Platinum(IV)-mediated nitrile-amidoxime coupling reactions: Insights into the mechanism for the generation of 1,2,4-oxadiazoles

Article abstract of DOI:10.1002/cplu.201100047

The nucleophilic addition of amidoximes R'C(NH₂)=NOH (4: R'=Me, 5: CH₂Ph, 6: Ph) to coordinated nitriles in the platinum( IV) complexes trans-[PtCl₄(RCN)₂] (1: R=Et, 2: Ph, 3: NMe ₂) proceeds in a 1:1 molar ratio and leads to the monoaddition products [PtCl₄(RCN){HN=C(R)ONC(R')NH₂}] (7: R/R': Et/CH₂Ph, 8: Et/Ph, 9: NMe₂/CH₂Ph, 10: NMe ₂/Ph). Meanwhile, if the nucleophilic addition proceeds in a 2:1 molar ratio the reaction gives the bisaddition species [PtCl₄{HN=C(R) ONC(R')NH₂}₂] (11: R/R'=Et/Me, 12: Et/CH₂Ph, 13: Et/Ph, 14: Ph/Ph, 15: NMe₂/Me, 16: NMe₂/CH ₂Ph, 17: NMe₂/Ph). All complexes 7-17 bear nitrogen-bound O-iminoacylated amidoxime groups. The addition of one equivalent of the corresponding amidoxime to each of 7-10 leads to 12, 13, 16, and 17, respectively. Complex [PtCl₄(NCNMe₂){HN=C(NMe ₂)-ONC(Ph)NH₂}] (10), when dissolved in MeNO₂, gave mer-[PtCl₃-{HN=C(NMe₂)ONC(Ph)NHC(NMe ₂)=NH}] (18) with the newly formed tridentate ligand derived from an unexpected coupling between two Me₂NCN ligands and the N and the O centers of the amidoxime. The O-imidoylamidoxime compounds R'C(NH ₂)=NOCR(=NH) (19-25) were liberated from the corresponding complexes 11-17 by treatment with excess NaCN and these metal-free species were characterized by ¹H and ¹³C{¹H} NMR spectroscopy. The conversion of 19-25 into the 3,5-substituted 1,2,4-oxadiazole compounds O^aN=C(R')N= C^b(R)(^a-b) (26: R/R'=Me/Et, 27: PhCH₂/Et, 28: Ph/Et, 29: Ph/Ph, 30: Me/NMe ₂, 31: PhCH₂/NMe₂, 32: Ph/NMe₂) occurs at room temperature and the cyclization is promoted by strong acceptor substituents R'.

Full text of DOI:10.1002/cplu.201100047

DOI: 10.1002/cplu.201100047
Platinum(IV)-Mediated Nitrile–Amidoxime Coupling
Reactions: Insights into the Mechanism for the Generation
of 1,2,4-Oxadiazoles
Dmitrii S. Bolotin,[a] Nadezhda A. Bokach,*[a] Matti Haukka,[b] and Vadim Yu. Kukushkin*[a, c]
The nucleophilic addition of amidoximes R’C(NH2)=NOH (4:
R’=Me, 5: CH2Ph, 6: Ph) to coordinated nitriles in the plati-
num(IV) complexes trans-[PtCl4(RCN)2] (1: R=Et, 2: Ph, 3:
NMe2) proceeds in a 1:1 molar ratio and leads to the monoad-
dition products [PtCl4(RCN){HN=C(R)ONC(R’)NH2}] (7: R/R’: Et/
CH2Ph, 8: Et/Ph, 9: NMe2/CH2Ph, 10: NMe2/Ph). Meanwhile, if
the nucleophilic addition proceeds in a 2:1 molar ratio
ONC(Ph)NH2}] (10), when dissolved in MeNO2, gave mer-[PtCl3-
{HN=C(NMe2)ONC(Ph)NHC(NMe2)=NH}] (18) with the newly
formed tridentate ligand derived from an unexpected coupling
between two Me2NCN ligands and the N and the O centers of
the amidoxime. The O-imidoylamidoxime compounds
R’C(NH2)=NOCR(=NH) (19–25) were liberated from the corre-
sponding complexes 11–17 by treatment with excess NaCN
the reaction gives the bisaddition species [PtCl4{HN= and these metal-free species were characterized by 1H and
C(R)ONC(R’)NH2}2] (11: R/R’=Et/Me, 12: Et/CH2Ph, 13: Et/Ph,
14: Ph/Ph, 15: NMe2/Me, 16: NMe2/CH2Ph, 17: NMe2/Ph). All
complexes 7–17 bear nitrogen-bound O-iminoacylated ami-
doxime groups. The addition of one equivalent of the corre-
sponding amidoxime to each of 7–10 leads to 12, 13, 16,
and 17, respectively. Complex [PtCl4(NCNMe2){HN=C(NMe2)-
13C{1H} NMR spectroscopy. The conversion of 19–25 into the
3,5-substituted 1,2,4-oxadiazole compounds OaN=C(R’)N=
Cb(R)(a–b) (26: R/R’=Me/Et, 27: PhCH2/Et, 28: Ph/Et, 29: Ph/Ph,
30: Me/NMe2, 31: PhCH2/NMe2, 32: Ph/NMe2) occurs at room
temperature and the cyclization is promoted by strong accept-
or substituents R’.
