Cobalt Catalyzed Reactions

“Cobalt Catalyzed Reactions”“Cobalt Catalyzed Reactions”

Keith ó Proinsias 20/12/2011

OOVERVIEWVERVIEW

� Introduction

� OXO process

� Cross coupling reactions using Grignard reagents

� Cobalt coupling Michael addition reactions

� Cobalt catalyzed Heck type reactions� Cobalt catalyzed Heck type reactions

� Reductive cyclization and Heck type reactions

� Cobalt catalyzed allylation of 1,3-dicarbonyl compounds

� Coupling of alkenes and alkynes

� Cobalt catalyzed syn-hydrophosphination of alkynes

� Cobalt catalyzed C-N coupling

� Cobalt catalyzed C-S coupling

IINTRODUCTIONNTRODUCTION

� The oxidation state of cobalt in organocobalt compounds

ranges from -1 to +4.

� The most common being -1, 0, +1 and +3.

� Co(0) complexes consists of homoleptic carbonyl: Co2(CO)8and Co4(CO)12.

� Co2(CO)8 is used as a homogeneous catalyst in the

hydroformylation of alkenes.hydroformylation of alkenes.

� It is thermally unstable, decomposing above 50oC to give

Co4(CO)12.

SolidIn Solution

Kamiya, S. Synthesis of organometallic compounds: A practical guide, John Wiley & Sons.


� Co(I) complexes contain π-acid ligands: Cp, CO, RNC,

and PR3.

� Co(I) complexes are usually five-coordinated and

trigonal bipyramidal.

� In oxidative addition reactions give Co(III) in which one

ligand is eliminated.

� Monocyclopentadienyl (Cp) complexes are one on the

most extensively studied cobalt complexes.

� CoCpL2 (L= PPh3, CO) are capable of catalyzing the

cyclotrimerization of alkynes as well a variety of other

compounds to give other types of bonds.

Kamiya, S. Synthesis of organoetallic compounds: A practical guide, John Wiley & Sons.




� Since the discovery of vitamin B12 coenzyme there has been

much work done on organocobalt (III) complexes with a

metal-carbon bond.


OXO POXO PROCESSROCESSOXO POXO PROCESSROCESS

OXO POXO PROCESSROCESS

• OXO process is the hydroformylation of alkenes (such as

propene) to make aldehydes.

• This process is catalyzed by Rh or Co.


OXO POXO PROCESSROCESSCatalytic cycle:

• π-Complex formation.

• Hydrometallation to produce an alkyl metal species.

• Coordination of carbon monoxide followed by insertion.

• Reductive cleavage with hydrogen to produce the metal-hydride

intermediate.


CCROSSROSS CCOUPLINGOUPLINGCCROSSROSS CCOUPLINGOUPLING

CCROSSROSS CCOUPLINGOUPLING

• Cross-coupling reactions between an organometallic reagent and an

organic halide or triflate.

• Reaction requires a transition metal catalyst. Pd is commonly used.

MechanismMechanism

• Oxidative addition of the halide to the initial palladium(0)complex to form a

palladium(II) species.

• Transmetallation: the nucleophile is transferred from the organometallic

reagent to the palladium and the counter ion moves in the metal.

•The new palladium(II) complex with two organic ligands undergoes reductive

elimination to give the coupled product

Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. Organic chemistry, Oxford University Press, 2001

CCROSSROSS CCOUPLINGOUPLING

• The halide partner must be chosen with care, as β-hydride elimination

would decompose the first intermediate during the slow transmetallation

step.

• The choice for is restricted to substituent's without β-hydrogen atoms:

vinyl, allyl, benzyl, and polyfluoroalkyl halides,triflates, and phosphates have

all been coupled successfully.

•The organometallic reagent can be based on magnesium, zinc, copper, tin,

silicon, zirconium, aluminium, or boron

• The organic fragment can have a wide variety of structures as coupling is • The organic fragment can have a wide variety of structures as coupling is

faster than β-hydride elimination.

Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. Organic chemistry, Oxford University Press, 2001

CCOBALTOBALT CCATALYZEDATALYZED

CCROSSROSS CCOUPLINGOUPLING USINGUSINGCCROSSROSS CCOUPLINGOUPLING USINGUSING

GGRIGNARDRIGNARD RREAGENTSEAGENTS

CCOBALTOBALT CCATALYZEDATALYZED CCROSSROSS

CCOUPLINGOUPLING USINGUSING GGRIGNARDRIGNARD

RREAGENTSEAGENTS• The first cobalt catalyzed cross coupling reaction was described the

homocoupling reaction of Grignard reagents

• In 1939 Gilamn and Lichtenwatler obtained almost quantitative yields

of diphenyl homocoupled product by treating aromatic Grignard reagents

with a stoichiometric amount of cobalt bromide.

