Reaction of arylhydroxylamines with [Pd(Neoc)(NO3)2] (Neoc = neocuproine). Non-innocent behavior of the nitrate anion

Article abstract of DOI:10.1016/j.ica.2017.05.014

In an effort to understand the first stages of the reduction of nitroarenes to anilines by palladium/phenanthroline complexes and suspecting that arylhydroxylaminato complexes may be intermediates in this process, we investigated the reactivity of [Pd(Neoc)(NO₃)₂] (Neoc = neocuproine = 2,9-dimethyl-1,10-phenanthroline) with 3,5-dichlorophenylhydroxylamine. Spectroscopic evidence indicates that the desired [Pd(Neoc)(ONHC₆H₃Cl₂)(NO₃)] is indeed formed, but the complex is not stable and decomposes within a few hours. Two of the decomposition products were characterized by single crystal X-ray diffraction. They are a N-aryl-N-nitrosohydroxylaminato complex, [Pd(Neoc)(ON(3,5-C₆H₃Cl₂)NO)][NO₃] (major decomposition product) and a nitro-nitrate complex [Pd(Neoc)(NO₂)(NO₃)]. The results indicate that the nitrate ion is not innocent in the starting complex and oxidize hydroxylamine, being reduced itself to NO₂^? and NO.

Full text of DOI:10.1016/j.ica.2017.05.014

Inorganica Chimica Acta xxx (2017) xxx–xxx
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Research paper
Reaction of arylhydroxylamines with [Pd(Neoc)(NO ) ]
3
2
(
Neoc = neocuproine). Non-innocent behavior of the nitrate anion
Francesco Ferretti , Martino Rimoldi a,1, Fabio Ragaini a, , Piero Macchi b
a
⇑
a
Università degli Studi di Milano, Dipartimento di Chimica, via C. Golgi 19, 20133 Milano, Italy
University of Bern, Department für Chemie und BioChemie, Freiestrasse 3, CH 3012 Bern, Switzerland
b
a r t i c l e i n f o
a b s t r a c t
Article history:
In an effort to understand the first stages of the reduction of nitroarenes to anilines by palladium/phenan-
throline complexes and suspecting that arylhydroxylaminato complexes may be intermediates in this
Received 6 April 2017
Received in revised form 5 May 2017
Accepted 7 May 2017
Available online xxxx
process, we investigated the reactivity of [Pd(Neoc)(NO
phenanthroline) with 3,5-dichlorophenylhydroxylamine. Spectroscopic evidence indicates that the
desired [Pd(Neoc)(ONHC Cl )(NO )] is indeed formed, but the complex is not stable and decomposes
within a few hours. Two of the decomposition products were characterized by single crystal X-ray diffrac-
tion. They are a N-aryl-N-nitrosohydroxylaminato complex, [Pd(Neoc)(ON(3,5-C Cl )NO)][NO ] (major
decomposition product) and a nitro-nitrate complex [Pd(Neoc)(NO )(NO )]. The results indicate that the
3 2
) ] (Neoc = neocuproine = 2,9-dimethyl-1,10-
H
6 3
2
3
Dedicated to Dr. Carlo Mealli on occasion of
his 70th birthday.
6
H
3
2
3
2
3
Keywords:
Palladium
nitrate ion is not innocent in the starting complex and oxidize hydroxylamine, being reduced itself to
À
NO
2
and NO.
Arylhydroxylamines
Phenanthroline
Nitrate
Ó 2017 Elsevier B.V. All rights reserved.
Nitroarenes
1
. Introduction
Carbonylation reactions of nitroarenes to give isocyanates, car-
atmosphere, but decompose quickly in the presence of a proton
source, even a weak one like an alcohol, to generate arylamines.
