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Edited byMasahiro Murakami andNaoto Chatani

Cleavage of Carbon-Carbon SingleBonds by Transition Metals

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Edited by Masahiro Murakami and Naoto Chatani

Cleavage of Carbon-Carbon Single Bondsby Transition Metals

The Editors

Prof. Dr. Masahiro MurakamiKyoto UniversityDepartment of Synthetic Chemistry andBiological ChemistryKatsuraKyoto 615-8510Japan

Prof. Dr. Naoto ChataniOsaka UniversityDepartment of Applied ChemistrySuitaOsaka 565-0871Japan

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V

Contents

Preface IXList of Contributors XI

1 Fundamental Reactions to Cleave Carbon–Carbon 𝛔-Bonds withTransition Metal Complexes 1Masahiro Murakami and Naoki Ishida

1.1 Introduction 11.2 Oxidative Addition 11.2.1 Oxidative Addition Utilizing Ring Strain 31.2.2 Chelation-Assisted Oxidative Addition 51.2.3 Oxidative Addition Driven by Aromatization 61.2.4 Oxidative Addition of Ketones 71.2.5 Oxidative Addition of Nitriles 111.2.6 Others 131.3 β-Carbon Elimination 141.3.1 β-Carbon Elimination of Late Transition Metal Alkyls 151.3.2 β-Carbon Elimination from Early Transition Metal Alkyls 161.3.3 β-Carbon Elimination of Late Transition Metal Alcoholates 171.4 Retroallylation 201.5 Migratory Deinsertion of a Carbonyl Group 221.6 Decarboxylation 241.7 Retro-oxidative Cyclization 251.8 1,2-Migration 271.9 Cleavage of C–C Multiple Bonds 291.10 Summary 30

References 30

2 Reactions of Three-Membered Ring Compounds 35Takanori Matsuda

2.1 Introduction 352.2 Cyclopropanes 352.3 Bicyclo[1.1.0]butanes 402.4 Bicyclo[2.1.0]pentanes 43

VI Contents

2.5 Quadricyclanes and Related Compounds 452.6 Spiropentanes 472.7 Cyclopropanols 482.8 Vinylcyclopropanes 512.9 Methylenecyclopropanes 592.10 Alkynylcyclopropanes 702.11 Cyclopropyl Ketones and Imines 712.12 Cyclopropenes 732.13 Benzocyclopropenes 782.14 Cyclopropenones 802.15 Conclusion 82

References 83

3 Reactions of Four-Membered Ring Compounds 89Takanori Matsuda

3.1 Introduction 893.2 Cubane Derivatives 893.3 Biphenylenes 903.4 Vinylcyclobutane and Methylenecyclobutane Derivatives 933.5 Cyclobutanol and Cyclobutanone Derivatives 953.5.1 Reactions Involving β-Carbon Elimination of Transition Metal

Cyclobutanolates 953.5.2 Reactions Involving Formation of Five-Membered

Metallacycles 1083.6 Cyclobutenones and Cyclobutenediones 1123.7 Conclusion 115

References 115

4 Reactions Involving Elimination of CO2 and Ketones 119Tetsuya Satoh and Masahiro Miura

4.1 Introduction 1194.2 Reactions of Benzoic Acids 1194.2.1 Arylation 1194.2.2 Alkenylation 1274.2.3 Annulation 1304.2.4 Miscellaneous Reactions 1324.3 Reactions of Heteroarenecarboxylic Acids 1344.4 Reactions of Acrylic Acids 1394.5 Reactions of Propiolic Acids 1424.6 Reactions of α-Keto Carboxylic Acids 1444.7 Reactions of Alkanoic Acids 1484.8 Reactions of Tertiary Alcohols 1514.8.1 Arylation 1514.8.2 Alkenylation, Annulation, and Alkylation 155

Contents VII

4.9 Summary and Conclusions 159References 160

5 Retro-allylation and Deallylation 165Hideki Yorimitsu

5.1 Introduction 1655.2 Retro-allylation 1655.2.1 Ruthenium Catalysis: The Pioneer 1675.2.2 Palladium Catalysis: Regio- and Stereoselective Allylation of Aryl

Halides 1685.2.2.1 Advantage of Palladium-Catalyzed Allylation via

Retro-allylation 1685.2.2.2 Palladium-Catalyzed Regio- and Stereoselective Allylation via

Retro-allylation 1705.2.2.3 Variants of Palladium-Catalyzed Retro-allylation 1765.2.3 Nickel Catalysis 1795.2.4 Rhodium Catalysis 1815.2.5 Copper Catalysis 1845.3 Deallylation 1855.3.1 Oxidative Addition of Allylic Compounds 1855.3.2 Metalation–β-Carbon Elimination Sequence 1875.4 Summary and Conclusions 189

References 190

6 Reactions via Cleavage of Carbon–Carbon Bonds of Ketones andNitriles 193Mamoru Tobisu

6.1 Introduction 1936.2 Catalytic Reactions of Ketones via C–C Bond Cleavage 1946.2.1 Reactions of Ketones without Chelation Assistance 1946.2.2 Reactions of Ketones Containing a Directing Group 1966.2.3 Reactions of Ketones Using a Temporary Directing Group 2006.2.4 C–C Bond Cleavage of Ketones via Pathways Other than Oxidative

