121. Acceptorless Dehydrogenation with Metal

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Transcript 121. Acceptorless Dehydrogenation with Metal

Acceptorless Dehydrogenation with Metal-Ligand Cooperation Strategy by Aromatization-Dearomatization Zhou Xiao-Le 2014.06.21

Contents

Brief introduction to AD

Pioneering works

Metal-ligand Cooperation

Long-Range Metal-Ligand Cooperation

Conclusion

Additionals

Brief Introduction Dehydrogenation: basic oxidation reaction in organic chemistry Oxidant or sacrificial hydrogen acceptor was used to absorb the H.

In acceptorless dehydrogenation, H was released as hydrogen or was in situ consumption and no net hydrogen gas is liberated David Milstein Michael J. Krische Alan S. Goldman

Pioneering Work of Dehydrogenation of Alkanes Catalyzed by Transition Metal Phosphine Complex Stoichiometric Reaction with Sacrificial Hydrogen Acceptor R. H. Crabtree, J. M. Mihelcic, J. M. Quirk. J. Am. Chem. Soc. 1979, 101, 7738-7740 The First Acceptorless Dehydrogenation Reaction K. Nomura, Y. Saito. J. Chem. Soc., Chem. Commun. 1988, 161-162 Problems: Slow rates, harsh conditions, low number of turnovers, and catalyst instability.

Pioneering Work of Dehydrogenation Catalyzed by Metal P-C-P Pincer Complexes The First Dehydrogenation Reaction with Sacrificial Hydrogen Acceptor C. M. Jensen, et al. Chem. Commun. 1996, 2083; The First Acceptorless Dehydrogenation Reaction by Pincer Complexes Alan S. Goldman, et al. Chem. Commun. 1997, 2273;

The Thermodynamic Reason for the Problems of the Dehydrogenation reaction The ΔH of some chemical bonds:

Chemical bonds

C-C C=C C-H H-H

ΔH/(kJ/mol)

342 613 416 435.9

Let’s start from the reaction : ΔH = (ε C-C +6ε C-H )-(ε C=C +4ε C-H +ε H-H ) = (342+6*416)-(613+4*416+435.9) = +125.1 kJ/mol ΔG of a spontaneous reaction must be minus, that is: ΔG = ΔH-TΔS < 0 Problems: Slow rates, harsh conditions, low number of turnovers, and catalyst instability.

ΔS > 0, and ΔH >> 0, so T have to >> 0 to make ΔG < 0. That is the same to say: A strong heat was need to make the reaction proceed.

Proposed Mechanism of Transfer Dehydrogenation (TD) or Acceptorless Dehydrogenation (AD) No structural changes of ligands in the reaction

Metal-ligand Cooperation by Aromatization Dearomatization David Milstein, et al.

J. Am. Chem. Soc. 2006, 128, 15390-15391 Dalton Trans. 2009, 9433–9439 Organometallics 2010, 29, 3817–3827 Chidambaram Gunanathan, David Milstein Acc. Chem. Res. 2011, 44, 588-602

X-Ray Structure of Dearomatization Pincer Complex David Milstein, et al.

J. Am. Chem. Soc. 2006, 128, 15390-15391 X-Ray Structure of A

Facile Transformation of Alcohols into Esters, Amides, and Imines with Liberation of H 2

Facile Transformation of Alcohols or Amine into Esters, Acids, Amides, and Imines with Liberation of H 2 David Milstein. Organometallics 2004, 23, 4026-4033

Transformation of Alcohols into Esters David Milstein, et al.

J. Am. Chem. Soc. 2005, 127, 10840-10841 2 possible mechanisms from aldehydes to esters: right

Tishchenko

反应

Transformation of Alcohols into Acids David Milstein, et al.

Nature Chemistry, 2013, 5, 122-125.

Transformation of Alcohols and Amines into Amides C. Gunanathan, Y. Ben-David, D. Milstein. Science 2007, 317, 790–792.

D. Milstein. U.S. Patent.

Zeng Han-Xiang, Guan Zhi-Bin. J. Am. Chem. Soc. 2011, 133, 1159–1161.

Transformation of Alcohols and Amines into Imines D. Milstein, et al.

Angew. Chem. Int. Ed. 2010, 49, 1468 –1471

Transformation of Alcohols or Amine and Esters into Amides David Milstein, et al. Adv. Synth. Catal. 2010, 352, 3169 – 3173 David Milstein, et al. J. Am. Chem. Soc. 2011, 133, 1682–1685

Proposed Mechanism for the Transformation

Long-Range Metal-Ligand Cooperation David Milstein, et al. J. Am. Chem. Soc. 2010, 132, 14763–14765

Transformation of Alcohols into Acetals David Milstein, et al. J. Am. Chem. Soc. 2009, 131, 3146–3147

Transformation of Alcohols and Ammonia into Primary Amines David Milstein, et al. Angew. Chem. Int. Ed. 2008, 47, 8661 –8664

Direct Pyrrole Synthesis via Dehydrogenative Coupling Wang Zhi-Xiang. J. Am. Chem. Soc. 2014, 136, 4974−4991

Conclusions

Advantages

 Efficiency of the Metal-ligand Cooperation catalysts are quite high. Catalysts load   can be as high as 0.1%.

Scope of the substrates are quite large. Aryl, alkyl, alkeyl(some examples) are both appropriate substituent groups of the substrates.

Detailed studied about the operation pattern of catalysts will be a new orientation in modern chemistry.

Limits

 The majority of the reactions are activation of X-H(O-H or N-H), and formation of C-X bonds. Few applications in alkane metathesis failed to make good yield and selectivity.

 Achiral pincer-ligands occupying more orbitals makes it hard to control the stereoselectivity in C-C bond formation.

Additionals Michael J. Krische, et al. Science 2012, 336, 324-327 Michael J. Krische, et al. J. Am. Chem. Soc. 2014, 136, ASAP