Even if the palladium metallacycle appears to be able to generate
isocyanates under forcing conditions, kinetic measurements
clearly show that in the presence of alcohols or amines, this consti-
tutes at most a very minor pathway, most of the nitroarene being
again intermediately transformed into an arylamine [17,18]. The
steps leading from arylamine to carbonylated products have been
investigated in some depth both with ruthenium-DPPE
(DPPE = 1,2-bis(diphenylphosphino)ethane) [6,7] and palladium-
phenanthroline [18] complexes and, at least in these cases, are rel-
atively well understood. However, virtually nothing is known on
how arylamines are formed from the initial nitrosoarene com-
plexes. Imido (nitrene) complexes have often been proposed to
be intermediates in the reaction, especially in the older literature,
but no strong evidence in favor of an active role of such species in
the reactions has ever been obtained. In some cases, it has been
shown that trinuclear ruthenium or iron imido complexes previ-
ously supposed to play an active role in the formation of iso-
cyanates or amines from nitroarenes, actually play no role in
such transformations [12,13,25,26]. In recent years, we have
focused our attention on palladium-phenanthroline catalysts
because these systems are the most active for the carbonylation
of nitroarenes to give carbamates or ureas [14–17,27–32]. During
our studies we evidenced that the addition of acids increases the
bamates and ureas constitutes one of the most promising alterna-
tives to the use of phosgene for the industrial production of these
key intermediates [1–5]. The reaction is catalyzed under homoge-
neous conditions by many different transition metal complexes,
among which the most actively investigated are based on palla-
dium, rhodium or ruthenium. For all of the catalytic systems most
active in this transformation, it has been proven that the nitroarene
is intermediately reduced to the corresponding arylamine and only
at a later stage the latter is carbonylated [6–18]. It is generally
agreed that the nitroarene is reduced by CO to the corresponding
nitrosoarene, which should remain bound to the metal, either in
an
g
2
complex [19] or as part of a metallacycle that also includes
[8,9,20–24]. Although ‘‘on paper” it is easy to draw
CO and/or CO
2
mechanisms that lead to the direct evolution of aryl isocyanates
from the isolated metallacycles, this does not appear to be a possi-
ble, or at least a catalytically relevant pathway. The isolated ruthe-
nium [20] and rhodium [8,9] metallacycles are stable in a CO
⇑
Corresponding author.
E-mail address: fabio.ragaini@unimi.it (F. Ragaini).
Present address: Northwestern University, Department of Chemistry, 2145
1
Sheridan Road, Evanston, IL 60208, United States.
http://dx.doi.org/10.1016/j.ica.2017.05.014
0
020-1693/Ó 2017 Elsevier B.V. All rights reserved.
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2
F. Ferretti et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
selectivity towards carbonylated products, whereas the presence
of bases, even a large excess of basic phenanthroline ligands,
boosts the formation of azo- and azoxyarenes as byproducts. Since
carbonylated products derive from intermediately formed arylami-
nes, one role of the acid may be that of influencing the formation of
the latter. On the other hand, the addition of bases has a positive
effect on the outcome of several reactions in which an intermedi-
ately formed nitrosoarene couples with an unsaturated group
and its complete reduction to aniline must be avoided [33,34].
A simplified reaction scheme leading from a nitrosoarene com-
plex to aniline in the presence of CO and an acid is shown in
Scheme 1. More possibilities can be envisaged if one considers that
the acid counteranion may attack a coordinated CO rather than
directly the metal.
Very few palladium complexes featuring structure A are known
[
35–37], none with nitrogen ligands. A nickel complex featuring
structure B has been very recently reported [38], but we are not
aware of any palladium complex with this structure. However,
the idea that the nitrogen ligand in an [L
has a tendency to interact with other electrophilic centers even
without disrupting its coordination to palladium is supported
by the existence of several polynuclear complexes in which the
nitrosoarene is bridging two palladium atoms in a way
39,40]. We are also not aware of any palladium complex having
n 2
Pd(g -ArNO)] complex
g
2
2 1
g -g
[
a
1
g –ONHAr ligand like in structure C. However, this kind of ligand
is known for other metals [41].
Several attempts in our group to synthesize a palladium-
phenanthroline nitrosoarene complex (type
A complex in
Scheme 1) by reaction of palladium(0) phenanthroline complexes
with nitrosoarenes always yielded insoluble polymeric materials.
The only indication on the composition of the product of the reac-
tion between [Pd(Phen)(dba)] (dba = dibenzylideneacetone) and
PhNO is the elemental analysis, indicating a composition [Pd
2
(-
Scheme 1.