Introduction
1,2,4-Oxadiazole derivatives represent an important class of
five-membered heterocycles, and their versatile chemistry has
been repeatedly reviewed over the years.[1] The increased
number of publication about the oxadiazoles relates to the im-
portance of these heterocycles and their derivatives in both
materials chemistry (e.g. they serve as components of
polymers,[1a] liquid crystals and ionic liquids,[1a,2] lumines-
cent[1a,2c] and optoelectronic materials,[1a] and corrosion inhibi-
tors[3]) and medicinal chemistry[1a,4] (e.g. they are applied as an-
tidiabetic,[1a] antiinflammatory,[1a,5] antimicrobial,[1a,2a,6] antitu-
mor agents,[1a,4,7] immunosuppressors,[1a,2a] and neuroprotective
agents,[1a,2a,4,8] as well as compounds exhibiting fungicidal and
larvicidal properties[9]). Among the known synthetic strategies
for the generation of 1,2,4-oxadiazoles, the two most common
approaches include the 1,3-dipolar cycloaddition of nitrile
oxides to nitriles (Scheme 1 path a1) and the reaction of ami-
doximes with activated carboxylic acids and a wide variety of
their derivatives (path c1 and e1) or nitriles (path d1 and e1).[1a]
The boxed intermediate with Y=NH shown in Scheme 1 has
never been observed in the past, although it is known for
Y=O.
Scheme 1. Synthetic strategies for the generation of 1,2,4-oxadiazole deriva-
tives.
PTSA[10a]). Many more reactive substrates bearing the CꢀN
group (e.g. nitrilium salts) were also transformed into 1,2,4-oxa-
[a] D. S. Bolotin, Dr. N. A. Bokach, Prof. Dr. V. Y. Kukushkin
Department of Chemistry, St. Petersburg State University
Universitetsky Pr. 26, 198504 Stary Petergof (Russian Federation)
E-mail: bokach@nb17701.spb.edu
kukushkin@vk2100.spb.edu
The syntheses of 1,2,4-oxadiazoles that are based on the re-
action between RCN and amidoximes species[10] require rather
harsh conditions (100–1808C) when performed with metal-free
protocols.[11] Alternatively, these reactions could be conducted
as metal-mediated processes under milder conditions (20–
808C)[10a,c,d] in the presence of catalytic amounts of ZnCl2 (and
subsequent addition of HCl[10d] or p-toluenesulfonic acid,
[b] Prof. Dr. M. Haukka
Department of Chemistry, University of Eastern Finland
P.O. Box 111, 80101 Joensuu (Finland)
[c] Prof. Dr. V. Y. Kukushkin
Institute of Macromolecular Compounds of Russian Academy of Sciences
V.O. Bolshoii Pr. 31, 199004 St. Petersburg (Russian Federation)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201100047.
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V. Y. Kukushkin, N. A. Bokach et al.
diazoles upon their reaction with amidoximes, and this process
occurs through the cyclization of the initially formed iminium
salt.[10b]
Our research group has been interested in extending our
ongoing project on nucleophilic additions to the metal-activat-
ed CN triple bond (for reviews see reference [12], for recent
studies see reference [13]), and we focused our attention on
reactions of nucleophiles bearing the (NH2)C=NOH functionali-
ty[14] that lead to metal-stabilized O-iminoacylated amidoximes.
These HN=C(R)ON=(NH2)CR’ species have a similar structural
unit to the proposed intermediate (Scheme 1, Y=NH) in the
reaction between amidoximes and nitriles leading to 1,2,4-oxa-
diazoles. Our particular interest in studying the addition of the
amidoximes R’C(NH2)=NOH (R’=Me, PhCH2, Ph) to the nitrile li-
gands in the platinum(IV) complexes trans-[PtCl4(RCN)2] (R=Et,
Ph, NMe2) was at least two-fold. First, we intended the exten-
sion of the metal-mediated nitrile–oxime coupling reaction[15]
to nitriles and amidoximes of various structures. Second, we
anticipated the liberation of the iminoacylated amidoximes
from the PtIV center for verifying a possibility for the cyclization
of these metal-free species into 1,2,4-oxadiazoles. The latter ex-
periment was planned to gain an insight into the mechanism
for both the metal-free and the metal-mediated generation of
1,2,4-oxadiazoles from RCN and amidoximes.
Results and Discussion
Scheme 2. Synthetic transformations. Compound numbering and yields are
given in the tables.
Iminoacylation of oximes proceeds rapidly under mild condi-
tions when metal centers in high oxidation states (e.g. PtIV,
RhIII, or ReIV) are applied for activation of RCN species.[15c,d,16]
Therefore, as the starting materials for this study we addressed
the nitrile platinum(IV) complexes trans-[PtCl4(RCN)2] (R=Et,
rously stirred suspension of 3 in MeNO2 in a 1:1 molar ratio of
Ph, NMe2). The reaction between the amidoximes R’C(NH2)= the reactants brings about a mixture of bisaddition product 14
NOH (4–6) and the trans-[PtCl4(RCN)2] complexes (1–3) pro-
ceeded rapidly (1–10 min) at room temperature at both 1:1
and 2:1 molar ratio of the reactants and afford complexes 7–
17 (Scheme 2, path a2–c2). Compounds 1 and 2 were treated
with one equivalent of amidoximes 4 or 5 (in all possible com-
binations) to form monoaddition species 7–10 (Scheme 2,
path a2) in 81–95% yield after column chromatography; com-
plex 9 was not separated from some by-products (because of
its close retention indexes to these species) and therefore it
was characterized in the reaction mixture.
and 3 in an approximate 1:1 ratio.
