(Diene)iron tricarbonyl

In organometallic chemistry, (diene)iron tricarbonyl describes a diverse family of related coordination complexes consisting of a diene ligand coordinated to a Fe(CO)₃ center. Often the diene is conjugated, e.g., butadiene, but the family includes nonconjugated dienes as well. The compounds are yellow, air-stable, often low-melting, and soluble in hydrocarbon solvents. The motif is so robust that even unstable dienes form easily characterized derivatives, such as norbornadienone and cyclobutadiene.

Scope

structure of the Fe(CO)₃ adduct of vitamin A aldehyde.^[1]

The inventory of complexes is large.

Selected (diene)Fe(CO)₃ Complexes

diene	CAS RN	physical properties	notes
(cyclobutadiene)Fe(CO)3	12078-17-0	orange solid, b.p. 47 °C (3 mm)	antiaromatic ligand[2]
(butadiene)Fe(CO)3	12078-32-9	yellow-orange, m.p. 19 °C	major prototype
(Isoprene)Fe(CO)3	32731-93-4	yellow liquid	chiral[3]
(1,3-Cyclohexadiene)Fe(CO)3	12252-72-6	yellow, m.p. 8-9 °C	major prototype for steroidal and terpenoid derivatives[4]
(norbornadiene)Fe(CO)3	12307-07-2	yellow, m.p. -2 °C	non-conjugated diene[5]
(norbornadienone)Fe(CO)3	12307-01-6	yellow, m.p. 93-95 °C	free diene-one is unstable[6]
(1,5-Cyclooctadiene)Fe(CO)3	12093-20-8	yellow, m.p. 76 °C	non-conjugated diene[7][8]
(1,3-Cyclooctadiene)Fe(CO)3	33270-50-7	yellow, m.p. 36 °C	isomeric with 1,5-cyclooctadiene derivative[7][9]
(η4-Thiepine)Fe(CO)3	-	yellow, , m.p. 54.5-55 °C	chiral, thiepine = cyclo-C6H6S, which is antiaromatic[10]

Preparation and uses

Many of diene complexes were originally prepared by reaction of iron pentacarbonyl with the diene under UV-radiation. Often yields are modest because the complexes, which are often liquids, volatilize during workup.^[5] Some derivatives derivatives are prepared displacement of bda from (benzylideneacetone)iron tricarbonyl (Fe(bda)(CO)₃)^[11]

The Fe(CO)₃ unit serves as a protecting group for the diene, preventing the diene from participating in Diels-Alder reactions and hydrogenation. The diene is usually deprotected with ceric ammonium nitrate.^[12]

These complexes are mainly of academic interest. Some iron tricarbon complexes of cyclopentadienones catalyze hydrogenation, see Knolker complex.

Characterization

Sample of (butadiene)Fe(CO)₃, illustrating the color typical of this family of compounds.

IR spectra of these complexes show ν_CO bands near 2040 and 1969 cm^-1. At low temperatures, the lower energy band splits, which has been interpreted as evidence for fluxionality on the IR timescale.^[13]

References

1. Mason, R.; Robertson, G. B. (1970). "Crystal and molecular structure of (Vitamin-A aldehyde)tricarbonyliron". Journal of the Chemical Society A: Inorganic, Physical, Theoretical: 1229. doi:10.1039/J19700001229.
2. Pettit, R.; Henery, J. (1970). "Cyclobutadieneiron Tricarbonyl". Organic Syntheses. 50: 21. doi:10.15227/orgsyn.050.0021.
3. King, R. B.; Manuel, T. A.; Stone, F. G. A. (1961). "Chemistry of the Metal Carbonyls—IX. Diene Complexes of Iron". Journal of Inorganic and Nuclear Chemistry. 16 (3–4): 233–239. doi:10.1016/0022-1902(61)80495-8.
4. Pearson, Anthony J.; Sun, Huikai (2008). "Cyclohexadieneiron Tricarbonyl". e-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00791. ISBN 978-0471936237.
5. Green, M. L. H.; Pratt, L.; Wilkinson, G. (1960). "206. Spectroscopic Studies of Some Organoiron Complexes". Journal of the Chemical Society (Resumed): 989. doi:10.1039/JR9600000989.
6. Landesberg, Joseph M.; Sieczkowski, J. (1971). "Synthesis and Chemistry of Tricarbonyl(7-norbornadienone)iron". Journal of the American Chemical Society. 93 (4): 972–980. doi:10.1021/ja00733a032.
7. Deeming, A. J.; Ullah, S. S.; Domingos, A. J. P.; Johnson, B. F. G.; Lewis, J. (1974). "Reactivity of co-ordinated ligands. Part XX. Preparation and Reactions of Cyclo-octadiene Complexes of Iron, Ruthenium, and Osmium". Journal of the Chemical Society, Dalton Transactions (19): 2093. doi:10.1039/DT9740002093.
8. Kruczynski, Leonard.; Takats, Josef. (1976). "Intramolecular Rearrangement in (.eta.-diene)tricarbonyliron and -Ruthenium Compounds. A Carbon-13 Nuclear Magnetic Resonance Study". Inorganic Chemistry. 15 (12): 3140–3147. doi:10.1021/ic50166a041.
9. Lewis, J.; Cotton, F. A.; Deeming, A. J.; Josty, P. L.; Ullah, S. S.; Domingos, A. J. P.; Johnson, B. F. G. (1971). "Tricarbonyl(cyclooctadiene) Complexes of Iron(0), Ruthenium(0), and Osmium(0)". Journal of the American Chemical Society. 93 (18): 4624–4626. doi:10.1021/ja00747a066.
10. Nishino, Keitaro; Takagi, Masanobu; Kawata, Teruhisa; Murata, Ichiro; Inanaga, Junji; Nakasuji, Kazuhiro (1991). "Thiepine-iron tricarbonyl: Stabilization of thermally labile parent thiepine by transition metal complexation". Journal of the American Chemical Society. 113 (13): 5059–5060. doi:10.1021/ja00013a051.
11. Domingos, A. J. P.; Howell, J. A. S.; Johnson, B. F. G.; Lewis, J. (1990). Reagents for the Synthesis of η-Diene Complexes of Tricarbonnyliron and Tricarbonylruthenium. Inorganic Syntheses. pp. 52–55. doi:10.1002/9780470132593.ch11. ISBN 9780470132593.
12. Donaldson, William A.; Chaudhury, Subhabrata (2009). "Recent Applications of Acyclic (Diene)iron Complexes and (Dienyl)iron Cations in Organic Synthesis". European Journal of Organic Chemistry. 2009 (23): 3831–3843. doi:10.1002/ejoc.200900141. PMC 3121309. PMID 21709767.
13. Turner, James J.; Bühl, Michael (2018). "Infrared Dynamics of Iron Carbonyl Diene Complexes". The Journal of Physical Chemistry A. 122 (14): 3497–3505. Bibcode:2018JPCA..122.3497T. doi:10.1021/acs.jpca.7b12309. hdl:10023/16989. PMID 29394061.