Phen) (PhNO) [42,43]. Thus, we tried to isolate putative inter-
2
3 n
]
mediates B or C in Scheme 1 by reaction of a palladium(II)
phenanthroline complex with an arylhydroxylamine rather than
from a palladium(0) complex and a nitrosoarene. As a starting
point we used a complex of 2,9-dimethyl-1,10-phenanthroline
3
remains in the flask. If the reaction is performed in CDCl , the same
stoichiometry is observed. The NMR spectrum of the solution after
the addition of one or two equivalents of hydroxylamine is very
similar, indicating that no intermediate products are formed and
two equivalents of hydroxylamine are required to obtain the first
(
neocuproine, Neoc) rather than one of simple phenanthroline
because this ligand previously allowed us to observe, and even iso-
late, some intermediate complexes that could not be directly
observed when using unsubstituted phenanthroline as the ligand
3
observable complex. The solubility of 1 in CDCl is so low that its
signals are not observable by NMR. The only clearly observable sig-
nals are due to a complex (2) that contains a neocuproine ligand in
a non-symmetric coordination environment and an equivalent
amount of monodeprotonated hydroxylamine. Two signals in 2:1
ratio and a very broad one are always present, that can be ascribed
to the formation of 3,5-dichlorophenylhydroxylammonium nitrate,
by deprotonation of the first equivalent of hydroxylamine by the
second one, exchanging with an unreacted neutral form in solu-
tion. The experiment was performed several times by adding even
larger amounts of hydroxylamine. In all cases, the signals related to
complex 2 discussed above were observable at the beginning of the
reaction. The position of the broad peak and of those attributed to
the hydroxylammonium nitrate shifts depending on the concentra-
tion of the hydroxylamine, in accord with a fast proton exchange
with excess hydroxylamine.
[
18,29]. Nitrate was employed as the anion because this is the least
coordinating anion among those which allow the synthesis of a
complex with composition [Pd(Neoc)X
2
] [44,45]. With even less
À
coordinating anions, e.g. BF
Neoc) ][X]
4
, only complexes of composition [Pd
(
2
2
can be obtained and we deemed that substitution of
a chelating nitrogen ligand in these systems may be more difficult.
However, we found nitrate not to be an innocent anion/ligand dur-
ing the reaction and some unexpected results have been obtained
that will be described in this work.
2
. Results and discussion
3 2
2.1. Reactions of [Pd(Neoc)(NO ) ] with 3,5-dichlorophenylhydroxy-
lamine
The NMR spectrum of the main species in solution (2) is consis-
tent with a hydroxylaminato complex, but the observed signals
cannot discriminate between a structure of type B or C in
Scheme 1.
3
,5-Dichlorophenylhydroxylamine was chosen as a reagent
because it is our and others experience that the presence of chlo-
rine atoms on the aryl ring stabilizes complexes related to those
expected in this work and, most importantly, affords complexes
Addition of benzene to the reaction solution a few minutes after
the addition of two equivalents of hydroxylamine and concentra-
tion of the reaction mixture resulted in the precipitation of a solid
that crystallize more easily [9,19]. [Pd(Neoc)(NO
insoluble in CH Cl , but dissolves quickly upon addition of 3,5-Cl
NHOH. At least two equivalents of hydroxylamine are
required to complete the reaction, otherwise undissolved
3 2
) ] (1) is almost
+
2
2
2
-
that was immediately analyzed by mass spectroscopy (FAB ). The
C H
6 3
only clearly observable group of peaks perfectly matches the mass
+
1
and isotopic distribution of the [Pd(Neoc)(ONHC
H
6 3
Cl
2
)] fragment
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F. Ferretti et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
3
(Fig. S2). This observation strongly supports our proposal for the
composition of 2, but again does not allow a definitive conclusion
on the structure since the nitrate ligand, if coordinated, is expected
to be very labile and may be easily lost under the mass analysis
conditions. Analysis of the same precipitate by IR spectroscopy,
on the other hand, supports a structure of type C for 2. The coordi-
nated nature of the NO
absorption bands at 830–825 cm
3
ligand is suggested by the lack of IR
À1
typical of free nitrate ion
[
7
1
46,47] and by the presence of strong bands at 807 and
À1
92 cm , a broad weak one at 993, and a medium one at
À1
270 cm that can be attributed to a O-coordinated NO
3
group
))(NO )].