Complexes 7–10 were converted into corresponding bisad-
dition species 12, 13, 16, and 17 by the reaction using than
more one equivalent of the corresponding amidoxime
(Scheme 2, path c2). Alternatively, 11–17 were obtained by the
reaction of starting nitrile complexes 1–3 using two equiva-
lents of amidoximes 4–6 (in all possible combinations) in a
CH2Cl2 solution for 1–10 minutes at room temperature (72–
91%; Scheme 2, path b2). Reaction between benzonitrile com-
plex 3 and each of the aliphatic amidoximes (5 and 6) upon
vigorous stirring in the commonly used organic solvents
(CH2Cl2, CHCl3, Me2CO, MeOH, and EtOH) accompanied by ul-
trasound treatment of suspensions led to a mixture of yet un-
identified products where uncomplexed benzonitrile was de-
tected, but no amidoxime addition products were observed in
ESI-MS.
The compounds [PtCl4(RCN){HN=C(R)ONC(Me)NH2}] (R=Et,
NMe2)—derived from the reaction of 1 or 2 and one equivalent
of 6—decompose on silica gel and thus they were not purified
by column chromatography. However, the formation of these
complexes was confirmed by high resolution electrospray
mass spectrometry (for R=Et: calcd for ([MÀCl]+): 484.004;
found: 484.011, calcd for ([MÀEtCN+H]+): 466.935; found:
466.943, for R=NMe2: calcd for ([MÀCl]+): 514.026; found:
514.032).
As far as the driving forces of the coupling is concerned, no
reaction between each of 4–6 and benzonitrile, propiononitrile,
or dimethylcyanamide in either CD2Cl2 or [D6]Me2SO was ob-
served for seven days at room temperature. These blank ex-
periments suggest that the nucleophilic addition of the ami-
doximes to the RCN species is mediated by PtIV.
The monoaddition products formed in the reaction of
trans-[PtCl4(PhCN)2] (3) and amidoximes 4–6 were not be ob-
tained because of a poor solubility of the starting complex in
the most common organic solvents. Thus, for example slow
addition (over 6 h) of a nitromethane solution of 4 to a vigo-
Before the above-described experiments, only one example
of the nitrile–amidoxime coupling reaction had been report-
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Coordination Chemistry
ed.[14] It was observed that the heterogeneous reac-
tion between [PtCl4(MeCN)2] and the amidoxime
PhC(NH2)=NOH requires prolonged heating (27 h at
568C) owing to poor solubility of the starting plati-
num(IV) material. We found that in the homogenous
liquid media the nitrile–amidoxime coupling pro-
ceeded even faster than the previously described[15d]
nitrile–ketoxime coupling (1–10 min at 20–258C vs.
10 min at 55–608C, respectively) and this phenomen-
on can be explained by the +M effect of the NH2
group[17] that increases the nucleophilicity of the
oxime functionality.
Figure 2. ORTEP structure of 11 with the atom-numbering scheme. Thermal ellipsoids
are drawn at the 50% probability level. The imino ligands adopt the E configuration.
Characterization of complexes 7–17
Complexes 7–17 give satisfactory C, H, and N ele-
mental analyses for the proposed formulae (10 was
characterized only in situ) and these species were
also characterized by IR, high resolution ESI-MS, and
NMR spectroscopy techniques; the structures of
seven complexes (8, 11, and 13–17) were studied by
X-ray crystallography. Complexes 11, 13, and 17 crys-
tallized as the Me2CO solvates, whereas 16 and 17
formed solvates 16·1= H2O and 17·2CHCl3; no solvent
2
was observed in the crystal lattices of 8, 14, and 15
(Figure 1, Figure 2, Figure 3, and Figures S1–S5 in the
Supporting Information).
Figure 3. ORTEP structure of 17 with the atom-numbering scheme. Thermal ellipsoids
are drawn at the 50% probability level. The imino ligands adopt the Z configuration.
The imino ligands in 7–17 exist in the different E
(R=Et, Ph; for 7, 8, 11–14) or Z (R=NR’2; for 9, 10,
15–17) forms as confirmed by IR and NMR data, and
lography (Figure 4). The obtained X-ray data disclose the struc-
ture of 18 that, at least formally, originates from an unusual
coupling between two Me2NCN ligands and the N and O cen-
ters of the oxime (Scheme 2, path d2).
All attempts to optimize reaction conditions to increase
yield of 18, such as alteration of the solvent (CHCl3, Me2CO,
MeOH, EtOH, and MeNO2 were tested), varying temperature in
Figure 1. E configuration (left; for 7, 8, 11–14) and Z configuration (right; for
9, 10, 15–17) of the iminoacylated amidoxime ligands.
also by X-ray crystallography (see Figure 1 and see the Sup-
porting Information for detailed discussion of the NMR and X-
ray data). The difference in the E and Z configurations for 7–17
could be accounted for by a fine balance between steric fac-
tors and degree of conjugation of the substituents R or NR’2
with the platinum(IV)-bound imino group.
Unexpected nitrile–amide coupling
We observed that 10, being dissolved in MeNO2, underwent
gradual conversion at room temperature for three weeks and
gave a mixture of metal-containing species. When the solvent
was evaporated at 20–258C to dryness, the brownish oily resi-
due that was formed contained a small amount of red crystals
that were mechanically separated and studied by X-ray crystal-
Figure 4. ORTEP structure of 18 with the atom-numbering scheme. Thermal
ellipsoids are drawn at the 50% probability level. Selected bond lengths [ꢁ]
and angles [8]: Pt1ÀN2 1.959(5), Pt1ÀN1 2.000(4), Pt1ÀN6 2.012(4), N1ÀC1
1.292(6), N3ÀC1 1.324(7), N2ÀC2 1.257(7); N2-Pt1-N1 80.2(2), N2-Pt1-N6
91.5(2), N1-Pt1-N6 171.70(17).
