Preparation and Characterization of Ferrocene



Preparation and Characterization of Ferrocene

Kevin F. Dunn

Department of Chemistry & Physics, Georgia College and State University,

Milledgeville, GA 31061

October 22, 2008

Inorganic Laboratory Fall 2008

Abstract

In the preparation and characterization of ferrocene, the chemistry of organometallic complexes was explored. In this particular experiment, ferrocene, was prepared through the reaction of cyclopentadiene with FeCl2 to give a structure in which iron is sandwiched between two cyclic rings. Physical and chemical analyses including IR, 1H-NMR, and melting point support and confirm the successful synthesis of approximately 10.6 g of this organometallic complex.

Introduction

The discovery of ferrocene was a landmark achievement in the field of organometallics that sparked the search for other π-bond organic ligands. In 1951, ferrocene was accidentally prepared by Pauson and Kealy at Duquesne University.1 Their goal was to oxidatevely couple cyclopenadienyl magnesium bromide and ferric chloride to prepare fulvalene.1 Instead a light orange powder was obtained with significant stability that was attributed to the aromatic character of the cyclopentadienyls, but the sandwich structure of ferrocene was not recognized by them. This task was accomplished by Woodward and Wilkinson, who deduced the structure based upon its reactivity.2

Ferrocene is an organomettalic complex consisting of an iron atom sandwiched between two cyclopentadiene rings.1 Because of this, ferrocene is also referred to as a sandwich compound or a metallocene. The general reaction of cyclopentadiene with iron (II) chloride to yield ferrocene is given below.

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Figure 1: General reaction mechanism of cyclopentadiene with iron (II) chloride to yield ferrocene.3

Cyclopentadiene is a η5 (pentahapto) ligand and as a result ferrocene is also classified the same way since it bonds through all five atoms. Since the structure is composed of two cyclopentadiene rings, numbering of the compound can proceed through either cyclic ring.

[pic]

Figure 2: Structure of ferrocene.

An important thing to note about this structure is the symmetry aspect of the complex. In its stable state, ferrocene exists in the staggered conformation with a symmetry corresponding to a D5d point group.4 Although if the molecule is exposed to temperature changes, the complex can then exist is three conformations: staggered, eclipsed, and skewed in which each contain a unique point group.

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Figure 3: Conformations of ferrocene.

Ferrocene and its derivatives do not have much large-scale applications but does play a role in fuel additives and have some pharmaceutical role. In fuel additives ferrocene and its derivatives are known as antiknock agents for petrol engines.5 This means that this additive can be added to unleaded fuel to enable it to be used in engines which were designed to run on leaded. And recently, it has been shown that a few ferrocene derivatives exhibit some anti-cancer activity.5

Experimental3

Dicyclopentadiene was thermally cracked under a vacuum using a microscale fractional distillation apparatus until approximately 11.0 mL was obtained. A solution of powder KOH (50.0 g) and 1,2-dimethoxyethane (120 mL) was purged with a stream of nitrogen on the shlink line before the cyclopentadiene was added. Once the air had been flushed, a solution of FeCl2.4 H2O (13.0 g) and dimethyl sulfoxide (50.0 mL) was added dropwise over a forty-five minute period creating large chunks in the mixture. After this addition, the solution was allowed to stir for an additional thirty minutes before being added to a mixture of 6 M HCl (180.0 mL) and crushed ice (200.0 g). The precipitate, yellowish-orange, was collected using vacuum filtration and once dried, the powdered product was purified using sublimation until crystals were obtained (~10.6 g).

Results/Discussion

A melting point was taken on both the powdered form of ferrocene as well as the crystal form after purification through sublimation. The melting point of both the powdered and crystal form was 173ºC. This corresponds to literature values for the melting point of ferrocene which is 173 – 174ºC.3

An infrared spectrum as well as a 1H-NMR spectrum were obtained from the purified form of ferrocene.

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Figure 4: IR spectrum of ferrocene.

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Figure 5: 1H-NMR spectrum for ferrocene.

From the irreducible representation the IR active orbitals of ferrocene consist of the A2g , E1g , A2u , and the E1u orbital. The infrared spectrum indicates C=C stretching at approximately 1500.00 cm-1 which corresponds to the double bonds found on the cyclic portion of the structure. Also there is C-H stretching around 3000.00 cm-1 indicating the hydrogen stretching involved with the cyclic ring. The peak around 475.00 cm-1 indicates stretching due to the M-C bond. Literature values for the IR spectrum of ferrocene indicate peaks at 3085.00 cm-1, 1620.00 cm-1, and 478.00 cm-1 corresponding to the stretching and bending mentioned above.3

The 1H-NMR spectrum shows one singlet around 4.16 ppm corresponding to only one type of hydrogen present on the structure which is found on the cyclic rings.