Addition 2026.2.4.1 C–C Bond Cleavage of 1,3-Dicarbonyl Compounds 2026.2.4.2 C–C Bond Cleavage of Ketones Other than 1,3-Dicarbonyl

Compounds 2036.3 Catalytic Reactions of Nitriles via C–C Bond Cleavage 2056.3.1 C–CN Bond Cleavage via Oxidative Addition 2056.3.2 C–CN Bond Cleavage via Silylmetalation/Isocyanide Extrusion

Sequence 2126.3.3 C–CN Bond Cleavage via Other Mechanisms 2156.4 Summary and Outlook 216

References 217

VIII Contents

7 Miscellaneous 221Masahiro Murakami and Naoki Ishida

7.1 Introduction 2217.2 Cleavage of C–C Single Bonds 2217.3 Cleavage of C=C Double Bonds 2357.4 Cleavage of C–C Bonds of Aromatics 2377.5 Cleavage of C≡C Triple Bonds 2427.6 Summary 248

References 248

8 Total Syntheses of Natural Products and Biologically ActiveCompounds by Transition-Metal-Catalyzed C–C Cleavage 253Masahiro Murakami and Naoki Ishida

8.1 Introduction 2538.2 Synthesis of (±)-Nanaomycin A through Alkyne Insertion into a

C–C Bond of Benzocyclobutenedione 2538.3 Enantioselective Synthesis of (−)-Pseudolaric Acid B via an

Intramolecular [5+2] Cycloaddition Reaction of a Vinylcyclopropanewith an Alkyne 254

8.4 Enantioselective Synthesis of (−)-Esermethole via AsymmetricAlkene Insertion into a C–C Bond of Aryl Cyanides 256

8.5 Enantioselective Synthesis of Benzobicyclo[2.2.2]octenones viaAsymmetric Alkene Insertion into a C–C Bond ofCyclobutanones 257

8.6 Synthesis of the Proposed Structure of Cycloinumakiol throughSite-Selective Insertion of Alkenes into a C–C Bond ofBenzocyclobutenones 259

8.7 Enantioselective Synthesis of (−)-(R)-Herbertenol throughAsymmetric C–C Cleavage 260

8.8 Enantioselective Synthesis of (+)-Laurene via Ring-Expansion of1-Vinylcyclobutanol 261

8.9 Synthesis of (±)-Cuparenone through Skeletal Reorganization ofSpiropentanes 262

8.10 Total Synthesis of (−)-Cyanthiwigin F by DecarboxylativeAsymmetric Allylation 264

8.11 Total Syntheses via Hydrogenolysis of Cyclopropanes 2658.12 Total Syntheses via Decarbonylation 2668.13 Summary and Conclusions 269

References 270

Index 273

IX

Preface

A number of transformations are currently available for organic compounds.Mechanistically, most reactions are related to their π-bonds (e.g., C=C, C=O) orpolar σ-bonds (e.g., C–Br, C–Li). The frontier orbitals of those bonds are ener-getically as well as sterically accessible for interaction with other orbitals. On theother hand, the frontier orbitals of nonpolar σ-bonds like C–H and C–C bondsare, in general, much less accessible both energetically and sterically (See Chapter1 for details). They remain intact under most conventional reaction conditions.Nonetheless, it would provide more straightforward synthetic pathways if aspecific one among the ubiquitous nonpolar σ-bonds was selectively cleaved anddirectly employed for construction and/or functionalization of organic skeletons.

In 1993, Prof. Shinji Murai and his coworkers reported a selective addition reac-tion of an aromatic C–H bond across a C–C double bond catalyzed by ruthenium,demonstrating the feasibility, and the synthetic potential, of metal-catalyzedcleavage of nonpolarσ-bonds. Since then, a number of catalytic transformations ofnonpolar σ-bonds have been developed and even applied to the synthesis of com-plex natural products and functional materials. This book focuses on transition-metal-mediated and -catalyzed reactions involving C–C bond cleavage. It consistsof eight chapters. The first chapter deals with fundamental reactions (stoichio-metric reactions) on C–C bond cleavage. This chapter serves as the basis forunderstanding the mechanisms of the complex catalytic reactions described inChapters 2–7. Chapter 8 exemplifies applications of C–C bond cleavage reactionsto total syntheses of natural products and biologically active molecules.

Each chapter is written by a distinguished chemist who has made a significantcontribution to the progress of the chemistry related to C–C bond activation. Iwould like to thank all the authors for their enormous efforts for this book project.I also appreciate the staff of the editorial team of Wiley-VCH for their continuoushelp. I hope this book assists the readers to overview this emerging field of chem-istry, and also inspires new ideas for the reader’s own endeavors in the future.

