The production of NO from the reaction of Fe(III) schiff base complexes and nitrite ions in acetonitrile

Article abstract of DOI:10.1016/S0277-5387(00)00662-8

The Fe(III) Schiff base complexes: FesalenNO₂, FesalenCl, [Fesalen]₂O⁺BF₄^- and FeacacenCl have been treated with the nitrite reagents: PPNNO₂, AgNO₂ and NaNO₂ in aceto

Full text of DOI:10.1016/S0277-5387(00)00662-8

Polyhedron 20 (2001) 623–625
www.elsevier.nl/locate/poly
The production of NO from the reaction of Fe(III) Schiff base
complexes and nitrite ions in acetonitrile
Dale L. Ankers, James C. Fanning *
Department of Chemistry, Clemson Uni6ersity, Clemson, SC 29631, USA
Received 4 August 2000; accepted 4 December 2000
Abstract
The Fe(III) Schiff base complexes: FesalenNO2, FesalenCl, [Fesalen]2O+BF4− and FeacacenCl have been treated with the
nitrite reagents: PPNNO2, AgNO2 and NaNO2 in acetonitrile. Only FesalenNO3 and FesalenCl produced NO with all of the
reagents according to the equation: 2Fesalen++3NO2− =2NO+(Fesalen)2O+NO3−. No evidence of Fe(III) nitrite complex
formation was found. FeacacenCl did not react under these conditions and the Fe(III,IV) compound, [Fesalen]2O+BF4, produced
NO2(g). © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Nitrite; Nitric oxide; Iron Schiff base complexes; Acetonitrile
(Fesalen)2O in dichloromethane solution being treated
with NO followed by O2. The black solid product from
the reaction gave upon recrystallization the nitrate,
FesalenNO3 [11]. The latter compound had been pre-
pared earlier by reacting (Fesalen)2O in solution with
dilute nitric acid [12].
An attempt to prepare FesalenNO2 using a simple
replacement reaction was carried out by mixing aceto-
nitrile solutions of PPNNO2 and the nitrate,
FesalenNO3. Surprisingly, NO was rapidly generated at
room temperature with no apparent formation of the
nitrite or nitrosyl complexes. This report considers this
reaction in more detail. For comparison, reactions with
PPNNO2 and the Fe(III)chloro complex of the Schiff
base, acacen, and the Fe(III, IV) complex, [Fesalen]2O+
BF4− were carried out. Nitrite salts other than
PPNNO2 were also used.
1. Introduction
There is considerable interest in the nitrite complexes
of Fe(III) [1,2], especially those of the iron(III) por-
phyrins. Several of these have been prepared and their
structure and chemical nature examined [3–5]. In solu-
tion they slowly disproportionate to produce the nitro-
syl and nitrate complexes [6]. The porphyrin nitrite
complexes have an active oxygen atom which is able to
oxidize a number of different species [7,8], including O2
to produce O3 [9].
Early attempts to prepare the Fe(III) Schiff base
nitrite, FesalenNO2,1 were carried out by reacting (Fe-
salen)2O in dichloromethane with N2O3, the anhydride
of nitrous acid, using a vacuum line at low temperature
[10]. A black solid resulted which had an indefinite
analysis, but spectral properties indicated that it was a
mixture of the nitrate, nitrite and m-oxo compound.
Attempts to prepare a pure nitrite complex by this
method were unsuccessful. A related reaction involved
2. Experimental
2.1. Chemicals
* Corresponding author. Tel.: +1-864-656-3065; fax: +1-864-656-
6613.
Literature procedures were used to prepare
FesalenNO3 [12], FesalenCl [13], [Fesalen]2O+BF4− [14]
and Fe(acacen)Cl [15]. PPNNO2, AgNO2, and NaNO2
were obtained as reagent grade materials and used as
E-mail address: sybjim@msn.com (J.C. Fanning).
1 salen, N,N%-ethylenebis(salicylideneimine) 2-anion; acacen, N,N%-
ethylene-bis(acetyl-acetonylideneimine) 2-anion; PPNNO2, bis-
(triphenylphoshoranylidene)- ammonium nitrite.
0277-5387/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0277-5387(00)00662-8

