and M. Pucheault

6.1.28.24 Vinylboranes

6.1.28.24.1 Synthesis of Vinylboranes

6.1.28.24.1.1 Method 1: Insertion of Borylenes into C—H Bonds

6.1.28.24.1.2 Method 2: Dimetalation of Allenes and Alkynes

6.1.28.24.1.2.1 Variation 1: Palladium-Catalyzed Enantioselective Diboration of Allenes

6.1.28.24.1.2.2 Variation 2: Silaboration of Alkynes

6.1.28.24.1.2.3 Variation 3: Silaboration of Allenes

6.1.28.24.1.2.4 Variation 4: Silaborative C—C Cleavage Reactions of Methylenecyclopropanes

6.1.28.24.1.2.5 Variation 5: Copper-Catalyzed Addition of Diboron Reagents to Alkynes

6.1.28.24.1.3 Method 3: Transmetalation of Vinylic Metal Complexes with Boron Reagents

6.1.28.24.1.3.1 Variation 1: Copper Hydride Catalyzed Addition of Pinacolborane to Acetylenic Esters

6.1.28.24.1.3.2 Variation 2: Transmetalation of Vinylaluminums

6.1.28.24.1.3.3 Variation 3: Transmetalation of Cyclic Vinyllithium Compounds

6.1.28.24.1.3.4 Variation 4: Palladium-Catalyzed Borylation of Vinyl Halides

6.1.28.24.1.4 Method 4: Carboboration of Alkynes

6.1.28.24.1.5 Method 5: Miscellaneous Methods

6.1.28.24.1.5.1 Variation 1: Protodeboronation of Alkenyl Geminal Diboron Species

6.1.28.24.1.5.2 Variation 2: Stereoselective Synthesis of Tetrasubstituted Vinylboronates

6.1.28.24.2 Applications of Vinylboranes in Organic Synthesis

6.1.28.24.2.1 Method 1: Reduction of Double Bonds

6.1.28.24.2.2 Method 2: Synthesis of Cyclopropylboronates and Oxiran-2-ylboronates

6.1.28.24.2.3 Method 3: Cycloadditions

6.1.28.24.2.4 Method 4: Heck Reactions

6.1.28.24.2.5 Method 5: Substitution Reactions

6.1.28.24.2.5.1 Variation 1: Vinylogous Intramolecular Alkyl-Transfer Reactions

6.1.28.24.2.5.2 Variation 2: Reactions of Borylated Allylic Reagents

6.1.28.24.2.6 Method 6: Formation of Carbon—Halogen Bonds

6.1.28.24.2.6.1 Variation 1: Formation of a C—Cl Bond through Iodination of a Double Bond

6.1.28.24.2.6.2 Variation 2: Fluorination through Tandem Transmetalation–Fluorination

6.1.28.24.2.7 Method 7: Formation of C—N Bonds

6.1.28.24.2.7.1 Variation 1: Chan–Lam–Evans Cross Coupling

6.1.28.24.2.7.2 Variation 2: Formation of Imines

6.1.28.24.2.8 Method 8: Formation of C—O Bonds

6.1.28.24.2.9 Method 9: Formation of C—S and C—Se Bonds

6.1.28.24.2.10 Method 10: Addition to Heteroatom—Carbon Double Bonds

6.1.28.24.2.11 Method 11: Addition to Carbon—Carbon Multiple Bonds

6.1.28.24.2.12 Method 12: Homocoupling of Vinylboranes

6.1.28.24.2.13 Method 13: Cross Coupling of Vinylboranes

Volume 9: Fully Unsaturated Small-Ring Heterocycles and Monocyclic Five-Membered Hetarenes with One Heteroatom

9.14 Product Class 14: Phospholes

9.14.4 Phospholes

F. Mathey

9.14.4 Phospholes

9.14.4.1 λ3-1H-Phospholes

9.14.4.1.1 Synthesis by Ring-Closure Reactions

9.14.4.1.1.1 By Formation of Two P—C Bonds

9.14.4.1.1.1.1 Method 1: Reaction of Primary Phosphines with Diynes

9.14.4.1.1.2 By Formation of One C—C Bond

9.14.4.1.1.2.1 Method 1: Ring Closure of Dialk-1-ynylphosphines

9.14.4.1.2 Synthesis by Ring Transformation

9.14.4.1.2.1 Method 1: Reaction of Dihalophosphines with Zirconacyclopentadienes

9.14.4.1.2.1.1 Variation 1: Reaction of Zirconacyclopentadienes with Iodine, Butyllithium, and Dihalophosphines

9.14.4.1.2.1.2 Variation 2: Reaction of Zirconacyclopentadienes with Copper(I) Chloride and Dihalophosphines

9.14.4.1.2.1.3 Variation 3: Reaction of Dihalophosphines with Titanacyclopentadienes

9.14.4.1.3 Aromatization

9.14.4.1.3.1 Method 1: Dehydrohalogenation of 1-Halodihydrophospholium Ions

9.14.4.1.4 Synthesis by Substituent Modification

9.14.4.1.4.1 Method 1: Reaction of Electrophiles with Phospholide Ions

9.14.4.1.4.2 Method 2: Reaction of Nucleophiles with Phospholes

9.14.4.1.4.3 Method 3: Electrophilic Functionalization of Phospholes

9.14.4.1.4.4 Method 4: Transformation of α-Substituents

9.14.4.1.4.5 Method 5: Reduction of λ5-Phospholes

9.14.4.2 Phospholide Ions

9.14.4.2.1 Method 1: Cleavage of the Exocyclic P—R Bond of 1H-Phospholes by Alkali Metals

9.14.4.2.1.1 Variation 1: Cleavage of the Exocyclic P—C Bond of 1H-Phospholes by Bases

9.14.4.2.1.2 Variation 2: Deprotonation of Transient 2H-Phospholes

9.14.4.3 η5-Phospholyl Complexes

9.14.4.3.1 Method 1: Synthesis from λ3-1H-Phospholes

9.14.4.3.2 Method 2: Synthesis from λ3-2H-Phospholes

9.14.4.3.3 Method 3: Synthesis from Phospholide Ions

9.14.4.3.3.1 Variation 1: Via Intermediate 1-Stannylphospholes

9.14.4.3.4 Method 4: Electrophilic Functionalization

9.14.4.3.5 Method 5: Transformation of Substituents

Volume 40: Amines, Ammonium Salts, Amine N-Oxides, Haloamines, Hydroxylamines and Sulfur Analogues, and Hydrazines

