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Iron Derivatives of Five-membered Carbon-Nitrogen Heterocycles.

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Iron Derivatives of Five-membered
Carbon-Nitrogen Heterocycles
By F. See1 and V. Sperber[*I
Dedicated to Professor B. Eistert on his 65th Birthday
By treating pyrazole ( I ) , imidazole (2), and 1,2,4-triazole
(3) with penta- or tetra-carbonyliron, mercury tetracarbonyl-
ferrate(rI), ferrocene, or dicarbonylcyclopentadienyliron in
the presence or absence of a solvent (benzene, toluene, or
mesitylene) we have been able to prepare the almost colorless
iron(I1) derivatives of these nitrogen-heterocycles, namely,
Fe(N2C3H3)2 from ( I ) , Fe(N~C3H3)2.0.5 N2C3H4 from (2),
and Fe(N3CzHz)z from ( 3 ) . In the case of imidazole, the
synthesis can be effected even with iron powder. In the
reaction of dicarbonylcyclopentadienyliron,cyclopentadiene
and cyclopentene are by-products;
The deep brownish-red iron(rr1) derivative Fe(NzC3H3)3 is
formed on reaction of dicarbonylcyclopentadienyliron
chloride with ( I ) , together with dicarbonylcyclopentadienyliron which can be separated by extraction with toluene:
The iron(r1r) derivative of ( I ) is obtained in moderate yield
by reaction of iron(m) chloride with the potassium salt in
liquid ammonia. Also, reaction of the iron(1i) compounds
with silver salts of the heterocycles gives the iron(nr) compounds:
The iron derivatives of the five-membered carbon-nitrogen
heterocycles ( I ) , (2), and (3) are clearly not aza analogs of
ferrocene, but are coordination polymers. As such they
dissolve in other substances only with decomposition. The
iron(rr) compounds are very sensitive to air, but the iron(m)
compounds are not. A change in the type of chemical
bonding is indicated in particular by the fact that the sandwich complex, z-cyclopentadienyl-n-pyrrolyliron(“azaferrocene”) [I] can be converted into ferrocene by cyclopentadiene,
whereas the iron@) derivatives of the five-membered heterocycles ( I ) , (2), and (3) with two or more nitrogen atoms do
not undergo this reaction. Complexes of the type FeL&
[L = (1) or (2)], which were obtained from tetracarbonyliron(r1) iodide, show that the coordination number of the
metal atom is four in the iron(1t) derivatives of (1) and (2)
as well as in the poly-(1-pyrazolyl)iron(rI) borates [21.
The behavior of pyrrole deviates to a remarkably large
extent from that of heterocycles with two or more nitrogen
atoms. It and its N-methyl derivative react with Fe(C0)412
to give coordination compounds of type FeLZIz (L= C4H4NH
or C4H4NCH3). Synthesis of the still unknown dipyrrolyliron(1r) is apparently difficult because it can exist, if at all,
only as an unstable sandwich complex (“diazaferrocene”) and
not as the more stable coordination polymer. In view of the
stability of the coordination polymers {Fe(N2C3H4)4& it
is intelligible that the only pyrrole-iron compound isolated
to date is [Fe(NC4H4)4]K2 [31.
Complex compounds of the type CsHsFe(C0)2L (L=NC4H4,
N2C3H3, or N3CzH2) have been obtained by treating dicarbonylcyclopentadienyliron chloride with the potassium
salts of all the five-membered nitrogen heterocycles in liquid
ammonia. Of these, however, only the pyrrole derivative could
be converted into the dumbbell complex CsHsFeNC4H4 141.
Experimental :
In order to prepare the iron(ir) derivative of imidazole from
ferrocene the two starting materials, mixed in the weight
proportion 10: 1, were warmed slowly to 250 “ C in an highly
evacuated sealed tube. An orange-colored solution resulted
in the temperature region 90 “C [m.p. of (2)] to 120 OC. At
180°C reaction begins, with lightening of the color of the
melt and separation of a yellow crystalline precipitate.
After 3 h the contents of the tube are allowed to solidify and
then the excess of imidazole is sublimed off at 7OoC in a
vacuum over a period of several hours, leaving a quantitative
yield of Fe(N2C3H3)2.0.5N2C3H4 as yellowish-brown needles,
3 mm in length.
For preparation of the iron(m) derivative of pyrazole from
dicarbonylcyclopentadienyliron chloride, the two components in the weight ratio 3 : l were dissolved in just sufficient toluene and boiled under reflux in a n atmosphere of
nitrogen. The solution changes from red to reddish-brown
even before it boils, and a precipitate begins to separate.
After 2 h the solvent is distilled off and the residual mixture
is extracted with 50 ml of toluene per g of substance with
exclusion of air. The brown residue is the desired product.
I t is washed with 0.05 N hydrochloric acid i n the air.
Received: September 29, 1967; revised: October 24, 1967 [Z 656 IE]
German version: Angew. Chem. 80, 38 (1968)
[*I Prof. Dr. F. See1 and Dipl.-Chem. V. Sperber
Institut fur Anorganische Chemie der Universitlt
66 Saarbrucken 15 (Germany)
111 Cf. K . K . Joshi, P . L. Pauson, A. R. Qazi, and W. H . Stubbs,
J. organometallic Chem. 1,471 (1964); R. B. King and M. B. Bisnefte, J. inorg. Chem. 3, 796 (1964).
[2] J. P. Jesson, S . Trofimenko,and D . R. Eaton, J. Amer. chern.
Soc. 89, 3148 (1967).
131 0.Schmitz-Dumont and St. Pateras, Z. anorg. allg. Chern.
224, 63 (1935).
[4] See also P . L. Pauson and A. R. Qazi, J. organometallic
Chern. 7, 321 (1967).
Identification of the Benzoylium Cation by
IR Spectroscopy
By H.-H. Perkampus and W. Weiss[*l
In recent years numerous complexes between acid halides
and Lewis acids have been studied by I R spectroscopy r1-3151,
and a new band around 2300 cm-1 was ascribed to an oxocarbonium ion. Repeated attempts were made to detect a
corresponding band for the complex between a benzoyl
halide and a Lewis acidIz,41. Ionic complexes were obtained
only from benzoyl fluoride and SbFS or AsF5[31 and o n
treatment of methylbenzoyl chlorides with Lewis acids (2851.
On the basis of conductivity measurements for the complex
benzoyl chloride/GaC13 in the liquid state Greenwood and
Wader61 postulated an ionic structure [C6H5COl@[GaC14]9,
and Oulevey [71 demonstrated an exchange reaction between
AlC13 and benzoyl chloride by means of radioactive chlorine,
from which he deduced that the complex exists partly in an
ionic form.
Our measurements were carried out with a cuvet described
previously [81, wherein the substances can be measured
directly as solids or as liquid films. Benzoyl chloride and
A I B r 3 were placed in the cuvet a t -196 OC and the spectrum
was recorded from 2350 to 2100 cm-1 while the specimen
was warmed cautiously. The substance film began to melt at
about O’C, and at +7OC a sharp band of low intensity
appeared in the spectrum at 2209 cm-1. The intensity of this
band increased with rising temperature and reached a maximal value between 40 and 5OOC. After cooling, the bands
had disappeared, but they reappeared on repeated increase
in temperature. It is thus demonstrated that a temperaturedependent equilibrium between a coordinate and an ionic
complex exists also in the system benzoyl chloridelAlBr3.
Angew. Chem. internat. Edit. 1 Vol. 7 (1968) 1 No. I
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iron, nitrogen, membered, five, heterocyclic, carbon, derivatives
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