Abstracts

p 31.1.1 General Principles of Metal/Metal Dual Catalysis

Y. Nakao

The background and principles of dual metal/metal catalysis are briefly introduced in thissection, with a particular focus on novel C-C bond-forming cross-coupling-type reac-tions. By taking advantage of synergistic dual metal/metal catalysis, these transforma-tions have provided the synthetic and organometallic communities with new ideas to de-sign challenging transformations that are difficult to catalyze using a conventional, sin-gle metal catalyst.

R1 M1 R2 M2 X

R1 M1 XR1 X

R1 R2

R2 M2

M1

R2 M3

M3 X

Keywords: dual catalysis • transition-metal catalysis • synergistic catalysis •

cross coupling • Sonogashira reaction • Stille reaction • C-H arylation • allylic alkylation •

arylboration

p 91.1.2 Palladium/Copper and Palladium/Nickel Dual Catalysis

O. Riant and S. K. Rout

Recent years have witnessed significant advances in molecular synthesis through ration-ally designed dual catalysis. Major achievements in dual catalysis have been accom-plished with the aid of highly chemoselective palladium/copper and palladium/nickel cat-alyst systems. These examples have showcased the full compatibility of transition-metalcatalysts with one another. To date, numerous examples of palladium/copper or palladi-um/nickel catalysis have been successfully performed, demonstrating the achievement ofchemical syntheses via greener processes with alternative energy sources.

catalyst A catalyst B

Nu−E+

Keywords: dual catalysis • transition-metal catalysis • palladium • copper • nickel • crosscoupling • Sonogashira coupling • Stille coupling • Hiyama-type coupling • allylation • hy-droarylation • carboboration

IX

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p 571.1.3 Rhodium/Palladium Dual Catalysis

U B. Kim and S.-g. Lee

This chapter reviews the development and applications of rhodium/palladium dual catal-ysis in organic synthesis. Dual catalysis can be broadly classified into two types: (1) Syner-gistic dual catalysis, where two independent rhodium and palladium catalytic cycles op-erate simultaneously to activate two different starting materials with balanced kinetics toafford two catalytically activated intermediates. These activated intermediates react witheach other to afford the final product. (2) Orthogonal tandem dual catalysis, where twocatalytic cycles operate in a sequential manner, one after the other, to promote two ormore mechanistically distinct reaction steps in a single pot to furnish the product. Thefirst part of the chapter covers synergistic rhodium/palladium dual catalysis, detailing ex-amples that feature a direct reaction between rhodium-activated intermediates and or-thogonal, palladium-activated intermediates. The second part of the chapter describesone-pot reactions that utilize initial rhodium catalysis and sequential palladium catalysis.A single example where initial palladium catalysis is followed by subsequent rhodium ca-talysis is also presented.

A B

product

[Rh] [Pd]

synergistic catalysis

BA product[Pd]

orthogonal tandem catalysis

[Rh]

Keywords: dual catalysis • transition-metal catalysis • rhodium • palladium • synergisticcatalysis • orthogonal tandem catalysis • �-allylpalladium(II) species • rhodium carbenoids •

multicomponent reactions • heterocycle synthesis • one-pot reactions • allylation •

carbonylation

p 831.1.4 Iridium/Zinc and Iridium/Copper Dual Catalysis

X. Huo, R. He, and W. Zhang

Synergistic bimetallic catalysis is gaining increasing attention due to its advantages overtraditional catalytic methodologies. These advantages include double activation, accuratecontrol of reaction sites, double stereochemical control, and potential in stereodivergentsynthesis. This review documents advances in the field and provides an up-to-date over-view of recent developments in the use of iridium/zinc and iridium/copper catalyst sys-tems.

L

L

Ir

Zn or Cu

L

Ir

L

Zn or Cu

• bimetallic catalyst libraries for target reactions• double activation• accurate reaction sites• double stereochemical control• stereodivergent synthesis

Keywords: dual catalysis • transition-metal catalysis • iridium • zinc • copper • synergisticbimetallic catalysis • stereodivergence • allylation • hydroamination • cyclization

X Abstracts

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p 1071.1.5 Gold/Iron Dual Catalysis

X. Shi and J. Wang

Dual gold/iron catalysis has emerged in the past decade as a fast, efficient and economicalmethod to access molecular complexity. Preliminary results are reviewed herein.

iron catalysis

goldcatalysis

Keywords: gold • iron • dual catalysis • relay catalysis • synergistic catalysis • propargylicalcohols • hydroxylamines • dihydroisoxazoles • isoxazoles • reductive hydroamination

p 1171.1.6 Gold Dual Catalysis with Palladium, Nickel, or Rhodium

N. T. Patil, A. G. Tathe, and V. W. Bhoyare

The unique intermediates accessible by exploiting the soft �-acid character of gold cata-lysts, make them an attractive option for dual metal catalysis reactions. Together withpalladium, nickel, or rhodium, each having their own distinct character, dual catalysiswith gold offers exclusive opportunities for reactivity and selectivity in installing car-bon-carbon and carbon-heteroatom linkages. For instance, gold dual catalysis with pal-ladium can be an advanced tool for cross-coupling reactions. On the other hand, unlikepalladium, nickel is more readily susceptible to single-electron redox processes andhence can offer reactivity both parallel to and different from that of palladium. Anotherpotential candidate, rhodium, is considered for dual catalysis with gold because it show-cases unique reactivity such as C-H activation/transmetalation and conjugate addition.When compared to using single-metal catalyst systems, such dual-metal associations re-sult in efficient one-pot approaches to highly regio- and stereoselective syntheses of mol-ecules via cross couplings, cycloadditions, or rearrangements.

dual catalysisAu + Pd/Ni/Rh

new reactivitiesand selectivities

Rh

Ni

Pd

P

P

P

R

R

R

Au

Abstracts XI

Science of Synthesis Reference Library Dual Catalysis in Organic Synthesis Volume 1 © Georg Thieme Verlag KG

Keywords: dual catalysis • cooperative catalysis • relay catalysis • sequential catalysis •

asymmetric catalysis • gold • palladium • nickel • rhodium • transmetalation • crosscoupling • Heck • Stille • Sonogashira • cascade • rearrangement • cycloisomerization

p 1631.1.7 Gold/Gold Dual Catalysis

A. S. K. Hashmi

This chapter summarizes the reactions that have been reported that are based on dualgold catalysis. The chemistry typically involves diyne substrates, and leads to a broadrange of carbo- and heterocycles. The literature up to 2019 is covered.