Unfortunately, we have been unable to obtain crystals of 2 suit-
[
44,46,47]. Complex 2 is thus [Pd(Neoc)(ONH(3,5-C
6
3
H Cl
2
3
Fig. 1. ORTEP plot of [Pd(Neoc)(ON(3,5-C
6
H
3
Cl
2
)NO)][NO
3
] in 3. Solvent molecules
able for X-ray diffraction analysis. This is partly due to the instabil-
ity of 2 both in solution and in the solid state. Indeed, when a
solution of 2 is left at RT for several hours, a yellow/orange precip-
of CHCl3 and H atoms are omitted for the sake of clarity. Ellipsoids are drawn at 50%
À
probability level. The (NO
3
)
anion is not coordinated to the metal complex.
3
itate invariably forms. In one case, from a CDCl solution stored at
crystals of a new complex, 4, formed. Single crystal X-ray analysis
of 4 showed it to be an unusual nitro-nitrato complex (Fig. 2).
The structure of 4 is described in more details in the following
paragraph. What is important to evidence here is that the isolation
of this compound leads strong support to the idea that the NO moi-
ety in 3 derives from the reduction of a nitrate ion. Such scenario
also indirectly supports the conclusion drawn from the IR spectra
that the nitrate ion is coordinated in 2. Indeed, coordinated nitrate
should be a stronger oxidant than the free anion and the cis dispo-
sition of the hydroxylaminato and nitrate anions forced by the
chelating ligand is ideally suited to promote an interaction
between the two. Scheme 2 summarizes the results obtained.
À20 °C, some crystals were present which were suitable for X-ray
diffraction analysis. The characterized compound, 3, is a N-aryl-N-
nitrosohydroxylaminato complex, [Pd(Neoc)(ON(3,5-C
6 3 2
H Cl )NO)]
[
NO ], in which a nitrosoarene moiety is coupled with a nitrogen
3
oxide molecule (Fig. 1). A more detailed description of the solid
state structure of this compound is given in the following
paragraph.
Complex 3, as well as the analogous palladium phenanthroline
complexes, have not previously been reported in the literature but
several complexes are known featuring a -ON(Ar)NO- ligand. In
most cases, they were obtained by reaction of a nitrosoarene com-
plex with NO (for an example of a palladium complex see [48]),
although in some cases the preformed anionic ligand, a stable
organic molecule, was employed (for an example of a palladium
complex see [49]).
2.2. Crystal structure of [Pd(Neoc)(ON(3,5-C
[Pd(Neoc)(NO )(NO )] (4)
6 3 2 3
H Cl )NO)][NO ] (3) and
3
2
When the reaction was conducted for a prolonged time (4 h) in
CH
2
Cl
2
, a sample of the bulk of the solid precipitated by the addi-
Both compounds feature a square planar Pd(II) metal ion and a
distorted neocuproine ligand. The two Pd–N bond length are very
close, although no molecular (nor of course any crystal) symmetry
tion of benzene, not a single crystal, was subjected to mass analysis
+
+
(
6 3 2
FAB ). Only the peaks due to the [Pd(Neoc)(ON(3,5-C H Cl )NO)]
ion could be identified clearly, supporting the view that the ana-
lyzed single crystal is not a minor component of the solid, but a
major one.
exists. In Figs. 1 and 2, the molecular geometries of the two com-
À
plexes are shown. For 3, the nearest (NO
3
)
non-coordinated coun-
terion is also shown, whereas clathrated solvent molecules are
omitted.
