Synthesis, structure, and reactivity of aliphatic primary nitrosamines stabilized by coordination to [IrCI5]2-

Article abstract of DOI:10.1021/om700985h

In the present work the formation of several primary aliphatic coordinated nitrosamines by reaction of the extremely reactive K[IrCl₅(NO)] in acetonitrile solution with the corresponding amine is described. Complete characterization, including

Full text of DOI:10.1021/om700985h

Organometallics 2008, 27, 1985–1995
1985
Synthesis, Structure, and Reactivity of Aliphatic Primary
Nitrosamines Stabilized by Coordination to [IrCl5]2-
Florencia Di Salvo,† Darío A. Estrin,† Gregory Leitus,‡ and Fabio Doctorovich*,†
Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET, Facultad de
Ciencias Exactas y Naturales, UniVersidad de Buenos Aires, Ciudad UniVersitaria, Pabellón II, piso 3,
C1428EHA Buenos Aires, Argentina, and Department of Chemical SerVices, The Weizmann Institute of
Science, RehoVot 76100, Israel
ReceiVed October 2, 2007
In the present work the formation of several primary aliphatic coordinated nitrosamines by reaction of
the extremely reactive K[IrCl5(NO)] in acetonitrile solution with the corresponding amine is described.
Complete characterization, including X-ray diffraction determinations for some examples, are reported,
and experimental evidence of their stability. Density functional theory calculations (DFT) helped to
understand the role of the coordination environment of these complexes and to support, with excellent
correlation with the experimental data, the proposed reaction pathways and stability studies. Complexes
containing the highly unstable primary nitrosamines as ligands are generally scarce, and moreover, to
our knowledge, our group has recently reported the first examples of isolated primary nitrosamines
coordinated to the metal center only through the NO moiety.
adenine gives exclusively uracil and hypoxantine, whereas
guanine gives rise to several byproducts.9 The direct observation
by LC/MS of the diazoate of 2′-deoxycytidine was reported by
Makino et al.,10 but there is no information about the isolation
of diazo intermediates obtained by nitrosation reactions of
nucleobases.
Introduction
Secondary nitrosamines (R1R2NNdO) were first described
in the chemical literature over 150 years ago, but not until the
1960s did they receive much attention, when positive carcino-
genic studies were reported.1 These are very stable compounds
that are obtained when typical nitrosating agents2 react with
secondary amines.3 For example, they can be found in foods,
tobacco products, and in ViVo. Endogenous generation takes
place by the nitrosation of amines in the body, via acid- or
bacterial-catalyzed reactions, with nitrite or oxidative products
of NO. In foods, they can be formed when amines react with
nitrite salts, which are used as a common preservative.4 In
tobacco products, many specific nitrosamines were found, and
several studies indicate their activity as chemical carcinogens.5
On the other hand, primary nitrosamines (R1N(H)NdO) are
very unstable and together with their tautomeric isomers, diazoic
acids (R1NdNOH), are considered important intermediates in
the deamination of DNA bases6 and in the formation of
diazonium salts.7 When nitrous acid (HNO2) reacts with guanine,
adenine, and cytosine, it causes deamination and interstrand
cross-linked products. These alterations represent one of the
most abundant sources of endogenous DNA damage, and it
constitutes a relevant portion of injures in various disease stages
via mutagenesis and cytotoxicity.8 Deamination of cytosine and
Aromatic diazonium ions have been known for a long time,
showing multiple applications in synthesis, covering a large area
of organic chemistry.11 On the contrary, the closely related
diazonium ions attached to sp3 carbons have been very elusive,
and except for a few examples observed at low temperature,6
only rearranged and nucleophilic attack products are observed
when aliphatic amines are nitrosated with different nitrosating
agents (Scheme 1). Our group has previously explored the
possibility of obtaining stabilized coordinated diazonium ions
by reaction of nitrosyl complexes with aromatic and aliphatic
primary amines,12 a route previously pointed out by Meyer et
al.,13 who isolated coordinated aromatic diazonium salts. In the
case of the reaction of [Fe(CN)5NO]2- (nitroprusside) and
[Ru(bpy)2(NO)Cl]2+ with aliphatic amines, only organic prod-
ucts derived from nucleophilic attack to the diazonium ion or
the carbocation could be obtained (bottom part of Scheme 1).12
However, quantitative analysis of the rearranged/unrearranged
products ratio allowed an estimation of the diazo intermediate
relative stability. For example, the main organic product derived
* E-mail: doctorovich@qi.fcen.uba.ar.
† Universidad de Buenos Aires.
(9) Glaser, R.; Rayat, S.; Lewis, M.; Son, M.; Meyer, S. J. Am. Chem.
Soc. 1999, 121, 6108–6119., and references therein.
‡ The Weizmann Institute of Science.
(1) Magee, P. N.; Barnes, J. M. Br. J. Cancer. 1956, 10, 114.
(2) These agents include N2O4, ClNO, BuONO, NO+, and acidified
NO2- salts; see: Lee, J.; Chen, L.; West, A. H.; Richter-Addo, G. B. Chem.
ReV. 2002, 102, 1019.
(10) Suzuki, T.; Nakamura, T.; Yamada, M.; Ide, H.; Kanaori, K.;
Tajima, K.; Morii, T.; Makino, K. Biochemistry 1999, 38, 7151.
(11) Patai, S. The Chemistry of Diazonium and Diazo Groups; Wiley:
New York, 1978.
(3) Mirvish, S. S. Toxicol. Appl. Pharmacol. 1975, 31, 325.
(4) Ridd, J. H. Q. ReV. Chem. Soc. 1961, 15, 418.
(5) Hecht, S. S. Chem. Res. Toxicol. 1998, 11, 1998–560.
(6) Caulfield, J.; Wishnok, J.; Tannenbaum, S. J. Biol. Chem. 1998, 273
(21), 12689.
(12) (a) Doctorovich, F.; Trápani, C. Tetrahedron Lett. 1999, 40, 4635.
(b) Doctorovich, F.; Escola, N.; Trápani, C.; Estrin, D. A.; Turjansky, A. G.;
González Lebrero, M. C. Organometallics 2000, 19, 3810. (c) Doctorovich,
F.; Granara, M.; Di Salvo, F. Transition Met. Chem. 2001, 26, 505. (d)
Trápani, C.; Escola, N.; Doctorovich, F. Organometallics. 2002, 21 (10),
2021–2023. (e) Di Salvo, F.; Crespo, A.; Estrin, D. A.; Doctorovich, F.
Tetrahedron 2002, 58, 4237.
(7) (a) Mohrig, J. R.; Keegstra, K. J. Am. Chem. Soc. 1967, 89, 5492.
(b) Berner, D.; McGarrity, J. F. J. Am. Chem. Soc. 1979, 101, 3135.
(8) Rayat, S.; Wu, Z.; Glaser, R. Chem. Res. Toxicol. 2004, 17, 1998–
1157.
(13) Bowden, W. L.; Little, W. F.; Meyer, T. J. J. Am. Chem. Soc. 1977,
99, 4340.
10.1021/om700985h CCC: $40.75
2008 American Chemical Society
Publication on Web 04/05/2008

1986 Organometallics, Vol. 27, No. 9, 2008
Di SalVo et al.
complexes are known as bioorganometallic compounds,17 so
we consider the last example as an application of this reaction
to this growing area of bioorganometallic chemistry.
Scheme 1. Formation of Aliphatic N-Nitrosamines: Stable
Secondary Nitrosamines vs Unstable Primary Nitrosamines
(for the last case, equilibrium and decomposition pathways
are shown)
As an interesting addition to the chemical study of these
compounds, we also report their stability and derived products
when these compounds are subject to nucleophilic attack. In
this way, we show how these diazo derivatives could act in a
similar way to the aromatic diazonium salts: as stable precursors
for organic synthesis.
As it was mentioned before, density functional theory (DFT)
calculations performed by our group have shown a great concor-
dance with the experimental results related to the chemistry of
nitroso compounds coordinated to transition metal complexes.12,18,19
We complement the experimental study by performing com-
putational calculations at the DFT level in Vacuo and with a
continuum sovation model in order to investigate the structure,
stability, properties, and the feasibility of the nucleophilic attack
reaction pathways for the described nitrosamines and related
diazo compounds.
