Studies Surrounding the Reaction and Mechanism for the ...
Application of Organometallic Chemistry Breaking the Inert C-H Bond Literature Special Topic Date Created by [John Lee, University of Tennessee Chattanooga, [email protected]] and posted on VIPEr (www.ionicviper.org) on [July 16, 2012], Copyright [July, 16, 2012]. This work is licensed under the Creative Commons [Attribution-NonCommercial-ShareAlike 3.0 Unported] License. To view a copy of this license visit
http://creativecommons.org/about/license/ You want to break which bond! Example Organic Molecules -Why do we draw line structures for Organic molecules? -High bond energy methane 100 kcal/mol benzene 110 kcal/mol
-High pKa on the order of >40 **,butNature uses the C-H bond: See methane monooxygenase and vitamin-b12 In organic chemistry. Generic Substitution Reaction (SN1 shown)
Leaving Groups (LG) TsO-, NH3 > I-, H2O > Br- > Cl- > HO-, NH2-, RO- Carey, F. A. Organic Chemistry, 4th ed. 2001, McGraw-Hill, Chapter 8. In organometallic chemistry. Cross-Coupling Reactions
Heck, R. F.; Negishi, E.; Suzuki, A. palladium catalyzed cross couplings in Organic Synthesis: Great Art in a Test Tube. http://nobelprize.orglnobeljrizes/chemistry/laureatesl}O10/press.html (March 17, 2011). but wait I said C-H not C-X activation? If it aint broke why fix it? -Nearly everything comes from coal, oil or natural gas Coal: 1,000 2,000 years Oil: 50 150 years
Natural gas: 207 590 years -However this is not sustainable for population growth Why? -We are a good 10-20 (optimistic) years from solar -For the interim time we should use our resources to the best of our ability How? Lewis, N. S.; Nocera, D. G. Proc. Nat. Acad. Sci. 2006, 103,
15729-15735. How? Rationale design and synthesis Metal + Ligands
C-donor, N-donor, O-donor, P-donor, or S-donor etc What it is really all about! Shriver and Atkins Inorganic Chemistry, 5th ed. 2001, Freeman, Chapter 1.
Some typical mechanisms Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507-514. Example 1: Oxidative addition Qualitative MO Diagram -The metals oxidation state increases by two units Must be accessible
-Requires an electron rich metal Low oxidation state Electron donating ligands -The metals coordination # increases by two Must be accessible -Many d8 metals meet these criteria: Primarily RhI and IrI Sometimes PdII and PtII
Example of oxidative addition: Alkane dehydrogenation Example 2: -Bond metathesis Qualitative MO Diagram -Early transition metals that do not have a n+2 oxidation state available -Late transition metals that do not have an accessible n+2 oxidation state
-Many d0 metals meet these criteria: For example, ScIII, ZrIV, TaV Example of -bond metathesis: Hydromethylation of propylene Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 7971-7977. Example #3: Electrophilic substitution
Qualitative MO Diagram Milstein, D. et al. J. Am. Chem. Soc. 1998, 120, 12539-12544 Example of electrophilic substitution: Methane oxidation Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T; Fuji, H. Science 1998, 280, 560-564.
C-H Functionalization: A challenge C-C Bond Formation Olefin Insertion Foley, N. A.; Lee, J. P.; Ke, Z.; Gunnoe, T. B.; Cundari, T.. R. Acc Chem. Res. 2009, 42, 585-597.
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