discovery of environmentally benign reactions of … of environmentally benign reactions of alcohols...

Discovery of Environmentally Benign Reactions of Alcohols Catalyzed by Pyridine-Based Pincer Ru and

Amido Rh Complexes

Chathurika Ruwanthi Jayasundara Michigan State University

Chemistry Department 1

Dehydrogenation/Oxidation by Conventional Oxidants

Gunanathan, C.; Milstein, D. Science 2013, 341 , 249-260. 2

Jones Oxidation

Classes of Dehydrogenation Reaction

Hydrogen Transfer Reaction

Gunanathan, C.; Milstein, D. Science 2013, 341, 249-260. 3

Oppenauer Oxidation (Meerwein-Ponndorf-Verley reduction)



Gunanathan, C.; Milstein, D. Science 2013, 341, 249-260. 4

Hydrogen transfer reaction

5

Dehydrogenation Reactions Catalyzed by Rh(I) Amido Complex

Zweifel, T.; Naubron, J. V.; Grutzmacher, H. Angew Chem Int Edit 2009, 48 , 559-563.

Grützmacher and Co-workers

catalyst MTCA+Cl- = methyltricapryl ammonium chloride

Rhodium(I) Amido Complex

Zweifel, T.; Naubron, J. V.; Buttner, T.; Ott, T.; Grutzmacher, H. Angew Chem Int Edit 2008, 47 , 3245-3249. Trincado, M.; Grutzmacher, H.; Vizza, F.; Bianchini, C., Chem-Eur J 2010, 16 , 2751-2757. Buttner, T.; Breher, F.; Grutzmacher, H., Chem Commun 2004, , 2820-2821.

6

No heterolytical H2 splitting

Rhodium(I) Amido Complex

Zweifel, T.; Naubron, J. V.; Buttner, T.; Ott, T.; Grutzmacher, H. Angew Chem Int Edit 2008, 47 , 3245-3249. Trincado, M.; Grutzmacher, H.; Vizza, F.; Bianchini, C., Chem-Eur J 2010, 16, 2751-2757. Buttner, T.; Breher, F.; Grutzmacher, H., Chem Commun 2004, 2820-2821.

7

Unstable but split H2 heterolytically

Pre-catalyst

Maire, P.; Buttner, T.; Breher, F.; Le Floch, P.; Grutzmacher, H. Angew Chem Int Edit 2005, 44, 6318-6323. Zweifel, T.; Naubron, J. V.; Buttner, T.; Ott, T.; Grutzmacher, H., Angew Chem Int Edit 2008, 47, 3245-3249.

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Hydrogenation Catalyzed by Rh(I) Amide Complex

Heterolytic and Oxidative Addition of H2 with Rh(I) Amide Complex

Maire, P.; Buttner, T.; Breher, F.; Le Floch, P.; Grutzmacher, H. Angew Chem Int Edit 2005, 44, 6318-6323.

9

[Rh(Cht2N)PH3] cht = cycloheptatrienyl

Computed Frontier Orbital Diagram

Maire, P.; Buttner, T.; Breher, F.; Le Floch, P.; Grutzmacher, H. Angew Chem Int Edit 2005, 44, 6318-6323.

10

[Rh(Cht2N)PH3] cht = cycloheptatrienyl

Maire, P.; Buttner, T.; Breher, F.; Le Floch, P.; Grutzmacher, H. Angew Chem Int Edit 2005, 44, 6318-6323. Zweifel, T.; Naubron, J. V.; Buttner, T.; Ott, T.; Grutzmacher, H. Angew Chem Int Edit 2008, 47, 3245-3249.

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Hydrogenation Catalyzed by Rh(I) Amide Complex

12

Dehydrogenation Reactions Catalyzed by Rh(I) Amido Complex

Zweifel, T.; Naubron, J. V.; Grutzmacher, H.,Angew Chem Int Edit 2009, 48 (3), 559-563.

Grützmacher and Co-workers

catalyst


13

Dehydrogenative coupling of primary alcohols


14

Simplified Catalytic Cycle

15 Zweifel, T.; Naubron, J. V.; Grutzmacher, H. Angew Chem Int Edit 2009, 48 , 559-563.

Conversion of Ethanol and Water to Acetic Acid

16 Zweifel, T.; Naubron, J. V.; Grutzmacher, H. Angew Chem Int Edit 2009, 48, 559-563.

Conversion of Ethanol and Water

to Acetic Acid

17 Zweifel, T.; Naubron, J. V.; Grutzmacher, H.Angew Chem Int Edit 2009, 48, 559-563.

Conversion of Ethanol and Water

to Acetic Acid


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Dehydrogenative coupling of primary alcohols

Pros and Cons

19

Pros :

• Mild reaction conditions.

• Low catalytic loading(0.1 mol%)

• Functional group tolerance.

• Chemeoselectivity.

Cons : • Rh is an expensive metal.

• Formation of salt.

• Using a hydrogen acceptor.



Gunanathan, C.; Milstein, D., Science 2013, 341 (6143), 249-260. 20

Dehydrogenation/Oxidation by Conventional Oxidants

Hydrogen Transfer Reaction

Acceptorless Dehydrogenation Leads to Liberation of H2

21 Dobson, A.; Robinson, S. D., J Organomet Chem 1975, 87 , C52-C53. Blum, Y.; Shvo, Y., J Organomet Chem 1985, 282 , C7-C10. Inorganic Chemistry, Vol. 16, No. I , I977

1975 Robinson catalyst

1985 Shvo catalyst

Dehydrogenation of Primary and Secondary Alcohols

Dehydrogenation of Primary and Secondary Alcohols

22

2005-2013

• Low catalytic loading

• H2 as the only byproduct

• Higher yields and turnover numbers

• Broad substrate scopes and mild reaction conditions

• Atom economy

• Mechanistic studies

“After initial studies more than 30 years ago this method remains strongly neglected” -Friedrich, A.; Schneider, S., Chemcatchem 2009, 1 (1), 72-73.