•AuL

AuL

AuL

AuL

Keywords: alkynes • bidirectional synthesis • carbocyclic compounds • cyclobutenes • di-halides • dual catalysis • fulvenes • gold • halides • heterocycles • macrocycles • pentalenes •

vinylidenes

p 2091.2.1 General Principles of Transition-Metal/Photocatalyst Dual Catalysis

J. C. Tellis

The combination of transition-metal catalysis and visible-light photocatalysis offers op-portunities for the development of unique new forms of reactivity. Presented in this chap-ter is an overview of the various strategies that can be used to design these dual catalytictransformations. Emphasis is placed on understanding the specific role that a photocata-lyst can play in augmenting the reactivity of a substrate or cocatalyst to achieve otherwisechallenging transformations.

photocatalysttransitionmetal

+ R1 R2R2 ZR1 Y

Keywords: transition-metal catalysis • photocatalysis • photoredox • energy transfer •

single-electron transfer • cross coupling • oxidative addition • transmetalation • reductiveelimination

XII Abstracts

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p 2411.2.2 Nickel/Photocatalyst Dual Catalysis

D. N. Primer and G. A. Molander

This chapter outlines the broad scope of photoredox/nickel dual catalysis. Among thenewer approaches to organic synthesis that engender the concept of dual catalysis, photo-redox/nickel dual-catalytic cross-coupling reactions comprise one of the most rapidly de-veloping and powerful tactics. Taken as a whole, these transformations enable novel car-bon-carbon and carbon-heteroatom bond constructions that were previously challeng-ing, if not impossible, to carry out. Most remarkably, these processes are most often car-ried out under near-neutral reaction conditions at ambient temperatures, with the energyto drive the reactions being provided solely by visible-light sources, thus enabling the in-corporation of a broad range of diverse functional groups. As described, the developmentof these processes therefore provides one means to address the longstanding challenge oflate-stage assembly of highly functionalized molecules via cross-coupling strategies.

[PCn−1]R2 AG

R2

NiIIL

L

X

R1

NiIIIL

L

R1

X

R2

NiIL

LX

R1X

R1 R2

R2

Ni0L

L

[PCn]

[PCn]∗

photoredox cyclecross-coupling cycle

hν

AG

AG = activating group [e.g., BF3K, Si(cat)2NR13, CO2Cs, etc.]

+

SET

SETNiIL

L

R2

R2

R1X

path A

path B

Keywords: dual catalysis • nickel • photocatalysis • photoredox • cross coupling • carbon-carbon bond formation • carbon-heteroatom bond formation • radicals • late-stage func-tionalization

Abstracts XIII

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p 3331.2.3 Palladium/Photocatalyst Dual Catalysis

K. Muralirajan and M. Rueping

Palladium-catalyzed cross-coupling reactions are of great importance in chemistry. Merg-ing palladium catalysis with photoredox catalysis has recently led to promising improve-ments, and typical problems associated with the use of stoichiometric oxidants, highertemperature, and harsh reaction conditions could be addressed. This chapter outlines re-cent developments in palladium/photoredox dual catalyzed C-C and C-N bond-forma-tion reactions using visible-light irradiation.

Pdn

PdmR1

R2PdmR1

PC* PC

palladiumcycle

photocatalyticcycle

ground stateexcited state

hν

R2

R1

R1 R2

product

R1 R2+

reactants

Keywords: dual catalysis • palladium catalysis • photoredox catalysis • single-electrontransfer • C-H activation • arylation • acylation • decarboxylation • allylation • dehydroge-nation • carboxylation • amination • oxidation

XIV Abstracts

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p 3771.2.4 Gold/Photocatalyst Dual Catalysis

L. Barriault, M. Zidan, S. Rohe

The use of gold catalysts in classical two-electron cross-couplings is notoriously impracti-cal due to the high oxidation potential of gold(I)/gold(III) [e.g., E0 (AuI/AuIII) = +1.36 V]. How-ever, when used in tandem with photocatalysts, the gold center can be oxidized one elec-tron at a time, making cross-coupling style reactions with gold more viable. The gold(III)intermediate also has the potential to act as a Lewis acid prior to its reductive eliminationstep, which has spurred development of multi-bond-forming dual catalytic transforma-tions. This dual-catalytic strategy is also applied in reactions with gold as a photocatalystin conjunction with an organocatalyst to effectuate traditionally challenging cross cou-plings.

[RuIII]

[RuII]

[RuII]∗

Ar1N2+ BF4

−

Ar1

AuI Cl

photoredoxcatalysis

Lewis acidcatalysis

L

Nu

AuIII

L

Ar1ClNu

Nu Ar1

AuIII Cl

L

Ar1

AuII Ar1L

Cl

Nu

hν

Keywords: photochemistry • Lewis acid catalysts • gold complexes • cross-coupling reac-tions • diazonium salts • free radicals • tandem reaction

Abstracts XV

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