40.1 Product Class 1: Amino Compounds

40.1.1.5.6 Transition-Metal-Catalyzed Functionalization of C(sp3)—H Bonds of Amines

J. Ipaktschi and M. R. Saidi

40.1.1.5.6 Transition-Metal-Catalyzed Functionalization of C(sp3)—H Bonds of Amines

40.1.1.5.6.1 Transition-Metal-Catalyzed Oxidation of α-C(sp3)—H Bonds of Tertiary N-Methylamines and Amides

40.1.1.5.6.1.1 Method 1: Ruthenium-Catalyzed Oxidation of Tertiary Amines

40.1.1.5.6.1.2 Method 2: Palladium-Catalyzed Acetoxylation of tert-Butoxycarbonyl-Protected N-Methylamines

40.1.1.5.6.2 Transition-Metal-Catalyzed Cross-Dehydrogenative Coupling Reactions of C(sp3)—H Bonds at the α-Position of Amines

40.1.1.5.6.2.1 Method 1: Transition-Metal-Catalyzed Alkynylation of α-C(sp3)—H Bonds of Tertiary Amines

40.1.1.5.6.2.1.1 Variation 1: Synthesis of Propargylamines by Copper(I)-Catalyzed Alkynylation of Tertiary Amines

40.1.1.5.6.2.1.2 Variation 2: Alkynylation of Tertiary Amines Catalyzed by Iron(II) Chloride

40.1.1.5.6.2.2 Method 2: Synthesis of β-Amino Ketones (Mannich Products) by Transition-Metal-Catalyzed C(sp3)—H Bond Functionalization

40.1.1.5.6.2.2.1 Variation 1: Synthesis of β-Amino Ketones Catalyzed by Copper Salts

40.1.1.5.6.2.2.2 Variation 2: Synthesis of β-Amino Ketones (Mannich Products) Catalyzed by a Combination of a Transition-Metal Catalyst and an Organocatalyst

40.1.1.5.6.2.2.3 Variation 3: Synthesis of β-Amino Ketones (Mannich Products) by Aerobic Oxidative Coupling of Tertiary Amines with Silyl Enol Ethers and Ketene Acetals

40.1.1.5.6.2.3 Method 3: Nitro-Mannich (Aza-Henry) Reaction via C(sp3)—H Functionalization

40.1.1.5.6.2.3.1 Variation 1: Copper-Catalyzed Cross-Dehydrogenative Coupling of Tertiary Amines and Nitroalkanes

40.1.1.5.6.2.3.2 Variation 2: Aza-Henry and Mannich Reaction by Platinum-Catalyzed Cross-Dehydrogenative Coupling of Tertiary Amines in the Absence of Oxidant

40.1.1.5.6.2.3.3 Variation 3: Aza-Henry (Nitro-Mannich) Reactions in the Presence of Ruthenium Complexes via Visible Light Photoredox Catalyzed C(sp3)—H Functionalization

40.1.1.5.6.2.4 Method 4: Transition-Metal-Catalyzed Oxidative α-Cyanation of Tertiary Amines

40.1.1.5.6.2.4.1 Variation 1: Aerobic Oxidative α-Cyanation of Tertiary Amines with Sodium Cyanide/Acetic Acid

40.1.1.5.6.2.4.2 Variation 2: α-Cyanation of Tertiary Amines with Sodium Cyanide/Acetic Acid in the Presence of Hydrogen Peroxide or tert-Butyl Hydroperoxide

40.1.1.5.6.2.4.3 Variation 3: α-Cyanation of Tertiary Amines Catalyzed by Gold Complexes under Acid-Free Conditions

40.1.1.5.6.2.5 Method 5: Iron(III)-Catalyzed Oxidative Allylation of a C—H Bond Adjacent to a Nitrogen Atom: Synthesis of Homoallyl Tertiary Amines

40.1.1.5.6.2.6 Method 6: Copper-Catalyzed Aerobic Phosphonation of C(sp3)—H Bonds

40.1.1.5.6.2.7 Method 7: Transition-Metal-Catalyzed (Het)Arylation of C(sp3)—H Bonds Adjacent to Nitrogen

40.1.1.5.6.2.7.1 Variation 1: Iron-Catalyzed Oxidative Coupling of Hetarenes and Tertiary N-Methylamines

40.1.1.5.6.2.7.2 Variation 2: Copper-Catalyzed Cross-Dehydrogenative Coupling Reaction of Tertiary Amines and Indoles Using tert-Butyl Hydroperoxide as Oxidant

40.1.1.5.6.2.7.3 Variation 3: Ruthenium-Catalyzed Cross-Dehydrogenative Coupling Reactions of Tertiary Amines and Indoles

40.1.1.5.6.2.7.4 Variation 4: Iron-Catalyzed Cross-Dehydrogenative Coupling Reactions of tert-Butoxycarbonyl-Protected 1,2,3,4-Tetrahydroisoquinoline and Indoles

