Ferrole

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]

Structure of the ferrole Fe₂C₄H₄(CO)₆.^[1] Color scheme: red = O, gray = C, dark blue = Fe, white = H.

Not to be confused with Ferrule.

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]}