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V. Y. Kukushkin, N. A. Bokach et al.
the range from 20 to 1008C (depending on b.p. of the em-
ployed solvent), additions of a base to deprotonate the amide
moiety (stoichiometric quantities of pyridine or solid NaHCO3
were added), or addition of one equivalent AgSO3CF3 to ab-
stract a chloride atom and to promote the coupling, were so
far unsuccessful. In spite of that, we believe that our observa-
tions deserve further investigation of other similar systems in-
sofar as the coupling is a rare example of nitrile–amide cou-
pling[18] and the first example of the dual reactivity of amidox-
imes toward nitriles. In addition, the NCNCN[Pt] ring is relevant
to 1,3,5-triazapentadiene chelates,[19] with respect to a class of
complexes intensively studied in the past five years.[20]
imine. The latter, after the liberation of the HN= functionality,
give the oxadiazole via cyclization. Yet another report[10b] de-
scribes a facile nitrilium salt/amidoxime interplay leading to
the moderately stable iminium salts, which then under heating
undergo cyclization to achieve the 1,2,4-oxadiazoles
(Scheme 3, path c3). Kabakchi et al.[21] synthesized O-imidoyla-
midoximes starting from nitriles bearing strong acceptor per-
flourinated alkyl groups as substituents. For these products no
structural transformations were detected at room temperature,
but addition of CF3COF promoted the cyclization of the imines
into the corresponding 1,2,4-oxadiazoles[21] (Scheme 3,
path d3).
The PtIV-mediated reaction between the nitrile ligands and
the amidoxime derivatives allows the generation of the mono-
dentate coordinated imines HN=C(R)ON=C(NH2)R’ under mild
reaction conditions. The imino species formed are stabilized
through binding to the platinum center,[22] and to study reac-
tivity of the imines toward cyclization they should be decoordi-
nated. For the liberation of the imino ligands we attempted
different routes that are described in the paragraphs that
follow.
Insight into the mechanism for the generation of 1,2,4-oxa-
diazoles from nitriles and amidoximes
Among purely synthetic studies, some works dealt with the
mechanism for the generation of 1,2,4-oxadiazole derivatives
in the reaction between nitrile and amidoxime functionalities[10]
and these reports illustrate different views on occurrence of
the reaction (Scheme 3).
Augustine et al.[10a] applied the ZnCl2/PTSA system to facili-
tate the nitrile–amidoxime interaction and assumed that the
zinc(II) center abstracts ammonia from the amidoxime to give
the nitrile oxide, which then reacts with the nitrile group as a
1,3-dipole (Scheme 3, path a3). Yarovenko et al.[10d] employed
the 15N NMR technique to study the mechanism for the gener-
ation of the oxadiazoles in the reaction between nitriles and
amidoximes catalyzed by the ZnCl2/HCl system and suggested,
albeit intermediates were not separated individually, that the
nitrile–amidoxime integration proceeds in the coordination
sphere of ZnII followed by formation of a bidentate coordinat-
ed imine (Scheme 3, path b3). Hydrochloric acid, which is
added after the zinc salt, is required for decoordination of the
Despite significant kinetic inertness of platinum(IV) com-
plexes, several methods for displacement of the strongly
bound open-chain imines[15b,23] and heterocycles with the
ÀN=CÀ moiety[24] from their PtIV complexes have been devel-
oped and they are based on reactions with an excess amount
of pyridine[23b,24] or diphosphines.[15b,23a] We observed that in 7–
17 the newly formed imino ligands are so strongly bound to
the platinum(IV) center that the decoordination cannot be ach-
ieved even in neat pyridine at 858C for one day. However, it
was previously reported that the alkali metal cyanides could
be used for decoordination of some chelated phosphine li-
gands[25] and N-heterocyclic ligands strongly bound to PtII cen-
1
ters.[13b,c] In addition, cyanides are transparent in the H NMR
region and this facilitates monitoring the reaction by using
NMR spectroscopy. In accord with this method, imines 19–25
were liberated from 11–17, correspondingly, by treatment with
excess NaCN in a solution of [D6]Me2SO at room temperature
to furnish uncomplexed substituted N’-(1-iminopropoxy)imida-
mides (19–21), N’-(imino(phenyl)methoxy)benzimidamide (22),
N’-((N,N-dimethylcarbamimidoyl)oxy)imidamides (23–25), and
Na2[Pt(CN)6].[13b,25]
Monitoring with 1H and 13C{1H} NMR techniques indicates
that 19–22, after the liberation, undergo further conversion by
two routes to give, first, the parent nitrile and amidoxime in
the retrocoupling (Scheme 4, path b4) and, second, to produce
3,5-substituted 1,2,4-oxadiazoles (Scheme 4, path c4). Genera-
tion of these heterocycles was confirmed by comparison of
their NMR characteristics with those for the corresponding oxa-
diazoles obtained by independent syntheses.[26]
We also observed that acetic acid (2 mol% with respect to
19–21), which was added immediately after the liberation, has
no effect on the transformation of N’-(1-iminopropoxy)imida-
mides. Meanwhile a stoichiometric quantity of the stronger
picric acid (1:1 mol/mol with respect to 19) substantially accel-
erates the conversions of the imine but makes the transforma-
tions less selective. Furthermore, the addition of the anhydrous
Scheme 3. Previously suggested mechanisms for the generation of 1,2,4-oxa-
diazole derivatives from nitrile and amidoxime functionalities.