Kyoto, April 2015 Masahiro Murakami

XI

List of Contributors

Naoki IshidaKyoto UniversityDepartment of SyntheticChemistry and BiologicalChemistryKatsuraNishikyo-kuKyoto 615-8510Japan

Takanori MatsudaTokyo University of ScienceDepartment of AppliedChemistry1-3 KagurazakaShinjuku-kuTokyo 162-8601Japan

Masahiro MiuraOsaka City UniversityDepartment of AppliedChemistryFaculty of Engineering2-1 Yamada-okaSuitaOsaka 565-0871Japan

Masahiro MurakamiKyoto UniversityDepartment of SyntheticChemistry and BiologicalChemistryKatsuraNishikyo-kuKyoto 615-8510Japan

Tetsuya SatohOsaka City UniversityDepartment of ChemistryGraduate School of Science3-3-138 SugimotoSumiyoshi-kuOsaka 558-8585Japan

and

Osaka City UniversityDepartment of AppliedChemistry, Faculty ofEngineering2-1 Yamada-okaSuitaOsaka 565-0871Japan

XII List of Contributors

Mamoru TobisuOsaka UniversityDepartment of AppliedChemistryCenter for Atomic and MolecularTechnologiesGraduate School of Engineering2-1 Yamada-okaSuitaOsaka 565-0871Japan

Hideki YorimitsuKyoto UniversityDepartment of ChemistryGraduate School of ScienceKitashirakawa Oiwake-choSakyo-kuKyoto 606-8502Japan

1

1Fundamental Reactions to Cleave Carbon–Carbon 𝛔-Bondswith Transition Metal ComplexesMasahiro Murakami and Naoki Ishida

1.1Introduction

Transition metal-catalyzed reactions proceed through multiple elementary stepsin general and, consequently, the mechanisms are often complicated, especiallywhen backbone structures are reconstructed through a sequence of cleavageand formation of C–C bonds. A step-by-step understanding of elementary stepswould be valuable to understand such catalytic transformations. This chapterfocuses on elementary steps during which carbon–carbon σ-bonds are cleavedby means of organometallic complexes.

An elementary step to cleave C–C bonds is a reverse process of a C–C bondforming process. Oxidative addition of a C–C bond to a low-valent transitionmetal complex is a reverse process of reductive elimination, which occurs witha high-valent diorganometal, forming a C–C bond. β-Carbon elimination is areverse process of insertion of an unsaturated bond into a carbon–metal bond,that is, carbometallation, or 1,2-addition of an organometal across a doublebond. Such fundamental reactions are described along with typical examples.Besides this chapter, there are some excellent reviews on C–C bond cleavageavailable [1].

1.2Oxidative Addition

Oxidative addition is insertion of a metal into a covalent bond. It involves formaltwo-electron oxidation of the metal center or one-electron oxidation of two metalcenters (Scheme 1.1).

C CMn +

+

CMn+2

C

C C2Mn Mn+12 C Scheme 1.1

Cleavage of Carbon-Carbon Single Bonds by Transition Metals, First Edition.Edited by Masahiro Murakami and Naoto Chatani.© 2016 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2016 by Wiley-VCH Verlag GmbH & Co. KGaA.

2 1 Fundamental Reactions to Cleave Carbon–Carbon σ-Bonds with Transition Metal Complexes

Oxidative addition offers a direct method to cleave a covalent bond. Althougha wide variety of bonds, such as C–I and C–Br, are known to facilely undergooxidative addition reactions to low-valent transition metal complexes, examplesof oxidative addition of C–C single bonds are far more rare. The scarcity is inpart associated with the thermodynamic stability of C–C bonds. Whereas oxida-tive addition of C–Br and C–I bonds to low-valent metals is thermodynamicallyfavored in general, that of a C–C single bond is often thermodynamically disfa-vored.

The kinetic reason for the difficulty in breaking C–C single bonds is the con-strained directionality of theirσ-orbital. Figure 1.1 shows the interaction of a metalorbital with a C–C single bond. The interactions with C–C double bonds andC–H single bonds are also depicted for comparison. The π-orbital of a C–C dou-ble bond is oriented sideways, and thus it interacts with a metal orbital withoutsignificant strain and severe steric repulsion. The σ-orbital connecting hydrogenand carbon atoms lies along the bond axis and the directionality is less matchedwith the metal orbital. However, the constituent 1s orbital of the hydrogen atomis spherical, and can interact with a metal orbital from any direction without dis-tortion. The hydrogen atom has no other substituents except the bonded carbon,thus sterically rendering the direct approach of the metal center less cumbersome.On the other hand, the σ-orbital of a C–C single bond possesses high direction-ality along the bond axis. Moreover, there are several substituents on both ends,which sterically prevent the approach of metal orbitals. Thus, interaction of sucha C–C σ-orbital with a metal orbital is much more difficult than those of a C–Cdouble bond and a C–H bond. Not only the thermodynamic stability, but also thiskinetic barrier renders C–C σ-bonds considerably inert.

