Ferrole Explained

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.^[1]

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.^{[2] [3]}

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 + 6CO

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

2Na₂Fe(CO)₄ + 4tmsCl → Fe₂(CO)₆C₄(Otms)₄ + 2CO + 4NaCl (warning: unbalanced reaction !)

Reactions

Some ferroles react with tertiary phosphines to give the substituted flyover complex Fe₂(CO)₅(PR₃)(C₄R₄CO).^{[4] [5]}

References

1. Book: 10.1016/B978-008046518-0.00051-9. Dinuclear Iron Compounds with Hydrocarbon Ligands. Comprehensive Organometallic Chemistry. 1982. Fehlhammer. W.P.. Stolzenberg. H.. 513–613. 9780080465180. Geoffrey Wilkinson. F. Gordon A. Stone. Edward W. Abel.
2. Book: Organic Syntheses via Metal Carbonyls Volume 1. 1968. Piero Pino. Irving Wender. Wiley Interscience. NY.
3. 10.1021/cr60218a001. Synthesis of Organic Compounds by Direct Carbonylation Reactions Using Metal Carbonyls . 1962 . Bird . C. W. . Chemical Reviews . 62 . 4 . 283–302 .
4. 10.1016/0022-328X(95)05936-J. 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}]. 1996. Giordano. Roberto. Sappa. Enrico. Cauzzi. Daniele. Predieri. Giovanni. Tiripicchio. Antonio. Journal of Organometallic Chemistry. 511. 1–2. 263–271.
5. Book: 10.1016/B978-008046519-7.00058-7. Dinuclear Iron Compounds with Hydrocarbon Ligands. Comprehensive Organometallic Chemistry II. 1995. Fagan. Paul J.. 231–258. 9780080465197.