Experimental Section
General Comments. Unless otherwise noted all manipulations
were performed with exclusion of oxygen and moisture using
standard Schlenk procedures. 1H and 13C NMR spectra were
recorded using a Bruker AM500 equipped with a broadband probe.
1H and 13C shifts are reported relative to CD3CN (δ ) 1.95 and
118 ppm, respectively) or to DMSO-d6 (δ ) 2.50 and 39.5 ppm,
respectively), and correlations were confirmed through 2D and
DEPT 135° experiments. ESI-MS (electrospray ionization mass
spectrometry) measurements were performed using a high-resolution
hybrid quadrupole (Q) and orthogonal time-of-flight (Tof) mass
spectrometer (QTof from Micromass, UK) operating in the negative
ion electrospray ionization mode set from 2100 to 3500 V; for
details see ref 20. IR spectra were recorded using a Nicolet Avatar
320 FTIR spectrometer with a Spectra Tech cell for KBr pellets.
UV–visible spectra were recorded using a Hewlett-Packard 8453
diode array spectrometer in 10 mm optical path quartz cuvettes.
CHN elemental analysis was made in a Carlo Erba EA 1108
apparatus. GC-mass spectra were recorded on a Shimadzu GC-
17A gas chromatograph with a HP Ultra 2 capillary column attached
to a GCMS-QP5000 mass spectrometer operating in the positive
ion electronic impact ionization mode at 70 eV. Data collection
and processing of the X-ray diffraction studies were performed in
a Nonius KappaCCD diffractometer, Mo KR (λ ) 0.71073 Å),
graphite monochromator, T ) 120(2) K. The data were processed
with Denzo-Scalepack. Solution and refinement: Structure solved
by Patterson method with SHELXS. Full matrix least-squares
refinement is based on F2 with SHELXL-97.
from the reaction of nitroprusside with aliphatic amines is, in
most cases, the corresponding diamine (95% for n-butylamine
and 30% for benzylamine). For the ruthenium nitrosyl complex,
alkenes, rearranged alcohols and chlorides, and small quantities
of radical oxidation products were observed apart from the
organic products derived from the concerted nucleophilic attack
(Scheme 1). This fact suggested that the [Fe(CN)5]3- moiety is
more successful in stabilizing the intermediate diazonium ion
through back-donation, as supported by DFT calculations.12
Recently, we reported the complete characterization, including
X-ray crystallography determinations, of an aromatic and an
aliphatic coordinated primary nitrosamine by reaction of the
extremely reactive K[IrCl5(NO)] with p-toluidine and 2,2,2-
trifluoroethylamine, respectively.14 Examples of complexes
containing primary nitrosamines as ligands are generally
scarce,15 and moreover, to our knowledge these examples were
the first ones of isolated primary nitrosamines coordinated to
the metal center only through the NO moiety. The facile
formation and stabilization of coordinated N-nitroso compounds,
which do not exist in free form, could be achieved thanks to
the high electrophilicity (due to very weak back-bonding) and
the inertness of the [IrCl5]2- moiety. These two qualities,
generally not compatible, define the anion [IrCl5(NO)]- as a
rather unique reagent.16 In the present work we show more
examples of coordinated primary nitrosamines derived from the
aliphatic amines: benzylamine, n-butylamine, cyclopropylamine,
and the pseudoaromatic amine 9-octyladenine. Some examples
of DNA bases and their derivatives as ligands in transition metal
Reagents. Acetonitrile was purchased from J. T. Baker and
distilled from CaH2; toluene was purchased from Cicarelli and
distilled from Na-benzophenone. 2,2,2-Trifluoroethylamine, ben-
zylamine, cyclopropylamine, adenine, tetraphenylarsonium chlo-
ride, tetraphenylphosphonium bromide, octylbromide, K3[IrCl6],
Na15NO2, deuterated solvents, and acids were purchased from
Sigma-Aldrich Argentine and used as received. n-Butylamine was
purchased from Rieder-de Haën and used as received. K[IrCl5(NO)]
(14) Doctorovich, F.; Di Salvo, F.; Escola, N.; Trápani, C.; Shimon, L.
Organometallics 2005, 24, 4707.
(15) (a) Schramm, K.; Dahl Schramm; Ibers, J. A. J. Am. Chem. Soc.
1978, 100, 2932. (b) Keefer, L. K.; Wang, S.; Anjo, T.; Fanning, J. C.;
Day, C. S. J. Am. Chem. Soc. 1988, 110, 2800. (c) Vaughan, G. A.;
Chadwick, D. S.; Hillhouse, G. L. J. Am. Chem. Soc. 1989, 111, 5491–
5493. (d) Lalor, F. J.; Desmond, T. J.; Ferguson, G.; Siew, P. Y. J. Chem.
Soc., Dalton Trans. 1982, 10, 1981.
(17) Fish, R. H.; Jaouen, G. Organometallics 2003, 22, 2166.
(18) Perissinotti, L. L.; Estrin, D. A.; Leitus, G.; Doctorovich, F. J. Am.
Chem. Soc. 2006, 128, 2512.
(19) Escola, N.; Llebaria, A.; Doctorovich, F.; Leitus, G. Organome-
tallics 2006, 25, 3799.
(16) (a) Di Salvo, F.; Escola, N.; Estrin, D. A.; Sherlis, D. A.; Shimon,
L.; Doctorovich, F. Chem.-Eur. J. 2007, 13, 8428. (b) Doctorovich, F.; Di
Salvo, F. Acc. Chem. Res. 2007, 40, 985.
(20) Escola, N.; Di Salvo, F.; Haddad, R.; Perissinotti, L.; Nogueira
Eberlin, M.; Doctorovich, F. Inorg. Chem. 2007, 46, 4827.

Aliphatic Primary Nitrosamines
Organometallics, Vol. 27, No. 9, 2008 1987
was purchased from Strem, and K[IrCl5(15NO)] was prepared from
K3[IrCl6] and Na15NO2 by known procedures.21
ONNHCH2CF3), 7.24–7.34 (m, 5H, ONNHCH2Ph), 7.72–8 ppm
(m, 42H, 2PPh4). 13C NMR (DMSO): δ 48.5 (s, ONNHCH2Ph),
127.4–128.5 and 134.6 (ONNHCH2Ph), 130.4, 130.5, 134.5, 134.6,
135.2, 135.3 ppm (s, 2PPh4). X-ray crystal structure data:
C55H48N2O4P2Cl5Ir, (PPh4)2[IrCl5(ONNHC7H7)] · 3H2O (water pro-
tons are not included in the X-ray refinement), Mr 1232.34, orange
prisms, triclinic, dimensions 0.20 × 0.10 × 0.10 mm3, group )
P(-1) (#2), a ) 14.034(3) Å,b ) 14.109(3) Å, c ) 16.251(3) Å,
R ) 87.69(3)°, ꢀ ) 65.47(3)°, γ ) 66.00(3)°, V ) 2643.0(9) Å3,
Z ) 2, Dx ) 1.548 Mg m-3, λ ) 0.71073 Å, cell parameters from
11 071 reflections, θ ) 2.886 mm-1, T ) 120(2) K. X-ray crystal
collection and refinement: Tmin ) 0.5960, Tmax ) 0.7612, 7588
mesured and independent reflections, 6738 reflections with >2σ(I),
θmax ) 23.26°, h ) -13 f 15, k ) -15 f 15, l ) 0 f 18,
refinement based on F2, R ) 0.0533 (for data with F2 > 2σ(F2)),
wR(F2) ) 0.1153, S ) 1.242, R1 ) 0.0619 on 7588 reflections,
612 parameters, largest electron density peak ) 2.638 e · Å-3, H
atoms treated by a mixture of independent and constrained
refinement.