Despite the intrinsic difficulties mentioned above, a number of strategies havebeen devised to realize oxidative addition of C–C σ-bonds. For example, releaseof ring strain of a substrate molecule affords both kinetic and thermodynamicdrive for oxidative addition. A chelating effect also assists both kinetically and

M

M

M

M

C C C H

C C C H

M

C C

M

C C

R

R

R

R

R

R

R

RBonding

Back-Bonding

R

RR

R

RR

R R

R R

R R

RRR

R

R

R

Figure 1.1 Orbital interactions of a metal with C=C, C–H, C–C bonds.

1.2 Oxidative Addition 3

M

C C

M

C C

Figure 1.2 Orbital interactions of a metal with a C–C bond of cyclopropane.

thermodynamically. Aromatization is also exploited as the driving force for oxida-tive addition of a C–C bond. Each case is exemplified in the following sections.

1.2.1Oxidative Addition Utilizing Ring Strain

The orbitals of cyclopropane C–C bonds form “banana bonds”, which protrudeaway from the bond axis between the two carbon atoms (Figure 1.2). Consequentlya metal center can interact with them similarly, to some extent, to the case of ametal–olefin interaction. This interaction lowers the kinetic barrier of the C–Coxidative addition. In addition, the enlargement of the three-membered cyclo-propane ring to a four-membered metallacyclobutane relieves the structural strainowing to its constrained bond angles. Thus, the use of cyclopropanes as substratesfor oxidative addition of C–C bonds is advantageous both kinetically and thermo-dynamically.

In fact, PtCl2 reacted with cyclopropane to form platinacyclobutanes(Scheme 1.2) [2]. Cyclopropanes substituted with more electron-donating groupsreacted faster and cyano and keto-substituted cyclopropanes remained intact [3].

PtCl2Ac2O, rt

PtCl2+

Scheme 1.2

It is often observed that C–H activation precedes C–C activation. Forinstance, photoirradiation of Cp*Rh(PMe3)(H2) generated coordinatively unsatu-rated Cp*Rh(PMe3) with liberation of dihydrogen (Scheme 1.3) [4]. The rhodiumcomplex reacted with cyclopropane at −60 ∘C to furnish a C–H oxidativeaddition product. No cleavage of a C–C bond was observed at this low tem-perature. Upon raising the temperature to 0–10 ∘C, the cyclopropylrhodiumrearranged to a rhodacyclobutane. This result indicates that oxidative additionof a C–H bond is kinetically favored and oxidative addition of a C–C bond is

Cp*Rh(PMe3)(H2) Cp*Rh(PMe3)

−60 °CRh

Me3P

HCp*Rh

Me3P

Cp*0−10 °C

h𝜈

−H2

Scheme 1.3


RhP

Me

H

i-Pr

i-Pr

[BArF4] ArF =

CF3

CF3

1

2

3

4

Figure 1.3 A rhodium complex with an agostic interaction with a C–C bond.

thermodynamically favored in this case. The kinetic preference for the oxidativeaddition of the C–H bond demonstrates the greater steric accessibility of theC–H bond compared with the C–C bond. The analogous rearrangement of a(cyclobutyl)(hydride)rhodium complex into rhodacyclopentane has also beenreported [5].

Oxidative addition would proceed via coordination of the σ-bond to the metal(agostic interaction). A rhodium complex with an agostic interaction between acyclopropane C–C σ-bond and a rhodium center has been reported (Figure 1.3)[6]. The bond lengths of Rh–C3 and Rh–C4 are 2.352 and 2.369 Å, longer thantypical Rh–C single bonds, but within the sum of the van der Waals radii of Rhand C. The C3–C4 bond (1.6 Å) is longer than typical cyclopropane C–C bonds(about 1.5 Å), but again within the sum of the van der Waals radii of two carbons.The bonding between Rh and C3–C4 indicates that it might be the precursorystructure for oxidative addition of cyclopropane C–C bonds.

Biphenylenes undergo oxidative addition to various low-valent metals toform the corresponding dibenzometalloles [7]. The reaction with Cp*Rh(PMe3)involved C–H activation prior to C–C activation, as with the case of C–C acti-vation of cyclopropane [7c]. On the other hand, the reaction with [Rh(Pi-Pr3)2]+initially formed the η6-arene complex, which led to the dibenzorhodacycle[7g]. Density functional theory (DFT) calculation suggested the C–C activationproceeds via the rhodium η4-cyclobutadiene intermediate (Scheme 1.4).

Rh rt, 5 min

1,2-difluorobenzene

F+

+

+ +

Pi-Pr3i-Pr3PRh

Pi-Pr3i-Pr3P

Rh

Pi-Pr3i-Pr3P

Pi-Pr3

Pi-Pr3

Rh

Suggested by DFT

Scheme 1.4


A wide variety of strained C–C bonds, such as methylenecyclopropanes[8], vinylcyclopropanes [9], perfluorocyclopropenes [10], and cubane [11], alsoundergo oxidative addition. The oxidative addition of small ring molecules servesfor initiation of their catalytic transformations (Chapters 2 and 3).

