- Sandwich compound
units.
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 byX-ray crystallography . [cite journal | author = J. Dunitz, L. Orgel, A. Rich | title = The crystal structure of ferrocene | journal = Acta Crystallographica | year = 1956 | volume = 9 | pages = 373–5 | doi = 10.1107/S0365110X56001091] The correct structure had been proposed several years previously byRobert Burns Woodward . Of particular interest, the structure helped explain puzzles about ferrocene's conformers, the molecule features an iron atom "sandwiched" between two parallelcyclopentadienyl rings. This result further demonstrated the power ofX-ray crystallography , accelerating the growth oforganometallic chemistry . [cite book | last = Miessler | first = Gary L. | authorlink = Gary L. Miessler | coauthors = Donald A. Tarr | year = 2004 | title = Inorganic Chemistry | publisher = Pearson Education, Inc. Pearson Prentice Hall | location = Upper Saddle River, New Jersey | id = ISBN 0-13-035471-6]Classes of sandwich compounds
The best known members are the
metallocene s of the formula M(C5H5)2 where M = Cr, Fe, Co, Ni, Zr, Ti, V, Mo, W, Zn. 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 beingBis(benzene)chromium .
*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-. [cite journal| author = Urnezius, E.; Brennessel, W. W.; Cramer, C. J.; Ellis, J. E. and von Rague Schleyer, P. | title = A Carbon-Free Sandwich Complex [(P5)2Ti] 2- | journal = Science | year = 2002 | volume = 295 | pages = 832–834 | doi = 10.1126/science.1067325| pmid = 11823635]
Half sandwich compounds
Monometallic half sandwich compounds
Metallocene s including just one facially-bound planar organicligand instead of two gives rise to a still larger family of "half sandwich" compounds. The most famous example is probablymethylcyclopentadienyl manganese tricarbonyl . Such species are occasionally referred to "piano stool" compounds, at least when there are three diatomic ligands in addition to the hydrocarbon "seat" of the piano stool. The name derives from the similarity of the structure to such a "stool" with the seat being a facial planarorganic compound , e.g.benzene orcyclopentadiene , and the legs being ligands such as CO orallyl .Dimetallic half sandwich compounds
Compounds such as the
cyclopentadienyliron dicarbonyl dimer andcyclopentadienylmolybdenumtricarbonyl 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 twoperylene units. [cite journal | title = Perylene-Tetrapalladium Sandwich Complexes | author = Tetsuro Murahashi, Tomohito Uemura, and Hideo Kurosawa | journal =J. Am. Chem. Soc. | year = 2003 | volume = 125 | issue = 28 | pages = 8436–8437 | format = Communication | doi = 10.1021/ja0358246] Thecounterion s are bulky tetraarylborates.Multidecker sandwiches
The first multidecker sandwich complex was the dicationic tris
cyclopentadienyl dinickel complex [Ni2Cp3] (BF4)2. This motif has been replicated many times, especially by attachment ofCp* Ru+ to preformed sandwich complexes. [cite journal | author = Fagan, P. J.; Ward, M. D.; Calabrese, J. C. | title = Molecular engineering of solid-state materials: organometallic building blocks | journal =J. Am. Chem. Soc. | year = 1989 | volume = 111 | pages = 1698–719 | doi = 10.1021/ja00187a024]References
Wikimedia Foundation. 2010.