Beryllocene

Structural formula
Crystal system	monoclinic
General
Surname	Beryllocene
other names	Bis (cyclopentadienyl) beryllium (II) BeCp 2
Molecular formula	BeC 10 H 10
Brief description	colorless crystals
External identifiers / databases
CAS number 37048-03-6 Wikidata Q17310521
properties
Molar mass	139.2 g mol −1
Physical state	firmly
Melting point	59 ° C
boiling point	233 ° C
solubility	soluble in benzene , diethyl ether and petroleum ether
safety instructions
GHS labeling of hazardous substances Beryllium compounds danger H and P phrases H: 350i-330-301-372-319-335-315-317-411 P: ?
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Beryllocene or, according to the IUPAC nomenclature, bis ( η ¹ , η ⁵ - cyclopentadienyl ) beryllium (II) , is an organometallic compound from the metallocenes family . The colorless substance can be crystallized from petroleum ether in the form of white needles at −60 ° C and quickly decomposes on contact with atmospheric oxygen and water.

Extraction and presentation

Beryllocene was first synthesized in 1959 by Ernst Otto Fischer and Hermann Pankraz Hofmann from beryllium chloride and cyclopentadienyl sodium in benzene or diethyl ether .

${\displaystyle \mathrm {BeCl_{2}+\ 2\ M(C_{5}H_{5})\ {\xrightarrow[{}]{Diethylether}}Be(C_{5}H_{5})_{2}+2\ MCl\ \ M=Na,K} }$

properties

Physical Properties

In contrast to the uncharged metallocenes of the transition metals V, Cr, Fe, Co, Ni, Ru and Os, which have a strictly symmetrical and therefore dipole-free structure, beryllocene has a clear dipole moment of 2.46 Debye (in benzene) or 2 , 24 Debye (in cyclohexane ), which indicates an asymmetry of the molecule. In the IR spectrum one finds signals at 1524, 1610, 1669, 1715 and 1733 cm ⁻¹ , which also prove that the structure cannot correspond to that of ferrocene. In contrast, the ¹ H-NMR spectrum shows only one signal down to a temperature of −135 ° C, which indicates either a symmetrical structure or a rapid fluctuation of the rings.

Beryllocene shows different molecular geometries depending on the physical state. The low-temperature X-ray structure analysis shows a slipped sandwich structure, i.e. H. the rings are offset from one another - one ring is coordinated η ⁵ with a Be- Cp distance of 152 pm, the second only coordinated η ¹ (Be-Cp distance: 181 pm). The reason for the η ⁵ , η ¹ structure is that the orbitals of the beryllocene can only be occupied by a maximum of 8 valence electrons. In the gas phase, both rings seem to be coordinated η ⁵ . In fact, one ring is significantly further away from the central atom than the other (190 and 147 pm) and the apparent η ⁵ coordination is due to a rapid fluctuation in the bond. On the basis of gas-phase electron diffraction studies at 120 ° C, Arne Haarland concluded in 1979 that the two rings are only shifted by about 80 pm and are not coordinated η ⁵ , η ¹ , but rather η ⁵ , η ³ .

Ernesto Carmon et al. a. investigated the structure of beryllocenes with sterically more demanding ligands by means of X-ray structure analysis : Be (C ₅ Me ₄ H) ₂ and Be (C ₅ Me ₅ ) ₂ . They found that Be (C ₅ Me ₄ H) _{2 has} a slipped sandwich structure with η ⁵ , η ¹ coordination in the solid state , while Be (C ₅ Me ₅ ) _{2 has} the classic η ⁵ , η ⁵ -Coordination shows. In the crystal, however, the Be-C distances are not of the same length, but vary between 196.9 (1) and 211.4 (1) pm.

Chemical properties

In tetrahydrofuran (THF), beryllocene decomposes relatively quickly to form a yellowish gel. Beryllocene crystals quickly form an oxide layer on the surface with atmospheric oxygen, while they violently react with water to form beryllium hydroxide and cyclopentadiene .

${\displaystyle \mathrm {Be(C_{5}H_{5})_{2}+\ 2\ H_{2}O\ {\xrightarrow[{}]{}}\ Be(OH)_{2}+2\ C_{5}H_{6}} }$

As magnesocene also forms beryllocene with iron (II) chloride ferrocene . The driving force is the formation of the very stable ferrocene molecule.

${\displaystyle \mathrm {Be(C_{5}H_{5})_{2}\ +\ FeCl_{2}{\xrightarrow[{}]{THF}}\ BeCl_{2}\ +Fe(C_{5}H_{5})_{2}\ } }$

safety instructions

Beryllium and beryllium compounds are toxic and carcinogenic .

Individual evidence

1. ↑ ^{a b} C.-H. Wong, T.-Y. Lee, K.-J. Chao and S. Lee: Crystal structure of bis (cyclopentadienyl) beryllium at -120 ° C . In: Acta Cryst. B28, 1972, p. 1662-1665 , doi : 10.1107 / S0567740872004820 .
2. ^ ^{A b c d e f g h i} Ernst Otto Fischer, Hermann P. Hofmann: About aromatic complexes of metals, XXV. Di-cyclopentadienyl-beryllium . In: Chem. Ber. tape 92 , no. 2 , 1959, p. 482-486 , doi : 10.1002 / cber.19590920233 .
3. ↑ Entry on beryllium compounds in the GESTIS substance database of the IFA , accessed on June 24, 2014(JavaScript required) .
4. ↑ ^{a b} Arne Almenningen, Arne Haaland, Janusz Lusztyk: The molecular structure of beryllocene (C ₅ H ₅ ) ₂ Be. A reinvestigation by gas phase electron diffraction . In: J. Organomet. Chem. Band 170 , no. 3 , 1979, pp. 271-284 , doi : 10.1016 / S0022-328X (00) 92065-5 .
5. ↑ Christoph Elschenbroich : Organometallchemie . BG Teubner Verlag, 2008, ISBN 978-3-8351-0167-8 ( page 60 in the Google book search).
6. ^ J. Huheey, E. Keiter, R. Keiter: Inorganische Chemie . de Gruyter Verlag, 1993, ISBN 3-11-017903-2 ( page 799 in the Google book search).
7. ↑ Erwin Riedel: Modern Inorganic Chemistry . de Gruyter, 2007, ISBN 978-3-11-019060-1 ( page 623 in the Google book search).
8. ↑ María del Mar Conejo, Rafael Fernández, Enrique Gutiérrez-Puebla, Ángeles Monge, Caridad Ruiz, Ernesto Carmona: Synthesis and X-ray Structures of [Be (C ₅ Me ₄ H) ₂ ] and [Be (C ₅ Me ₅ ) ₂ ] . In: Angewandte Chemie . tape 112 , no. 11 , 2000, pp. 2025-2027 , doi : 10.1002 / 1521-3757 (20000602) 112: 11 <2025 :: AID-ANGE2025> 3.0.CO; 2-A .