General Synthesis of [IrCl5(N-nitrosamines)]2-. For the
preparation of the corresponding coordinated N-nitrosamine 3.6 µL
(0.046 mmol) of 2,2,2-trifluoroethylamine for the synthesis of
[IrCl5(N-nitroso-2,2,2-trifluoroethylamine)]2- (1), 5.0 µL (0.046
mmol) of benzylamine for [IrCl5(N-nitrosobenzylamine)]2- (2), 4.6
µL (0.046 mmol) of n-butylamine for [IrCl5(N-nitroso-n-butyl-
amine)]2- (3), 3.2 µL (0.046 mmol) of cyclopropylamine for
[IrCl5(N-nitrosocyclopropylamine)]2- (4), and 11.4 mg (0.046
mmol) of 9-octyladenine (dissolved in 0.25 mL of acetonitrile) for
[IrCl5(N-nitroso-9-octyladenine)]2- (5) were added under Ar at-
mosphere at RT to 10 mg (0.023 mmol) of K[IrCl5(NO)] in 0.25
mL of acetonitrile. 9-Octyladenine was prepared from adenine and
the corresponding alkyl bromide by known procedures.22 In all cases
the resultant product was K(NH3R)[IrCl5(ONNHR)], with R )
-CH2CF3 for 1, -CH2C6H5 for 2,-C4H9 for 3, -c-C3H5 for 4,
and -C13H19N4 for 5; in some cases up to 5% of the ammonium
salt was replaced by H+, giving a coordinated nitrosamine:
ammonium salt ratio of about 1:0.9.
Data for the potassium and ammonium salt. 1H NMR (DMSO):
δ 4.04 (s, 2H, +NH3CH2Ph), 4.74 and 4.76 (s, 2H, ONNHCH2Ph),
8.08 (br s, 2.5 H, ( NH3CH2Ph), 13.1 (br s, 0.6H, ONNHCH2CF3),
7.3–7.4 (m, 5H, +NH3CH2Ph), 7.4–7.5 ppm (m, 5H, ONNHCH2Ph).
To increase the yield of 3 and 4, different reaction temperatures
were explored. The use of an ethanol-liquid nitrogen slush bath
(ca. -35 °C) was found to be the best option. In all cases, the
product that precipitated immediately was separated from the
solution by centrifugation (the counterions are the ammonium salt
of the corresponding amine and a potassium ion); the yield obtained
for the corresponding product was from 80 to 90% and the
precipitate colors were light orange for 1, 3, and 4, yellow for 2,
and dark red for 5. All nitrosamine products are soluble in only
water and DMSO; the last one was chosen for NMR and ESI-MS
experiments. The tetraphenylphosphonium salts, (PPh4)2-
[IrCl5(ONNHR)], were obtained by adding a saturated aqueous
solution of the crude product to an acetonitrile saturated solution
of tetraphenylphosphonium bromide. After slow evaporation of the
supernatant, the so produced orange crystals were separated by
centrifugation and carefully dried. The crystals obtained for the
2,2,2-trifluoroethylamine and benzylamine products were suitable
for X-ray analysis.
13C NMR (DMSO):
δ
43.2 (s, +NH3CH2Ph), 48.8 (s,
ONNHCH2Ph), 127.4–128.5 and 134.6 ppm (ONNHCH2Ph and
+NH3CH2Ph). FTIR frequencies: v(HNNO) 1530 cm-1
,
v(HN15NO) 1508 cm-1. UV–visible absorption in water, λmax (ꢀmax
in M-1 cm-1): 198(4.2 × 104), 310(1.8 × 103), 377(6 × 103),
429(3 × 103). Anal. C ) 24.9% (calc 25.0), H ) 2.7% (calc 2.7),
N ) 6.0% (calc 6.3), calculated values are according to a 1:0.9
coordinated nitrosamine:ammonium salt counterion ratio found by
1H NMR. ESI-MS: for M ) [IrCl5(ONN(H)CH2C6H5)]2-, [M +
K]- ) 544.834 m/z (calc 544.8313), [M - Cl]- ) 470.900 m/z
(calc 470.8990).20
[IrCl5(N-nitroso-n-butylamine)]2- (3). The products obained
at RT are mainly N2(g), n-butylalcohol(sc), [IrCl5(NH2-
C4H9)]KNH3C4H9(s), and coordinated N-nitroso-n-butylamine with
a yield of 30%. When the reaction is performed at -35 °C, the
nitrosamine yield increases to 78%.
[IrCl5(N-nitroso-2,2,2-trifluoroethylamine)]2- (1). Data for the
1
tetraphenylphosponium salt. H NMR (DMSO): δ 4.42 and 4.43
Data for the potassium and ammonium salt. 1H NMR (DMSO):
δ 0.91 (m, 7H, +NH3CH2(CH2)2CH3 and ONNHCH2(CH2)2CH3),
1.35 (m, 4H, +NH3CH2(CH2)2CH3), 1.52 (m, 4H, ONNHCH2-
3
(q, 2H, JHF ) 9.37 Hz, ONNHCH2CF3), 13.1 ppm (br s, 0.8H,
ONNHCH2CF3), 7.75–8 ppm (m, 42H, 2PPh4). 13C NMR (DMSO):
2
1
δ 44.3 (q, JCF ) 35 Hz, ONNHCH2CF3), 121.3 (q, JCF ) 280
Hz, ONNHCH2CF3), 130.3, 130.4, 134.4, 134.5, 135.2, 135.3 ppm
(s, 2PPh4). Anal. C ) 49.5% (calc 49.5), H ) 3.5% (calc 3.9), N
) 2.3% (calc 2.3); for the calculated values 2 molecules of water
were taken into account, data confirmed by X-ray crystallography
and 1H NMR. See ref 14 for the X-ray crystal structure analysis of
this compound.
(CH2)2CH3), 2.77 (br t, 2H, +NH3CH2(CH2)2CH3), 3.58 (t, 2H, 3JHH
(
)
6.69 Hz, ONNHCH2(CH2)2CH3), 7.5 (br s, 2.2 H,
NH3CH2(CH2)2CH3), 12.8 ppm (br s, 0.7H, ONNHCH2(CH2)2CH3).
13C NMR (DMSO): 13.2 (s, +NH3CH2(CH2)2CH3 and
δ
ONNHCH2(CH2)2CH3), 18.9 (s, +NH3CH2(CH2)2CH3), 28.7 and
29.2 (s, ONNHCH2(CH2)2CH3), 38.6 (s, +NH3CH2(CH2)2CH3), 44.9
ppm (s, ONNHCH2(CH2)2CH3). FTIR frequencies: ν(HNNO) 1535
cm-1, ν(HN15NO) 1487 cm-1. UV–visible absorption in DMSO,
λmax (ꢀmax in M-1 cm-1): 260(2 × 103), 322(2.3 × 102), 363(2.7
× 102), 422(93). Anal. C ) 15.7% (calc 15.8), H ) 3.4% (calc
3.7), N ) 6.9% (calc 7.0), calculated values are according to a
1:0.9 coordinated nitrosamine:ammonium salt counterion ratio found
Data for the potassium and ammonium salt. 1H NMR (DMSO):
3
3
δ 3.84 (q, 2H, JHF ) 9.41 Hz, +NH3CH2CF3), 4.50 (q, 2H, JHF
) 9.37 Hz, ONNHCH2CF3), 9.31 (br s, 2.5H, +NH3CH2CF3), 13.0
ppm (br s, 0.8H, ONNHCH2CF3). 13C NMR (DMSO): δ 39.86 (q,
2JCF ) 34.99 Hz, +NH3CH2CF3), 44.4 (q, JCF ) 34.6 Hz,
2
ONNHCH2CF3), 122.44 (q, JCF ) 279.74 Hz, +NH3CH2CF3),
1
1
by H NMR. ESI-MS: for M ) [IrCl5(ONN(H)C4H9)]2-, [M +
123.53 ppm (q, 1JCF ) 277.71 Hz, ONNHCH2CF3). FTIR frequen-
cies: ν(HNNO) 1547 cm-1, ν(HN15NO): 1534 cm-1. UV–visible
absorption in water, λmax (ꢀmax in M-1 cm-1): 195(2.3 × 104),
321(1.6 × 103), 384(103), 436(6.5 × 103). ESI-MS: for M )
[IrCl5(ONN(H)CH2CF3)]2-, [M + K]- ) 536.789 m/z (calc
536.7877), [M - Cl]- ) 462.853 m/z (calc 462.9856).20
K]- ) 510.834 m/z (calc 510.8473), [M + NH3C4H9]- ) 545.972
m/z (calc 545.9805).20
[IrCl5(N-nitrosocyclopropylamine)]2- (4). The products obained
at RT are N2(g), n-cyclopropylalcohol(sc), several ring-opening
alkanes and alkenes derivatives found in solution, and KNH3(c-
CHCH2CH2)[IrCl5(CH3CN)] · xCH3CN(s) in a 50% yield. Charac-
terization data of the solid product: 1H NMR (DMSO): δ 3.00 ppm
(s, coordinated CH3CN). 13C NMR (DMSO): δ 2.3 and 113.5 ppm
(s, coordinated CH3CN) (see later for the couterion data). Anal. C
) 11.9% (calc 11.8), H ) 2.3% (calc 2.2), N ) 5.8% (calc5.5);
[IrCl5(N-nitrosobenzylamine)]2- (2). Data for the tetraphe-
nylphosponium salt (Ph ) phenyl group, C6H5). 1H NMR (DMSO):
δ 4.67 and 4.76 (s, 2H, ONNHCH2Ph), 13.00 (br s, 1H,
(21) Bottomley, F.; Clarkson, S. G.; Tong, S. B. J. Chem. Soc., Dalton
Trans. 1974, 21, 2344.
