11238
J. Am. Chem. Soc. 2000, 122, 11238-11239
The Catalytic Reduction of Nitrite. Metal
Coordination and Reaction of Nitrosyl with
Hydrazine: Two-Electron Oxidants Can Also Lead
to Ammonia
†
†
Alberto A. Chevalier, Luis A. Gentil,
,†
†
Valent ´ı n T. Amorebieta,* Mar ´ı a M. Guti e´ rrez, and
Jos e´ A. Olabe*,‡
Departamento de Qu ´ı mica
Facultad de Ciencias Exactas
UniVersidad Nacional de Mar del Plata
B7602AYL Mar del Plata, Rep u´ blica Argentina
Departamento de Qu ´ı mica Inorg a´ nica
Anal ´ı tica y Qu ´ı mica F ´ı sica, Inquimae
UniVersidad de Buenos Aires
Figure 1. Plot of the second-order rate constant, kexp (M- s-1) against
1
NO2 ] ) 1 × 10 M;
-
-4
pH. T ) 25.0 °C; I ) 1 M (NaCl); [Fe(CN)
5
-
3
Pabell o´ n 2, Ciudad UniVersitaria
[N
2
H
4
]
T
) 7.5 × 10 M.
C1428EHA Buenos Aires, Rep u´ blica Argentina
The stoichiometry is described by eq 1
ReceiVed June 6, 2000
2
-
+
The electrophilic reactions of NO bound to transition metals
Fe(CN) NO + N H + H O f
5 2 4 2
with ancillary coligands are important within the subject of NO
3-
+
Fe(CN) H O + N O + NH + H (1)
1
-
5
2
2
3
reactivity. The reactions of OH , amines, and thiolates are also
relevant to modern studies on the physiology of NO dealing with
the mechanisms of transport and reactivity upon coordination to
iron enzymes. NO binds to many transition metals by forming
an electronically delocalized [M-N-O] moiety, with the N-atom
being the site either for nucleophilic addition or outer-sphere
electron transfer. This is a key condition for the reduction of
nitrite, requiring its coordination and proton-assisted dehydration
leading to an Fe -NO species in a d system with low-spin
configuration. This occurs also for the initial steps in the reactivity
The formation of ammonia appears as of high mechanistic
significance, as shown below. All yields were checked for eq 1:
2
9
3
-
the Fe(CN)
5
H
2
O
ion was quantitatively determined by generat-
II
3-
12
ing the Fe (CN)
5
isonicotinamide ion.
2 3
N O and NH were
3
13
+
identified by mass spectrometry, and the delivery of H was
quantified through a pH-stat titration. Under excess of hydrazine,
II
+
6
3-
14
Fe(CN)
5 2
N H
4
is formed. Consumed hydrazine, measured by
4
titration, agrees with eq 1.
5
of the nitrite reductase enzymes.
The rate law, measured through the buildup of products,
3-
2-
We show that nitrite can be catalytically reduced in several
Fe(CN)
5 2
H O
and N
2 5 2 4
O, was: V ) kexp [Fe(CN) NO ] [N H ].
3
-
steps, starting with coordination to Fe(CN)
5
H
2
O , acid-base
Figure 1 shows the dependence of kexp on pH, according to: kexp
NO2 (a well-recognized hypotensive
-
) khydr/{1 + [H ]/K
+
}, where K
corresponds to N
H
5
+
conversion to Fe(CN)
5
a
a
2
2 4
T N H
agent)2 and further attack by hydrazine. The nucleophilic
,6
+ H , and khydr relates to the reactivity of N
+
H
2
4
.
+
reactivity of hydrazine toward NO , promoting nitrosation in
a
A very good fit to the rate law was found by taking pK )
9
competition with outer-sphere reductions, has been considered
8.1, in agreement with the literature value, 8.0, and khydr ) 0.40
5b
-1 -1
+
in the studies of dissimilatory nitrite reductases. Although
( 0.02 M
s
(25.0 °C); the results also show that N
2
H
5
is
7
7
8
q
hydroxilamine, azide, and ammonia were used as nucleophiles
unreactive. Activation parameters (pH 9.2) were: ∆H ) 26.8 (
2-
1
-1
q
-1
-1
with Fe(CN)
5
NO , strikingly, hydrazine was not. The reactivity
0.2 kJ mol , ∆S ) -163 ( 5 J K mol .