1.2.2Chelation-Assisted Oxidative Addition

The Lewis basic functionalities, like phosphines, facilely coordinate to a metal,whereby the metal center is brought into proximity to a specific C–C bond. Thecoordination facilitates insertion of the metal into a C–C bond both kineticallyand thermodynamically. For example, a system consisting of [RhCl(olefin)2]2 anda bulky, pincer diphosphine ligand led to site-selective metal insertion into anaryl–methyl bond at room temperature (Scheme 1.5) [12]. Initially, the simul-taneous formation of a C–H activated complex and a C–C activated complexwas observed. The C–H activated complex was gradually converted to the C–Cactivated complex at room temperature, demonstrating that the C–C activatedcomplex is thermodynamically more stable than the C–H activated product.Furthermore, a kinetic study revealed that, if the numbers of bonds availablefor activation are taken into account, metal insertion into the C–C bond isalso kinetically preferred over the competing insertion into the C–H bondin this case. Electronic perturbation of the aromatic ring by introduction of amethoxy group had no significant influence on the reaction rate and the productratio, suggesting that the C–C oxidative addition proceeds via a three-centerednonpolar transition state similar to that postulated for C–H bond activation.

Pt-Bu2

Pt-Bu2

Me

Me

Me + [RhCl(CH2=CH2)2]2benzene, rt

Pt-Bu2

Pt-Bu2

Me

Me

RhCl

Pt-Bu2

Pt-Bu2

Me

Me

Rh ClH

Me

+

Scheme 1.5

Other pincer systems also undergoes oxidative addition of C–C bonds. Aphosphine-amine pincer ligand reacted with a rhodium olefin complex moreeasily than diphosphine pincer ligands to give a C–C bond activated complexin minutes at room temperature (Scheme 1.6) [13]. In this case, the formationof a C–H activated complex was not observed upon monitoring the reaction,even at −50 ∘C. It was proposed that the failure to observe the C–H activatedproduct is attributed to the rapid, reversible dissociation of the amine ligand;


Pt-Bu2

NEt2

Me

Me

Me + [RhCl(CH2=CH2)2]2benzene, rt

Pt-Bu2

NEt2

Me

Me

Rh Cl

Me

Scheme 1.6

the dissociation would lower the electron density on the rhodium center tosignificantly facilitate the C–H reductive elimination process.

The presence of a C–C–H η3-agostic interaction was proposed as the inter-mediate for oxidative addition of an SCS-pincer rhodium complex on the basisof the DFT calculation (Scheme 1.7) [14]. Both the C–C and C–H σ-bondsdonate bonding electrons to the d orbital of rhodium (Figure 1.4). The olefinligand located at the trans-position accepts electrons, which reinforces electrondonation from C–C and C–H σ-bonds. The agostic complex is the intermediateleading to both C–C and C–H activations.

P

P

S

S

Me + [Rh(coe)2(acetone)2][BF4]acetone, rt

i-Pri-Pr

i-Pr

i-PrP

P

S

S

+

+ +

i-Pri-Pr

i-Pri-Pr

Rh

H

P

P

S

SMe

i-Pr

i-Pr

i-Pri-Pr

Rh

P

P

S

SMe

i-Pri-Pr

i-Pr

i-Pr

Rh OO

Me

[BF4]−Me

MeH

Scheme 1.7

1.2.3Oxidative Addition Driven by Aromatization

Aromatization brings significant stabilization to molecules. Consequently,the formation of an aromatic molecule assists C–C bond cleavage thermo-dynamically. For example, an η4-(endo-ethylcyclopentadienyl)molybdenum

C

H

C

CRh

Figure 1.4 Schematic model of orbital interaction in arhodium complex with a C–C–H η3-agostic interaction.


complex rearranged with oxidative addition of the Cp–Et bond to an η5-(cyclopentadienyl)(ethyl)molybdenum complex upon treatment with thalliumtetrafluoroborate (Scheme 1.8) [15].

MoPPhMe2

+

EtMo

PPhMe2

Cl

Et

H

TlBF4 [BF4]−

Scheme 1.8

Analogous oxidative addition reactions have been reported with nickel, iron,manganese, rhenium, and iridium complexes [16]. Crabtree et al. have reportedthe stereochemistry of the migration of the alkyl group on the Cp ring on irid-ium (Scheme 1.9) [16e]. When the endo-methyl complex was heated at 150 ∘C,the methyl group selectively migrated onto the iridium. On the other hand, thecorresponding exo-methyl derivative afforded a complex mixture.

Me

EtIr[P(p-FC6H4)3]2

++

Ir[P(p-FC6H4)3]2Et

Me

[PF6]− [PF6]−

150 °C

Scheme 1.9

Heating of the 1,1-diethyl complex caused isomerization to form a mixture of1,2- and 1,3-diethyl complex [16]. This isomerization reaction may indicate micro-scopic reversibility of the oxidative addition/reductive elimination of the C–Cbond (Scheme 1.10).

Et

EtIr[P(p-FC6H4)3]2

+

++

+

Ir[P(p-FC6H4)3]2

Et

EtIr[P(p-FC6H4)3]2

Et

Et

HH

[PF6]−

[PF6]− [PF6]−

150 °C

Scheme 1.10

1.2.4Oxidative Addition of Ketones

The carbonyl sp2 carbon is trigonal planar so that it is sterically less hindered thantetrahedral sp3 carbons. Additionally, the lone pair and π-electrons of the carbonyl


group can interact with the metal center to locate the metal in proximity to theC(carbonyl)–C bond. Therefore, oxidative addition of C(carbonyl)–C bonds iskinetically more favored than that of ordinary C–C bonds.