(22) Bunton, C. A.; Wolfe, B. B. J. Am. Chem. Soc. 1974, 96, 7747.
ESI-MS: for M ) [IrCl5(CH3CN)]2-, [M - Cl - AcN]-
332.8319 m/z (calc 332.8383), [M - Cl + K]-• ) 4128429 m/z
)

1988 Organometallics, Vol. 27, No. 9, 2008
Di SalVo et al.
(calc 412.8286), [M + K]- ) 488.8628 m/z (calc 488.8240). When
the reaction is performed at -35 °C, the yield of the nitrosamine
is 92%.
double-ꢁ plus polarization (DZPV) basis set27 for N, O, F, H, and
Cl atoms and the LANL2DZ basis set and effective core potential
for the metals (Ir, Fe).28,29 A normal modes analysis was performed
in order to obtain vibrational frequencies, force constants, and zero-
point energy corrections for the total energy. Atomic charges have
been calculated using the Mulliken and NPA30 schemes. Solvent
effects were modeled using a variety of the self-consistent reaction
field method (SCRF): the polarized continuum model (PCM)
schemes. This model considers that the solute is placed in a cavity
of a quite realistic molecular shape The PCM implementation given
in ref 31, in which the self-consistency between the solute wave
function and solvent polarization is achieved during the self-
consistent-field cycle, has been employed. Solvent calculations were
performed on the in Vacuo-optimized structures using the GAUSS-
IAN 98 software package.21
1
Data for the potassium and ammonium salt product. H NMR
(DMSO): δ 0.60 and 0.72 (m, 4H, +NH3CH(CH2CH2), 0.66 and
0.91 (m, 4H, ONNH CH(CH2CH2), 2.52 (m, 1H, +NH3-
(
CH(CH2CH2), 3.16 (m, 1H, ONNHCHCH2CH2), 8.5 (br s, 3H,
NH3CHCH2CH2), 12.5 ppm (br s, 0.8H, ONNHCHCH2CH2). 13C
NMR (DMSO): δ 3.8 (+NH3CH(CH2CH2), 6.5 (ONNHCH-
(CH2CH2), 22.9 (+NH3CH(CH2CH2), 29.2 ppm (ONNH-
CHCH2CH2). FTIR frequencies: ν(HNNO) 1410 cm-1, ν(HN15NO)
1394 cm-1. UV–visible absorption in DMSO, λmax (ꢀmax in M-1
cm-1): 260(2 × 103), 326(6.9 × 102), 353(7 × 102), 379(5.4 ×
102), 420(2.6 × 102). Anal. C ) 13.2% (calc 13.0), H ) 2.7%
(calc 2.6), N ) 7.3% (calc 7.6).
[IrCl5(N-nitroso-9-octyladenine)]2- (5). 1H NMR (DMSO)
(data for a complex with a 2:1 coordinated nitrosamine:ammonium
salt counterion ratio): δ 0.84 (t, 5 H, CH3 from C8H17), 1.4 and 2.0
Results and Discussion
3
(m, 21 H, CH2 from C8H17), 4.12 (t, 1 H, JHH ) 7.08 Hz, CH2
Formation of Nitrosamines. When an amine was added to
an acetonitrile solution of K[IrCl5(NO)], immediate formation
of the corresponding coordinated nitrosamine precipitate was
observed (1 in the case of 2,2,2-trifluoroethylamine, 2 for
benzylamine, 3 for n-butylamine, 4 for cyclopropylamine, and
5 for 9-octyladenine); except for 5, which was a dark red
product, the obtained solids were all yellow to light orange
colored. For most of the experiments the observed counterions
were K+ and the corresponding ammonium salt. These facts
bound to the indol ring in the ammonium salt counterion), 4.28 (t,
3
2 H, JHH ) 7.08 Hz, CH2 bound to the indol ring in the
+
nitrosamine), 7.75 (br s, 2 H, ammonium salt NH3 signal), 8.24
and 8.26 (s, 2 H, indol ring signals of the ammonium salt
counterion), 8.64 and 8.74 (s, 2 H, indol ring signals in the
nitrosamine), 14.48 ppm (s, 0.7 H, ONNH C13H19N4). 13C NMR
(DMSO): δ 13.66 (CH3 from C8H17), 21.78, 21.62, 25.62, 28.10,
28.22, 28.94, 30.88 (CH2 from C8H17), 43.11 (CH2 bound to the
indol ring of the ammonium salt counterion), 43.4 (CH2 bound to
the indol ring of the nitrosamine), 117.84, 140.01, 145.26, 148.09,
150.68 (C1, C4, C5, C2, C3 indol ring signals in the ammonium
salt), 123.38, 143.39, 145.256, 147.29, 148.39 ppm (C1, C4, C5,
C2, C3 indol ring signals of the nitrosamine). FTIR frequencies:
1
were evidenced by H and 13C NMR and by stoichiometric
analysis of the reaction mixture (see Figure 1A). Although in
all cases the main product was the solid nitrosamine complex,
the stability was different for each compound. Depending on
the amine, temperature conditions had to be optimized; 2,2,2-
trifluoroethylamine, benzylamine, and 9-octyladenine products
were easily obtained at RT or even higher temperatures, but
isolation of the nitrosamines derived from n-butylamine and
cyclopropylamine was only possible at temperatures around -30
°C. For these two cases, the nitrosamines obtained at the very
first moment rapidly decomposed at RT, giving more stable
products. The evolution of N2(g), changes in the solution color,
and final appearance of precipitates were clear evidence of this
fact. In the case of n-butylamine, the observed products were
n-butyl alcohol and coordinated amine, which precipitated from
the media. For cyclopropylamine, several products derived from
ring-opening, nucleophilic attack, and elimination reactions were
observed in solution and a precipitate was identified as [IrCl5-
(CH3CN)]K(NH3CH(CH2)2) · xCH3CN. When the reaction was
performed at-35 °C, the results for these two amines were the
same as for the other three examples: clean reactions with the
generation of a unique product in high yield and easily isolated
(see Table 1).
ν(HNNO) 1449 and 1438 cm-1, ν(HN15NO) 1436 and 1430 cm-1
.
UV–visible absorption in water, λmax (ꢀmax in M-1 cm-1): 263(4.5
× 103), 271(4 × 103), 325(2 × 103), 384(103), 427(7 × 102). ESI-
MS: for M ) [IrCl5(ONN(H)C13H19N4)]2-, [M + HCl]•-
)
610.040 m/z (calc 609.9975), [M - Cl + H2O]- ) 629.034 m/z
(calc 629.0158).20
Nitrosamine Decomposition Reactions. The decomposition of
the nitrosamines after the addition of strong acids was analyzed. The
experiments were performed for all the nitrosamines. The acids used
in these reactions were acetic, hydrochloric, deuterated hydrochloric,
trifluoroacetic, perchloric, and trifluoroacetic acid solutions with sodium
iodide. The lifetime of the nitrosamine and appearance of final products
1
was first checked by H NMR and then by GC-MS. For the NMR
experiments, the acid was added to a DMSO-d6 or D2O solution of
the nitrosamine in a 2:1 ratio. GC-MS experiments were made on
organic solutions of the decomposition products. These solutions
were obtained after extracting with CH2Cl2 the organic compounds
derived from the addition of acid to a saturated water solution of
the corresponding nitrosamine.
