Sandwich compound

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Space-filling model of ferrocene, the archetypal sandwich compound Ferrocene 3d model 2.png
Space-filling model of ferrocene, the archetypal sandwich compound

In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic, covalent bonds to two arene (ring) ligands. The arenes have the formula CnHn, substituted derivatives (for example Cn(CH3)n) and heterocyclic derivatives (for example BCnHn+1). Because the metal is usually situated between the two rings, it is said to be "sandwiched". A special class of sandwich complexes are the metallocenes.

Contents

The term sandwich compound was introduced in organometallic nomenclature in 1956 in a report by J. D. Dunitz, L. E. Orgel and R. A. Rich, who confirmed the structure of ferrocene by X-ray crystallography. [1] The correct structure, in which the molecule features an iron atom sandwiched between two parallel cyclopentadienyl rings, had been proposed several years previously by Robert Burns Woodward and, separately, by Ernst Otto Fischer. The structure helped explain puzzles about ferrocene's conformers. This result further demonstrated the power of X-ray crystallography and accelerated the growth of organometallic chemistry. [2] [ page needed ]

Classes

(Cycloheptatrienyl)(cyclopentadienyl)titanium (troticene) is an unsymmetrical sandwich complex. Troticene.svg
(Cycloheptatrienyl)(cyclopentadienyl)titanium (troticene) is an unsymmetrical sandwich complex.

The best known members are the metallocenes of the formula M(C5H5)2 where M = Cr, Fe, Co, Ni, Pb, Zr, Ru, Rh, Os, Sm, Ti, V, Mo, W, Zn. These species are also called bis(cyclopentadienyl)metal complexes. Other arenes can serve as ligands as well.

Small carborane sandwiches.png

Structure of (Me4N )2[Fe(C2B9H11)2], showing only one Me4N. KIWJOP.png
Structure of (Me4N )2[Fe(C2B9H11)2], showing only one Me4N .

Closely related are the metal complexes containing H3C3B2R2 (diborolyl) ligands. [7] In addition to these, other sandwich complexes containing purely inorganic ligands are known, such as Fe(C5Me5)(P5) and [(P5)2Ti]2−. [8]

Half-sandwich compounds

Half sandwich complexes have only one facially-bound planar organic ligand instead of two gives rise to a still larger family of half-sandwich compounds. One well studied example is probably methylcyclopentadienyl manganese tricarbonyl. Such species are occasionally referred to as piano-stool compounds, at least when there are three diatomic ligands. In such cases, the facially-bound planar organic ligand comprises the "seat" of the piano stool.

Multidecker sandwiches

The first isolated multidecker sandwich was the tris(cyclopentadienyl)dinickel triple-decker complex [Ni2Cp3]BF4 , a highly air- and water-sensitive compound reported in 1972, [9] with X-ray crystallographic confirmation in 1974. [10]

In 1973 the electrically neutral air-stable triple-decker cobaltacarborane sandwiches 1,7,2,3- and 1,7,2,4-CpCo(RHC2B3H3)Cp (where R = H, Me) were isolated and characterized by multinuclear NMR and X-ray studies [11] (the structure of the 1,7,2,3 isomer is shown).

1,7,2,3- CpCo(MeC2B3H4)CoCp, the first structurally confirmed multidecker sandwich. Co2C2B3 triple-decker1.jpg
1,7,2,3-CpCo(MeC2B3H4)CoCp, the first structurally confirmed multidecker sandwich.

Since then many three-, four-, five-, and six-decker sandwich complexes have been described. [12] [13] The largest structurally characterized multidecker sandwich monomer is the hexadecker shown at lower right. [14]

A structurally characterized cobaltacarborane hexadecker. Hexadecker.jpg
A structurally characterized cobaltacarborane hexadecker.

