Ferrole

Structure of the ferrole Fe₂C₄H₄(CO)₆. Color scheme: red = O, gray = C, dark blue = Fe, white = H.

Not to be confused with Ferrule.

In organoiron chemistry, a ferrole is a type of diiron complex containing the (OC)₃FeC₄R₄ heterocycle that is pi-bonded to a Fe(CO)₃ group. These compounds have Fe-Fe bonds (ca. 252 pm) and semi-bridging CO ligands (Fe-C distances = 178, 251 pm). They are typically air-stable, soluble in nonpolar solvents, and red-orange in color. ^[2]

Synthesis

Ferroles typically arise by the reaction of alkynes with iron carbonyls. Such reactions are known to generate many products, e.g. complexes of cyclopentadienones and para-quinones. ^{[3] [4]}

Another route involves the desulfurization of thiophenes (SC₄R₄) by iron carbonyls, shown in the following idealized equation:

Fe₃(CO)₁₂ + SC₄R₄ → Fe₂(CO)₆C₄R₄ + FeS + 6 CO

An unusual route to ferroles involves treatment of Collman's reagent with trimethylsilyl chloride (tms = (CH₃)₃Si):

2 Na₂Fe(CO)₄ + 4 tmsCl → Fe₂(CO)₆C₄(Otms)₄ + 2 CO + 4 NaCl

Reactions

Some ferroles react with tertiary phosphines to give the substituted flyover complex Fe₂(CO)₅(PR₃)(C₄R₄CO). ^{[5] [6]}

References

1. Dettlaf, Gerd; Weiss, Erwin (1976). "Kristallstruktur, ¹H-NMR- und Massenspektrum von Tricarbonylferracyclopentadien-tricarbonyleisen, C₄H₄Fe₂(CO)₆". Journal of Organometallic Chemistry. 108 (2): 213–223. doi:10.1016/S0022-328X(00)82143-9.
2. Fehlhammer, W.P.; Stolzenberg, H. (1982). "Dinuclear Iron Compounds with Hydrocarbon Ligands". In Geoffrey Wilkinson; F. Gordon A. Stone; Edward W. Abel (eds.). Comprehensive Organometallic Chemistry. pp. 513–613. doi:10.1016/B978-008046518-0.00051-9. ISBN   9780080465180.
3. Piero Pino; Irving Wender, eds. (1968). Organic Syntheses via Metal Carbonyls Volume 1. NY: Wiley Interscience.
4. Bird, C. W. (1962). "Synthesis of Organic Compounds by Direct Carbonylation Reactions Using Metal Carbonyls". Chemical Reviews. 62 (4): 283–302. doi:10.1021/cr60218a001.
5. Giordano, Roberto; Sappa, Enrico; Cauzzi, Daniele; Predieri, Giovanni; Tiripicchio, Antonio (1996). "Reactions of the 'ferrole' complex [Fe2(CO)6(C2Et2)2] with group 15 donor ligands and with alkynes. Stepwise formation and disengagement of tropones. Crystal and molecular structure of [Fe2(CO)5{(CEt)2 CO(CEt)2 CHCPH}]". Journal of Organometallic Chemistry. 511 (1–2): 263–271. doi:10.1016/0022-328X(95)05936-J.
6. Fagan, Paul J. (1995). "Dinuclear Iron Compounds with Hydrocarbon Ligands". Comprehensive Organometallic Chemistry II. pp. 231–258. doi:10.1016/B978-008046519-7.00058-7. ISBN   9780080465197.