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Coordination Chemistry
Scheme 5. Plausible mechanism for the generation of 1,2,4-oxadiazole deriv-
atives from nitrile and amidoxime species.
and amidoximes comprises two steps. The first includes a re-
versible nucleophilic addition of an amidoxime to a nitrile pro-
ducing an equilibrium concentration of D (for the metal-free
Scheme 4. Liberation of the O-iminoacylated amidoximes and their further
transformations. Compound numbering and relative amount of the products
are given in the table.
process) or
C (for the metal-catalyzed transformation;
Scheme 5). The concentration of D is very small when R is a
donor group, but becomes much higher for electron-deficient
nitriles, for example, those with perfluorinated alkyl groups.[21]
Furthermore, one should mentioning that metal-free inter-
mediates structurally relevant to D were previously isolated as
the alkylated iminium salts [H(R’’)N=C(R)ON=C(NH2)R’]+[10b] or
as the imines HN=C(RF)ON=C(NH2)R’[21] in the reaction between
the corresponding nitrilium salts or perflourinated nitriles, re-
spectively, and amidoximes.
ZnCl2 (1 mol% with respect to 19) switches the process to the
almost quantitative splitting of 19 to the parent nitrile and the
amidoxime (Scheme 4, path b4).
1H NMR data indicate that 23–25, after the liberation, under-
go decomposition with a half-decay period of approximately
7 minutes to yield a broad mixture of products, where, in par-
ticular, the corresponding amidoxime, dimethylcyanamide, and
3-substituted 5-dimethylamino-1,2,4-oxadiazole were detected
in trace amounts, along with N,N-dimethylurea (35%, 32%,
and 30%, respectively, with respect to the starting quantity of
23–25).
Based upon experimental data we found that, first, the O-
iminoacylated amidoxime derivatives bearing donor and mod-
erate acceptor substituents R (R=Et, Ph, NMe2) split to give
the parent nitriles and amidoximes much faster than the
imines with the strong acceptor substituents (R=perfluorinat-
ed alkyl), that is, if the former split at room temperature and
the latter convert only in toluene at reflux at about 1108C[21]
(Scheme 5, path d5 and path e5). Second, the cyclization of
O-iminoacylated amidoximes into 3,5-substituted 1,2,4-oxadia-
zoles is more efficient when R’ is an acceptor group; the stron-
ger acceptor group R’ leads to the higher yield of the hetero-
cycles. Third, the cyclization (Scheme 5, path e5 and path f5) is
not affected by zinc(II). All these observations give novel in-
sights into a plausible mechanism for the generation of 1,2,4-
oxadiazoles from nitriles and amidoximes.
For path b5 of Scheme 5 the equilibrium point strongly de-
pends on the nature of the metal centers, that is, the equilibri-
um is almost completely shifted to C in the case of plati-
num(IV), while for the ZnII center the concentration of the reac-
tants is higher. However, the ZnII center still activates the CN
triple bond toward the nucleophilic addition to provide more
iminoacylated product C (Scheme 5, path b5) than in the
metal-free reaction (Scheme 5, path d5). In addition, the equi-
librium shown in path c5 of Scheme 5 is shifted to the right for
the kinetically inert platinum(IV) center, meanwhile the kineti-
cally labile zinc(II) center provides D. One should notice that
the zinc(II) center more likely forms the intermediate with an
open-chain rather than the chelated (see Scheme 3, path b3)
O-iminoacylated product as suggested by Yarovenko et al.[10d]
Indeed, graphical search of Chemical Abstracts gives 23 struc-
tures where amidoximes behave as bidentate ligands with the
five-membered amidato ring M{O-N=C(R)-NH} and no struc-
tures similar to that shown in Scheme 3 were found.
In the second step, D undergoes an intramolecular cycliza-
tion (Scheme 5, path e5 and path f5) to form 3,5-substituted
1,2,4-oxadiazole F. This reaction does not require a metal
By summarizing the thus-far obtained experimental and the
literature data, we anticipate that the reaction between nitriles
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35

V. Y. Kukushkin, N. A. Bokach et al.
(4000–400 cmÀ1) were recorded on a Shimadzu FTIR-8400S instru-
ment in KBr pellets. The 1H and 13C{1H} NMR spectra were mea-
sured on a Bruker DPX 300 spectrometer at ambient temperature
in [D6]Me2CO, [D6]Me2SO, or CDCl3; residual solvent signals were
used as internal standards.
center, however, the cyclization is more efficient when D bears
strong acceptor groups R’; the latter functionalities facilitate in-
tramolecular nucleophilic attack (E). Ammonia (Scheme 5,
path f5) derives from the R’CNH2 moiety as confirmed by the
15N NMR study.[10d]
X-ray crystal structure analysis
Conclusion
The crystals of 8, 11, and 13–18 were immersed in cryo-oil, mount-
ed in a Nylon loop, and measured at a temperature of 100 K. The
X-ray diffraction data were collected on a Bruker Axs Smart Apex II,
Bruker Axs Kappa Apex II, or Nonius KappaCCD diffractometer
using Mo Ka radiation (l=0.71073 ꢁ). The Apex2[32] or Denzo-Sca-
lepack[33] program packages were used for cell refinements and
data reductions. The structures were solved by direct methods
using the SIR97,[34] SIR2008,[35] SUPERFLIP,[36] or SHELXS-97[37] pro-
gram with the WinGX[38] graphical user interface. A semiempirical
or numerical absorption correction (SADABS[39]) was applied to all
data. Structural refinements were carried out using SHELXL-97.[37]
In 11, the acetone of crystallization was disordered over two sites
around a center of symmetry with equal occupancy. The heavy
atoms of the disordered molecule were restrained so that their Uij
components approximate to isotropic behavior. These atoms were
further constrained so that they all have equal displacement pa-
rameters. In 14, one of the phenyl rings (C9–C14) was disordered
over two sites with equal occupancies. In these rings, the carbon
atoms C9, C10, C9B, and C10B were restrained so that theirs Uij
components approximate to isotropic behavior. In 8, 11, 16, 17,
and 18, the hydrogen atoms of NH, NH2 and H2O were located
from the difference Fourier map but constrained to ride on their
parent atom, with Uiso =1.5 Ueq(parent atom). In 13, the hydrogen
atoms of NH and NH2 were located from the difference Fourier
map and refined isotropically. All other hydrogen atoms were posi-
tioned geometrically and constrained to ride on their parent
In the area of coordination chemistry, we observed the step-
wise coupling between nitriles and amidoximes that is mediat-
ed by the platinum(IV) center (Scheme 2) and proceeds faster
than the relevant couplings involving ketoximes. The E/Z confi-
guration of the formed iminoacylated amidoxime ligands de-
pends on the R substituent in the starting RCN ligands—the
ligand is E configured for R=Et or Ph and always Z configured
for the dialkylcyanamide (Figure 1–Figure 3). Furthermore, by
identification of tridentate product 18 (Scheme 2 and
Figure 4), we found a rare example of nitrile–amide coupling[18]
and the first example of the dual reactivity of amidoximes
toward nitriles.