40.1.1.5.6.2.7.5 Variation 5: Copper-Catalyzed Cross-Dehydrogenative Coupling Reaction of Hetarenes Using Air/Oxygen as Oxidant

40.1.1.5.6.2.7.6 Variation 6: Transition-Metal-Catalyzed Oxidative Coupling of Alkylamides with Electron-Rich (Het)Arenes

40.1.1.5.6.2.7.7 Variation 7: Copper-Catalyzed Oxidative Coupling of Tertiary Amines and Siloxyfurans

40.1.1.5.6.2.7.8 Variation 8: Dirhodium(II) Caprolactamate Catalyzed Oxidative Coupling of Tertiary Amines and Siloxyfurans

40.1.1.5.6.2.8 Method 8: Copper-Catalyzed Oxidative C(sp3)—H Bond Arylation with Arylboronic Acids (Petasis–Mannich Reaction)

40.1.1.5.6.2.9 Method 9: Synthesis of Nonnatural Amino Acids via Functionalization of α-C(sp3)—H Bonds of Tertiary Amines

40.1.1.5.6.2.9.1 Variation 1: Functionalization of Glycine Derivatives by Direct C—C Bond Formation

40.1.1.5.6.2.9.2 Variation 2: Cross-Dehydrogenative Coupling Reactions of Amino Acids and Ketones by Cooperative Transition-Metal and Amino Catalysis

40.1.1.5.6.2.10 Method 10: α-Functionalization of Nonactivated Aliphatic Amines in the Absence of Oxidant: Ruthenium-Catalyzed Alkynylations

40.1.1.5.6.3 Transition-Metal-Catalyzed Nonoxidative Functionalization of α-C(sp3)—H Bonds of Amines

40.1.1.5.6.3.1 Transition-Metal-Catalyzed Hydroaminoalkylation

40.1.1.5.6.3.1.1 Method 1: Transition-Metal-Catalyzed Intermolecular Hydroaminoalkylation of Unactivated Alkenes

40.1.1.5.6.3.1.1.1 Variation 1: Hydroaminoalkylation of Unactivated Alkenes with N-Alkylarylamines

40.1.1.5.6.3.1.1.2 Variation 2: Hydroaminoalkylation of Unactivated Alkenes with Dialkylamines

40.1.1.5.6.3.1.1.3 Variation 3: Hydroaminoalkylation with Secondary Amines: Enantioselective Synthesis of Chiral Amines

40.1.1.5.6.3.1.2 Method 2: Transition-Metal-Catalyzed Intramolecular C—H Activation of Primary and Secondary Amines

40.1.1.5.6.4 α-C(sp3)—H Bond Functionalization of Amines via Transition-Metal-Catalyzed Hydride Transfer Cyclization

40.1.1.5.6.4.1 Method 1: Coupling of Unactivated Alkynes and C(sp3)—H Bonds

40.1.1.5.6.4.1.1 Variation 1: Direct Coupling of Unactivated Alkynes and C(sp3)—H Bonds Catalyzed by Platinum(IV) Iodide

40.1.1.5.6.4.1.2 Variation 2: A Two-Step, One-Pot Gold-Catalyzed Cyclization of 1-(But-3-ynyl)piperidine Derivatives

40.1.1.5.6.4.2 Method 2: Coupling of Electron-Deficient Alkenes and α-C(sp3)—H Bonds of Amines

40.1.1.5.6.4.2.1 Variation 1: Enantioselective Synthesis of 1,2,3,4-Tetrahydroquinolines via Cobalt(II)-Catalyzed Tandem 1,5-Hydride Transfer/Cyclization

40.1.1.5.6.4.2.2 Variation 2: Gold-Catalyzed Enantioselective Functionalization of C(sp3)—H Bonds by Redox-Neutral Domino Reactions

40.1.1.5.6.5 Transition-Metal-Catalyzed α-Arylation of Saturated Amines

40.1.1.5.6.5.1 Method 1: C(sp3)—H Bond Arylation Directed by an Amidine Protecting Group: α-Arylation of Pyrrolidines and Piperidines

40.1.1.5.6.5.2 Method 2: Iron-Catalyzed Arylation at the α-Position of Aliphatic Amines

40.1.1.5.6.6 Remote Functionalization of Unactivated C(sp3)—H Bonds of Amines and Amides

40.1.1.5.6.6.1 Method 1: Palladium-Catalyzed Picolinamide-Directed Remote Arylation of Unactivated C(sp3)—H Bonds

40.1.1.5.6.6.2 Method 2: Synthesis of Fused Indolines by Palladium-Catalyzed Asymmetric C—C Coupling Involving an Unactivated Methylene Group at the Position β to Nitrogen

40.1.1.5.6.6.3 Method 3: C(sp3)—H Bond Activation with Ruthenium(II) Catalysts and C3-Alkylation of Cyclic Amines

Author Index

Abbreviations

1.2.5 Product Subclass 5: Palladium(III)-Containing Complexes

D. C. Powers and T. Ritter

General Introduction

Compared with the chemistry of palladium in the 0, I, II, and IV oxidation states, organopalladium(III) chemistry is in its infancy, and complexes containing palladium in the III oxidation state are rare.[1–4] Recent studies have expanded the family of characterized palladium(III) complexes and have also begun to elucidate the potential roles of palladium(III) intermediates in catalysis. This section will review preparative methods for the synthesis of palladium(III) complexes and discuss reactions in which palladium(III) intermediates are proposed.

SAFETY:

The palladium complexes reported herein can be prepared using the standard precautions generally taken with other potentially hazardous substances found in a chemistry laboratory. Many of the reagents used to prepare palladium(III) complexes are strong oxidants, which can be particularly hazardous.