When the reaction between 1 and 3,5-Cl
formed in the presence of one equivalent of triethylamine, in
CDCl , just a 10% molar excess of hydroxylamine with respect to
2 6 3
C H NHOH was per-
In 3, the similarity of the coordination by the two oxygens of the
N-aryl-N-nitrosohydroxylaminato moiety to Pd, makes also the
neocuproine ligand more symmetrically attached to Pd. As a mat-
ter of facts, Pd1–O20 and Pd1–O21 distances are almost identical
(1.991(3) and 2.003(3) Å, respectively), and so are Pd1–N1A and
Pd1–N1B (2.041(3) and 2.031(3) Å, respectively). The ONN(Ar)O
system is very delocalized, in fact N20-O20 is just slightly longer
than N(21)–O(21) (1.336(4) Å and 1.300(4) Å, respectively) and
N20–N21 is 1.273(5) Å, which would be a rather short distance
for a N–N single bond. This high delocalization justifies the rather
similar Pd-O bonds. On the other hand, the N(20)–Ar distance is
quite long (1.439(5) Å), indicating a clearly localized C–N single
bond.
3
1
palladium was sufficient to complete the reaction. The H NMR
spectrum of the solution showed the signals due to complex 2
(
Fig. S1). No broad peaks were detected and just very small peaks
related to non-coordinated hydroxylamine were present. In addi-
tion, two peaks related to Et N were detected (quartet at 3.16
and triplet at 1.35 ppm) whose chemical shift are typical of triethy-
lammonium salts in CDCl (quartet at around 3.1 and triplet at
around 1.3 ppm, free Et N: 2.53 (q), 1.03 (t) ppm). This result con-
3
3
3
firms that the second equivalent of hydroxylamine required to
complete the reaction when no other reagent is added is simply
acting as a base and is not necessary if another, stronger, base is
present.
In 4, the coordination of nitro and nitrato ligands is quite differ-
ent. Pd1–N41 (2.016(7) Å) is in perfect agreement with the average
distance in –NO coordinated Pd complexes (2.018(2) Å), as found
2
3 2
Crystalline 3 is insoluble in CDCl , but soluble in D O and a
1
clean H NMR spectrum could be obtained by dissolving some sin-
gle crystals in the latter solvent (Fig. S3). The spectrum is in accord
with the structure determined by X-ray diffraction.
in the Cambridge crystallographic database [52]. The coordination
to the nitrate oxygen is instead shorter than the average from the
Cambridge crystallographic database (2.030(7) vs. 2.080(5) Å).
The difference between the two bonds produces a slight asym-
metry also in the coordination of neocuproine. In fact, Pd1–N1A,
which is trans to the nitro-ligand, is slightly longer than Pd1–
N1B (2.064(5) vs. 2.029(6) Å), which is trans to the nitrate ligand.
The steric effect of the methyl groups is quite evident in the
angle between the average plane of the neocuproine ligand and
the square plane defined by the Pd and the four atoms attached
The origin of the NO moiety in 3 is not obvious at this stage. The
nitrate anion is clearly a candidate, but a NO group may also derive
from a decomposition of hydroxylamine. Loss of the –NO group
2
from nitroarenes is known to occur in some cases [50] and NO loss
from nitroso compounds is also known, albeit it usually requires
irradiation [51]. A piece of information on this point was obtained
fortuitously when a CH
two equivalents of 3,5-Cl
2
Cl
C H
2 6 3
2
solution obtained by reacting 1 with
NHOH was stored at À20 °C. A few
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4
F. Ferretti et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
[
Pd(Neoc)
2 2
][X] , the latter type being invariably obtained with
À
À
6
non-coordinating anions like BF
4
or PF . However, its oxidizing
power was underestimated and caused an easy decomposition of
the complex. Future studies will focus on the use of non-oxidizing
counteranions.
4
. Experimental section
4.1. Methods and materials
All the syntheses were performed under a dinitrogen atmo-
sphere using standard Schlenk techniques. CH
distilled over CaH and stored under a dinitrogen atmosphere.
THF and benzene were distilled over sodium/benzophenone ketyl
and stored under a dinitrogen atmosphere. [Pd(Neoc)(NO ] was
synthesized as previously reported by us [45]. CDCl was passed
over basic alumina, degassed and kept over activated 4 Å molecu-
lar sieves under an inert atmosphere (N ). All the other reagents
2 2 3
Cl and Et N were
2
Fig. 2. ORTEP plot of [Pd(Neoc)(NO
atoms are omitted. Ellipsoids are drawn at 50% probability level. Here, the (NO
directly coordinated to the metal.