All open-chain iminoacylated ligands formed in the coupling
reaction were liberated by the reaction of the platinum(IV)
complexes with NaCN (Scheme 4). As a consequence, in the
area of metal-free organic chemistry, we observed rather fast
transformation of the O-iminoacylated amidoxime species by
two routes to achieve either parent nitriles and amidoximes
(formed through retrocoupling) or 1,2,4-oxadiazoles (generated
by intramolecular cyclization). These experiments give novel in-
sights into a plausible mechanism for the generation of 1,2,4-
oxadizoles upon the reaction between nitriles and amidoximes,
and suggests that it involves the nucleophilic attack of amidox-
imes to the nitrile group followed by the cyclization of thus
formed O-iminoacylated oxime; if the former step is affected
by a metal center, the latter proceeds as a metal-free process
(Scheme 5).
atoms, with CÀH=0.95–0.99 ꢁ, NÀH=0.88 ꢁ, and
Uiso =1.2–
1.5 Ueq(parent atom). The crystallographic details are summarized
in Table S2 in the Supporting Information.
Synthesis
General method for the nucleophilic addition of amidoximes
to the (nitrile)PtIV complexes
Experimental Section
Nucleophilic addition of R’C(NH2)=NOH (1 equiv) to trans-[PtCl4-
(RCN)2] (R=NMe2; Et): A solution of amidoxime (0.075 mmol) in di-
chloromethane (2 mL) was added dropwise to an vigorously stirred
solution of trans-[PtCl4(RCN)2] (R=NMe2; Et; 0.075 mmol) in di-
chloromethane (25 mL, R=Et; 10 mL, R=NMe2) over 15 min at RT.
After stirring for 5 min at RT the resulting solution was subjected
to column chromatography on silica gel (eluent: acetone/chloro-
form=1:10, 0.2:2.0 mL). The first fraction was collected and the
solvent was evaporated under vacuum at 20–258C. The resultant
crystalline residues were dried in air at RT.
Materials and instrumentation
Solvents were obtained from commercial sources and used as re-
ceived. The amidoximes were synthesized by literature methods.[27]
Complexes cis/trans-[PtCl2(RCN)2] (R=Et[28], Ph[29], NMe2[30]) were
synthesized in accord with the published procedures;[28–30] the cis-
and trans-isomers were separated by column chromatography on
silica gel (SiO2 60 F254, 0.063–0.200 mm, Merck). The platinum(IV)
complexes trans-[PtCl4(RCN)2] were obtained by chlorination of the
corresponding platinum(II) species.[15d,30,31] TLC was performed on
Silufol UV254 SiO2 plates. Elemental analyses for C, H, and N were
carried out on a Hewlett Packard 185B Carbon Hydrogen Nitrogen
Analyzer. The electrospray ionization mass spectra were measured
on a Bruker micrOTOF spectrometer equipped with electrospray
ionization (ESI) source. The instrument was operated both in posi-
tive and negative ion mode using an m/z range of 50–3000. The
capillary voltage of the ion source was set at À4500 V (ESI-MS) and
the capillary exit at Æ(70–150) V. The nebulizer gas flow was
0.4 bar and drying gas flow was 4.0 LminÀ1. For ESI analysis the
compounds were dissolved in MeOH or MeCN. In the isotopic pat-
tern, the most intensive peak is reported. The infrared spectra
1
Compound 7: Yield 81%. m.p. 1338C (decomp); H NMR (300 MHz,
CDCl3, 208C): d=8.78 (s, br, 1H, NH), 7.45–7.25 (m, 5H, Ph), 4.86 (s,
br, 2H, NH2), 3.26 (q, 2H, CH2), 3.10 (q, 2H, CH2), 1.53 (t, 3H, CH3),
36
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ChemPlusChem 2012, 77, 31 – 40

Coordination Chemistry
1.31 ppm (t, 3H, CH3); the signals of Et2O (1.20, t and 3.48 ppm, q)
were detected in the spectrum, their integral intensities are in
agreement with the elemental analyses data; IR (KBr, selected