624
D.L. Ankers, J.C. Fanning / Polyhedron 20 (2001) 623–625
obtained from the manufacturer, except PPNNO2 was
dried at 100°C for 24 h prior to use. NO gas from
Matheson Gas Products was passed through a KOH
column prior to use. Chromatography grade acetoni-
trile from newly opened bottles was used.
2.4. UV–Vis spectra
Solution spectra were taken using a B&L Spectronic
2000 Spectrophotometer and a 1.0 cm quartz cell.
2.2. Vacuum line reactions
3. Results and discussion
A total of 0.50 mmol each of the solid Fe(III)
complex and nitrite reagent along with a magnetic
stirring bar were placed into a dry reaction tube and the
atmosphere removed. The tube was cooled to liquid
nitrogen temperature and 50 ml of acetonitrile was
added by vacuum distillation. The acetonitrile was de-
oxygenated prior to distillation by three cycles of freez-
ing and thawing on the vacuum line. The solution was
allowed to warm to room temperature and stirred. The
pressure became constant after about 3 h.
A sample of the gas was collected in a 10 cm IR gas
cell attached to the vacuum system and the IR spec-
trum measured on a Nicolet Model 5DX spectrophoto-
meter. A NO calibration curve (absorbance at 1875.2
cm−1 vs. the NO pressure, PNO) was established for the
gas cell using pure NO gas.
When FesalenNO3 was treated with PPNNO2 in
equimolar amounts (0.5 mmol/50 ml) in acetonitrile on
the vacuum line, NO was liberated and the color of the
solution changed from purple to brown. The reagents
were mixed in equimolar amounts since it was antici-
pated that only the simple replacement of the nitrate by
nitrite would take place. It took about three hours for
the reaction to reach an equilibrium gas pressure as the
reaction mixture warmed from liquid nitrogen tempera-
ture to room temperature. No unusual species were
observed as the temperature slowly increased. If the
reagents were mixed at room temperature they reacted
immediately. Only the spectrum of NO was observed in
the IR gas cell [17]. Since the equilibrium gas pressure
might be due to both PNO and solvent vapor pressure,
the amount of NO was determined from the gas IR
spectrum using a calibration curve. From the volume of
the vacuum system, PNO, and the temperature, the
moles of NO produced were calculated.
2.3. Ion chromatography
Nitrate and nitrite analyses were obtained using a
Dionex Series 2003i ion chromatograph equipped with
an HPIC-CS5 analytical column, a visible detector and
a Model 4270 integrator. The indirect photometric de-
tection method of Hayakawa et al. [16] was used with
determinations made at a detection wavelength of 330
nm. The eluant was 1.5 mM Na2[Cu(edta)], pH 6.5, and
a flow rate of 0.5 ml min−1. The injection volume was
25 ml. Nitrate and nitrite ions produced negative peaks
with retention times of 4.0 and 5.1 min, respectively.
Table 1 gives the results of the reactions of the Fe
Schiff base complexes in the vacuum system with sev-
eral nitrite reagents in equimolar amounts. In these
reactions if the equation is assumed to be:
2Fesalen++3NO2− =2NO+(Fesalen)2O+NO3−
(1)
then the nitrite reagent is the limiting reagent and the
yields were calculated by multiplying the quantity of
NO produced by three halves and dividing by the
amount of nitrite reagent originally present (0.50
mmol). The reactions of FesalenNO3 with PPNNO2,
NaNO2 and AgNO2 and that of FesalenCl with
PPNNO2 gave essentially quantitative results. The pres-
ence of water in the reaction medium reduces the yield,
probably resulting from the conversion, by hydrolysis,
of some of the Fe(III) complex to the (Fesalen)2O. The
slightly less than 100% yields are likely due to the
presence of trace amounts of moisture in the reaction
mixtures.
Table 1
Reactions of Fe complexes with nitrite reagents on the vacuum line in
50 ml of acetonitrile with a 10 mM concentration of each reactant
Fe Complex
Nitrite reagent
NO produced?
Yield a (%)
FesalenNO3
FesalenNO3
FesalenNO3
FesalenCl
PPNNO2
NaNO2
AgNO2
PPNNO2
PPNNO2+1 ml yes
yes
yes
yes
yes
97
90
95
98
63
The possibility existed wherein the Fesalen+ species
might react with trace water
FesalenNO3
3H2O+2Fesalen+=(Fesalen)2O+2H3O+
H2O
FeacacenCl
FeacacenCl
[Fesalen]2O
+BF−4
PPNNO2
AgNO2
PPNNO2
no
no
no, NO2
produced
3H3O++NO2− =2NO+NO3− +H2O
(2)
in the mixture to produce H3O+ which might then react
with NO2− to generate NO. Hydrolysis of the Fe
complex did not result in NO formation.
a See text for calculation.