It is difficult to observe oxidative addition of C(carbonyl)–C bonds of ordinaryketones directly because of spontaneous carbonyl extrusion to form a metalcarbonyl complex with elimination of a decarbonylated organic fragment. Anearly example of the oxidative addition is seen in a reaction of rhodium(III)chloride with triphenylphosphine in refluxing cyclohexanone, producingRhCl(CO)(PPh3)2 [17]. Although other products derived from cyclohexanoneare not identified, the carbonyl ligand of RhCl(CO)(PPh3)2 would originate fromcyclohexanone via cleavage of the C(carbonyl)–C bond. A more explicit exampleis a decarbonylation reaction of cyclododecanone by Wilkinson complex, whichafforded cycloundecane and RhCl(CO)(PPh3)2 (Scheme 1.11) [18]. Decarbo-nylation of benzophenones and calcone took place upon treatment with acyclopentadienylrhodium(I) complex [19].

+ RhCl(PPh3)3benzonitrile, 150 °C

+ Rh(CO)Cl(PPh3)2

O

Scheme 1.11

Oxidative addition of a C(carbonyl)–C bond has been observed directly withhighly strained unsaturated ketones. When a platinum(0) ethylene complex wastreated with a cyclopropenone, the ethylene ligand was replaced with the olefinmoiety of the cyclopropenone to produce a platinum η2-cyclopropenone complex.The platinum center then inserted site-selectively into the sterically less-crowdedC(carbonyl)–C bond of the cyclopropenone to form a platinacyclobutenone(Scheme 1.12) [20].

O

Me

+ Pt(CH2=CH2)(PPh3)2CDCl3, −65 °C

O

Me

PtPPh3

PPh3 −30 °C PtPPh3

PPh3

O

Me

Scheme 1.12

Treatment of a cyclopropenone with a rhodium(I) complex initially generatedthe corresponding O-bound complex (Scheme 1.13) [21]. Heating of the O-boundcomplex at 60–65 ∘C led to the formation of the rhodacyclopentenediones. It wasproposed that the oxidative addition takes place via nucleophilic attack of therhodium center on the carbonyl group and subsequent 1,2-migration of the C(sp2)atom from carbon to rhodium. Subsequent insertion of a carbon monoxide ligandinto the C–Rh bond furnishes the rhodacyclopentenedione.


O

Ph

+ Rh(CO)(PPh3)2(OTf)

benzene, rtPh

O

Ph

+Ph

Rh

PPh3

PPh3

OC

benzene, 60 °CRh

O

O

TfO

Ph3P

Ph3P

Ph

Ph

O

Ph

Ph

[Rh][Rh]

O

Ph

Ph

[OTf]−

[Rh]O

Ph Ph

+

−

Scheme 1.13

Cyclobutenones undergo oxidative addition to rhodium(I) and cobalt(I)(Scheme 1.14) [22]. The metals inserted site-selectively into the C(carbonyl)–C(sp3) bond to form the corresponding metallacyclopentenones.

EtO

O

+ RhCl(PPh3)3benzene, 60 °C Rh

O

Cl

PPh3

PPh3EtO

Scheme 1.14

A reaction of benzocyclobutenone with Wilkinson complex took place at 130 ∘Cto afford a regioisomeric mixture of oxidative addition products (Scheme 1.15)[22]. On the other hand, a reaction with an electron-rich rhodium(I) complex

N

NP

P

BRh

O+

O

benzene, rt

N

NP

P

BRhH

N

BN

HRh

n

P = Pt-Bu2

O+ RhCl(PPh3)3

chlorobenzene, 130 °C Rh

O

Cl

PPh3

PPh3

Rh Cl

PPh3

PPh3

O

+

1:3

Scheme 1.15


equipped with a PBP-pincer ligand proceeded, even at room temperature, to givea 2-rhodaindan-1-one exclusively [23].

Cyclobuten-1,2-diones underwent oxidative addition to various low-valentmetals such as Pt(PPh3)4 and RhCl(PPh3)3 with site-selective cleavage of theC(arene)–C(carbonyl) bond (Scheme 1.16) [24]. The rhodium complex subse-quently underwent rearrangement to furnish the phthaloylmetal complexes.