Computational Methodology. All gas phase DFT calculations
performed in this work were carried out using the GAUSSIAN 98
software package.23 Unless otherwise indicated, geometries were
fully optimized at the B3LYP24,25 and/or BPW9126 level with a
After recrystallization and change of both counterions by
tetraphenylphosphonium (PPh4+) (Figure 1B), crystals suitable
for X-ray diffraction were obtained for the trifluoroethyl (1) and
benzyl (2) derivatives (see Figures 2 and 3 and Experimental
Section).
An outstanding characteristic of these compounds is that the
nitrosamines are placed in a syn arrangement. Fishbein et al.
have studied the decay of different free alkanediazoates,
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R.; Burant, J.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J.
V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez,
C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, ReV. A7;
Gaussian, Inc.: Pittsburgh, PA, 1998.
(25) Lee, C.; Yang, W.; Parr, R. Phys. ReV. B 1998, 37, 785.
(26) Becke, A. D. Phys. ReV. A 1998, 38, 3098.
(27) Godbout, N.; Salahub, D. R.; Andzelm, J.; Wimmer, E. Can.
J. Chem. 1992, 70, 560.
(28) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270.
(29) Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(30) Reed, A. E.; Curtis, L. A.; Weinhold, F. Chem. ReV. 1988, 88,
899.
(24) Becke, A. D. J. Chem. Phys. 1988, 98, 5648.

Aliphatic Primary Nitrosamines
Organometallics, Vol. 27, No. 9, 2008 1989
Figure 1. 1H NMR (DMSO-d6): (A) 2,2,2-trifluoroethylamine product 1 as K+/ammonium salt; (B) 2,2,2-trifluoroethylamine product 1 as
+
PPh4 salt.
Table 1. Temperature Conditions, Products, and Yield for the Reaction of Aliphatic Amines with K[IrCl5(NO)] (solvent: CH3CN, 2:1
amine:complex ratio)
amine
reaction temperature (°C)
producta
yield (%)
2,2,2-trifluoroethylamine
benzylamine
n-butylamine
cyclopropylamine
9-octyladenine
RT
[IrCl5(ONNHCH2CF3)]2- (1)
[IrCl5(ONNHCH2Ph)]2- (2)
[IrCl5(ONNHC4H9)]2- (3)
82
90
78
92
75
RT
-35b
-35c
RT
[IrCl5(ONNH(c-CHCH2CH2))]2- (4)
[IrCl5(ONNHC13H19N4)]2- (5)
a In all cases the counterions are K(NH3R), where NH3R is the ammonium salt of the corresponding amine. b Products obtained at RT: N2(g), n-butyl
alcohol, KNH3C4H9[IrCl5(ONNHC4H9)](s) (20–30%), KNH3C4H9[IrCl5(NH2C4H9)](s). c Products obtained at RT: N2(g), cyclopropyl alcohol,
ring-opening derivatives, traces of KNH3(c-CHCH2CH2)[IrCl5(ONNH(c-CHCH2CH2))] and KNH3(c-CHCH2CH2)[IrCl5(CH3CN)] · xCH3CN(s) (50%).
reporting evidence that the decomposition of a single primary
(Z)-alkanediazoate was 2600 times grater than its E analogue.32
It must be noted that the conformation is syn with respect to
the nitrosamine itself (Figure 4), but is anti to the [IrCl5]2-
fragment. In that sense, both bulky groupssthe [IrCl5]2- moiety
and the R fragmentsare placed as far as possible in order to
diminish steric repulsions (see Figure 4), which is the main
factor that could explain the higher relative stability of the syn
conformers.
In order to analyze conformer stabilities, DFT calculations
in Vacuo and applying a solvent model (PCM) were performed
on the nitrosamine complexes. A phenyl analogue was included
in order to compare the results obtained for the aliphatic amines
against an aromatic compound. The stabilization energies found
by DFT calculations in acetonitrile for the syn conformers with
respect to the anti ones were between 4 and 14 kcal mol-1
(Figure 5; for the in Vacuo results see the Supporting Informa-
tion). The different values obtained for the various complexes
Figure 2. X-ray crystal structure and atom numbering for [IrCl5(N-
nitroso-2,2,2-trifluoroethylamine)]2- (1). Thermal ellipsoids are
14
drawn at the 50% level.
(31) Cossi, M.; Barone, V.; Cammi, R.; Tomasi, J. Chem. Phys. Lett.
1996, 255, 327.
could be explained by analyzing the steric repulsion generated
by the organic groups next to the HN-NdO moiety. Notice
(32) Ho, J.; Fishbein, J. C. J. Am. Chem. Soc. 1994, 116, 6611.

1990 Organometallics, Vol. 27, No. 9, 2008
Di SalVo et al.
performed by DFT calculations in Vacuo and applying a
solvation model. In Figure 6, all the optimized structures
corresponding to the nitrosamines and diazoic acids complexes
are shown.
H
R- -N)O h R-N)N-OH
(1)
N
As it was already introduced, X-ray data showed that the
nitrosamines and not the diazoic acids were the most probable
structures for the crystallized precipitated products. However,
diazoic acids turned out to be stable local minima in the DFT
calculations. In Table 2 relevant DFT-calculated and experi-
mentally determined angles and distances data for 2 are shown.
The calculated structural parameters for the corresponding
diazoic acid are also included. The calculated DFT values for
the remaining coordinated nitrosamines along with the X-ray
experimental data for 114 may be found in the Supporting
Information.
Comparing the X-ray data and the DFT results for compound
2, it can be seen that the calculations are in very good agreement
with the experimental data. In addition, the data also confirm
the correct convergence of the crystallographic X-ray data to
an N-nitrosamine structure instead of a diazoic acid one.
Consequently, it is possible to establish comparisons along the
different nitrosamine compounds based just on DFT structural
parameters. For instance, parameters related to the N-N and
N-O bonds are the most sensitive since double bonds are
significantly shorter than single bonds and present different bond
angles. Experimental bond values correlate better with the
N-nitrosamine structures than the diazoic acid ones. Larger
differences can be pointed out when relevant angles of diazoic
acid structures are compared with the experimental ones. So,
coincident with the X-ray data, DFT calculations show that the
nitrosamine structure would be the best assignment for the
reaction products in the solid state. Energetic value comparison
between both derivatives will be shown in the nitrosamine
mechanism discussion section.
Figure 3. X-ray crystal structure and atom numbering for [IrCl5(N-
nitrosobenzylamine)]2- (2). Thermal ellipsoids are drawn at the
50% level.
Figure 4. Coordinated nitrosamine conformers.
Experimental FTIR frequencies found for ν(N-H) were about
3180 cm-1 and for ν(H-N-N-O) between 1547 and 1439
cm-1 (see Experimental Section). ν(H-N-N-O) data have
been clearly confirmed through isotopic 15N labeling of the
“NO” nitrogen atom. No bibliographic data are available for
coordinated primary nitrosamines, but these values correlate
considerably well with free secondary nitrosamine frequencies:
for ν(N-N-O) the values are between 1550 and 1425 cm-1
and for ν(N-N) between 1150 and 930 cm-1 33
In addition,
.
normal-mode analyses were performed to obtain computational
data that helped to confirm all the signal assignments and modes
(see Supporting Information).
Stability and Reactivity of the Coordinated Nitrosa-
mines. On the basis of the discussion started in the previous
section, it is possible to make some preliminary conclusions
about the coordinated nitrosamine stability by analyzing the
required temperatures to observe the best product yields. While
good yields for 1, 2, and 5 were obtained at RT, for 3 and 4
good yields were only possible by working at temperatures lower
than -20 °C. For the last two cases, the RT reaction proceeded
up to the formation of the diazonium salts and their subsequent
decomposition, facilitated by the higher solubility of these
compounds with respect to the nitrosamines (Scheme 2). Quick
extraction of the supernatant containing OH-/H2O produced by
Figure 5. DFT-calculated conformer energy difference (E(anti-syn)
in kcal/mol) in acetonitrile for the nitrosamine complexes 1 to 4
(B3LYP, DZVP basis sets for N, O, C, H, Cl; LANL2DZ basis set
and pseudopotential for Ir, PCM model for acetonitrile). Only the
organic residues are shown.
that the higher energy difference value was observed for the
phenyl ring substituent followed by the value obtained for the
cyclopropyl ring, both being rigid groups, although the second
is less voluminous. For the adenine derivative, the anti
conformer always converged into the syn one. This observation
is consistent with the fact that its structure could be considered
as the most voluminous of all the studied compounds.