3
)(NO
2
)] (4). Solvent molecules of CH
2
Cl
2
and H
À
3
)
is
3 2
)
3
to it: 15(1)° in 3 and 28(1)° in 4. Moreover, in 4, the steric hin-
drance between NO and NO groups, makes their planes almost
vertical with respect to the coordination plane of the Pd atom
2
2
3
were purchased form Sigma Aldrich and used without further
purification. All glassware and magnetic stirring bars were kept
in an oven at 125 °C overnight and let to cool under vacuum before
(
69(1)° and 80(1)°, respectively).
Despite not directly coordinated to the Pd atom, the nitrate
group in 3 is packed close to the complex, forming weak interac-
tions with the N-aryl-N-nitrosohydroxylaminato group. Additional
interactions of the nitrate are formed with the CHCl molecules.
3
The complex, instead, features a weak antiparallel stacking with
1
use. H NMR spectra were recorded on a Bruker Avance DRX 300 or
on a Bruker Avance DRX 400. Chemical shifts are reported in ppm
relative to TMS. Elemental analyses were performed on a Perkin
Elmer 2400 CHN elemental analyzer. IR spectra were registered
on a Varian Scimitar FTS-1000.
À
another complex molecule, so that the motif (NO
3
) Á Á ÁONN(Ph)
À
OÁ Á ÁON(Ph)NOÁ Á Á(NO
3
)
is recognizable. In 4, almost all inter-
Cl
interactions.
molecular interactions are mediated by the co-crystallized CH
with the only exception of some weak C–HÁ Á ÁO–NO
2
2
,
4.2. Synthesis of N-(3,5-dichlorophenyl)hydroxylamine
2
The synthesis was performed by a modification of a previously
3
. Conclusions
reported method [53]. 3,5-Dichloronitrobenzene (1.011 g,
.26 mmol) was dissolved in THF (50 mL) in a three-neck flask.
5
Our study was aimed at isolating and characterizing a palla-
10% Pd/C (0.110 g) was added under nitrogen while stirring. After
cooling to 0 °C with an ice bath, 35 wt.% hydrazine in water
(1.2 mL, 13.2 mmol) was added and the mixture stirred for 1 h.
The end of the reaction was check by TLC (EtOAc/Hexanes = 3:7).
The reaction mixture was filtered through Celite and the volatiles
removed by rotary evaporation to afford a yellow solid. The pro-
dium arylhydroxylaminato complex with a phenanthroline-type
ligand. The results were only partly successful because the desired
complex was apparently obtained indeed, but was not stable
enough to be isolated in a pure form and characterized by X-ray
diffraction. On the other hand, two of the decomposition products
could be identified clearly and give a plausible picture of what is
occurring in solution. Retrospectively, the choice of nitrate as a
counterion for palladium was not the right one. It had been chosen
because it was considered to be the most labile anion still able to
2 2 2 4
duct was dissolved in CH Cl and dried over Na SO . Filtration
and evaporation of the solvent afforded the hydroxylamine in
90% yield (0.846 g, 4.75 mmol). The product was stored under
1
nitrogen at À20 °C to avoid decomposition. H NMR (300 MHz,
allow the isolation of a complex of type [Pd(Neoc)(X)
2
] instead of
3
CDCl ): d 6.94 (s, 1H), 6.88 (s, 2H), 6.78 (br s, 1H, OH), 5.23 ppm
Scheme 2.
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F. Ferretti et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
5
À2
(
br s, 1H, NH). The NMR spectrum was in accordance with that pre-
ylamine (9.1 mg, 5.1 Â 10 mmol) was added while stirring. The
initial complex 1 is only partially dissolved even after 5 min. The
viously reported [54]. Elem. Anal calcd for C Cl NO: C 40.48, H
H
6 5
2
2
.83, N 7.87; found: C 40.69, H 2.71, N 8.05.