Milstein and coworkers: - reported unprecedented dehydrocoupling of alcohols to acetals in high yield This lead to finding of environmentally benign reactions.

Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D., J Am Chem Soc 2005, 127 , 12429-12429. Friedrich, A.; Schneider, S., Chemcatchem 2009, 1, 72-73.

Acceptorless Reactions Catalyzed by Ru Pincer Complexes

Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D., Nat Chem 2013, 5, 122-125. Gunanathan, C.; Milstein, D. Science 2013, 341, 249-260.

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• Is a type of chelating ligand that binds tightly on a transition metal using three adjacent sites.

• Properties:

• Extraordinary thermal stability. • high melting points. • Hemi labile property.

Pincer Ligands

Morales-Morales, D. Mini-Rev Org Chem 2008, 5, 141-152. 24

Dehydrogenative Coupling of Alcohols to Esters

Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J Am Chem Soc 2005, 127, 10840-10841. 25


26 Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J Am Chem Soc 2005, 127, 10840-10841.

Alcohols to Esters Without KOH

Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J Am Chem Soc 2005, 127 , 10840-10841. 27


28 Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D., J Am Chem Soc 2005, 127 (35), 10840-10841.

Overall reaction scheme

Plausible Mechanism for Ester Synthesis

29 Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D., J Am Chem Soc 2005, 127, 10840-10841. Milstein, D., Top Catal 2010, 53 , 915-923

Hemilabile Ligands

30 Braunstein, P.; Naud, F. Angew Chem Int Edit 2001, 40 (4), 680-699.

• Hybrid ligands contain at least two different types of chemical functionality capable of binding to metal centers.

• Functionalities are chosen to be very different from each other to increase the differentiation between their resulting interactions with the metal center.

• Achieved by combining hard and soft donors in the same ligand.

• Hemilabile ligands have at least one labile donor function Z while the other donor group(s) D remain firmly bound to the metal center.

Aromatization and Dearomatization of The PNN Ligand

Yang, X. Z.; Hall, M. B. J Am Chem Soc 2010, 132 , 120-130. Sacco, A.; Vasapollo, G.; Nobile, C. F.; Piergiovanni, A.; Pellinghelli, M. A.; Lanfranchi, M. J Organomet Chem 1988, 356 , 397-409.

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Calculated relative gas-phase electronic energies (kcal/mol)

Proposed Mechanism for The Direct Acylation of Amines

32 . Gunanathan, C.; Ben-David, Y.; Milstein, D. Science 2007, 317, 790-792.

Dehydrogenative Coupling of Alcohols to Amides

33

b= The remaining alcohol was converted into corresponding ester.

Gunanathan, C.; Ben-David, Y.; Milstein, D. Science 2007, 317, 790-792.

Proposed Mechanism for The Direct Acylation of Amines


Different Mechanism for Amide Synthesis


36 Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D. Nat Chem 2013, 5, 122-125.

Catalytic Transformation of Alcohols to Carboxylic Acid Salts and H2

37 Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D., Nat Chem 2013, 5 (2), 122-125.

?

“The PNN complex also catalyzes this reaction, but less efficiently. The reason for that is not clear at this stage” - Prof. David Milstein

Catalytic Transformation of Alcohols to Carboxylic Acid Salts and H2

Hydrogenation of Double Bonds

38 Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D. Nat Chem 2013, 5, 122-125.

Proposed Mechanism for Formation of Carboxylate From Alcohol

Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D., Nat Chem 2013, 5 (2), 122-125.

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Relative Enthalpies for Alcohol to Carboxylic Acid Transformation



41

Carboxylic Acid-Addition Complex

Pros and Cons

42

Pyridine based Ru pincer complexes • Acceptorless dehydrogenation of

alcohol • Higher atom economy • Low catalytic loading (0.1-0.3 mol%) • H2 gas as the only byproduct • Chemeoselectivity • Good yields and turnover numbers • At high pH no aldol products Cons • Salt production • Metal and ligand are expensive

Conventional methods • Stoichiometric amount of

oxidant • Give rise to stoichiometric

amount of waste, with toxic metals

• Less atom economy

Previous catalytic systems • High catalytic loading (1-

5 mol%) • Strong acid or base

conditions • Less turnover numbers

Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D., Nat Chem 2013, 5 (2), 122-125. Gunanathan, C.; Ben-David, Y.; Milstein, D., Science 2007

Advancing From Py Based Ru Pincer Complexes to Iron Pincer Complexes

43 Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D., Angew Chem Int Edit 2011, 50 (9), 2120-2124.

Advancing From Py Based Ru Pincer Complexes to Iron Pincer Complexes

44 Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew Chem Int Edit 2011, 50, 2120-2124.

Hydrogenation of Ketones by Iron Pincer Complex

45 Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew Chem Int Edit 2011, 50 , 2120-2124.

“An important goal yet to be achieved”

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-Zweifel, T.; Naubron, J. V.; Grutzmacher, H.,Angew Chem Int Edit 2009, 48 (3), 559-563.

47

Acknowledgement

• Dr. Maleczka

• Dr. Huang

• Dr Jackson, Dr. Mitch

• Salinda and Dilini

• All my group members

• Behnaz, Dmitrijs, Souful, Tayeb, Yu-Ling, Tim, Buddhadeb

• All my friends

discovery of environmentally benign reactions of … of environmentally benign reactions of alcohols...

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