1.2.5.1 Synthesis of Palladium(III)-Containing Complexes

1.2.5.1.1 Mononuclear Palladium(III) Complexes

Mononuclear palladium(II) complexes are typically square planar whereas mononuclear palladium(IV) complexes are typically octahedral.[5] Based on the molecular orbital diagram in ▶ Figure 1, mononuclear palladium(III) complexes are anticipated to be paramagnetic, low-spin d7, tetragonally distorted octahedral complexes, in which the unpaired electron resides predominantly in the orbital.[6]

▶ Figure 1 Molecular Orbital Diagram for Mononuclear Palladium(II), Palladium(III), and Palladium(IV) Complexes[5,6]

Unlike complexes based on platinum(III),[7–15] compounds containing palladium(III) are rare. Several mononuclear coordination complexes, proposed to contain palladium(III), have been observed by electrochemical measurements as well as EPR spectroscopy.[16–25] The spin density in these complexes, either metal- or ligand-centered, is the source of continuing discussion.[26–29] The various methods that have been developed for the preparation of mononuclear palladium(III) complexes are presented in the following sections.

1.2.5.1.1.1 Method 1: Disproportionation of Palladium(II) Complexes

Facially coordinating 1,4,7-triazacyclononane and 1,4,7-trithiacyclononane ligands have been used to stabilize mononuclear palladium(III) complexes.[30–33] Complex 2, in which two facially coordinating tridentate ligands compose the octahedral coordination environment of the palladium(III) center, has been prepared by disproportionation of palladium(II) (▶ Scheme 1). X-ray crystallographic characterization has established the distorted octahedral geometry of the palladium centers, as expected for low-spin, d7 palladium(III). Electrochemical and spectroscopic investigations have indicated that the unpaired electron in complex 2 resides predominantly in the orbital, consistent with the molecular orbital diagram in ▶ Figure 1.[34–39]

▶ Scheme 1 Synthesis of Mononuclear Palladium(III) Werner Complexes by Disproportionation of Palladium(II)[34]

Bis(1,4,7-triazacyclononane-κ3N)palladium(III) Hexafluorophosphate (2):[34]

PdCl2 (0.50 g, 2.8 mmol, 1.0 equiv) was dissolved in deionized H2O (20 mL) and the soln was adjusted to pH 9 with NaOH. The soln was warmed to 50 °C. 1,4,7-Triazacyclononane (0.90 g, 7.0 mmol, 2.5 equiv) was added directly to the PdCl2 soln, in which it dissolved rapidly. Heating was continued for 1 h at this temperature, during which time the remaining solid PdCl2 dissolved, yielding a lemon-yellow soln with deposited Pd metal (0.13 g; 45% of total Pd); the metallic solid was removed by filtration. The yellow filtrate contained two species; the major constituent was the cation of complex 2 with a minor amount of the cation of complex 1. Addition of sat. NH4PF6 soln caused precipitation of 2 as a yellow powder.

1.2.5.1.1.2 Method 2: Oxidation of Palladium(II) Complexes with Perchloric Acid

Mononuclear palladium(III) complex 4 has been prepared by chemical oxidation of mononuclear palladium(II) complex 3 with perchloric acid (▶ Scheme 2).[30] Experimental details of the oxidation of 3 with perchloric acid are unavailable.

▶ Scheme 2 Preparation of a Mononuclear Palladium(III) Complex by Oxidation of a Mononuclear Palladium(II) Complex with Perchloric Acid[30]

1.2.5.1.1.3 Method 3: Electrochemical Oxidation of Palladium(II) Complexes

In 2010, controlled potential electrolysis (CPE) was used to prepare the first mononuclear organometallic complexes of palladium(III) (complexes 6, ▶ Scheme 3).[40] One-electron oxidation of complexes 5 results in the formation of mononuclear palladium(III) complexes 6, in which the palladium(III) centers are stabilized by chelating tetradentate ligands.

▶ Scheme 3 Preparation of Mononuclear Palladium(III) Complexes by Controlled Potential Electrolysis of Mononuclear Palladium(II) Complexes[40]

R

1

X

−

Conditions

Yield (%)

Ref

Me

BF

4

−

Bu

4

NBF

4

, CH

2

Cl

2

78

[

40

]

Me

PF

6

−

Bu

4

NPF

6

, THF

63

[

40

]

Me

ClO

4

−

Bu

4

NClO

4

, THF

86

[

40

]

Ph

ClO

4

−

Bu

4

NClO

4

, THF

52

[

40

]

1.2.5.1.1.4 Method 4: Oxidation of Palladium(II) with Single-Electron Oxidants

One-electron oxidation of mononuclear palladium(II) complex 7 with either ferrocenium hexafluorophosphate or thianthrenyl hexafluoroantimonate affords mononuclear palladium(III) complex 8 (▶ Scheme 4).[40] Electrochemical and chemical oxidations (▶ Sections 1.2.5.1.1.3 and 1.2.5.1.1.4, respectively) allow access to complementary substrate classes; electrochemical oxidation of 7 failed to provide access to mononuclear palladium(III) complex 8.