O

+ Pt(PPh3)4benzene, rt

O

O

+ RhCl(PPh3)3chlorobenzene110 °C, 10 minO

PPh3

PPh3

Cl

O

O

Rhchlorobenzene110 °C, 5 h

Rh Cl

PPh3

PPh3

OO

PtPPh3

PPh3

OO

Scheme 1.16

Chelation facilitates oxidative addition of unstrained C(carbonyl)–C bonds.For example, 8-quinolyl alkyl ketones underwent oxidative addition to rhodium(I)(Scheme 1.17) [25]. Addition of phosphorus ligands to the rhodacycle inducedreductive elimination [26]. The stereochemistry of the α-carbon was retainedduring the oxidative addition/reductive elimination [27]. It was proposed that atetrahedral intermediate arises by nucleophilic attack of rhodium on the carbonyl

N

OMeO

Ph

+ [RhCl(CH2=CH2)2]2benzene, rt

N

O[Rh]

Ph

MeO

pyridineN

O[Rh]

PhMeO

N

ORhCl

NMeO

Ph

P(OMe)3 N

OMeO

Ph

+−

Scheme 1.17


carbon en route to C–C bond cleavage without the intervention of a C–H activa-tion process. This direct pathway contrasts with the sequential oxidative additionof C–H and C–C bonds observed with cyclopropanes [4] and biphenylenes [7].

Phosphorus also functions as a chelating group. The carbonyl group of aphosphine-tethered benzophenone/nickel complex was extruded upon heatingto give a biaryl (Scheme 1.18) [28]. The extrusion/insertion of CO was reversible,indicating that the aryl–aryl bond also adds to nickel(0) facilely. The relatedoxidative addition reaction to iridium(I) and rhodium(I) was also reported [29].

O

OP

P

O NiCO

CO

i-Pr i-Pr

i-Pr i-Pr

O

OP

P

Ni

i-Pr i-Pr

i-Pr i-Pr

CO

CO

toluene, 95 °C

CO (5 bar)toluene, 95 °C

P

O

Ni

O

PO

i-Pri-Pr

i-Pri-Pr

Scheme 1.18

Oxidative addition of C–C(carbonyl) bonds has been applied to various cat-alytic reactions, which are described in Chapter 6.

1.2.5Oxidative Addition of Nitriles

A C–N triple bond coordinates to metals in either an endo-on or a side-on mode,which kinetically facilitates the access of the metal center to the C–CN bond.Furthermore, the metal cyanide bond is generally thermodynamically stable.Consequently, various C–CN bonds underwent oxidative addition, particularlyto zerovalent Group 10 metals (Scheme 1.19) [30]. The oxidative addition reactionwas facilitated by addition of Lewis acids (Scheme 1.20).

Me CN

CN

CN

Pt(PPh3)4+ Pt

Ph3P

Ph3P

CNCN

MeCN

Pt(PEt3)3+

CN

benzene, reflux

toluene, reflux

PtNC

Et3P

PEt3

Scheme 1.19

CN

NiP

P

+ BPh3THF-d8, −30 °C Ni

P C

N

BPh3

i-Pr2

i-Pr2Pi-Pr2

i-Pr2

Scheme 1.20


In addition to zerovalent Group 10 metals, ansa-molybdenocene dihydridereacted with nitriles upon liberation of dihydrogen by photoirradiation (Scheme1.21) [31]. Acetonitrile underwent oxidative addition of the C–CN bond to themolybdenum center. On the other hand, when the complex was treated withbulkier pivalonitrile, the side-on coordination complex was formed.

MoMe2SiH

H+ MeCN MoMe2Si

CN

Me

h𝜈

MoMe2SiH

H+ t-BuCN MoMe2Si

N

C

h𝜈

t-Bu

Scheme 1.21

Oxidative addition with formal one-electron oxidation of the metal center hasbeen observed with a uranium complex (Scheme 1.22) [32]. Heating of an end-onacetonitrile complex of Cp3U afforded a mixture of the methyl and the cyanidecomplexes with liberation of one molecule of acetonitrile.

2[Cp3U(NCMe)] Cp3UMe Cp3UCN ++toluene-d8, 80 °C

MeCN

Scheme 1.22

The C(carbonyl)–CN bonds also undergo oxidative addition to late-transitionmetals like nickel(0), rhodium(I), and palladium(0) [33]. For example, aroylcyanides underwent decarbonylation in the presence of a rhodium(I) catalyst,probably through oxidative addition, deinsertion of CO and reductive elimination(Scheme 1.23) [33a]. The oxidative addition of a C(carbonyl)–CN bond wasdirectly observed in the reaction of a cyanoformate with a nickel(0) complex(Scheme 1.24) [33c].

O CN

Δ

RhCl(PPh3)3 (cat.)CN

87%

Scheme 1.23

N

EtO CN

O+ Ni(cod)2 +

THF, −10 °CN

Ph2P

PPh2

PPh2

NiEtO2C

Ph2P PPh2

CN

PPh2

Scheme 1.24


1.2.6Others

Curved polyaromatic hydrocarbons undergo oxidative addition. A strainedfive-membered ring of a C60-derived molecule reacted with a CpCo fragment(Scheme 1.25) [34]. Analogously, a bowl-shaped fullerene subunit reacted with aplatinum(0) complex (Scheme 1.26) [35].