(33) Lin-Vien, D.; Colthup, N. B.; Fateley, W. G.; Grassetti, J. G. The
Handbook of Infrared and Raman Characteristic Frequencies of Organic
Molecules; AP, Inc.: San Diego, CA, 1991; p 194.
To analyze the N-nitrosamine T diazoic acid tautomeric
equilibria (eq 1), optimization of the different structures was

Aliphatic Primary Nitrosamines
Organometallics, Vol. 27, No. 9, 2008 1991
Figure 6. DFT-optimized structures for coordinated nitrosamines (a-f) and diazoic acids (g-l) (B3LYP, DZVP basis sets for N, O, C, H,
Cl; LANL2DZ basis set and pseudopotential for Ir); phenyl (a and g), 2,2,2-trifluoroethyl (b and h), benzyl (c and i), n-butyl (d and j),
cyclopropyl (e and k) and 9-methyladenyl (model for the 9-octyladenyl) (f and l). For the g to l structures an intramolecular H bond
interaction is shown with dotted lines.
Table 2. Experimental and DFT (B3LYP, DZVP basis sets for N, O, C, H, Cl; LANL2DZ basis set and pseudopotential for Ir) Optimized
Structural Parameters for syn-[IrCl5(N-nitrosobenzylamine)]2- and Calculated Values for syn-[IrCl5(diazoic benzylic acid)]2- (distances are in Å
and angles in deg)
d(IrN)
d(NN)
d(NO)
d(NH) d(OH)
d(NC)
d(IrCltrans
)
(IrNO)
125.84
(IrNN)
117.28
(CNN)
122.09
X-ray parametersa
2.000
1.316
1.232
0.880
1.459
2.366
DFTb
syn-[IrCl5(PhCH2RNHNO)]2-(nitrosamine)
syn-[IrCl5(PhCH2RNNOH)]2-(diazoic acid)
2.003
2.022
1.344
1.240
1.228
1.383
1.038
1.017
1.436
1.450
2.427
2.414
128.27
117.61
115.52
126.83
121.84
118.20
a Data for (PPh4)2(syn-[IrCl5(N-nitrosobenzylamine)]) · 3H2O. b In Vacuo calculations.
Scheme 2. Nitrosation of Primary Amines: Nucleophilic Attack to NO+, Nitrosation Reaction Intermediates, and Products
Originated from Nucleophilic Atack to the Diazonium Salt (blue box); N-Nitrosamines Are Stabilized, Allowing Their Isolation
(red box)
the reaction itself partially avoided the nitrosamine decomposi-
tion. In the case of 2, the formation of benzyl alcohol and amine
complex was observed when the nitrosamine was kept in the
presence of the supernatant during one week, while for 1 or 5
the nitrosamine remained unaltered during weeks or months.
The amine complexes that in general precipitate from the media
are produced by substitution of the very labile coordinated
nitrogen molecule by the excess of amine present (see right side
of Scheme 2). Both products, coordinated amine and alcohol,
were observed by H NMR for 1 to 4 and have been isolated
for 2 and 3. Decomposition products derived from 5 are still
under analysis. As it was presented before, for the coordinated
N-nitrosocyclopropylamine (4), a variety of decomposition
products were found: ones originated by nucleophilic attack to
1

1992 Organometallics, Vol. 27, No. 9, 2008
Di SalVo et al.
Table 3. Products Obtained from the Reaction of the Coordinated
Nitrosamines KNH3R[IrCl5(NHNOR)] in the Presence of Strong
Acids or the Supernatant Generated in their Synthesis
the diazonium ion or to the alkyl cation and others produced
by elimination reactions that occurred in either the unaltered or
opened cyclopropyl ring. Apart from these compounds, the
precipitate KNH3(c-CHCH2CH2)[IrCl5(CH3CN)] · xCH3CN, re-
sulting from the displacement of the organic ligand by a solvent
molecule, was also found. This nitrosamine (4) was the only
one of the analyzed derivatives that showed this behavior. The
information found in the literature shows that traditional
nitrosation reactions2 of cyclopropylamine result in the formation
of several products, like the ones found in this reaction.34
products detected by 1H NMR
condition
and/or GC-MSa
solid nitrosamine kept in contact
with the CH3CN supernatant
RCH2OH, [IrCl5(RCH2NH2)]2- in a
1:1 ratio for 1, 2, 3 allyl alcohol,
cyclopropyl alcohol,
[IrCl5(RCH2NH2)]2- in a 0.5:0.5:1
ratio for 4
+
HCl
RCH2OH, RCH2Cl, RCH2NH3 for
1, 2, 3 in an approximate ratio of
0.9:0.1:1; also found 1–5% of
1-butene for 3
allyl alcohol, cyclopropyl alcohol,
cyclopropylamine in a 0.75:0.25:1
ratio for 4
Analyzing the fact that for most of the cases unrearranged
alcohols were exclusively observed as nitrosamine decomposi-
tion products, two important conclusions could be pointed out.
The first one is that, unless in the case of 4, due to the absence
of any organic chloride products, the Ir-Cl bond could be
considered as nonlabile, showing the outstanding inertness of
the [IrCl5]2- unit. A different situation was found when 2,2,2-
trifluoroethylamine or n-butylamine reacted with [Ru(bpy)2Cl-
(NO)]2+: the chloride derivatives 1-chloro-2,2,2-trifluoroethane
and 1-chlorobutane, respectively, were found as the main
reaction products.12e The same was observed when hydrochloric
acid solutions were added to an aqueous solution of the here-
presented coordinated nitrosamines (see later). The second
conclusion to be pointed out is related to the stabilization
experienced by the diazonium ions when coordinated to
[IrCl5]2-. Unrearraged alcohols found as products can only be
attributed to a concerted nucleophilic attack of hydroxide ion
to the coordinated diazonium ions; if they were released, they
would produce rearranged and elimination products (Scheme 1
and ref 12).
9-octyladenine,
cloro-9-octyladenine, and
unknown products for 5
RCD2OD, RCD2Cl for 1, 2
(confirmed by the absence of the
expected signal)b
DCl
CF3COOH
RCH2OH, RCH2OC(O)CF3,
RCH2NH3 for 1, 2, 3 in an
+
approximate ratio of 0.7:0.3:1;
also found 1–5% of 1-butene for 3
allyl alcohol, cyclopropyl alcohol,
cyclopropylamine in a 0.7:0.3:1
ratio for 4
9-octyladenine and unknown
products for 5
CF3COOH/KI
HClO4
RCH2OH, RCH2OC(O)CF3, RCH2I,
+
RCH2NH3 for 1, 2, 3
+
RCH2OH, RCH2NH3 for 1, 2, 3 in
an approximate ratio of 1:1
9-octyladenine and unknown
products for 5
The addition of strong acids accelerates the decomposition
of the nitrosamines. The high stability of 1 was demonstrated
when practically no changes were observed during weeks after
adding acetic acid or a few hours after the addition of
concentrated solutions of strong acids such as hydrochloric
(HCl), trifluoroacetic (TFA), or perchloric acid (HClO4).
Products formed in the presence of the mentioned acids were
a The high volatility of the products obtained from 1 and 4 made the
GC analysis very difficult, so this technique was only applied for 2, 4,
and 5. b These reactions were only performed for 1 and 2; a discussion
about the isotopic replacement will be included in the next section.
Nitrosation Mechanism. The first step in the nitrosation
reaction of primary amines corresponds to the formation of
primary nitrosamines (first step, Scheme 2). A very important
aspect that must be discussed to understand the complete
nitrosation reaction and/or nitrosamine decomposition pathway
is the tautomeric equilibrium that could take place in this context
(eq 1). When a nitrosating complex such as nitroprusside
([Fe(CN)5(NO)]2-) or [Ru(bpy)2Cl(NO)]2+12 was chosen to
perform this kind of reaction, the results were far different from
those observed in this work: those reactions did not end in a
nitrosamine product. As it was already introduced, for all the
nitrosyl complexes studied before in our laboratory, the stability
of the diazo compounds produced by nucleophilic addition of
amines to coordinated nitrosyl was inferred only through the
amounts of unrearranged products detected. For those cases,
none of the postulated diazo compounds derived from primary
amines could be isolated.12 In this sense, the nitrosamine could
be considered as an intermediate of these reactions, whose
separation from the reaction media was feasible due to the
inertness of [IrCl5]2- and the insolubility of the coordinated
nitrosamine.
