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!
-Why do we draw line structures forOrganic molecules?
-High bond energymethane 100 kcal/molbenzene 110 kcal/mol
-High pKaon the order of >40
**,but…Nature uses the C-H bond: See methane monooxygenase and vitamin-b12
Example Organic Molecules
In organic chemistry….
Carey, F. A. Organic Chemistry, 4th ed. 2001, McGraw-Hill, Chapter 8.
Leaving Groups (LG)
Generic Substitution Reaction (SN1 shown)
TsO-, NH3 > I-, H2O > Br- > Cl- > HO-, NH2-, RO-
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).
In organometallic chemistry….
Cross-Coupling Reactions
but wait I said C-H not C-X activation?
If it ain’t broke why fix it?If it ain’t broke why fix it?
-Nearly everything comes from coal, oil or natural gasCoal: 1,000 – 2,000 yearsOil: 50 – 150 yearsNatural gas: 207 – 590 years
-However this is not sustainable for population growthWhy?
-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
C-donor,N-donor,O-donor,P-donor,or S-donor etc…
Metal + Ligands
What it is really all about!
Shriver and Atkins Inorganic Chemistry, 5th ed. 2001, Freeman, Chapter 1.
Some typical mechanismsSome typical mechanisms
Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507-514.
Example 1: Oxidative additionExample 1: Oxidative addition
-The metal’s oxidation state increases by two unitsMust be accessible
-Requires an electron rich metalLow oxidation stateElectron donating ligands
-The metal’s coordination # increases by twoMust be accessible
-Many d8 metals meet these criteria:Primarily RhI and IrI
Sometimes PdII and PtII
Qualitative MO Diagram
Example of oxidative addition:Alkane dehydrogenationExample of oxidative addition:Alkane dehydrogenation
Example 2: -Bond metathesisExample 2: -Bond metathesis
-Early transition metals that do not have a n+2oxidation 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
Qualitative MO Diagram
Example of -bond metathesis: Hydromethylation of propyleneExample of -bond metathesis: Hydromethylation of propylene
Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 7971-7977.
Example #3: Electrophilic substitutionExample #3: Electrophilic substitution
Milstein, D. et al. J. Am. Chem. Soc. 1998, 120, 12539-12544
Qualitative MO Diagram
Example of electrophilic substitution: Methane oxidationExample of electrophilic substitution: Methane oxidation
Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T; Fuji, H. Science 1998, 280, 560-564.