▶ Scheme 4 Preparation of a Mononuclear Palladium(III) Complex from a Mononuclear Palladium(II) Complex Using a One-Electron Oxidant[40]

[3,7-Di-tert-butyl-3,7-diaza-1,5(2,6)-dipyridinacyclooctaphane-κN4]dimethylpalladium(III) Perchlorate (8):[40]

A soln of ferrocenium hexafluorophosphate (58.7 mg, 177 μmol, 1.00 equiv) in MeCN (3 mL) was added dropwise to a stirred suspension of 7 (86.8 mg, 177 μmol, 1.00 equiv) in MeCN (7 mL) at rt in a N2-filled drybox. The mixture was stirred for 20 min, and then the solvent was removed under reduced pressure. The solid residue was redissolved in MeCN (2 mL) and the soln was filtered through a cotton plug. A solid sample of LiClO4 (56.7 mg, 533 μmol, 3.01 equiv) was added to the filtrate causing precipitation of a dark green crystalline solid. The suspension was stored at −30 °C for 30 min. The resulting dark green crystals were collected by filtration from the cold soln, washed with Et2O and pentane, and dried under vacuum; yield: 76.6 mg (73%); 1H NMR (CD3CN, δ): 12.9 (br s), 9.0, −1.0; UV-vis (MeCN) λ (ɛ): 741 (3.6 × 102), 350 nm (2.3 × 103). X-ray quality crystals of 10 were obtained by crystallization (concd MeCN soln, −30 °C).

1.2.5.1.1.5 Method 5: Oxidation of Palladium(II) Complexes with Oxygen

Oxidation of organometallic palladium(II) complexes with oxygen is of interest with regard to the potential relevance of such a process to palladium-catalyzed aerobic oxidation reactions.[41] Oxidation of mononuclear palladium(II) complex 7 with oxygen affords mononuclear palladium(III) complex 9, which demonstrates that mononuclear palladium(III) complexes can be accessed with oxygen (▶ Scheme 5).[42]

▶ Scheme 5 Aerobic Oxidation of a Mononuclear Palladium(II) Complex Affords a Mononuclear Palladium(III) Complex[42]

[3,7-Di-tert-butyl-3,7-diaza-1,5(2,6)-dipyridinacyclooctaphane-κN4]dimethylpalladium(III) Complex 9:[42]

A 4.7 mM soln of Pd complex 7 in fluorobenzene (1.0 mL, 1.0 equiv) was placed into a quartz cuvette (10-mm path length) equipped with a septum-sealed cap and a magnetic stirrer bar, and MeOH (1 mL) was added. O2 was bubbled through the soln for 10–15 min, and the mixture was stirred under O2 in the dark and the reaction progress was monitored by UV-vis. The cation of complex 9 was spectroscopically identical to the cation of complex 8 (▶ Section 1.2.5.1.1.4); the counterion of complex 9 is unknown.

1.2.5.1.2 Binuclear Palladium(III) Complexes without a Pd—Pd Bond

1.2.5.1.2.1 Method 1: Electrochemical Oxidation

Controlled potential electrolysis (CPE) of mononuclear palladium(II) complex 10 in the presence of exogenous chloride, added as tetrabutylammonium chloride, results in the formation of chloride-bridged binuclear palladium(III) complex 11 (▶ Scheme 6).[43] Complex 11 features two palladium(III) centers without a direct Pd—Pd bond. The Pd–Cl–Pd triad in 11 can be viewed as a structural model of M—X—M units of M—X—M—X chains. The two palladium centers in complex 11 are antiferromagnetically coupled via the bridging halide ligand.

▶ Scheme 6 Controlled Potential Electrolysis of a Mononuclear Palladium(II) Complex in the Presence of Chloride Affords a Chloride-Bridged Binuclear Palladium(III) Complex[43]

μ-Chlorobis[dichloro(1,4,7-trimethyl-1,4,7-triazacyclononane-κ3N)palladium(III)] Hexafluorophosphate (11):[43]

CPE of a soln of 10 (51.3 mg, 147 μmol, 1.00 equiv) and Bu4NCl (20.4 mg, 73 μmol, 0.5 equiv) in 0.1 M Bu4NPF6 in MeCN (8 mL) was carried out at a constant potential of 500 mV vs a nonaqueous Ag/AgNO3/MeCN reference electrode. A graphite rod was used as the working electrode. The electrolysis was stopped after the charge corresponding to one-electron oxidation was transferred (15.0 C). A dark purple soln and a small amount of purple precipitate formed after the electrolysis. The mixture was stored at −20 °C for 12 h. The resulting suspension was concentrated by rotary evaporation at 23 °C to a volume of 3–4 mL and cooled to −20 °C. The purple precipitate was collected by filtration, washed with cold (−20 °C) MeCN, and dried under vacuum to afford the product; yield: 52.7 mg (82%); 1H NMR (CD3CN, δ): 3.06 (br m); UV-vis (MeCN) λ (ɛ): 534 (2.1 × 104), 449 (sh, 4.9 × 103), 360 (6.0 × 103), 260 nm (4.3 × 104). X-ray quality crystals were obtained by slow diffusion of Et2O vapors into a soln of the complex in MeCN at rt.

1.2.5.1.2.2 Method 2: Comproportionation of Palladium(II) and Palladium(IV) Complexes

Halide-bridged binuclear palladium(III) complex 11 has been prepared by comproportionation of mononuclear palladium(II) complex 10 with mononuclear palladium(IV) complex 12 (▶ Scheme 7).[43]

▶ Scheme 7 Comproportionation of a Palladium(II) Complex and a Palladium(IV) Complex Affords a Chloride-Bridged Binuclear Palladium(III) Complex[43]

μ-Chlorobis[dichloro(1,4,7-trimethyl-1,4,7-triazacyclononane-κ3N)palladium(III)] Hexafluorophosphate (11):[43]

A soln of 10 (4.9 mg, 1.0 equiv) in 0.1 M Bu4NPF6 in MeCN (7 mL) was placed into a spectroelectrochemical cell (path length 1 mm). A stock 2.02 M soln of Et4NCl in MeCN (70 μL, 1.0 equiv) was added. The resulting soln was electrooxidized at a potential of 600 mV vs a Ag/AgNO3/MeCN reference electrode. The electrolysis was stopped when a charge corresponding to a two-electron oxidation was transferred giving a yellow soln of 12; UVvis (MeCN) λ (ɛ): 423 (sh, 9.7 × 102), 352 nm (3.2 × 103). To this soln, a soln of 10 (5.0 mg, 1.0 equiv) in 0.1 M Bu4NPF6 in MeCN (2 mL) was added. An immediate color change was observed and the reaction was complete in less than 1 min to give a dark purple soln of 11. The concentration of 11 was calculated to be 1.6 × 10−3 M based on the intensity of the band at 360 nm, which corresponds to a quantitative yield of 11. For spectroscopic data see ▶ Section 1.2.5.1.2.1.