The results can be included under a general mechanistic
framework, operative for the reactions of nitrosyl-complexes with
different nucleophiles, B:1
9
of hydrazine is interesting in its own right, and the mechanism
of its addition reactions to several complexes, as well as to nitrous
acid, remains an open subject.5
b,10,11
We first present a stoichiometric, kinetic, and mechanistic study
of the reaction of pentacyanonitrosylferrate(II) with hydrazine.
2-
2-
Fe(CN) NO + B T {Fe(CN) NO ‚B} f
5
5
†
Universidad Nacional de Mar del Plata.
Universidad de Buenos Aires.
3-
‡
Fe(CN) H O + redox products (2)
5 2
(1) (a) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University
Press: New York, 1992. (b) Bottomley, F. In Reactions of Coordinated
Ligands; Braterman, P. S., Ed.; Plenum: New York, 1989; Vol. 2, p 115. (c)
McCleverty, J. A. Chem. ReV. 1979, 79, 53.
The first reaction can be treated as an equilibrium, followed by
irreversible redox rearrangements. The nature of the elementary
(
2) (a) Feelisch, M.; Stamler, J. S., Eds. Methods in Nitric Oxide Research;
-
steps and relative rates are dependent on B; for B ) OH ,
Wiley: Chichester, 1996. (b) Clarke, M. J.; Gaul, J. B. Struct. Bonding (Berlin)
-
1
993, 81, 147. (c) Stamler, J. S.; Singel, D. J.; Loscalzo, J. Science 1992,
58, 1898.
unreactive NO
2
is formed, with no redox reactions. Below pH
2
(
3) Bottomley, F.; Grein, F. J. Chem. Soc., Dalton Trans. 1980, 1359.
4) (a) Barley, M. H.; Takeuchi, K. J.; Meyer, T. J. J. Am. Chem. Soc.
(10) (a) Douglas, P. G.; Feltham, R. D.; Metzger, H. G. J. Am. Chem. Soc.
1971, 93, 84. (b) Bottomley, F.; Kiremire, E. M. R. J. Chem. Soc., Dalton
Trans. 1977, 1125. (c) Bottomley, F.; Crawford, J. R. J. Am. Chem. Soc. 1972,
94, 9092.
(
1
986, 108, 5876. (b) Murphy, W. R.; Takeuchi, K.; Barley, M. H.; Meyer, T.
J. Inorg. Chem. 1986, 25, 1041.
(
5) (a) Averill, B. A. Chem. ReV. 1996, 96, 2951. (b) Kim, C. H.; Hollocher,
T. C. J. Biol. Chem. 1984, 259, 2092.
6) (a) Butler, A. R.; Glidewell, C. Chem. Soc. ReV. 1987, 16, 361. (b)
Swinehart, J. H. Coord. Chem. ReV. 1967, 2, 385.
7) Wolfe, S. K.; Andrade, C.; Swinehart, J. H. Inorg. Chem. 1974, 13,
567.
8) Katz, N. E.; Blesa, M. A.; Olabe, J. A.; Aymonino, P. J. J. Inorg. Nucl.
Chem. 1980, 42, 581.
9) Stanbury, D. M. Prog. Inorg. Chem. 1998, 47, 511.
(11) (a) Perrott, J. R.; Stedman, G.; Uysal, N. J. Chem. Soc., Dalton Trans.
1976, 2058. (b) Doherty, A. M. M.; Howes, K. R.; Stedman, G.; Naji, M. Q.
J. Chem. Soc., Dalton Trans. 1995, 3103.
(
(12) Toma, H. E.; Malin, J. M. Inorg. Chem. 1973, 12, 1039.
(
2 3
(13) N O was determined by gas-volumetric techniques, and NH was
2
titrated with acid, after separation from the reaction mixture through ion-
(
interchange.
(14) Katz, N. E.; Olabe, J. A.; Aymonino, P. J. J. Inorg. Nucl. Chem. 1977,
39, 908.
(
1
0.1021/ja0020052 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/01/2000