bonds): n(NamideÀH)=3476 (m-s), 3352 (s); n(NimineÀH···N)=3253 (m,
br); n(CÀH)=3059 (w), 3029 (w), 2987 (w-m), 2941 (w), 2921 (w),
2881 (w); n(CꢀN)=2340 (m-s); n(C=N)oxime and/or n(C=N)imine =1653
(m); n(C=N)imine and/or n(C=N)oxime and d(NÀH)=1627 (vs, br); d(CÀ
H)=1492 (m), 1464 (s), 1438 (s); d(NamideÀH)=1406 (m-s); d(CÀ
H)Ar =722 (m), 703 (m); d(CÀH)=627 (w), 544 (m) cmÀ1; HRESI-MS:
m/z calcd for ([2MÀEtCN+H]+): 1139.963; found: 1139.991; calcd
for ([2MÀEtCN+Na]+): 1161.945); found: 1161.939; elemental anal-
Compound 10: Yield 85%. m.p. 1398C (decomp); 1H NMR
(300 MHz, CDCl3, 208C): d=7.65 (d, 2H, o-CH), 7.53–7.39 (2 t, 3H,
2
m-CH and p-CH), 5.79 (s, br, 2H, NH2), 4.88 (s+d, JH,Pt =34 Hz, br,
1H, NH), 3.21 (s, 6H, NMe2), 3.13 ppm (s, 6H, NMe2); IR (KBr, select-
ed bonds): n(NamideÀH)=3466 (m), 3384 (m); n(NimineÀH)=3362 (m);
n(CꢀN)=3052 (w), 2934 (w) n(CÀH); 2307 (m); n(C=N) and/or n(C=
C)=1648 (m), 1621 (s); d(NÀH) and/or n(C=N) and/or n(C=C)=
1577 (w); d(CÀH)=773 (w), 703 (w) cmÀ1; HRESI-MS: m/z calcd for
([MÀNCNMe2 +Na]+):564.941; found: 564.930; calcd for ([MÀCl]+):
577.036; found: 577.029; calcd for ([MÀClÀH+Na]+): 599.018;
found: 599.011; calcd for ([MÀClÀH+K]+): 614.992; found:
614.986; calcd for ([2MÀCl]+): 1191.041; found: 1191.010; calcd for
([3MÀ2ClÀH]+): 1767.069; found: 1767.026; elemental analysis (%)
calcd for C13H20N6Cl4OPt: C 25.46, H 3.29, N 13.70; found: C 25.78,
H 3.19, N 13.29; TLC (eluent chloroform/acetone=5:1, 2:0.4 mL)
Rf =0.52.
ysis (%) calcd for C14H20N4Cl4OPt·1= Et2O: C 29.26, H 3.68, N 9.10;
4
found: C 29.18, H 3.55, N 9.22; TLC (eluent: chloroform/acetone=
5:1, 2:0.4 mL) Rf =0.65.
1
Compound 8: Yield 95%. m.p. 1448C (decomp); H NMR (300 MHz,
Nucleophilic addition of R’C(NH2)=NOH (2 equiv) to trans-[PtCl4-
CDCl3, 208C): d=8.87 (s, br, 1H, NH), 7.66 (d, 2H, o-CH), 7.58 (t, 1H,
p-CH), 7.49 (t, 2H, m-CH), 5.32 (s, br, 2H, NH2), 3.32 (q, 2H, CH2),
3.10 (q, 2H, CH2), 1.52 (t, 3H, CH3), 1.39 ppm (t, 3H, CH3); the sig-
nals of Et2O (1.20, t and 3.48 ppm, q) were detected in the spec-
trum, their integral intensities are in agreement with the elemental
analyses data; IR (KBr, selected bonds): n(NamideÀH)=3548 (w), 3482
(m), 3415 (m), 3362 (m); n(NimineÀH···N)=3245 (w-m, br); n(CArÀH)=
3067 (vw); n(CÀH)(CH2)=2984 (w), 2917 (w) n(CÀH)(CH3); 2942 (w),
(RCN)2]:
A solution of R’C(NH2)=NOH (R’=Ph, CH2Ph, Me;
0.15 mmol) in dichloromethane (1 mL) or in nitromethane (2 mL,
R=Ph) was added to a homogeneous solution of trans-[PtCl4-
(RCN)2] (R=NMe2, Et; 0.075 mmol) in dichloromethane (20 mL, R=
Et; 10 mL, R=NMe2) or to a suspension in nitromethane (5 mL, R=
Ph) under ultrasound treatment, and stirred for 1 min (or for
10 min under ultrasound treatment, R=Ph), whereupon the sol-
vent was evaporated to dryness at RT. The precipitates formed
were washed with two portions of CHCl3 (1 mL) and three portions
of Et2O (3 mL) and dried in air at 20–258C.
2852 (w); n(CꢀN)=2327 (w-m); n(C=N)oxime and/or n(C=N)imine
=
1663 (m); n(C=N)imine and/or n(C=N)oxime and n(C=C)Ar and d(NÀH)=
1617 (vs, br); n(C=C)Ar =1565 (m); n(C=C)Ar and d(CÀH)Et =1466 (m),
1430 (m); d(NamideÀH)=1406 (m); d(CÀH)Ar =775 (m), 697 (m-s);
d(CÀH)Et =634 (w-m) cmÀ1; HRESI-MS: m/z calcd for ([MÀCl]+):
547.014; found: 547.011; calcd for ([2MÀH+Na]+): 1187.948;
found:
1187.965;
elemental
analysis
(%)
calcd
for
C13H18N4Cl4OPt·Et2O: C 27.71, H 3.37, N 9.37; found: C 27.59, H 3.11,
N 9.42; TLC (eluent: chloroform/acetone=5:1, 2:0.4 mL) Rf =0.70;
crystals suitable for X-ray diffraction were grown by the slow evap-
oration in air at RT of a solution in acetone/chloroform.
