Sandwich compound
The term sandwich compound was introduced in organometallic nomenclature in during the mid-1950s when J.D. Dunitz, L.E. Orgel and R.A. Rich confirmed the structure of ferrocene by X-ray crystallography.[1] The correct structure had been proposed several years previously by Robert Burns Woodward. Of particular interest, the structure helped explain puzzles about ferrocene's conformers, the molecule features an iron atom sandwiched between two parallel cyclopentadienyl rings. This result further demonstrated the power of X-ray crystallography, accelerating the growth of organometallic chemistry.[2]
Classes of sandwich compounds
The best known members are the metallocenes of the formula M(C5H5)2 where M = Cr, Fe, Co, Ni. These species are also called Bis(cyclopentadienyl)metal complexes.
- Mixed cyclopentadienyl complexes: M(C5H5)(CnHn). An example is Ti(C5H5)(C7H7)
- Bis(benzene) complexes: M(C6H6)2, the best known example being the chromium derivative.
- Bis(cyclooctatetraenyl) complexes: U(C8H8)2, the Th derivative is also known.
Sandwich complexes are even known containing purely inorganic ligands, such as Fe(C5Me5)(P5) and [(P5)2Ti]2-.[3]
Half sandwich compounds
Monometallic half sandwich compounds
A piano stool compound is a metallocene compound including just one facially-bound planar organic ligand instead of two. The name derives from the similarity of the structure to such a "stool" with the seat being a facial planar organic compound, e.g. benzene or cyclopentadiene, and the legs being ligands such as CO. Below is an example of such a rhodium piano stool compound.
Dimetallic half sandwich compounds
Compounds such as the cyclopentadienyliron dicarbonyl dimer and cyclopentadienylmolybdenumtricarbonyl dimer can be considered a special case of half-sandwiches, except that they are dimetallic. A structurally related species is [Ru(C6H6)Cl2]2.
Multimetallic sandwich compounds
The compound depicted below has four palladium atoms joined in a chain sandwiched between two perylene units [4]. The counterions are bulky tetraarylborates.
Multidecker sandwiches
The first multidecker sandwich complex was the dicationic triscyclopentadienyl dinickel complex [Ni2Cp3](BF4)2. This motif has been replicated many times, especially by attachment of Cp*Ru+ to preformed sandwich complexes.[5]
References
- ↑ J. Dunitz, L. Orgel, A. Rich (1956). "The crystal structure of ferrocene". Acta Crystallographica 9: 373–5. doi:10.1107/S0365110X56001091.
- ↑ Miessler, Gary L.; Donald A. Tarr (2004). Inorganic Chemistry. Upper Saddle River, New Jersey: Pearson Education, Inc. Pearson Prentice Hall. ISBN 0-13-035471-6.
- ↑ Urnezius, E.; Brennessel, W. W.; Cramer, C. J.; Ellis, J. E. and von Rague Schleyer, P. (2002). "A Carbon-Free Sandwich Complex [(P5)2Ti]2-". Science 295: 832–834. doi:10.1126/science.1067325.
- ↑ Perylene-Tetrapalladium Sandwich Complexes Tetsuro Murahashi, Tomohito Uemura, and Hideo Kurosawa J. Am. Chem. Soc.; 2003; 125(28) pp 8436 - 8437; (Communication) doi:10.1021/ja0358246
- ↑ Fagan, P. J.; Ward, M. D.; Calabrese, J. C., "Molecular engineering of solid-state materials: organometallic building blocks", Journal of the American Chemical Society, 1989, volume 111, pages 1698-719
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 |
Table of Contents In Alphabetical Order | By Individual Diseases | Signs and Symptoms | Physical Examination | Lab Tests | Drugs
Editor Tools Become an Editor | Editors Help Menu | Create a Page | Edit a Page | Upload a Picture or File | Printable version | Permanent link | Maintain Pages | What Pages Link HereThere is no pharmaceutical or device industry support for this site and we need your viewer supported Donations | Editorial Board | Governance | Licensing | Disclaimers | Avoid Plagiarism | Policies