An extensive family of multidecker sandwiches incorporating planar (R2R′C3B2R″2)3− (diborolyl) ligands has also been prepared. [15]

Numerous multidecker sandwich compounds featuring hydrocarbon bridging rings have also been prepared, especially triple deckers. [16] A versatile method involves the attachment of Cp*Ru+ to preformed sandwich complexes. [17]

Linked sandwiches

Monomeric double-decker and multidecker sandwiches have been used as building blocks for extended systems, some of which exhibit electron delocalization between metal centers. An example of a cyclic poly(metallacarborane) complex is the octahedral "carbon-wired" system shown below, which contains a planar C16B8 macrocycle. [18]

Carbon-wired tetracobaltacarborane2.jpg

Inverse sandwiches

In these anti-bimetallic compounds, the metals are found to be bridged by a single carbocyclic ring. Examples include [(THF)3Ca]2(1,3,5-triphenylbenzene) [19] and [(Ar)Sn]2 COT .

Perylene-tetrapalladium-sandwich-complex-from-xtal-3D-vdW.png
Perylene-tetrapalladium-sandwich-complex-from-xtal-3D-balls-B.png
PeryleneTetrapalladiumSandwichComplex.png
Perylene–tetrapalladium sandwich complex

Double- and multimetallic sandwich compounds

Another family of sandwich compound involves more than one metal sandwiched between two carbocyclic rings. Examples of the double sandwich include V2(indenyl)2, [20] Ni2(COT)2 [21] and Cr2(pentalene)2. Depicted at right is an example of a multimetallic sandwich compound, which has four palladium atoms joined in a chain sandwiched between two perylene units. [22] The counterions are bulky tetraarylborates.

Applications

Ferrocene and methylcyclopentadienyl manganese tricarbonyl have been used as antiknock agents. Certain bent metallocenes of zirconium and hafnium are effective precatalysts for the polymerization of propylene. Many half sandwich complexes of ruthenium, such as those derived from (cymene)ruthenium dichloride dimer catalyse transfer hydrogenation, a useful reaction in organic synthesis. [23] [ non-primary source needed ]

Metallocenes3.png

Ferrocene derivatives have also been used as photoinitiators in cationic polymerization. [24]

Related Research Articles

<span class="mw-page-title-main">Metallocene</span> Type of compound having a metal center

A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
5H−
5, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C5H5)2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride or vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp2ZrCH3]+ catalyze olefin polymerization.

Ferrocene is an organometallic compound with the formula Fe(C5H5)2. The molecule is a complex consisting of two cyclopentadienyl rings sandwiching a central iron atom. It is an orange solid with a camphor-like odor that sublimes above room temperature, and is soluble in most organic solvents. It is remarkable for its stability: it is unaffected by air, water, strong bases, and can be heated to 400 °C without decomposition. In oxidizing conditions it can reversibly react with strong acids to form the ferrocenium cation Fe(C5H5)+2. Ferrocene and the ferrocenium cation are sometimes abbreviated as Fc and Fc+ respectively.

<span class="mw-page-title-main">Cyclopentadienyl complex</span> Coordination complex of a metal and cyclopentadienyl groups

A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl groups. Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (η5-) bonding mode. The metal–cyclopentadienyl interaction is typically drawn as a single line from the metal center to the center of the Cp ring.

<span class="mw-page-title-main">Cobaltocene</span> Chemical compound

Cobaltocene, known also as bis(cyclopentadienyl)cobalt(II) or even "bis Cp cobalt", is an organocobalt compound with the formula Co(C5H5)2. It is a dark purple solid that sublimes readily slightly above room temperature. Cobaltocene was discovered shortly after ferrocene, the first metallocene. Due to the ease with which it reacts with oxygen, the compound must be handled and stored using air-free techniques.

<span class="mw-page-title-main">Hapticity</span> Number of contiguous atoms in a ligand that bond to the central atom in a coordination complex

In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated. In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity, and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.

<span class="mw-page-title-main">Chromocene</span> Chemical compound

Chromocene is the organochromium compound with the formula [Cr(C5H5)2]. Like structurally related metallocenes, chromocene readily sublimes in a vacuum and is soluble in non-polar organic solvents. It is more formally known as bis(η5-cyclopentadienyl)chromium(II).

<span class="mw-page-title-main">Group 2 organometallic chemistry</span>

Group 2 organometallic chemistry refers to the organic derivativess of any group 2 element. It is a subtheme to main group organometallic chemistry. By far the most common group 2 organometallic compounds are the magnesium-containing Grignard reagents which are widely used in organic chemistry. Other organometallic group 2 compounds are typically limited to academic interests.