H HCpCo

CpCo(CO)2xylene, 135 °C

+

Scheme 1.25

+ Pt(CH2=CH2)(PPh3)2toluene, rt, 15 h;then reflux, 1 h

Pt

Ph3P PPh3

Scheme 1.26

Cleavage of a C(sp)–C(sp) single bond by low-valent titanocene andzirconocene has been reported [36]. Treatment of a diyne with those metal-locenes in tetrahydrofuran (THF) produced the dimer of the alkynylmetallocenecomplex, in which the alkyne moiety was bonded to the metal center in both σ-and π-fashions (Scheme 1.27).

SiMe3

SiMe3

+ M

SiMe3

SiMe3

SiMe3

Cp2MMCp2

Me3SiM = Ti, Zr

Scheme 1.27

A C(sp)–C(sp2) single bond of arylalkynes was cleaved by photoirradiation ofa platinum–alkyne complex (Scheme 1.28) [37]. The oxidative addition productwas reverted to the starting η2-alkyne complex upon heating. This result indicatesthe photochemical oxidative addition is an endergonic process.


Pt

Ph

Ph

i-Pr2P

Pi-Pr2

hν

Pt

i-Pr2P

Pi-Pr2

Ph

Ph

Δ

Scheme 1.28

Oxidative addition of a C(sp3)–C(sp3) bond to two metals with one-electronoxidation was also reported (Scheme 1.29) [38]. A Rh(II)-porphyrin complexreacts with [2.2]-paracyclophane to give a bisalkylrhodium(III) species.

2 RhII(tmp) +C6D6, 150 °C

RhIII(tmp)RhIII(tmp)

tmp

N

N−

−

N

N

Me

Me Me

Me

Me

Me

Me

Me

Me

Me

Me

Me

Scheme 1.29

1.3𝛃-Carbon Elimination

β-Carbon elimination is a process eliminating a carbon atom connected to theβ-position of a metal. The bond between β- and γ-carbons is cleaved to result in anorganometallic species along with unsaturated bonds (Scheme 1.30). It is a reverseprocess of insertion of unsaturated bonds into a carbon–metal bond, that is,carbometallation.

M C M C Scheme 1.30

1.3 β-Carbon Elimination 15

The reversibility of carbometallation/β-carbon elimination was first demon-strated by a reaction of methylaluminum with isobutylene, which is in equilibriumwith neopentylaluminum (Scheme 1.31) [39].

Me3Al +

Me

Me

Me

Me

AlMe3-nn

Me

Scheme 1.31

Since then, various β-carbon elimination reactions have been reported.This section describes important examples of β-carbon elimination reactions.

1.3.1𝛃-Carbon Elimination of Late Transition Metal Alkyls

Acid treatment of an alkylpalladium complex having a cyclopentadiene moietygives an early example of β-carbon elimination of late transition metal alkyls(Scheme 1.32) [40]. A palladium–cyclopentadiene complex was generatedtogether with elimination of styrene.

Me

Me Me

Me

Me

PdCl

2

HCl

Ph

Me

Me Me

Me

Me

PdCl2

H

+ PhCHCl3, 25 °C

Scheme 1.32

Insertion of norbornene into a C–M bond is often reversible. For example,a π-allylnickel norbornene complex was in equilibrium with inserted alkyl-nickel species (Scheme 1.33) [41]. Whereas the chloride complex favored theπ-allylnickel form, the acetate complex favored the inserted alkylnickel species.

2

NiMeCl

KOAc

HCl

NiMe

OAc

Scheme 1.33

A palladacycle reacted with alkyl halides to afford a sterically bulky arylpalla-dium complex with liberation of norbornene (Scheme 1.34) [42]. β-Aryl elimi-nation from the norbornylpalladium intermediate would be responsible for theformation of these products.

A ruthenacyclobutane complex underwent β-carbon elimination to form a π-allyl(methyl)ruthenium complex (Scheme 1.35) [43]. Kinetic studies revealed that


2

Pd

Cl

+ R XDMF, rt

H

HPd

XLH

H

R

L

Pd

XL

LR

Pd

XL

LR

R

+ Pd

L

L

X

R

R

L = DMF

H

H

H

H

Scheme 1.34

Ru

P

PMe3

PP

Me

Me

SiMe

Ru

P

Me

PP

SiMe

Me

Ru

PP

P

SiMe

MeMe

‡

P = PMe2

Scheme 1.35

the entropy of activation was negative, indicating the more ordered unimoleculartransition state.

Relief of ring strain facilitates β-carbon elimination both thermodynamicallyand kinetically, as is the case with oxidative addition. Thus, a cyclobutyl-methylplatinum complex underwent β-carbon elimination, even at −40 ∘C, tofurnish a ring-opened product (Scheme 1.36) [44].

O Pt

PMe3

PMe3

Me

Me

Me

+

+

−40 °CPt

PMe3

Me3PMe

Scheme 1.36

β-Carbon elimination of late transition metal alkyls is involved in various multi-step catalytic reactions. See the following chapters for more examples.

1.3.2𝛃-Carbon Elimination from Early Transition Metal Alkyls

β-Carbon elimination from early transition metal alkyls has been extensivelystudied since it is related to chain termination of olefin polymerization. Anearly example is thermal decomposition of an isobutyllutetium complex, whichformed a methyllutetium complex along with various byproducts (Scheme 1.37)

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