1
analyzed by H NMR and by GC-MS (see Table 3). Together
with the nucleophilic attack products, free amines were also
observed probably due to hydrolysis of the amine complexes.
Another consequence of the presence of acid was related to the
formation of rearranged products detected for the more labile
nitrosamines, the ones derived from 3 and 4. In the case of the
cyclopropyl derivative 4, allyl alcohol was the major product,
and for the n-butyl derivative 3, small quantities of 1-butene
showed that probably a fraction of the nitrosamine or diazonium
ion was also labilized, resulting in these products. The mech-
anism of this reaction will be discussed in the next section.
The products obtained either when the coordinated nitro-
samines are attacked by strong acids or when they are kept in
the presence of the reaction supernatants are presented in Table
3. The corresponding alcohols are in most cases the major
products, and as it was already mentioned, amines were always
detected. Other products from nucleophilic attack were observed.
Alkyl chlorides, trifluoroacetates, and alkyl iodides were
detected in the presence of HCl, TFA, and TFA/I-, respectively.
The generation of esters could be attributed to the nucleophilic
attack of the trifluoroacetate ion. Rearranged products, allyl
alcohol and 1-butene, were only observed for the most labile
nitrosamines. In the particular case of 4, this observation was
promoted by the stability of the allyl radical.
When the nitrosamine remains in solution, the tautomeric
equilibrium involving the diazoic acid can take place (eq 1 and
central part in Scheme 2). Then, the diazoic acid is the
compound that allows the reaction to evolve to the formation
of the diazonium ion. So, taking apart the metal’s and coligands’
influence, the analysis of the diazoic acid acidity and its
proclivity to be dehydrated are the keys to understanding the
(34) (a) Roberts; J. D.; Chambers, V. C. J. Am. Chem. Soc. 1951, 73,
3176. (b) E. J. Corey, E. J.; Atkinson, R. F. J. Org. Chem. 1964, 29, 3703.

Aliphatic Primary Nitrosamines
Organometallics, Vol. 27, No. 9, 2008 1993
stability of the nitrosamines. In order to analyze the whole
mechanism in terms of the energy of each intermediate
compound, several steps must be taken into account: nitrosamine
formation (red box in central part of Scheme 2), diazoic acid
equilibrium, protonation of the -OH followed by dehydratation
of the diazoic acid, formation of the coordinated diazonium
shown in the central part of Scheme 2, and finally, decomposi-
tion of the last compound to form a dinitrogen complex and
the corresponding alcohol, mainly through a concerted nucleo-
philic attack reaction (right side of Scheme 2). Because the last
complex is not stable in solution, the amine or a solvent
molecule present in the media replaces the nitrogen molecule
to give the corresponding compound. As it was presented in
the previous section, if no other nucleophiles are added to the
reaction mixture, all the nitrosamines exhibit this behavior at
the end of the reaction pathway. When acids were added to
force the decomposition and to study the derived products,
alcohols were the major products again, but other products that
originated from nucleophilic attack to the diazonium were also
found (Table 3). As it was mentioned, in the central part of
Scheme 2 all the steps related to the formation of the coordinated
diazonium ions are shown and their decomposition is presented
to the right.
to the DFT data, it was even more stable that the trifluoroet-
hylamine one, a fact that is very difficult to prove experimentally
since both of them are extremely stable.
The first step in Figure 7 shows that the nitrosamines are
more stable than each corresponding diazoic acid. The higher
energies that correspond to the diazoate form suggest the
possibility that the generation of the diazonium ion could take
place directly from the diazoic acid through its protonation
([RNdN-OH2]+). That fact was indirectly confirmed by DFT
calculations because such intermediate structure never converged
resulting in the formation of diazonium ion and water. Here, it
is important to remark that the coordinated butyldiazonium is
the most stable with respect to the corresponding nitrosamine
in comparison to the other ones. This observation was also
demonstrated experimentally by the fact that although the butyl
carbocation is known to be a very unstable species, the products
derived from the decomposition of its nitrosamine were almost
100% unrearranged (see Table 3). The diazoalkanes derived
from the trifluoroethyl, benzyl, and n-butyl amines,36 which are
also included in Figure 7, showed energy values around 20 kcal/
mol higher than those corresponding to the diazonium ions.
These differences demonstrated that both competing pathways
are possible, but the diazonium one seems to be the most
favorable one at neutral pH. Finally, the very favorable steps
depicting the decomposition of each diazonium ion into the free
alcohols and nitrogen complexes are found to the right in Figure
7. For cyclopropylamine, cyclopropyl alcohol and the major
product found experimentally, allyl alcohol (at lower energy),
were both included. The adenine derivatives were included in
order to compare all the compounds studied in this work, but
as it was already mentioned, the identity of the decomposition
product obtained after adding acids to the coordinated nitro-
Fishbein et al. postulated the existence of another diazo
intermediate, which has not been mentioned in the previous
paragraph, the diazoalkane (R-CHdNdN), based on isotopic
labeling kinetic measurements of the decomposition pathway
of free (Z)-diazoalkanes.35 The incorporation of deuterium into
the ꢀ-carbon of the final decomposition product of diazo
compounds requires the intermediacy of a diazonium ion, which
can undergo proton exchange, competing with the hydrolysis
(eq 2).
When DCl (c) was used as an acid to force the decomposition
of the coordinated nitrosamines, deuterium incorporation was
observed (see Table 3). Although proton substitution was
complete, the nucleophilic attack pathway cannot be ruled out
since the excess acid acts as a driving force for the H+ exchange
and inhibits the nucleophile attack via its protonation.
In order to have more insight into the reaction mechanism,
energy calculations of the relevant species in Vacuo and in
acetonitrile using PCM schemes have been performed. In Figure
7, energies for the different intermediates corresponding to all
the studied amines are shown together (each value is referred
to the corresponding nitrosamine energy, taken as zero). A table
showing all the corresponding values for the in Vacuo and in
solvent model calculations is included in the Supporting
Information
First of all, it is important to remark that the stabilities for
the different nitrosamines agree very well with what has been
postulated in the first section based only on experimental
evidence: a greater stability of the nitrosamine derived from
2,2,2-trifluoroethylamine (1) with respect to the other aliphatic
ones (see Supporting Information). Calculations showed that
this nitrosamine was around 105 kcal/mol more stable than its
analogues. With respect to the adenine derivative (5), according
samine is still unknown. For the DFT calculations the chosen
final species was 3-methylhypoxantine, the tautomer of the
corresponding 3-methylpurinol.
Some amines form very stable carbocations. Consequently,
the dissociation of their diazonium salt complexes into the
corresponding species and nitrogen complex is highly favored.
Therefore, for such cases, smaller dissociation energies of the
N-C bonds are expected. In addition, once the carbocations
are released to the media, the observed behavior is the same as
that found for the free aliphatic diazonium salts: they are subject
to nucleophilic attack and to rearrangement and subsequent
nucleophilic attack or elimination reactions (Scheme 1). For
those cases, Scheme 2 must be completed with competing
reactions shown in Scheme 3.
DFT calculations were also performed to illustrate in a
quantitative way the stability of the carbocations and their
influences on the coordinated diazonium salt complexes. Table
4 shows the calculated C-N bond dissociation energy values
as well as relevant structural parameters for the studied
coordinated diazonium salt products. Results of some com-
pounds coordinated to [Fe(CN)5]3- are also included in order
(36) These diazoalkanes were the only ones tested for deuterium
incorporation by Fishbein et al. (refs 32 and 35).
(35) Finneman, J. I.; Fishbein, J. C. J. Am. Chem. Soc. 1996, 118, 7134.

1994 Organometallics, Vol. 27, No. 9, 2008
Di SalVo et al.
Figure 7. DFT-calculated energies (kcal/mol) in acetonitrile (PCM model) for the proposed intermediates of the nitrosation reaction (the
most relevant ones are depicted in square brackets).
