Application of Organometallic Chemistry – Breaking the Inert

C-H Bond

Literature Special Topic

Date

Created by [John Lee, University of Tennessee Chattanooga, John-Lee@utc.edu] 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.

C-H Functionalization: A challengeC-H Functionalization: A challenge

Foley, N. A.; Lee, J. P.; Ke, Z.; Gunnoe, T. B.;Cundari, T.. R. Acc Chem. Res. 2009, 42, 585-597.

C-C Bond Formation – Olefin Insertion