initial complex dissolves completely only after addition of triethy-
À2
lamine (7.5
l
L, 5.4 Â 10 mmol). The mixture was immediately
1
1
4.3. Reaction of [Pd(Neoc)(NO ] (1) with variable amounts of N-(3,5-
)
3 2
analyzed by H NMR. H NMR (400 MHz, CDCl
1H), 8.49 (d, J = 8.3 Hz, 1H, CH Neoc), 8.37 (d, J = 8.2 Hz, 1H, CH Neoc),
.91 (d, J = 8.6 Hz, 1H, CH Neoc), 7.85 (d, J = 8.6 Hz, 1H, CH Neoc), 7.80
3
) d 11.02 (br s,
dichlorophenyl)hydroxylamine in CDCl
3
7
In an NMR tube, 1 (5.0 mg,) was suspended in CDCl
under nitrogen. A CDCl (25 L) solution of N-(3,5-dichlorophe-
nyl)hydroxylamine (1 equivalent) was added. The initial complex
did not dissolve completely. A second equivalent of hydroxy-
3
(1.5 mL)
(s, 2H, CH Ar), 7.76 (d, J = 8.2 Hz, 1H, CH Neoc), 7.63 (d, J = 8.3 Hz, 1H,
CH Neoc), 7.29 (s, 1H, CH Ar), 2.81 (s, 3H,CH3 Neoc), 2.72 ppm (s, 3H,
CH3 Neoc). Additional signals related to species derived from N-(3,5-
dichlorophenyl)hydroxylamine: 6.80 (s), 6.75 ppm (s). Triethylam-
monium salt: 3.25–3.11 (m, 6H), 1.35 ppm (t, J = 7.2 Hz, 9H).
3
l
1
lamine was added and the tube thoroughly shaken. Complex 1 dis-
solved almost completely. Addition of 2 more equivalents of
hydroxylamine did not lead to any appreciable change in the
1
4.6. Single crystal X-ray diffraction
aspect of the reaction mixture. H NMR spectra were recorded after
1
every addition. H NMR after addition of 1 equiv. of Cl
(
8
2
C
6
H
3
NHOH
) d 11.47 (br s, 1H), 8.46 (d, J = 8.4 Hz, 1H, CH Neoc),
.38 (d, J = 8.4 Hz, 1H, CH Neoc), 7.89 (d, J = 9.1 Hz, 1H, CH Neoc), 7.85
For both crystal species, the samples were mounted in air at
ambient conditions and measured at ambient temperature. All
300 MHz, CDCl
3
measurements were made on
diffractometer [55] using graphite monochromated Mo K
a
Bruker-APEXII area-detector
radia-
(
d, J = 9.1 Hz, 1H, CH Neoc), 7.78 (d, J = 8.3 Hz, 1H, CH Neoc), 7.73 (s,
a
2
H, CH Ar), 7.65 (d, J = 8.4 Hz, 1H, CH Neoc), 7.29 (s, 1H, CH Ar),
tion (k = 0.71073 Å). The unit cell constants and an orientation
matrix for data collection were obtained from a least-squares
refinement of the setting angles of strongest reflections. The
2
.81 (s, 3H, CH3 Neoc), 2.68 ppm (s, 3H, CH3 Neoc). Additional signals
due to protonated N-(3,5-dichlorophenyl)hydroxylamine possibly
in exchange with the free one: 6.92 (s, 2H), 6.88 ppm (s, 1H) and
a broad signal shifting from 9.1 to 7.4 ppm depending on the
hydroxylamine concentration were present. From one reaction
frames were collected using
x scans, with 40 s (for 3) and 60 s
(
for 3) exposure time per frame, a rotation angle of 0.5° per frame,
a crystal-detector distance of 50.0 mm.
performed with 2 equivalents of hydroxylamine in CDCl
stored at À20 °C, single crystals of 3 suitable for X-ray diffraction
were obtained. The crystals were insoluble in CDCl , but soluble
O and a clean H NMR spectrum of 3 could be obtained this
3
and
Data reduction was performed using the APEX2 program. The
intensities were corrected for Lorentz and polarization effects,
and an absorption correction based on the multi-scan method
using SADABS [56].
