Decamethyldizincocene

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Decamethyldizincocene
Decamethyldizincocene.png
Decamethyldizincocene xtal.png
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/2C10H15.2Zn/c2*1-6-7(2)9(4)10(5)8(6)3;;/h2*1-5H3;;/q2*-1;2*+1
    Key: FZXUROULDKYZME-UHFFFAOYSA-N
  • C[C-]1C(=C(C(=C1C)C)C)C.C[C-]1C(=C(C(=C1C)C)C)C.[Zn+].[Zn+]
Properties
C20H30Zn2
Molar mass 401.22 g·mol−1
Appearancecolorless crystalline solid
Melting point 110 °C (230 °F; 383 K) (decomposes)
Reacts
Solubility soluble in diethyl ether, benzene, pentane, and tetrahydrofuran
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Decamethyldizincocene is an organozinc compound with the formula [Zn2(η5–C5Me5)2]. It is the first [1] and an unusual example of a compound with a Zn-Zn bond. [2] Decamethyldizincocene is a colorless crystalline solid that burns spontaneously in the presence of oxygen and reacts with water. It is stable at room temperature and especially soluble in diethyl ether, benzene, pentane, or tetrahydrofuran. [3]

Synthesis

The ability of metals to form heteronuclear or homonuclear metal-metal bonds varies throughout the periodic table. Among the group 12 elements, mercury readily forms [M-M]2+ units whereas the elements cadmium and zinc form fewer examples of such species. [2] Decamethyldizincocene was reported in 2004 by Carmona and coworkers as an unexpected product of the reaction between decamethylzincocene (Zn(C5Me5)2) and diethylzinc (ZnEt2). [2]

The half-sandwich compound [(e -C5Me5)ZnMe Structure of organometallic zinc complex (C5Me5)Zn(Me).png
The half-sandwich compound [(η -C5Me5)ZnMe

]

2 (η5-C5Me5)2Zn + Et2Zn → (η5-C5Me5)2Zn2 + 2 (η5-C5Me5)ZnEt + hydrocarbon(s)

The analogous reaction of zincocene (Zn(C5H5)2) with diethylzinc gives (η5-C5H5)ZnEt. [4] Therefore, the stabilizing effect of the methyl groups on the cyclopentadienyl rings is of great importance in the formation of decamethydizincocene. The use of ZnEt2 as a reactant is of particular significance.

The organozinc precursor is important. Diphenylzinc (Zn(C6H5)2), despite its lower solubility, can be utilized in place of ZnEt2. On the other hand, ZnMe2 gives only the half-sandwich compound [(η5-C5Me5)ZnMe]. [3]

Both (η5-C5Me5)ZnEt and decamethyldizincocene are produced from the reaction between Zn(η5-C5Me5)2 and ZnEt2. The relative amounts depend on reaction conditions, which can be optimized to favor one or the other. [2] For instance, if this reaction is conducted in pentane at -40 °C, (η5-C5Me5)ZnEt is the sole product. Conversely, if the reaction is conducted in diethyl ether at -10 °C, (Zn2(η5-C5Me5)2) is the major product.

Unpredictability of synthesis

The formation of decamethyldizincocene is, however, rather unpredictable. Several duplications of this reaction (under conditions that favor the formation of decamethyldizincocene) have inexplicably led to the formation of only the half-sandwich complex (η5-C5Me5)ZnEt. The formation of the products (η5-C5Me5)ZnEt and Zn2(η5-C5Me5)2 occur via separate, competitive reaction pathways and, therefore, the two products do not interconvert when left to react over extended periods of time. [3]

The formation of the half-sandwich complex is believed to occur via hydrocarbyl-bridged intermediates. The reaction mechanism is, however, uncertain. Previously it was hypothesized that the creation of decamethyldizincocene occurred through the decomposition of diethylzinc, whose decomposition products would have had the capability of reducing decamethylzincocene to decamethyldizincocene. However, it is now believed that the formation of decamethyldizincocene occurs via a radical reaction involving the combination of two (η5-C5Me5)Zn• radicals.

In a new more efficient and more general route to decamethyldizincocene, potassium hydride is used to reduce decamethylzincocene to decamethyldizincocene. Other reductants such as K, Na, or CaH2 may be used as well in the reduction of decamethylzincocene to decamethyldizincocene. [3]

DecamethyldizincoceneScheme.svg

This complex does not react with Lewis bases such PMe3, PPh3, NEt3, or pyridine nor does it react with H2, CO2, or CO. This compound appears to be indefinitely stable at room temperature (however storage at -20 °C is advised) and sublimes near 70 °C under vacuum. [2]

Structure

Various methods have been employed in order to determine the structure of decamethyldizincocene, including x-ray diffraction, 1H NMR, and mass spectrometry. Through X-ray diffraction methods it has been found that the zinc atoms are sandwiched between two parallel C5Me5 rings whose planes are perpendicular to the metal-metal bond axis. [3] The separation between the two ring planes is approximately 6.40 Å. The C5Me5 rings are in an eclipsed conformation with the methyl substituents bent slightly outward (away from the central metal atoms) at angles of 3 to 6 degrees. [5]

