Chapter 2 Complexes with One Cyclic Ligand CnHn

Christian Erich Zybill

Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-85747 Garching bei München, Germany

With contributions from:
Abugideiri, F., College Park
Cano, A. M., Alcalá de Henares
Cuenca, T., Alcalá de Henares
Daruwala, K. P., Lincoln
Dawson, B. T., Lincoln
de la Mata, J., Alcalá de Henares
Desai, J. U., College Park
Forkner, M. W., Lincoln
Gómez, R., Alcalá de Henares
Gordon, J. C., College Park
Gowik, P. K., Berlin
Green, M. L. H., Oxford
Herrmann, W. A., Garching
Hosang, A., Aachen
Käser, M., Aachen
Keogh, D. W., College Park
Klapötke, T. M., Glasgow
Legzdins, P., Vancouver
Marko, I., Aachen
Mountford, P., Oxford
Poli, R., College Park
Rieke, R., Lincoln
Rodríguez, G., Alcalá de Henares
Royo, P., Alcalá de Henares
Salzer, A., Aachen
Schulte, L. D., Lincoln
Veltheer, J. E., Vancouver
Yang, S. S., Lincoln

2.1 Carbonyl Complexes with One Cyclic Ligand

2.1.1 Synthesis

2.1.2 Reactions of Cyclopentadienyl Metal Carbonyl Complexes

2.1.3 Tetracarbonyl Complexes

2.1.4 Tricarbonyl Complexes

2.1.5 Di- and Monocarbonyl Complexes

2.2 Nitrosyl Complexes with Cyclic Ligands

2.3 Hydride Complexes with Cyclic Ligands

2.4 Halide Complexes with Cyclic Ligands

2.5 Sulfur Dioxide, Carbon Disulfide, Thiocarbonyl, and Related Complexes with Cyclic Ligands

2.6 Miscellaneous Complexes with Cyclic Ligands

2.6.1 Ansa-Dimethylsilylbis(η5-cyclopentadienyl) Complexes of Titanium(IV) and Titanium(III)

2.6.2 Fulvalenediyl Complexes

2.6.3 Ansa-Complexes of Zirconium

2.6.4 Vanadium and Niobium Complexes

2.6.5 Chromium and Molybdenum Complexes

2.1. Carbonyl Complexes with One Cyclic Ligand

Half-sandwich compounds of the general type M(η-cyclic polyene)Ln represent a major class of organotransition metal derivatives. When L is a good π-acidic ligand, e.g., CO or NO, these complexes adhere rigorously to the 18 e− rule and, consequently, their stoichiometries can be readily predicted on this basis. A typical series of complexes of this type is illustrated below. A most common structural motive are complexes with so-called piano stool geometry.

For a description of the bonding in 18e− half-sandwich complexes the interested reader should consult the current literature.

Dimeric complexes show interesting cis/trans isomerization and can also be subject to fluctionality by a CO scrambling process.

When L is not a good π-acceptor ligand such as NH3, SMe2, or PR3, the 18 e− rule has less predictive value and some examples with 16 or 17 valency electrons have been reported. Besides showing disregard for the 18e- rule, such complexes frequently have distorted geometries (metal not in the center of the cyclopentadiene ring, distortion of the benzene ring, etc.). These structural features have been subject of theoretical analyses.

2.1.1 Synthesis

In particular cyclopentadienyl metal complexes can be synthesized by a variety of methods. A most straightforward access is given by simple reaction of cyclopentadiene with a transition metal carbonyl complex. This approach proves to be successful for metals such as Fe, Ru, or Co.

The reaction involves the only moderately stable intermediate cyclopentadiene- or cyclopentadienyl-(hydrido) complexes which decompose under the given conditions to dimers.

A very widely used reaction is the combination of metal carbonyls or their metallates with cyclopentadienyl derivatives.

Na[V(CO)6] + C5H5HgCl → V(η-C5H5)(CO)4 + Hg + NaCl + 2 CO

Also in this case, the isolable hydrido complexes dimerize with elimination of hydrogen.

The combination of metallocenes with CO is particularly valuable for the synthesis of half-sandwich complexes of manganese, but requires the availability of the metallocene.

Furthermore, a “metathesis” reaction between a metallocene and a metal carbonyl can be applied to obtain the corresponding half-sandwich complexes.

Ni(η-C5H5)2 + Ni(CO)4 → [Ni(η-C5H5)(CO)]2 + 2 CO

2.1.2. Reactions of Cyclopentadienyl Metal Carbonyl Complexes

A very common reaction is the reduction of the complexes to carbonyl metallates with Na/Hg, Na/NH3 or Na(naph) as electron carrier.

