Oxidative addition
You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.
Oxidative addition and reductive elimination are two important classes of reactions in organometallic chemistry. Their relationship is shown below where y represents the number of ligands on the metal and n is the oxidation state of the metal.
Oxidative addition
In oxidative addition, a metal complex with vacant coordination sites and a relatively low oxidation state is oxidized by the insertion of the metal into a covalent bond (X-Y). Both the formal oxidation state of the metal, n, and the electron count of the complex increase by two.[1] Although oxidative additions can occur with the insertion of a metal into many different covalent bonds, they are most commonly seen with H-H and carbon(sp3)-halogen bonds. Carbon that is sp2 hybridized, as in the case of a vinyl group, can also undergo oxidative addition. This process proceeds with retention of configuration about the double bond.
The reverse of oxidative addition is reductive elimination.[2] Reductive elimination is favored when the newly formed X-Y bond is strong. For reductive elimination to occur the two groups (X and Y) should be adjacent to each other in the metal's coordination sphere.
An example of oxidative addition is the reaction of Vaska's complex, trans-IrCl(CO)[P(C6H5)3]2, with hydrogen. In this transformation, the metal oxidation state changes from Ir(I) to Ir(III) because the product is described as Ir3+ bound to three anions: Cl-, and two hydride, H-, ligands. As shown below, the metal complex initially has 16 valence electrons and a coordination number of four. After the addition of hydrogen, the complex has 18 electrons and a coordination number of six. The reaction can proceed in the opposite direction. In this case hydrogen gas would be lost and the metal complex would be reduced. This backwards reaction is an example of reductive elimination.
Just as a metal oxidatively inserts itself into a H-H bond, it can also oxidatively add to C-H bonds. This process is called C-H bond activation and is an active research area because of its potential value in converting petroleum-derived hydrocarbons into more complex products.
Oxidative addition and reductive elimination are seen in many catalytic cycles such as the Monsanto process and alkene hydrogenation using Wilkinson's catalyst.
References
- ↑ Compendium of Chemical Terminology, oxidative addition accessed 6 Feb 2007.
- ↑ Compendium of Chemical Terminology, reductive elimination accessed 6 Feb 2007.
- Inorganic Chemistry (3rd Edition) by Gary L. Miessler, Donald A. Tarr
- Inorganic Chemistry by D. F. Shriver, P. W. Atkins
Concepts in organometallic chemistry | |
|---|---|
| Principles | Electron counting, 18-Electron rule, Polyhedral skeletal electron pair theory, Isolobal principle, π backbonding, Hapticity |
| Reactions | Oxidative addition, Reductive elimination, Beta-hydride elimination, Transmetalation, Carbometalation |
| Types of compounds | Gilman reagent, Grignard reagents, Cyclopentadienyl complexes, Metallocenes, Sandwich compound, Transition metal carbene complexes |
| Applications | Monsanto process, Ziegler-Natta catalyst, Olefin metathesis |
| Related branches of chemistry | Organic chemistry - Inorganic chemistry - Bioinorganic chemistry |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