Cahiez, G.; Moyeux, A. Chemical Reviews 2010, 110, 1435-1462

Gilman, H.; Lichtenwalter, M. J. Am. Chem. Soc. 1939, 61, 957



RREAGENTSEAGENTS

• Kharasch continued these

homocoupling reactions by isolating

diphenyl compounds in good yields.

• 3 mol % of cobalt chloride required


Kharasch, M. S.; Fuchs, C. F. J. Am. Chem. Soc. 1941, 63, 2316



RREAGENTSEAGENTS• In 1943 Kharasch reported the first alkenylation reaction between

Grignard reagents and vinyl halides catalyzed by cobalt chloride.

• Catalytic amount of cobalt chloride (2.5 mol %).


Kharasch, M. S.; Fuchs, C. F. J. Am. Chem. Soc. 1943, 65, 504



RREAGENTSEAGENTS

• This work to still ongoing.

Yoshikai recently reported a

quaternary catalytic system

consisting of CoBr2, P(3-ClC6H4)3,

tBuCH2MgBr, and pyridine

promotes hydroarylation of an promotes hydroarylation of an

internal alkyne with an aromatic

imine through chelation-assisted

CH bond cleavage

Lee, P. S.; Fujita, T.; Yoshikai, N. J. Am. Chem. Soc. 2011, 133, 17283



RREAGENTSEAGENTS• Alkenylation

• From aromatic organomagnesium reagents

• From vinylic Grignard reagents

• From aryl halides and alkenyl acetates

• Aryl-Aryl Cross coupling

• From aromatic organometalic reagents

• From two aromatic halides• From two aromatic halides

• Alkynylation

• Benzylation of acetylenic Grignard reagents

• Alkylationof acetylenic Grignard reagents

• Alkenylation of acetylenic Grignard reagents

• Csp3-Csp2 Cross-coupling

• Allylation

• Benzylation

• Alkylation

• Acylation

• From organometallic compounds

• Cobalt- mediated acylation of aryl bromides

CCOBALTOBALT--MMEDIATEDEDIATED

MM AAMMICHAELICHAELAADDITIONDDITION

CCOBALTOBALT--MMEDIATEDEDIATED MMICHAELICHAEL

AADDITIONDDITION

• Giese describes a diastereoselective conjugative addition using

Vitamin B12 as a catalyst and Zn as a reducing agent



AADDITIONDDITION• Pfaltz developed the synthesis of C2-

symmetric bis-amides.

• He found by this ligand in Michael

addition reactions high ee could be

obtained but with low yield.


End, N.; Macko, L; Zehnder, M.; Pfaltz, A. Chem. Eur. J. 1998, 4, 818

Chen, C.; Zhu, S. F.; Wu. X. Y.; Zhou, Q. L. Tetrahedron: Asymmetry 2006,

17, 2761

• Using similar ligands Cheng

reported the Michael addition of

malonates to chalcone derivatives

using cobalt complexes and Et2Zn

• Good yield and moderate ee.


AADDITIONDDITION

•Bergman reported a one-pot,

direct C-H functionalizaion of

alkenes meditated by

[CpCo(NO)2].

•A variety of Michael acceptors •A variety of Michael acceptors

can be used

Zhao, C.; Toste, F. D.; Bergman, R. G. J. Am. Chem. Soc. 2011,

133, 10787

CCOBALTOBALT--CCATALYZEDATALYZED

HHECKECK TTYPEYPEHHECKECK TTYPEYPE

RREACTIONSEACTIONS

CCOBALTOBALT--CCATALYZEDATALYZED HHECKECK TTYPEYPE

RREACTIONSEACTIONS

• The “Heck Reaction” is a powerful tool in carbon-carbon bond formation

• There are limitations regarding substrate choice, which are limited to

aryl, heteroaryl, vinylic and benzylic halides and triflates as the

presence of an sp3 carbon in the β-position carrying a hydrogen rapidly

results in β-hydride elimination.

• Cobalt catalyzed Heck type reactions avoids this drawback.


Clayden, Greeves, Warren, Wothers, Organic chemistry, 1313


RREACTIONSEACTIONS• In 1991 Branchaud reported the first cobalt catalyzed Heck type reaction

between styrene and various alkyl halides.

• Reaction was catalyzed using Cobaloxine (II) and requires daylight.