<span class="mw-page-title-main">Organouranium chemistry</span> Area of chemistry

Organouranium chemistry is the science exploring the properties, structure, and reactivity of organouranium compounds, which are organometallic compounds containing a carbon to uranium chemical bond. The field is of some importance to the nuclear industry and of theoretical interest in organometallic chemistry.

<span class="mw-page-title-main">Sodium cyclopentadienide</span> Chemical compound

Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pink owing to traces of oxidized impurities.

<span class="mw-page-title-main">Organoscandium chemistry</span> Chemistry of compounds containing a carbon to scandium chemical bond

Organoscandium chemistry is an area with organometallic compounds focused on compounds with at least one carbon to scandium chemical bond. The interest in organoscandium compounds is mostly academic but motivated by potential practical applications in catalysis, especially in polymerization. A common precursor is scandium chloride, especially its THF complex.

<span class="mw-page-title-main">Rhodocene</span> Organometallic chemical compound

Rhodocene is a chemical compound with the formula [Rh(C5H5)2]. Each molecule contains an atom of rhodium bound between two planar aromatic systems of five carbon atoms known as cyclopentadienyl rings in a sandwich arrangement. It is an organometallic compound as it has (haptic) covalent rhodium–carbon bonds. The [Rh(C5H5)2] radical is found above 150 °C (302 °F) or when trapped by cooling to liquid nitrogen temperatures (−196 °C [−321 °F]). At room temperature, pairs of these radicals join via their cyclopentadienyl rings to form a dimer, a yellow solid.

<i>Ansa</i>-metallocene Organometallic compound

An ansa-metallocene is a type of organometallic compound containing two cyclopentadienyl ligands that are linked by a bridging group such that both cyclopentadienyl groups are bound to the same metal. The link prevents rotation of the cyclopentadienyl ligand and often modifies the structure and reactivity of the metal center. Some ansa-metallocenes are active in Ziegler-Natta catalysis, although none are used commercially. The term ansa-metallocene was coined by Lüttringhaus and Kullick to describe alkylidene-bridged ferrocenes, which were developed in the 1950s.

<span class="mw-page-title-main">Dicarbollide</span> Chemical compound

In organometallic chemistry, a dicarbollide is an anion of the formula [C2B9H11]2-. Various isomers exist, but most common is 1,2-dicarbollide derived from ortho-carborane. These dianions function as ligands, related to the cyclopentadienyl anion. Substituted dicarbollides are also known such as [C2B9H10(pyridine)]− (pyridine bonded to B) and [C2R2B9H9]2- (R groups bonded to carbon).

<span class="mw-page-title-main">Vanadocene</span> Chemical compound

Vanadocene, bis(η5-cyclopentadienyl) vanadium, is the organometallic compound with the formula V(C5H5)2, commonly abbreviated Cp2V. It is a violet crystalline, paramagnetic solid. Vanadocene has relatively limited practical use, but it has been extensively studied.

William J. Evans is a Distinguished Professor at the University of California, Irvine, who specializes in the inorganic and organometallic chemistry of heavy metals, specifically the rare earth metals, actinides, and bismuth. He has published over 500 peer-reviewed research papers on these topics.

Magnesocene, also known as bis(cyclopentadienyl)magnesium(II) and sometimes abbreviated as MgCp2, is an organometallic compound with the formula Mg(η5-C5H5)2. It is an example of an s-block main group sandwich compound, structurally related to the d-block element metallocenes, and consists of a central magnesium atom sandwiched between two cyclopentadienyl rings.

<span class="mw-page-title-main">Zirconocene</span> Chemical compound

Zirconocene is a hypothetical compound with 14 valence electrons, which has not been observed or isolated. It is an organometallic compound consisting of two cyclopentadienyl rings bound on a central zirconium atom. A crucial question in research is what kind of ligands can be used to stabilize the Cp2ZrII metallocene fragment to make it available for further reactions in organic synthesis.

<span class="mw-page-title-main">Lanthanocene</span>

A lanthanocene is a type of metallocene compound that contains an element from the lanthanide series. The most common lanthanocene complexes contain two cyclopentadienyl anions and an X type ligand, usually hydride or alkyl ligand.