In mononuclear metallocenes the bending of substituents attached to the rings serves to prevent steric hindrance; however, the radius of a methyl group is only 2.0 Å and therefore the bending in decamethyldizincocene does not serve this purpose since the distance between the two rings is much greater than this value. It is believed that in the case of decamethyldizincocene the bending of the methyl groups attached to the cyclopentadienyl ligands is preferential because it concentrates the electron density away from the central, positively charged metal atoms. The separation between each Zn atom and the center of the cyclopentadienyl ring attached to it is approximately 2.04 Å and the Zn-C(ring) distances range from 2.27 to 2.30 Å. [3] The Zn-Zn bond distance is 2.305 Å, which indicates considerably strong bonding between the two zinc atoms. This can be compared to the known [Hg-Hg]2+ bond length of 2.5 to 2.7 Å. [6] Two separate types of structures for dimetallocenes have been hypothesized including a coaxial structure (which is the structure of decamethyldizincocene) and a perpendicular structure in which the metal-metal bond axis is parallel to the plane of the cyclopentadienyl ligands (which is predicted to be the structure for dicuprocenes). [7] The compound addressed in this paper is essentially linear with Zn-Zn bond angles of approximately 177°: [3]

Absence of bridging ligands

1H NMR and mass spectrometry studies have been useful in proving that decamethyldizincocene does not include bridging ligands. This study is important considering that the complex previously hypothesized to be Co2(η5-C5Me5)2 was later found using 1H NMR and mass spectrometry data to be supported by three bridging hydrogens. [8] The 1H NMR of decamethyldizincocene shows only one signal at δ 2.02 due to the hydrogens attached to the methyl groups on the cyclopentadienyl ligands. [3]

Electronic structure and bonding characteristics

Decamethyldizincocene has an accumulation of electron density between the two zinc atoms, which indicates bonding. [9] This bond has a predicted dissociation energy of 62 kcal·mol−1 and is approximately as strong as those found among metal-halide bonds. NBO (Natural Bond Order) analysis has indicated that sigma bonding occurs between the 4s orbitals of the central metal atoms with a bonding orbital occupancy of 1.9445.9 Using fragment molecular orbital analysis (FMOA) it has been found that there is one principal molecular orbital that participates in the Zn-Zn bonding with approximately 88% bonding character concentrated between the Zn atoms.

Related Research Articles

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

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">Nickelocene</span> Chemical compound

Nickelocene is the organonickel compound with the formula Ni(η5-C5H5)2. Also known as bis(cyclopentadienyl)nickel or NiCp2, this bright green paramagnetic solid is of enduring academic interest, although it does not yet have any known practical applications.

<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">Titanocene dichloride</span> Chemical compound

Titanocene dichloride is the organotitanium compound with the formula (η5-C5H5)2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air. It shows antitumour activity and was the first non-platinum complex to undergo clinical trials as a chemotherapy drug.

<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">Dewar benzene</span> Chemical compound

Dewar benzene (also spelled dewarbenzene) or bicyclo[2.2.0]hexa-2,5-diene is a bicyclic isomer of benzene with the molecular formula C6H6. The compound is named after James Dewar who included this structure in a list of possible C6H6 structures in 1869. However, he did not propose it as the structure of benzene, and in fact he supported the correct structure previously proposed by August Kekulé in 1865.

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

Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis, and reactions. Organotitanium compounds in organometallic chemistry contain carbon-titanium chemical bonds. They are reagents in organic chemistry and are involved in major industrial processes.

<span class="mw-page-title-main">Cyclopentadienylindium(I)</span> Chemical compound

Cyclopentadienylindium(I), C5H5In, is an organoindium compound containing indium in the +1 oxidation state. Commonly abbreviated to CpIn, it is a cyclopentadienyl complex with a half-sandwich structure. It was the first (1957) low-valent organoindium compound reported.

In organometallic chemistry, a transition metal indenyl complex is a coordination compound that contains one or more indenyl ligands. The indenyl ligand is formally the anion derived from deprotonation of indene. The η5-indenyl ligand is related to the η5cyclopentadienyl anion (Cp), thus indenyl analogues of many cyclopentadienyl complexes are known. Indenyl ligands lack the 5-fold symmetry of Cp, so they exhibit more complicated geometries. Furthermore, some indenyl complexes also exist with only η3-bonding mode. The η5- and η3-bonding modes sometimes interconvert.

<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.

Zinc compounds are chemical compounds containing the element zinc which is a member of the group 12 of the periodic table. The oxidation state of zinc in most compounds is the group oxidation state of +2. Zinc may be classified as a post-transition main group element with zinc(II). Zinc compounds are noteworthy for their nondescript appearance and behavior: they are generally colorless, do not readily engage in redox reactions, and generally adopt symmetrical structures.