The structure was solved by direct methods using SHELXT [57],
which revealed the positions of all non-hydrogen atoms of the title
compound. All non-hydrogen atoms were refined anisotropically
3
1
in D
2
1
way: H NMR (300 MHz, D
.34 (d, J = 8.1 Hz, 1H, CH Neoc), 7.79–7.66 (m, 3H, CH Ar and CH
Neoc), 7.58 (d, J = 8.1 Hz, 1H, CH Neoc), 7.52 (d, J = 9.0 Hz, 1H, CH Neoc),
2
O) d 8.45 (d, J = 9.0 Hz, 1H, CH Neoc),
8
7
.43 (s, 2H, CH Ar), 2.79 (s, 3H, CH3 Neoc), 2.70 ppm (s, 3H, CH3 Neoc).
(
including solvent molecules). All H-atoms were placed in geomet-
rically calculated positions and refined using a riding model where
each H-atom was assigned a fixed isotropic displacement parame-
ter with a value equal to 1.2 Ueq of its parent atom.
4
.4. Reaction of [Pd(Neoc)(NO
3
)
2
] (1) with 2 eq. of N-(3,5-dichloro-
phenyl)hydroxylamine in CH
2
Cl
2
2
Refinement of the structure was carried out on F using full-
In an oven-dried Schlenk tube, 1 (21.8 mg, 0.05 mmol) was sus-
pended in CH Cl (8 mL) and N-(3,5-dichlorophenyl)hydroxy-
matrix least-squares procedures, which minimized the function
2
2
2
2 2
R
w(F
o
À F
c
) . The weighting scheme was based on counting statis-
lamine (18.6 mg, 0.10 mmol) was added while stirring. The initial
complex 1 dissolves almost immediately. Stirring was continued
for 15 min after which only a very little amount of insoluble solid
was present. The mixture was filtered by cannula technique. Part of
the solution was separated and cooled at -20 °C. Benzene (10 mL)
was added to the remaining part and the reaction concentrated
under vacuum until a yellow solid precipitated. The solid was col-
lected by filtration on a sintered frit under nitrogen, washed with
benzene (2 mL) and immediately analyzed by FAB MS (glycerol
tics and included a factor to downweight the intense reflections.
All calculations were performed using the SHELXL-2014/7 [58]
program.
Data collection and refinement parameters are given in Tables
S1 and S5. Details of the refined models are reported in Tables
S2–S4 and S6–S8.
CCDC 1540684 and 1540685 contain the supplementary crys-
tallographic data for this paper. The data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/structures.
1
matrix) and H NMR. MS (FAB): m/z 492 (calcd. for [Pd(Neoc)
+
(
ONHC
6
3
H Cl
2
)] = 492. See the Supporting information for a com-
parison between the experimental isotopic pattern and the calcu-
lated one). Single crystals of [Pd(Neoc)(NO )(NO )] (4) were
3
2
Acknowledgements
obtained from the part of the solution stored at À20 °C.
2 2
An analogous reaction was performed stirring the initial CH Cl
We thank Dr. Nicola Casati for help in the X-ray diffraction anal-
ysis, the Ministero dell’Università e della Ricerca (MiUR, PRIN
reaction mixture for 4 h. After addition of benzene (8 mL) and con-
centration of the reaction mixture, an orange/yellow solid was
2
1
0154X9ATP) and the Swiss National Science Foundation (project
60157) for financial support. F.F. thanks the University of Milano
obtained that was dried under vacuum for several hours. MS
+
(
FAB): m/z 521 (calcd for [Pd(Neoc)(ON(3,5-C
6
3
H Cl
2
)NO)] = 521.
for a postdoctoral fellowship.
See the Supporting information for a comparison between the
experimental isotopic pattern and the calculated one.).
Appendix A. Supplementary data
4
.5. Reaction of [Pd(Neoc)(NO
3 2
) ] (1) with N-(3,5-dichlorophenyl)
hydroxylamine using E N as external base
3
Copies of 1H NMR and mass spectra, crystallographic material
for compounds 3 and 4. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.ica.2017.05.014.
À2
In an oven-dried Schlenk tube, 1 (20.6 mg, 4.7 Â 10 mmol)
was suspended in CDCl (8 mL) and N-(3,5-dichlorophenyl)hydrox-
3
Please cite this article in press as: F. Ferretti et al., Inorg. Chim. Acta (2017), http://dx.doi.org/10.1016/j.ica.2017.05.014

6
F. Ferretti et al. / Inorganica Chimica Acta xxx (2017) xxx–xxx
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