<span class="mw-page-title-main">Organothorium chemistry</span> Study of the carbon-thorium bond

Organothorium chemistry describes the synthesis and properties of organothorium compounds, chemical compounds containing a carbon to thorium chemical bond.

<span class="mw-page-title-main">Metallaborane</span>

In chemistry, a metalloborane is a compound that contains one or more metal atoms and one or more boron hydride. These compounds are related conceptually and often synthetically to the boron-hydride clusters by replacement of BHn units with metal-containing fragments. Often these metal fragments are derived from metal carbonyls or cyclopentadienyl complexes. Their structures can often be rationalized by polyhedral skeletal electron pair theory. The inventory of these compounds is large, and their structures can be quite complex.

References

  1. ↑ Dunitz, J.; Orgel, L.; Rich, A. (1956). "The crystal structure of ferrocene". Acta Crystallographica . 9 (4): 373–375. doi: 10.1107/S0365110X56001091 .
  2. ↑ Miessler, G. L.; Tarr, Donald A. (2004). Inorganic Chemistry . Upper Saddle River, NJ: Pearson Education. ISBN   0-13-035471-6.
  3. ↑ Zeinstra, J.D.; De Boer, J.L. (1973). "Structure of Cyclopentadienylcycloheptatrienyl-titanium". Journal of Organometallic Chemistry. 54: 207–211. doi:10.1016/S0022-328X(00)85010-X.
  4. 1 2 Kang, H. C.; Lee, S. S.; Knobler, C. B.; Hawthorne, M. F. (1991). "Syntheses of Charge-Compensated Dicarbollide Ligand Precursors and Their Use in the Preparation of Novel Metallacarboranes". Inorganic Chemistry. 30 (9): 2024–2031. doi:10.1021/ic00009a015.
  5. ↑ Grimes, R. N. (1999). "Small Carborane Ligands as Spectators and as Players". Journal of Organometallic Chemistry. 581 (1–2): 1–12. doi:10.1016/S0022-328X(99)00050-9.
  6. ↑ Grimes, R. N. (2016). "13. Metallacarboranes of the Transition and Lanthanide Elements". Carboranes (3rd ed.). Oxford: Elsevier. ISBN   9780128019054.
  7. ↑ Siebert, W. (1988). "Polydecker sandwich complexes". Pure and Applied Chemistry. 60 (8): 1345–1348. doi: 10.1351/pac198860081345 .
  8. ↑ Urnezius, E.; Brennessel, W. W.; Cramer, C. J.; Ellis, J. E.; Schleyer, P. von R. (2002). "A Carbon-Free Sandwich Complex [(P5)2Ti]2−". Science . 295 (5556): 832–834. Bibcode:2002Sci...295..832U. doi:10.1126/science.1067325. PMID   11823635. S2CID   36455193.
  9. ↑ Salzer, A.; Werner, H. (1972). "Studies on the Reactivity of Metal π‐Complexes. 6. A New Route to Triple‐Decker Sandwich Compounds". Angewandte Chemie International Edition. 11 (10): 930–932. doi:10.1002/anie.197209301.
  10. ↑ Dubler, E.; Textor, M.; Oswald, H.-R.; Salzer, A. (1974). "X‐Ray Structure Analysis of the Triple‐Decker Sandwich Complex Tris(η‐cyclopentadienyl)dinickel Tetrafluoroborate". Angewandte Chemie International Edition. 13 (2): 135–136. doi:10.1002/anie.197401351.
  11. 1 2 Grimes, R. N.; Beer, D. C.; Sneddon, L. G.; Miller, V. R.; Weiss, R. (1974). "Small cobalt and nickel metallocarboranes from 2,3-dicarbahexaborane(8) and 1,6-dicarbahexaborane(6). Sandwich complexes of the cyclic C2B3H7(2^{-}) and C2B3H5(4^{-}) ligands". Inorganic Chemistry. 13 (5): 1138–1146. doi:10.1021/ic50135a025.