• The use of 3o bromides fail.



RREACTIONSEACTIONS

[A] CoCl2.dpph reacts with

Me3SiCH2MgCl.

[B] Monoelectronic transfer to the

alkyl halide forming a CoI species.

[C] CoI reacts with Me3SiCH2MgCl

forming an intermediate.

[D] Then reacts with the benzylic


[D] Then reacts with the benzylic

radical forming the organocobalt [E].

[F] The Heck product is obtained from

[E] by β-hydrogen elimination.


RREACTIONSEACTIONS


Ikeda, Y.; Yorimitsu, H.; Shinokubo, H,; Oshima, K. Adv, Synth. Catal. 2004, 346, 1631

RREDUCTIVEEDUCTIVE

CCYCLIZATIONYCLIZATION AANDND

HH --TTHHECKECK--TTYPEYPE

RREACTIONSEACTIONS

RREDUCTIVEEDUCTIVE CCYCLIZATIONYCLIZATION AANDND

HHECKECK--TTYPEYPE RREACTIONSEACTIONS

�INTERMOLECULAR RADICAL CYCLIZATION

�INTRAMOLECULAR RADICAL CYCLIZATION



�INTRAMOLECULAR RADICAL

CYCLIZATION

• Radical mediated aryl-aryl

coupling

• The first reported case was by

Tiecco in 1965


Tiecco, M. Chem. Commun. 1965, 555

Tiecco in 1965

• Methylmagnesium iodide was

used in a suspension of cobalt

chloride in an ethereal solution

affording phenanthrenein 75%

yield



• In 1982 Tada reported the

reductive cyclization of 2-

propargyloxyalkyl bromides in

the presence of cobaloxime.

• Hoffmann applied this method

to the synthesis of various to the synthesis of various

heterocyclic compounds.


Okabe, M.; Abe, M.; Taba, M. J. Org. Chem. 1982, 47, 1775

Abe, M.; Taba M. J. Org. Chem. 1982, 47, 5382

Last, K.; Hoffmann, H. M. R. Synthesis1989, 901



• Pattenden reported the radical

cyclization of 2-allyloxyalkyl

bromides using Vitamin B12 or

cobaloxime (I)




�INTERMOLECULAR RADICAL CYCLIZATION

• Typically this reaction is

catalyzed using Pd or Ni due

to the facile oxidative

addition of aryl halides to Pd

andand

Ni(0) metal complexes..

• Yamamoto shows the

addition of vinylpalladium

species to carbon

electrophiles such as a

carbonyl group

• This was the first

palladium-catalyzed

nucleophilic cyclic

vinylpalladation of aryl

ketones with alkynes to

produce

Indenols in good to high


Quan, L. G.; Gevorgyan, V.; Yamamoto, Y. J. Am. Chem. Soc. 1999, 121, 3545



• Cheng first reported that cobalt

phosphine complexes successfully

catalyse the reaction under mild

conditions to afford indenol derivatives

with excellent regioselectivity and in high

yields

• The cobalt catalyzed system is more

efficient than the palladium and nickel


Chang, K. J.; Rayabarapu, D. K.; Cheng, C. H. Org. Lett. 2003, 5, 3963

Chang, K. J.; Rayabarapu, D. K.; Cheng, C. H. J. Org. Chem. 2004, 69, 4781

efficient than the palladium and nickel

catalysts for this

carbocyclization reaction.




Chang, K. J.; Rayabarapu, D. K.; Cheng, C. H. Org. Lett. 2003, 5, 3963

Chang, K. J.; Rayabarapu, D. K.; Cheng, C. H. J. Org. Chem. 2004, 69, 4781


AALLYLATIONLLYLATION OFOF

1,31,3--DD1,31,3--DDICARBONYLICARBONYL

CCOMPOUNDSOMPOUNDS

CCOBALTOBALT CCATALYZEDATALYZED AALLYLATIONLLYLATION OFOF

1,31,3--DDICARBONYLICARBONYL CCOMPOUNDSOMPOUNDS

• Iqbal reported the allylation of 1,3-dicarbonyl compounds using a cobalt

catalyst.

• Reactions were conducted under neutral conditions, compared to Pd

catalyzed reactions


CCOBALTOBALT CCATALYZEDATALYZED AALLYLATIONLLYLATION OFOF

1,31,3--DDICARBONYLICARBONYL CCOMPOUNDSOMPOUNDS

• Reactions can also be repeated with allylic alcohol.