Ferrocene was also analyzed using molecular modeling and computational techniques. All of the calculations were performed using Amsterdam Density Functional (ADF), version 2006.01. The basis sets for the molecule was Slater-type, where all atoms except for hydrogen are modeled with frozen cores. Geometry optimization gradient corrections were preformed using Becke88 and Perdew86. These calculations were used in the construction of a molecular orbital diagram. They were also used to test the efficiency of the method for the specified molecule.

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Figure 6: Molecular orbital diagram for ferrocene.

Based off of this molecular orbital diagram, the highest occupied molecular orbital (HOMO) for ferrocene was the 3E2g orbital while the lowest unoccupied molecular orbital (LUMO) was the 4E1g orbital. It was also found that the symmetry aspect was correct once the calculations were complete.

The computational data for the core energy levels as well as the data for the internal atoms and the bond lengths for ferrocene is given in the following tables.

Table 1: Data for the core energies of ferrocene.

|Irrep. |# spin |Occup. |E (au) |E (eV) |

|A2u |3 |2.00 |-0.33617 |-9.1478 |

|E1g |3 |4.00 |-0.25812 |-7.0237 |

|E1u |3 |4.00 |-0.23521 |-6.4004 |

|A1g |4 |2.00 |-0.17875 |-4.8641 |

|E2g |3 |4.00 |-0.16468 |-4.4811 |

|E1g |4 |0.00 |-0.070688 |-1.9235 |

|E2u |3 |0.00 |-0.011276 |0.3068 |

|A1g |5 |0.00 |-0.021261 |0.5785 |

|E2g |4 |0.00 |-0.024499 |0.6666 |

|A2u |4 |0.00 |-0.059562 |1.6208 |

| | | | | |

|HOMO: |3 E2g |-0.16468 | | |

|LUMO: |4 E1g |-0.070688 | | |

Table 2: Data regarding the internal atoms.

|# |Atom |Z matrix Cordinates |

|Fe-C1 |1.994 |2.0889 |

|Fe-C2 |2.059 |2.0889 |

|Fe-C3 |2.078 |2.0889 |

|Fe-C4 |2.074 |2.0889 |

|Fe-C5 |2.034 |2.0889 |

|C1-C2 |1.396 |1.44276 |

|C2-C3 |1.4 |1.44276 |

|C3-C4 |1.365 |1.44276 |

|C4-C5 |1.413 |1.44276 |

|C5-C1 |1.409 |1.44276 |

Based off of the core energies for ferrocene, it is seen that the HOMO and LUMO are extremely close in energy. Also the bond lengths calculated computationally correspond to bond lengths of ferrocene found in literature.4 Therefore, the molecular modeling and computational work done for ferrocene correspond to models found in literature.

Conclusion

Based off the appearance as well as the number of characterization techniques performed, roughly 10.6 g of ferrocene was successfully prepared from the reaction of cyclopentadiene and FeCl2. The IR and 1H-NMR spectra obtained correspond to those found in literature, peaks of in the IR and a singlet at 4.16 ppm in the 1H-NMR. Also, the melting point is characteristic of known values for ferrocene, approximately 173ºC.

Acknowledgments

I would like to acknowledge my laboratory partners Joseph Tamasi and Claudia Ramirez for assisting with the experiment. I would also like to acknowledge Candace Rowell for providing the procedure used in the experiment. Many thanks are also due to the Department of Chemistry here at Georgia College and State University for providing the necessary resources to carry out the experiment.

References

1) Miessler, Gary L., Tarr, Donald A. Inorganic Chemistry: Third Edition. Pearson Education Inc., Upper Saddle River, New Jersey.

2) G. Wilkinson, M. Rosenblum, M. C. Whiting, R. B. Woodward. J. Amer. Chem. Soc. 1952, 74, 2125–2126.

3) Jolly, William L. The Synthesis and Characterization of Inorganic Compounds. 1970, Prentice-Hall, INC, 485.

4) Dunitz, J.D. Orgel, L.E. and Rich, R.A. Acta. Crystallography. 1956, 9, 373.

5) S. Top, B. Dauer, J. Vaissermann and G. Jaouen. J. Organo. Chem. 1997, 541, 355 – 361.

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