  12. ↑ Grimes, R. N. (2007). "Boron-Containing Rings Ligated to Metals". In Crabtree, R. H.; Mingos, D. M. P. (eds.). Comprehensive Organometallic Chemistry III. Vol. 3. Oxford: Elsevier. pp. 1–48. doi:10.1016/B0-08-045047-4/00042-X. ISBN   978-0-08-045047-6.
  13. ↑ Wang, X.; Sabat, M.; Grimes, R. N. (1995). "Organotransition-Metal Metallacarboranes. 43. Directed Synthesis of Carborane-End-Capped Multidecker Sandwiches". Journal of the American Chemical Society. 117 (49): 12218–12226. doi:10.1021/ja00154a023.
  14. 1 2 Wang, X.; Sabat, M.; Grimes, R. N. (1995). "Organotransition-Metal Metallacarboranes. 44. Construction of Pentadecker and Hexadecker Sandwiches from Triple-Decker Building Blocks". Journal of the American Chemical Society. 117 (49): 12227–12234. doi:10.1021/ja00154a024.
  15. ↑ Siebert, W. (1993). "Di- and Trinuclear Metal Complexes of Diboraheterocycles". Advances in Organometallic Chemistry. 35: 187–210. doi:10.1016/S0065-3055(08)60491-8. ISBN   9780120311354.
  16. ↑ Beck, V.; O'Hare, D. (2004). "Triple-decker transition metal complexes bridged by a single carbocyclic ring". Journal of Organometallic Chemistry . 689 (24): 3920–3938. doi:10.1016/j.jorganchem.2004.06.011.
  17. ↑ Fagan, P. J.; Ward, M. D.; Calabrese, J. C. (1989). "Molecular engineering of solid-state materials: organometallic building blocks". Journal of the American Chemical Society . 111 (5): 1698–1719. doi:10.1021/ja00187a024.
  18. ↑ Yao, H.; Sabat, M.; Grimes, R. N.; Fabrizi de Biani, F.; Zanello, P. (2003). "Organotransition‐Metal Metallacarboranes. 63. Metallacarborane‐Based Nanostructures: A Carbon‐Wired Planar Octagon". Angewandte Chemie International Edition. 42 (9): 1002–5. CiteSeerX   10.1.1.615.6577 . doi:10.1002/anie.200390255. PMID   12616549.
  19. ↑ Krieck, S.; Gorls, H.; Yu, L.; Reiher, M.; Westerhausen, M. (2009). "Stable "Inverse" Sandwich Complex with Unprecedented Organocalcium(I): Crystal Structures of [(thf)2Mg(Br)\sC6H2\s2,4,6\-Ph3] and [(thf)3Ca{μ\-C6H3\s1,3,5\-Ph3}Ca(thf)3]". Journal of the American Chemical Society . 131 (8): 2977–2985. doi:10.1021/ja808524y. PMID   19193100.
  20. ↑ Jonas, K.; Rüsseler, W.; Krüger, C.; Raabe, E. (1986). "Synthesis of Diindenyldivanadium—a New Variant of the Reductive Degradation of Metallocenes and Related Compounds". Angewandte Chemie International Edition . 25 (10): 928–929. doi:10.1002/anie.198609281.
  21. ↑ Brauer, D. J.; Kruger, C. (1976). "The stereochemistry of transition metal cyclooctatetraenyl complexes: di-η3,η3′-cyclooctatetraenedinickel, a sandwich compound with two enveloped nickel atoms". Journal of Organometallic Chemistry. 122: 265–273. doi:10.1016/S0022-328X(00)80619-1.
  22. ↑ Murahashi, T.; Uemura, T.; Kurosawa, H. (2003). "Perylene–Tetrapalladium Sandwich Complexes". Journal of the American Chemical Society . 125 (28): 8436–8437. doi:10.1021/ja0358246. PMID   12848540.
  23. ↑ Ikariya, T.; Hashiguchi, S.; Murata, K.; Noyori, R. (2005). "Preparation of Optically Active (R,R)-Hydrobenzoin from Benzoin or Benzil". Organic Syntheses . 82: 10. doi:10.15227/orgsyn.082.0010 .
  24. ↑ Dumur, F. (2020). Recent advances on iron-based photoinitiators of polymerization. European Polymer Journal, 139, 110026.
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