Scheme 3. Competing Pathways to the Concerted Nucleo-
philic Attack to the Coordinated Diazonium Iona
Taking into account some structural parameters showed in Table
4, it can be seen that back-donation is more efficient for the
iron compounds where a larger electronic density is available
due to the presence of electron-rich cyanides. The very sensitive
d(NN) distances could be used as a parameter for quantifying
this fact; in the case of the iron compounds the resulting values
were found to be higher than for each corresponding iridium
analogue. Calculated charges also demonstrate important dif-
ferences between both nitrogen atoms present in the diazonium
ion ligand (-NtN). In all cases the nitrogen atom bound to
the organic structure presents lower charges, even negative ones
for the iron systems, in comparison with the nitrogen atom
bound to the metal.
a
Nucleophilic attack to the carbocation is indicated above and
rearrangement process results are depicted below. R′ represents
rearranged R, R′′ represents the products obtained through elimination
reactions (E).
to establish pertinent comparisons. Here again, a phenyl
derivative was also taken into account to complete the analysis.
The computed results clearly show the significant differences
that exist between diazonium ions coordinated to [Fe(CN)5]3-
or [IrCl5]2-. Regarding the C-N bond dissociation energy
values, iron compounds were more stable than their iridium
analogues. The stabilization of these positive ligands can be
understood in terms of the possibility of charge delocalization:
three different resultant resonant structures, I, II, and III, are
indicated in eq 3. In the cases where back-donation from the
metal center into the π* orbital of the diazonium ion is more
significant, the delocalization would be considerably favored.
The back-bonding effect could also be understood comparing
structural parameters and charges of the diazonium metal
complexes with those corresponding to the free ions, where for
the latter the C-N-N moieties are practically linear ( (CNN)
≈ 180°) and show a shorter N-N bond distance and much more

Aliphatic Primary Nitrosamines
Organometallics, Vol. 27, No. 9, 2008 1995
Table 4. Calculateda C-N Bond Dissociation Energy and Structural Parameters for [ML5(diazonium)]n– Products; M, L, n: Fe, CN, 2 or Ir,
Cl, 1
bond dissociation bond dissociation
NPAbcharges
N(-M or
not bound)
energy (in Vacuo)
energy (PCM)
(kcal/mol)
d(MN) d(NN) d(CN)
(Å) (Å) (Å)
(MNN)
(deg)
(CNN)
(deg)
diazonium product
(kcal/mol)
M
N(-C)
[Fe(CN)5(N2Ph)]2-
[Fe(CN)5(N2CH2CF3)]2- c
[Fe(CN)5(N2CH2C6H5)]2-
[Fe(CN)5(N2C4H9)]2-
[IrCl5(N2Ph)]–
286.05
308.12
231.10
253.03
206.12
221.40
150.12
56.45
49.34
49.65
7.59
16.62
38.76
33.64
-14.02
8.01
-8.79
14.09
40.80
29.23
-12.04
8.82
-0.183
-0.136
-0.145
-0.178
0.809
0.817
0.801
0.800
0.806
0.219
0.193
0.177
0.204
0.121
0.118
0.118
0.138
0.122
0.150
0.129
0.159
0.162
0.145
0.128
0.133
-0.045 1.662
-0.068 1.693
-0.140 1.683
-0.033 1.675
0.043 1.806
0.005 1.820
0.033 1.820
0.064 1.808
0.025 1.820
-0.093 1.784
0.296
1.187 1.421
1.186 1.473
1.179 1.506
1.176 1.492
1.168 1.420
1.171 1.479
1.163 1.523
1.160 1.485
1.168 1.451
1.176 1.413
1.115 1.383
1.104 1.455
1.112 1.508
1.105 1.480
1.110 1.398
1.110 1.418
175.4
160.1
169.0
173.4
173.8
161.2
165.8
178.0
164.3
171.4
127.2
119.7
121.8
123.7
133.0
123.1
125.2
134.5
126.6
131.0
180.0
179.8
172.9
176.5
179.7
180.0
[IrCl5(N2CH2CF3)]–
[IrCl5(N2CH2Ph)]–
[IrCl5(N2C4H9)]–
[IrCl5(N2(c-C3H5))]–
[IrCl5(N2(C6H5N4))]–
161.24
171.29
43.95
0.867
+
PhN2
+
CH2CF3N2
30.79
0.383
0.310
0.336
0.316
+
PhCH2N2
-15.09
+
C4H9N2
7.11
+
(c-C3H5)N2
-3.70
11.95
-3.83
11.85
+
(C6H5N4)N2
0.340
a B3LYP, DZVP basis sets for N, O, C, H, Cl and LANL2DZ basis set and pseudopotential for Ir. b See ref 30. c Although this amine does not react
with the iron complex, this diazonium salt was included in order to obtain complete comparisons.
positive charges on both nitrogen atoms. It can be concluded
that, in general, structures II and III are predominant with
respect to structure I for both series of diazonium ions
coordinated to the metal, while structure I is assigned to the
free ones.
ruthenium compounds to stabilize diazonium ions.12 In those
cases, the stabilization of the diazo compounds through coor-
dination could be inferred by analyzing the unrearranged to
rearranged product ratio for the nitrosation reactions of aliphatic
primary amines by transition metal nitrosyls.
In addition, the nature of the organic skeletons generates
important variations for the dissociation energies along each
series through the stabilization of the free carbocations. Radicals
such as benzyl and cyclopropyl (or allyl), clearly contribute to
favor the diazonium ion C-N bond breakage. As expected,
dissociation energies corresponding to these derivatives were
shown to be significantly lower than for the rest of the group.
Calculations also show that for all the coordinated diazonium
ions ∆E for their C-N bond dissociation reaction in vacuum
are much higher than for the free ions. However, in the presence
of a solvent (such as acetonitrile) the situation is reversed in
some cases, or both values are practically the same for others
(for example, [IrCl5(N2C4H9)]- vs N2C4H9+). This is mainly
due to a charge stabilization effect: the dielectric solvent more
effectively stabilizes the doubly or triply charged iridium or
iron products than the singly or doubly charged corresponding
diazonium ion complexes. The opposite situation occurs for the
decomposition reactions of the coordinated diazonium ions
derived from [Ru(bpy)2Cl(NO)]2+ when a solvent model is taken
into account; for these cases the singly charged products are
unstabilized with respect to the corresponding doubly charged
precursors.12b,e Consequently, the inclusion of the solvent in
the iridium and iron systems promotes the coordinated diazo-
nium ion decomposition; this effect was much more important
for the ones coordinated to the metals than for the free ions.
Nevertheless, back-bonding effects and the characteristic inert-
ness of iridium in particular were shown to be very important
factors in conferring stability to the diazonium ion derivatives.
In this work the capability of the [IrCl5]2- unit to stabilize
nitrosamines and diazonium compounds has been shown. The
isolation and full characterization of unstable compounds such
as primary nitrosamines derived from several aliphatic amines
was only possible due to the presence of this particular moiety.
The outstanding stabilization effect of this iridium coordination
sphere was also observed when the forced or spontaneous
decomposition of the coordinated primary nitrosamines took
place through clean reactions giving rise only to unrearranged
nucleophilic attack products. This fact clearly shows a very
strong stabilization of the diazonium ion coordinated to the
studied iridium moiety, which is attacked by nucleophiles
present in the media through concerted mechanisms.
Therefore, [IrCl5(NO)]- was shown to be an excellent reagent
with several important qualities. Concerning its reactivity, this
nitrosyl is considered the most reactive ever known,16b giving
the possibility to react with a huge variety of nucleophiles, and
finally, it is important to remark again on its capacity to stabilize
diazo derivatives.
Acknowledgment. This work was supported by the
ANPCYT, CONICET, UBA, and Fundación Antorchas.
Thanks are due to Prof. David Milstein for his help with the
X-ray facilities.
Supporting Information Available: Tables and graphics con-
taining DFT calculated structural parameters, energy values and
normal mode analysis for all the nitrosamines and some experi-
mental data comparisons are included. This material is available
free of charge via the Internet at http://pubs.acs.org.
Conclusions
Experimental and computational results previously found in
our laboratory have shown the ability of some iron and
OM700985H