Reactions of dimeric complexes with elemental halogens allow a facile access to versatile monomeric halogen-substituted species.

[Fe(η-C5H5)(CO)2]2 + X2 → 2 Fe(η-C5H5)X(CO)2

X = Br, Cl

Furthermore, electrophilic displacement reactions at the cyclopentadienyl ring — similar to ferrocene — can be realized.

The substitution of CO by a phosphane is a common reactivity pattern and can be induced thermally or photochemically.

Mn(η-C5H5)(CO)3 + L → Mn(η-C5H5)(CO)2L + CO

Co(η-C5H5)(CO)2 + 2L → Co(η-C5H5)L2 + 2 CO

L = phosphane, olefin

Oxidative decarbonylation reactions play an important role. Oxo-derivatives, e. g., of rhenium complexes, are being increasingly used as catalysts.

A particularly important application of half-sandwich complexes is found in asymmetric synthesis and catalysis. A common entry into asymmetric synthesis with chromium arene complexes involves complexation of protected benzaldehydes (acetals).

The use, e.g., of cyclic acetals allows further functionalization reactions of the complex with ee′s as high as >98%. The mechanistic basis of these reactions is provided through a high conformational stability of the intermediate benzylic carbonium ions because of neighboring group participation of the arene chromium tricarbonyl moiety.

References

1 G. Wilkinson, F. G. A. Stone, E. W. Abel, (eds.), Comprehensive Organometallic Chemistry, Pergamon Press, 1982.

2 C. Elschenbroich, A. Salzer, Organometallchemie, Teubner, Stuttgart, 1986.

3 S. G. Davies, T. J. Donohoe, J. M. J. Williams, Pure Appl. Chem. 64, 379 (1992).

2.1.3 Tetracarbonyl Complexes

•Tetracarbonyl(η-cyclopentadienyl)vanadium — V(η-C5H5)(CO)4

V(η-C5H5)(CO)4 is available by carbonylation reaction from V(η-C5H5)2. Method A involving high CO pressure gives much better yields than Method B running at normal pressure. Purification of the product by column chromatography is not necessary.

Procedure for Method A

A 250-mL autoclave is charged with sublimed V(η-C5Η5)2 (27.2 g, 0.15 mol) under strict exclusion of air and moisture. For removal of oxygen, the whole pressure system of the autoclave is filled two times with 110 bar of H2. The reaction is started at a pressure of 100 bar of H2 and an additional 320 bar of CO. Upon slow heating to the reaction temperature of 140 °C, the pressure rises to a maximum of 470 bar. The reaction starts at ca. 75 °C as indicated by a slight decrease in pressure. After 5 h at 140 °C ca. 400 bar, after 20 h (140 °C) ca. 320 bar are maintained. After 15 – 20 h, the mixture is cooled to room temperature and all unreacted gases are removed. The orange to orange-brown crude product is subjected to a high vacuum sublimation at 70 – 100 °C. A brown to yellow oil, which might have formed, consisting of dicyclopentadiene, is removed with a piece of glass wool. The residue of the sublimation is pyrophoric and is decomposed by H20 in a nitrogen atmosphere. Yield: 29.1 – 31.1 g (85 – 91%).

In cases where the sublimate is still wet or not pure orange colored, a second high vacuum sublimation is performed. Purification by column chromatography on Si02/pentane + benzene (10:1) is also possible for smaller batches (ca. 3 g), but is not necessary. Oily products in the sublimate can be removed by n-pentane.

Procedure for Method B

A solution of V(η-C5H5)2 (8.65 g, 47.5 mmol; purified by sublimation) in 200 mL of tetrahydrofuran is stirred for 2 h at room temperature in an atmosphere of CO, and then Na powder (1.15 g, 50 mmol) is added. The solution is stirred for 12 h in a CO atmosphere. All volatile components are removed under aspirator vacuum and the residue is sublimed at ca. 80 °C under high vacuum. Crude yield: 9.64 g (89%).

For purification of the product, which is contaminated by V(η-C5H5)2, column chromatography on silica gel/pentane + benzene (10:1) is applied, V(η-C5H5)(CO)4 forming an orange zone. Yield: 3.25 g (30%).

Alternative Procedures

Treatment of a tetrahydrofuran solution of crude V(η-C5Fl5)2 (from VCl3 + NaC5H5) for 7 h with 60 bar of CO at 117 ± 6 °C. Yield: 23%.5

Reaction of [Na(diglyme)2][V(CO)6] with HgCl(C5H5). Yield: 78%.6

Properties

The compound is obtained as shining red, light- and air-sensitive crystals with a typical carbonyl odor, mp 138...