1.2.5.1.3 Binuclear Palladium(2.5) Complexes with a Pd—Pd Bond Order of 0.5

Overlap of the 4d orbitals of two palladium centers gives rise to the qualitative molecular orbital picture in ▶ Figure 2;[44] the orbital is predominantly metal–ligand bonding and is thus not included. Based on the illustrated molecular orbital diagram, both the σ and σ* orbitals should be filled in binuclear palladium(II) complexes and, as such, no attractive metal–metal interaction is expected.[45] Second-order, symmetry-allowed mixing of the palladium orbital with the 5pz and the 5s orbital, which is not accounted for on the simplified diagram in ▶ Figure 2, perturbs the molecular orbital diagram based only on d orbital interactions and can result in attractive Pd…Pd interactions.[46–48] Computational studies of Pd(II)…Pd(II) interactions have supported weak attractive interaction between the palladium in binuclear palladium complexes and have suggested bond orders as high as 0.19.[46–49]

▶ Figure 2 Molecular Orbital Diagram Based on Mixing the 4d Orbitals of Two Interacting Palladium Nuclei[44]

1.2.5.1.3.1 Method 1: Binuclear Palladium(2.5) Complexes by Electrochemical Oxidation

One-electron oxidation of binuclear palladium(II) complexes can afford binuclear palladium(2.5) complexes featuring a Pd—Pd bond order of 0.5. Controlled potential electrolysis (CPE) has been used to accomplish the one-electron oxidation of binuclear palladium(II) complex 13 affording binuclear palladium(2.5) complex 14 (counterion X− not reported; ▶ Scheme 8), which has been characterized by EPR spectroscopy. Detailed experimental procedures for the oxidation of 13 are not currently available.[50]

▶ Scheme 8 Controlled Potential Electrolysis of a Binuclear Palladium(II) Complex Affords a Binuclear Palladium(2.5) Complex[50]

1.2.5.1.3.2 Method 2: Binuclear Palladium(2.5) Complexes Using Single-Electron Oxidants

The one-electron oxidant silver(I) hexafluorophosphate has been used to effect the oxidation of binuclear palladium(II) complex 15 to binuclear palladium(2.5) complex 16 (▶ Scheme 9).[51] The relative Pd—Pd distances in 15 as compared to 16, which were determined by single-crystal X-ray diffraction, are consistent with a Pd—Pd 0.5 order bond in 16.

▶ Scheme 9 Preparation of a Binuclear Palladium(2.5) Complex by Oxidation of a Binuclear Palladium(II) Complex with Silver(I) Hexafluorophosphate[51]

Tetrakis[μ-N,N′-bis(4-methoxyphenyl)-4-methoxybenzimidamidato-1:2κ2N:N′]dipalladium(II)(Pd—Pd) Hexafluorophosphate (16):[51]

To a soln of complex 15 (350 mg, 0.284 mmol, 1.00 equiv) in CH2Cl2 (10 mL) was added AgPF6 (72.0 mg, 0.284 mmol, 1.00 equiv) dissolved in CH2Cl2 (10 mL) at −70 °C. An immediate color change from orange to black was observed. The mixture was stirred for 10 min at −70 °C, followed by filtration through Celite. A dark green powder was precipitated by addition of Et2O and dried under vacuum; yield: 0.275 g (70%); IR (KBr): 1608, 1591, 1499, 1464, 1438, 1423, 1325, 1294, 1246, 1226, 1132, 1094, 1024, 928, 844, 829, 803, 787, 722, 645, 585, 558, 540, 505, 406 cm−1.

1.2.5.1.4 Tetrabridged Binuclear Palladium(III) Complexes with a Pd—Pd Bond

1.2.5.1.4.1 Method 1: Binuclear Palladium(III) Complexes by Oxidation with Hypervalent Iodine

The first binuclear palladium(III) complex reported was complex 18, which was prepared by treatment of binuclear palladium(II) complex 17 with (dichloroiodo)benzene (▶ Scheme 10).[52] In both 17 and 18, the two palladium centers are bridged by four pyridine-2-thiolato ligands. Experimental procedures and characterization data of complex 18 have not been reported. Similarly, the guanidine-bridged binuclear palladium(III) complex 20 has been prepared by oxidation of binuclear palladium(II) complex 19 with (dichloroiodo)benzene (▶ Scheme 10).[53] The observed Pd—Pd contraction upon oxidation of 19 to 20, as determined by single-crystal X-ray diffraction, as well as computational studies of the electronic structure of 20, are consistent with a Pd—Pd single bond in 20 arising from removal of two electrons from a Pd—Pd σ* orbital during oxidation.