CCOUPLINGOUPLING OOFF

AALKENESLKENES AANDNDAALKENESLKENES AANDND

AALKYNESLKYNES

CCOUPLINGOUPLING OOFF AALKENESLKENES AANDND

AALKYNESLKYNES• Commonly copper mediated reactions are used for the preparation of

conjugated diynes.

• In 2001 Kraff reported cobalt catalyzed dimerization of terminal alkynes.


Krafft, M. E.; Hirosawa, C.; Dalal, N,; Ramsey, C.; Stiegman, A. Tetrahedron Lett. 2001, 42, 7733

CCOUPLINGOUPLING OOFF AALKENESLKENES AANDND

AALKYNESLKYNES•Cheng followed suit with the reductive dimerization of conjugated alkenes,

which were highly regio- and stereoselective.


Wang, C. C.; Lin, P. S.; Cheng, C. H. Tetrahedron Lett. 2004, 45, 6203

Chang, H. T.; Jayanth, T. T.; Wang, C. C.; Cheng, C. H. J. Am. Chem. Soc. 2007, 129, 12032

dppe=1,2-Bis(diphenylphosphino)ethane


SSYNYN--

HHHHYDROPHOSPHINATIONYDROPHOSPHINATION

OFOF AALKYNESLKYNES

CCOBALTOBALT--CCATALYZEDATALYZED SSYNYN--

HHYDROPHOSPHINATIONYDROPHOSPHINATION OFOF

AALKYNESLKYNES• Reaction traditionally with lanthanides, Pd or Ni

• Stereoselectivity of these reactions depend on the nature of the substrate


Mimeau, D.; Gaumont, A. C. J. Org. Chem. 2003, 68, 7016



AALKYNESLKYNES• Oshima developed a cobalt catalyzed universal stereoselective

hydrophosphination reaction of alkynes with diphenylphosphine and

butyllithium giving mainly syn-addition product.


Ohmiya, H.; Yorimitsu, H.; Oshima, K. Angew. Chem. Int. Ed. 2005, 44, 2368



AALKYNESLKYNES• Product can be used to perform Wittig reaction.


Ohmiya, H.; Yorimitsu, H.; Oshima, K. Angew. Chem. Int. Ed. 2005, 44, 2368


CC--N CN CCC--N CN COUPLINGOUPLING

CCOBALTOBALT CCATALYZEDATALYZED CC--N N

CCOUPLINGOUPLING• Cobalt-porphyrin catalyzed C-H amination has been extensively

examined by Cenini.

• Reactions are limited to cyclohexane.

• Substrates have been extended to benzylic C-H bonds.


Cenini, S.; Tollari, S.; Penoni, A.; Cereda, C. J. Mol. Catal. A. 1999, 135

Cenini, S.; Gallo, E.; Penoni, A.; Ragaini, F.; Tollari, S. Chem. Commun. 2000, 2265

CCOBALTOBALT CCATALYZEDATALYZED CC--N N

CCOUPLINGOUPLING

• Yamaguchi developed new • Yamaguchi developed new

methodology to prepare N-aromatic-

containing tertiary amines that are

useful

building blocks for bioactive

molecules.

• He was the first to use N-aromatic

2-chloro compounds for C–N bond-

forming reactions.

Toma, G.; Yamaguchi, R. Eur. J. Org. Chem. 2010, 6404

Toma, G.; Fujita, K.; Yamaguchi, R. Eur. J. Org. Chem. 2009, 4586


CC--S CS CCC--S CS COUPLINGOUPLING

CCOBALTOBALT--CCATALYZEDATALYZED CC--S S

CCOUPLINGOUPLING• Typically C-S coupling is conducted using Cu, Pd or Ni catalyst under

harsh conditions.


Bates, C. G.; Gujadhur, R. K.; Venkatamaran, D. Org. Lett. 2002, 4,

3517

CCOBALTOBALT--CCATALYZEDATALYZED CC--S S

CCOUPLINGOUPLING• Cobalt-catalyzed C-S coupling requires milder conditions.

• Low catalytic loading


Wong, Y. C.; Jayanth, T. T.; Cheng, C. H. Org. Lett. 2006, 8, 5613

CCONCLUSIONONCLUSION

• Cobalt and its complexes can catalyze many many different

reactions including:

• Cross-coupling reactions

• Heck-type reactions

• C-N coupling

• C-S coupling

• and many more

TTHANKHANK YYOUOU

FFOROR YYOUROUR AATTENTIONTTENTIONFF YY AA

AANYNY QQUESTIONSUESTIONS

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Cobalt Catalyzed Reactions

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