<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.

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

Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula C12H18 and the condensed structural formula C6(CH3)6. It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each been replaced by a methyl group. In 1929, Kathleen Lonsdale reported the crystal structure of hexamethylbenzene, demonstrating that the central ring is hexagonal and flat and thereby ending an ongoing debate about the physical parameters of the benzene system. This was a historically significant result, both for the field of X-ray crystallography and for understanding aromaticity.

<span class="mw-page-title-main">Cyclopentadienyliron dicarbonyl dimer</span> Chemical compound

Cyclopentadienyliron dicarbonyl dimer is an organometallic compound with the formula [(η5-C5H5)Fe(CO)2]2, often abbreviated to Cp2Fe2(CO)4, [CpFe(CO)2]2 or even Fp2, with the colloquial name "fip dimer". It is a dark reddish-purple crystalline solid, which is readily soluble in moderately polar organic solvents such as chloroform and pyridine, but less soluble in carbon tetrachloride and carbon disulfide. Cp2Fe2(CO)4 is insoluble in but stable toward water. Cp2Fe2(CO)4 is reasonably stable to storage under air and serves as a convenient starting material for accessing other Fp (CpFe(CO)2) derivatives (described below).

<span class="mw-page-title-main">Decamethylsilicocene</span> Chemical Compound

Decamethylsilicocene, (C5Me5)2Si, is a group 14 sandwich compound. It is an example of a main-group cyclopentadienyl complex; these molecules are related to metallocenes but contain p-block elements as the central atom. It is a colorless, air sensitive solid that sublimes under vacuum.

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

Beryllocene is an organoberyllium compound with the chemical formula Be(C5H5)2. It was first prepared in 1959. The colorless substance can be crystallized from petroleum ether in the form of white needles at −60 °C and decomposes quickly upon contact with atmospheric oxygen and water.

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

Tantalocene trihydride, or bis(η5-cyclopentadienyl)trihydridotantalum, is an organotanalum compound in the family of bent metallocenes consisting of two cyclopentadienyl rings and three hydrides coordinated to a tantalum center. Its formula is TaCp2H3, and it is a white crystalline compound that is sensitive to air. It is the first example of a molecular trihydride of a transition metal.

References

  1. ↑ Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. p. 843. ISBN   978-0-13-175553-6.
  2. 1 2 3 4 5 Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. (2004). "Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond". Science . 305 (5687): 1136–8. Bibcode:2004Sci...305.1136R. doi:10.1126/science.1101356. PMID   15326350. S2CID   38990338.
  3. 1 2 3 4 5 6 7 8 Grirrane, A; Resa, I; Rodriguez, A; Carmona, E; Alvarez, E; Gutierrez-Puebla, E; Monge, A; Galindo, A; et al. (2007). "Zinc-zinc bonded zincocene structures. Synthesis and characterization of Zn2(η5-C5Me5)2 and Zn2(η5-C5Me4Et)2". J. Am. Chem. Soc. 129 (3): 693–703. doi:10.1021/ja0668217. PMID   17227033.
  4. ↑ Haaland, A.; Samdal, S.; Seip, R. (1978). "The molecular structure of monomeric methyl(cyclopentadienyl)zinc, (CH3)Zn(η-C5H5), determined by gas phase electron diffraction". J. Organomet. Chem. 153 (2): 187. doi:10.1016/S0022-328X(00)85041-X.
  5. ↑ Philpott, M; Kawazoe, Y. THEOCHEM 2006, 733, 43.
  6. ↑ Xie, Y.; Schaefer, H.F.; King, R. B. (2005). "The Dichotomy of Dimetallocenes: Coaxial versus Perpendicular Dimetal Units in Sandwich Compounds". J. Am. Chem. Soc. 127 (9): 2818–9. doi:10.1021/ja042754+. PMID   15740094.
  7. ↑ Lutz, F.; Bau, R.; Wu, P.; Koetzle, T. F.; Kruger, C.; Schneider, J. J. (1996). "Neutron Diffraction Structure Analysis of a Triply-Bridged Binuclear Cobalt Hydride Complex, [(η5-Cp*)Co]2H3". Inorg. Chem. 35 (9): 2698–2700. doi:10.1021/ic951297i. PMID   11666493.
  8. ↑ Kang, H. (2005). "Theoretical Study of Complexes of Extended Cyclopentadienyl Ligands with Zinc and Cadmium". J. Phys. Chem. A . 109 (19): 4342–4351. Bibcode:2005JPCA..109.4342K. doi:10.1021/jp044293k. PMID   16833764.
  9. ↑ Kress, J. (2005). "Density Functional Theory Investigation of Decamethyldizincocene". J. Phys. Chem. A . 109 (34): 7757–7763. Bibcode:2005JPCA..109.7757K. doi:10.1021/jp051065x. PMID   16834152.
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