▶ Scheme 10 Preparation of Tetrabridged Binuclear Palladium(III) Complexes by Oxidation of Binuclear Palladium(II) Complexes with (Dichloroiodo)benzene[52,53]

Tetrakis(μ-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato-1:2κ2N1:N9)bis(chloropalladium)(Pd—Pd) (20):[54]

To a suspension of binuclear Pd(II) complex 19 (535 mg, 0.700 mmol, 1.00 equiv) in MeCN (10 mL) at 23 °C was added PhICl2 (192 mg, 0.700 mmol, 1.00 equiv) and the mixture was stirred for 1 h at 23 °C. The dark green precipitate from the mixture was filtered over a glass fiber filter paper and the solid residue was triturated with benzene (5 mL) (CAUTION:carcinogen). The suspension was filtered over a glass fiber filter paper, the dark green residue was collected and dissolved in CH2Cl2, and the solvent was removed under reduced pressure to afford compound 20 as a dark green solid; yield: 230 mg (27%); 1H NMR (500 MHz, CD2Cl2, −50 °C, δ): 3.90–3.84 (m, 8H), 3.12–3.05 (m, 16H), 2.93–2.88 (m, 8H), 1.88–1.81 (m, 8H), 1.72–1.65 (m, 8H); 13C NMR (1.25 MHz, CD2Cl2, 25 °C, δ): 165.1, 48.8, 48.6, 26.0; UV-vis (CH2Cl2, 22 °C) λ (ɛ): 648 (1.08 × 102), 324 nm (3.30 × 103). Crystals suitable for X-ray diffraction analysis were obtained by diffusion of pentane into a soln of 20 in CH2Cl2 at 0 °C.

1.2.5.1.4.2 Method 2: Inorganic Binuclear Palladium(III) Complexes via Ligand Metathesis

Guanidine-bridged binuclear palladium(III) complexes can be prepared by ligand exchange on preformed binuclear palladium(III) complexes, such as 20. Silver carboxylate salts 21 are employed to effect the ligand metathesis of chloride to carboxylate to generate binuclear palladium(III) complexes 22 (▶ Scheme 11).[54]

▶ Scheme 11 Preparation of Binuclear Palladium(III) Complexes by Ligand Exchange on a Binuclear Palladium(III) Chloride Complex with Silver Carboxylates[54]

R

1

Yield (%)

Ref

Ph

83

[

54

]

Pr

70

[

54

]

1.2.5.1.4.3 Method 3: Organometallic Tetrabridged Binuclear Palladium(III) Complexes

The first organometallic complexes of palladium(III) were reported in 2006.[55–57] A series of tetrabridged binuclear palladium(III) complexes 24, in which two bridging carboxylates and two bridging metalated arylphosphine ligands support the Pd—Pd bond, have been prepared by oxidation of binuclear palladium(II) complexes 23 (▶ Scheme 12). Two procedures have been used to prepare this family of complexes: oxidation with either (dichloroiodo)benzene or bromine.

▶ Scheme 12 Preparation of Binuclear Palladium(III) Halide Complexes by Oxidation of Binuclear Palladium(II) Complexes with (Dichloroiodo)benzene or Bromine[55–57]

R

1

Yield (%)

Ref

Me

90

[

55

]

t

-Bu

96

[

55

]

CF

3

78

[

55

]

Bis(μ-acetato-κO:κO′)[μ-(diphenylphosphino-1κP)phenyl-2κC][μ-(diphenylphosphino-2κP)phenyl-1κC]bis(bromopalladium)(Pd—Pd) (26):[57]

CAUTION:

Bromine is a severe irritant of the eyes, mucous membranes, lungs, and skin. Liquid bromine causes severe and painful burns on contact with eyes and skin.

A suspension of 25 (36 mg, 0.042 mmol, 1.0 equiv) in Et2O (6 mL) was cooled to −10 °C. A slight excess of Br2 (5.0 μL, 0.097 mmol, 2.3 equiv) in Et2O (1 mL) was added dropwise while the mixture was stirred. The color changed from yellow to dark red. The mixture was stirred for 15 min at ca. −5 °C. The pale red soln was decanted off and the red precipitate was washed with Et2O (3 × 3 mL) and then dried under vacuum to give the product; yield: 42 mg (98%); 1H NMR (CDCl3, 20 °C, δ): 8.41–8.35 (m, 4 H), 8.08–8.04 (m, 2H), 7.05–7.55 (m, 16H), 7.00–6.95 (m, 2H), 6.89–6.84 (m, 2 H), 6.81–6.74 (m, 2H), 1.23 (s, 6H); 31P NMR (CDCl3, 20 °C, δ): −15.0. Single crystals suitable for X-ray diffraction were obtained by diffusion of Et2O into a CH2Cl2 soln of 26 at −15 °C.

1.2.5.1.5 Binuclear Palladium(III) Complexes Supported by Two Bridging Ligands

A family of acetate-bridged binuclear palladium(III) complexes, in which two acetate ligands bridge the binuclear core and each palladium bears a cyclometalated arylpyridine ligand, have been prepared.[58–63] This family of complexes has been of interest in large part because carbon—heteroatom (C—X) bond-forming reductive elimination reactions have been observed from these complexes and it has been proposed that these, and related complexes, may be intermediates in various palladium-catalyzed C—H oxidation reactions.[58–63] The observed C—X reductive elimination reactions from acetate-bridged binuclear palladium(III) complexes constituted the first organometallic transformations documented from palladium(III) complexes.

1.2.5.1.5.1 Method 1: Oxidation with Hypervalent Iodine Reagents

The most common protocol for the preparation of binuclear palladium(III) complexes is oxidation of preformed binuclear palladium(II) complexes with hypervalent iodine reagents.[59,61] (Dichloroiodo)benzene and (diacetoxyiodo)benzene are both effective in the oxidation of binuclear palladium(II) complex 27 to afford binuclear palladium(III) complex 28 (▶ Scheme 13).