D.L. Ankers, J.C. Fanning / Polyhedron 20 (2001) 623–625
625
The solution from the reaction of FesalenCl and
Acknowledgements
PPNNO2 was evaporated to dryness on the vacuum
line. The solid residue was treated with 50 ml of water
and an aliquot of the solution removed, filtered through
a 30 mm syringe filter and injected into the ion chro-
matograph. The nitrite peak was absent and the nitrate
peak was present. The IR spectra of the solid residues
from the reactions with 90% or greater yields were
measured and all showed a band at 830 cm−1 indica-
tive of the presence of (Fesalen)2O.
All results indicate that the reaction is that shown in
Eq. (1) which is similar to the reaction of nitrite ions
with strong acid shown in Eq. (2). The Fe(III) complex
in Eq. (1) serves as a Lewis acid in its interaction with
the nitrite ion promoting the disproportionation of the
nitrite to NO and nitrate. As mentioned the Fe(III)
porphyrin nitrite complexes slowly decompose to the
porphyrin nitrate and nitrosyl complexes. It appears
that the Fe(III)salen group in acetonitrile has no great
tendency to form the nitrosyl complex. FesalenNO is
made in benzene by reacting Fe(II)salen with an excess
of NO [18] and seems to be much more reactive with O2
than the iron porphyrin nitrosyls.
We would like to thank Dr Larry Keefer of the
Frederick Cancer Research and Development Center
for his interest and encouragement of this work.
References
[1] N. Arulsamy, D.S. Bohle, B. Hansert, A.K. Powell, A.J. Thom-
son, S. Wocaldo, Inorg. Chem. 37 (1998) 746.
[2] J.C. Fanning, Coord. Chem. Rev. 110 (1991) 235.
[3] M.G. Finnegan, A.G. Lappin, W.R. Scheidt, Inorg. Chem. 29
(1990) 181.
[4] J.B. Fernandes, D.W. Feng, A.G. Chang, M.D. Ryan, Inorg.
Chem. 25 (1986) 2606.
[5] H. Nasri, J.A. Goodwin, W.R. Schiedt, Inorg. Chem. 29 (1990)
185.
[6] O.Q. Munro, W.R. Scheidt, Inorg. Chem. 37 (1998) 2308.
[7] M. Frangione, J. Port, M. Baldiwala, A. Judd, J. Galley, M.
DeVega, K. Linna, L. Caron, E. Anderson, J.A. Goodwin,
Inorg. Chem. 36 (1997) 1904.
[8] C.E. Castro, S.K. O’Shea, J. Org. Chem. 60 (1995) 1922.
[9] C.E. Castro, J. Am. Chem. Soc. 118 (1996) 3984.
[10] M.F. Settin, Diss. Abst. Int. B 48 (1987) 1683.
[11] J.L. Resce, J.C. Fanning, C.S. Day, S.-J. Uhm, A.F. Croisy,
L.K. Keefer, Acta Crystallogr., Sect. C 43 (1987) 2100.
[12] J.C. Fanning, J.L. Resce, G.C. Lickfield, M.E. Kotun, Inorg.
Chem. 24 (1985) 2884.
[13] M. Gerloch, J. Lewis, F. Mabbs, A. Richards, J. Chem. Soc.,
Sect. A (1968) 112.
[14] R.G. Wollman, D.N. Hendrickson, Inorg. Chem. 16 (1977)
723.
[15] X. Wang, W.T. Pennington, D.L. Ankers, J.C. Fanning, Poly-
hedron 17 (1992) 2253.
[16] K. Hayakawa, T. Sawada, K. Shimbo, K. Miyazaki, Anal.
Chem. 59 (1987) 2241.
[17] E.A. Burns, in: C.A. Streuli, P.R. Averell (Eds.), The Analytical
Chemistry of Nitrogen and its Compounds, Wiley, New York,
1970, p. 85.
[18] A. Earnshaw, A. King, L. Larkworthy, J. Chem. Soc., Sect. A
(1969) 2459.
FeacacenCl does not react with PPNNO2 or AgNO2
in acetonitrile to generate NO. The reaction with
AgNO2 does form AgCl, but no NO. Attempts to
isolate pure FeacacenNO2 were unsuccessful. The lack
of
a reaction with Fe(III)acacen compared with
Fe(III)salen may be the result of the difference between
the structures of the coordination spheres of the two
complexes. The salen complexes have more distortion
in their coordination spheres than do the acacen ones
[15]. Reaction (1) appears at this time to be a unique
property of the Fe(III)salen complexes.
The Fe(III,IV)salen, [Fesalen]2O+BF4−
, complex
readily oxidized the nitrite ion to produce NO2 and
[Fesalen]2O. On the vacuum system the brown NO2 gas
was found in the IR gas cell with no NO being present.
.