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
ΔH/(kJ/mol)
C-C
342
C=C
613
C-H
416
H-H
435.9
Let’s start from the reaction :
ΔH = (εC-C+6εC-H)-(εC=C+4εC-H+εH-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 AromatizationDearomatization
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 H2
Facile Transformation of Alcohols or Amine into
Esters, Acids, Amides, and Imines with Liberation of
H2
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