▶ Scheme 13 Oxidation of an Acetate-Bridged Binuclear Palladium(II) Complex with Hypervalent Iodine-Based Oxidants Affords Binuclear Palladium(III) Complexes[59,61]

PhIX

2

X

Yield (%)

Ref

PhICl

2

Cl

92

[

61

]

PhI(OAc)

2

OAc

88

[

59

]

1.2.5.1.5.2 Method 2: Oxidation with Peroxides

Oxidation of carboxylate-bridged binuclear palladium(II) complexes, e.g. 29, with dibenzoyl peroxides can afford binuclear palladium(III) complexes (▶ Scheme 14).[58] While at low temperature isomerically pure binuclear palladium(III) complexes, such as 30, have been obtained, carboxylate scrambling between apical and bridging positions has been observed at more elevated temperatures (0 °C) and can generate mixtures of binuclear palladium(III) isomers.

▶ Scheme 14 Preparation of a Binuclear Palladium(III) Complex by Oxidation with a Dibenzoyl Peroxide[58]

Bis(μ-benzoato–κO:κO′)bis[(4-nitrobenzoato-κO)(2-pyridyl-κN-phenyl-κC2)palladium](Pd—Pd) (30):[58]

1.2.5.1.5.3 Method 3: Oxidation with Halogens

Binuclear palladium(III) bromide complex 31 has been prepared by direct oxidation of binuclear palladium(II) complex 27 with elemental bromine (▶ Scheme 15).[61]

▶ Scheme 15 Preparation of a Binuclear Palladium(III) Bromide Complex by Oxidation of an Acetate-Bridged Binuclear Palladium(II) Complex with Bromine[61]

Bis(μ-acetato-κO:κO′)bis[bromo(benzo[h]quinolinyl-κC10,κN)palladium](Pd—Pd) (31):[61]

CAUTION:

Bromine is a severe irritant of the eyes, mucous membranes, lungs, and skin. Liquid bromine causes severe and painful burns on contact with eyes and skin.

1.2.5.1.6 Unbridged Pd(III)—Pd(III) Bonds

1.2.5.1.6.1 Method 1: Oxidation of Acetate-Bridged Binuclear Palladium(III) Complexes with Xenon Difluoride

Oxidation of binuclear palladium(II) complex 27 with xenon difluoride results in extended chains of palladium(III) centers organized by unbridged Pd—Pd bonds (▶ Scheme 16).[64] Both binuclear 32 as well as oligomeric 33 complexes have been characterized by X-ray crystallography in the solid state. Palladium(III) fluorides 32 and 33 have been used as precursors to ligand-capped binuclear palladium(III) complexes via ligand exchange of the fluoride ligands. Treatment of palladium(III) fluoride complexes 32 and 33 with various TMSX reagents affords fluorotrimethylsilane, the product of fluoride capture by the silane, and binuclear palladium(III) complexes, e.g. 34 (▶ Scheme 16).

▶ Scheme 16 Preparation of Palladium(III) Fluoride Complexes by Oxidation of a Binuclear Palladium(II) Complex with Xenon Difluoride, and Synthesis of a Binuclear Palladium(III) Complex by Ligand Exchange between a Palladium(III) Fluoride and Trimethylsilyl Acetate[64]

Bis(μ-acetato-κO:κO′)bis[(benzo[h]quinolinyl-κC10,κN)fluoropalladium](Pd—Pd) (32) and Oligomer 33:[64]

CAUTION:

Xenon difluoride is a powerful oxidant that sublimes rapidly. Some of its reactions with hydrocarbons in glassware have resulted in explosions.

Bis(μ-acetato-κO:κO′)bis[(acetato-κO)(benzo[h]quinolinyl-κC10,κN)palladium](Pd—Pd) (34):[64]

CAUTION:

Xenon difluoride is a powerful oxidant that sublimes rapidly. Some of its reactions with hydrocarbons in glassware have resulted in explosions.

1.2.5.2 Stoichiometric Organometallic Chemistry of Isolated Palladium(III) Complexes

1.2.5.2.1 Organometallic Chemistry of Mononuclear Palladium(III) Complexes

1.2.5.2.1.1 Method 1: C—C Bond-Forming Reactions of Mononuclear Palladium(III) Complexes

The isolation of mononuclear palladium(III) complexes has enabled the stoichiometric organometallic chemistry of these complexes to be investigated for the first time. Photolysis of mononuclear palladium(III) complex 35 affords a mixture of ethane, methane, and chloromethane, along with palladium(II) complex 36 (▶ Scheme 17).[40] The addition of radical scavengers, such as 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), suppresses the formation of ethane, methane, and chloromethane, instead leading only to the observation of 1-methoxy-2,2,6,6-tetramethylpiperidine (37) and palladium(II) complex 36. The observed reaction products are consistent with a reaction manifold initiated by photochemically induced Pd—C bond homolysis.

▶ Scheme 17 Observed Photochemistry of a Mononuclear Palladium(III) Complex, which Likely Proceeds via Homolytic Pd—C Bond Cleavage[40]

(Acetonitrile)chloro[3,7-di-tert-butyl-3,7-diaza-1,5(2,6)-dipyridina-κ2N-cyclooctaphane]palladium(II) Tetrafluoroborate (36):[40]

1.2.5.2.1.2 Method 2: C—C Bond-Forming Reactions Initiated by Ligation of Anionic Donors

Treatment of mononuclear palladium(III) complex 8 with various anionic donors, such as hydroxide or cyanide, promotes C—C coupling (▶ Scheme 18).[42] The observed reactivity is rationalized as due to anion-induced disproportionation of 8