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Transition Metal-Catalyzed Carbon-Carbon Bond Cleavage
(C-C Activation)
Group Meeting
01-15-2008
Timothy Chang
Outlines
- Fundamental considerations, C-H versus C-C activation- Orbital interactions- Evidence of M…C-C agostic interaction, C-C activation- Thermodynamics
- Stoichiometric reactions
- Catalytic reactions- Activation of strained molecules
- Direct cleavage- Utilization of a carbonyl group- b-Alkyl elimination
- Activation of unstrained molecules- b-Alkyl elimination, utilization of a p-allyl intermediate- Chelation assistance
- Conclusion
Orbital Interactions
Kinetic barriers of C-C activation due to:1. High directionality of C-C s bond2. Substituents on both carbons (steric congestion)3. Statistical abundance of C-H bonds
Murakami, M., Ito, Y. Topics in Organometallic Chemistry 1999, 97-129
Evidence of M…C-C Agostic Interaction
C25-H25 0.97(3) ÅC21-H21 0.95(3) ÅNo M…C-H agostic
interaction from Binor-S
Weller, A. S., et. al. ACIEE, 2006, 45, 452-456.
Weller, A. S., et. al. PNAS, 2007, 104, 6921-6926.1
Supports for M…C-C Agostic Interaction, C-C Activation
1H NMRC11, C15, C21 and C25 are all equivalent at 298 K (d(1H) = 3.23ppm , d(13C) = 25.5 ppm)5 signals (298 K) 10 signals (200 K)
Fluxional at RT
Thermodynamic Considerations
C-C bond90 kcal/mol
M-C bond x240-60 kcal/mol
Microscopic reversibility
M-H bonds are generally stronger than M-C bonds by 15 – 25 kcal/mol even though Me-H and H-H have almost the same BDE.
Labinger, J. A., Bercaw, J. E. Organometallics 1988, 7, 926-928.
Crabtree, R. H. The Organometallic Chemistry of the Transition Metals 4th Ed. P80.
Unlike in the gas phase, M-H bonds are generally stronger than M-C bonds in the solution.
Simões, J. A. M., et al. Chem. Rev. 1990, 90, 629-688.
Examples:(η5-C5Me5)(PMe3)2Ru−H 167.4 kcal/mol(η5-C5Me5)(PMe3)2Ru−CH3 142.3 kcal/mol
CRC 88th Ed.
Thermodynamic Considerations
Jun, C.-H Chem. Soc. Rev., 2004, 33, 610-618.
Milstein, D., Rybtchinski B. ACIEE 1999, 38, 870-883.
Strategies to facilitate C-C bond activation:1. Employing strained starting materials
E(C-C) 61 kcal/mol
Tipper (1955)Chatt (1961)
Thermodynamic Considerations
Jun, C.-H Chem. Soc. Rev., 2004, 33, 610-618.
Milstein, D., Rybtchinski B. ACIEE 1999, 38, 870-883.
Strategies to facilitate C-C bond activation (c ontd):2. Use high energy metal complexes
16 e Coordinatively
unsaturated
Thermodynamic Considerations
Jun, C.-H Chem. Soc. Rev., 2004, 33, 610-618
Strategies to facilitate C-C bond activation (contd):3. Extrusion of gas, aromatization
4. Formation of a stable metallacycle and chelation assistance
Five-membered metallacyclic complexes are relatively stable.Rh-Caryl and Ir-Caryl bonds are sometimes stronger than the corresponding M-H bonds.
Outlines
- Fundamental considerations, C-H versus C-C activation- Orbital interactions- Evidence of M…C-C agostic interaction, C-C activation- Thermodynamics
- Stoichiometric reactions
- Catalytic reactions- Activation of strained molecules
- Direct cleavage- Utilization of a carbonyl group- b-Alkyl elimination
- Activation of unstrained molecules- b-Alkyl elimination, utilization of a p-allyl intermediate- Chelation assistance
- Conclusion
Direct Cleavage
a 2.75 mM (PPh3)3RhCl and 0.138 M substrate in anhydrous toluene.b Turnover frequency determined at 18 h.
Chirik, P. J., et. al. JACS 2003, 125, 886.
Direct Cleavage
Murakami, M. et. al. JACS 2007, 129, 12596.
Utilization of a Carbonyl Group
Stoichiometric reactions showed that the insertion of Rh(I) into the a C-C bond is feasible
5 mol%
Murakami, M. et. al. Nature 1994, 370, 540.
Murakami, M. et. al. JACS 1996, 370, 8259.
87 % yield
Predict Products and Propose Mechanisms
Murakami, M. et. al. ACIEE 2000, 39, 2484.Both reactions were carried out under argon.
Utilization of a Carbonyl Group
Murakami, M. et. al. JACS 2002, 124, 13976.
b-Alkyl Elimination (1)
b-Alkyl elimination is the reverse of insertionUemura, S. et. al. JACS, 2000, 122, 12049.
Oxidative Addition
b-Alkyl Elimination (1)
b-Alkyl Elimination (1)
Uemura, S. et. al. JACS, 2003, 125, 8862.
79 % yield
78 % ee
93 % yield
73 % ee
+ 93 % yield
91 % ee
(S)
b-Alkyl Elimination (2)
Uemura, S. et. al. JACS, 2003, 125, 8862.
Murakami, M. et. al. JACS, 1997, 119, 9307.
C-C bond activation by1. Insertion of Rh(I) cat into a
C(O)-C bond2. b-Alkyl elimination
b-Alkyl Elimination (3)
Murakami, M. et. al. JACS, 2005, 127, 6932.
Other Strained Molecules for C-C Activation
O
O
OO
O
O
Mitsudo, T. et. al. Chem. Lett,
2005, 34, 1462.
Mechanism of the Pyranone Formation
Mitsudo, T. et. al. ACIEE,
2004, 43, 5369.
Outlines
- Fundamental considerations, C-H versus C-C activation- Orbital interactions- Evidence of M…C-C agostic interaction, C-C activation- Thermodynamics
- Stoichiometric reactions
- Catalytic reactions- Activation of strained molecules
- Direct cleavage- Utilization of a carbonyl group- b-Alkyl elimination
- Activation of unstrained molecules- b-Alkyl elimination, utilization of a p-allyl intermediate- Chelation assistance
- Conclusion
b-Alkyl Elimination, Utilization of a p-Allyl Intermediate
Mitsudo, T. et. al. JACS, 1998, 120, 5587.
5 mol%
b-Alkyl Elimination, Formation of a Pd-C(Sp2) Bond
Miura, M. et. al. JACS, 2001, 123, 10407.
b-Alkyl Elimination, Formation of a Pd-C(Sp) Bond
33-61 % yield
Uemura. S. et. al. JACS, 2003, 5, 2997.
Sequential b-Alkyl Elimination, Conjugate Addition
Hayashi. T. et. al. JACS, 2007, 129, 14158.
Sequential b-Alkyl Elimination, Conjugate Addition
Hayashi. T. et. al. JACS, 2007, 129, 14158.
Chelation Assistance
Jun, C.-H Chem. Soc. Rev., 1999, 121, 880.
Nickel-Catalyzed Arylcyanation of Alkynes
Hiyama, T. JACS, 2004, 126, 13904.time (h) yield(%)
Conclusion
- Different strategies toward C-C single bond activation have emerged
- Mild reaction conditions need to be developed
- Substrate scopes are limited in many cases
- Only a few enantioselective reactions have been reported
- This technology is still at the exploration stage
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