Compound 11: Yield 81%; m.p. 1548C (decomp); 1H NMR
(300 MHz, [D6]acetone, 208C): d=8.74 (s, br, 1H, NH), 6.60 (s, br,
2H, NH2), 3.09 (q, 2H, CH2), 1.30 (t, 3H, CH3), 1.99 ppm (s, 3H, CH3);
IR (KBr, selected bonds): n(NamideÀH)=3553 (w), 3501 (m-s), 3418
(w-m), 3367 (m-s); n(NimineÀH···N)=3268 (m, br); n(CÀH); 1663 (m)
n(C=N)oxime and/or n(C=N)imine =2980 (m), 2939 (w-m), 2876 (w);
n(C=N)imine and/or n(C=N)oxime and d(NÀH)=1610 (vs, br); d(CÀH)=
1465 (m), 1430 (s); d(NamideÀH)=1412 (s); d(CÀH)=588 (w), 528 (w-
m) cmÀ1; HRESI-MS: m/z calcd for ([2M+NH4]+): 1208.065; found:
1208.054; elemental analysis (%) calcd for C10H22N6Cl4O2Pt: C 20.18,
H 3.73, N 14.12; found: C 20.56, H 3.77, N 14.10; TLC (eluent:
chloroform/acetone=8:1, 2:0.25 mL) Rf =0.30; crystals suitable for
X-ray diffraction were grown by the slow evaporation in air at RT
of a solution in acetone.
Compound 9: 100% yield based on 1H NMR data. 1H NMR
(300 MHz, CDCl3, 208C): d=7.35–7.28 (m, 5H, Ph), 5.99 (s, br, 1H,
2
NH), 5.56 (s, br, 1H, NH), 4.84 (s+d, JH,Pt =34 Hz, br, 1H, NH), 3.18
(s, 6H, NMe2), 3.15 (s, 2H, CH2), 3.11 ppm (s, 6H, NMe2); IR (KBr, se-
lected bonds): n(NamideÀH)=3473 (s), 3415 (s); n(NimineÀH)=3336
(m); n(CÀH)=2969 (w), 2932 (w), 2851 (w), 2828 (w); n(CꢀN)=2305
(m); n(C=N) and/or n(C=C)=1653 (m-s), 1637 (s), 1617 (s); d(CÀ
H)=775 (w), 704 (w) cmÀ1; HRESI-MS: m/z calcd for ([MÀNCNMe2 +
Na]+): 579.959; found: 579.948; calcd for ([MÀCl]+): 590.057;
found: 590.050; calcd for ([2MÀCl]+): 1216.078; found: 1216.067;
TLC (eluent: chloroform/acetone=10:1, 2:0.2 mL) Rf =0.43.
Compound 12: Yield 91%; m.p. 1728C (decomp); 1H NMR
(300 MHz, [D6]DMSO, 208C): d=8.55 (s+d, 2JH,Pt =34 Hz, 1H, NH),
ChemPlusChem 2012, 77, 31 – 40
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37

V. Y. Kukushkin, N. A. Bokach et al.
7.4–7.2 (m, 5H, Ph), 7.09 (s, br, 2H, NH2), 3.47 (s, 2H, CH2Ph), 3.02
(q, 2H, CH2), 1.23 ppm (t, 3H, CH3); IR (KBr, selected bonds):
n(NamideÀH); 3480 (m-s)=3373 (s); n(NimineÀH···N)=3247 (m, br);
n(CÀH)=3031 (w), 2991 (w), 2943 (w), 2929 (w), 2880 (w); n(C=
N)imine and/or n(C=N)oxime and d(NÀH)=1620 (vs, br); d(CÀH)=1496
(m), 1464 (s), 1441 (s); d(NamideÀH)=1402 (m); d(CÀH)Ar =719 (m),
703 (m); d(CÀH)Et =586 (m) cmÀ1; HRESI-MS: m/z calcd for ([2M+
H]+ ): 1495.164; found: 1495.161; calcd for ([2M+Na]+): 1517.146;
found: 1517.149; elemental analysis (%) calcd for C22H30N6Cl4O2Pt:
C 35.35, H 4.05, N 11.24; found: C 35.41, H 4.07, N 11.18; TLC
(eluent: chloroform/acetone=10:1, 2:0.2 mL) Rf =0.48.
3469 (vs), 3395 (m-s); n(NimineÀH)=3360 (m-s); n(CAlkÀH)=2968 (w),
2926 (w), 2893 (w), 2872 (vw); n(C=N)oxime and/or n(C=N)imine =1655
(s); n(C=N)imine and/or n(C=N)oxime and d(NÀH)=1610 (vs); d(CÀ
H)Et =1469 (s); d(CÀH)NMe =1426 (m); d(NamideÀH)=1406 (s); d(CÀ
H)=623 (w), 592 (m) cmÀ1; HRESI-MS: m/z calcd for ([MÀ3Cl]+):
519.130; found: 519.122; ([MÀCl]+): 589.068; found: 589.055;
([M+H]+): 625.045; found: 625.030; ([MÀCl+NH=C(NMe2)ON=
C(NH2)Me]+): 733.169; found: 733.150; elemental analysis calcd for
C10H24N8Cl4O2Pt·1= Et2O·1= CHCl3: C 20.06, H 4.00, N 16.63; found:
4
2
Compound 13: Yield 84%; m.p. 1738C (decomp); 1H NMR
(300 MHz, [D6]DMSO, 208C): d=8.67 (s+d, 2JH,Pt =34 Hz, 1H, NH),
7.8–7.3 (m, 7H, Ph + NH2), 3.13 (q, 2H, CH2), 1.29 ppm (t, 3H, CH3);
IR (KBr, selected bonds): n(NamideÀH)=3514 (w), 3490 (m), 3408 (w-
m), 3371 (m-s); n(NimineÀH···N)=3239 (m, br); n(CArÀH); 3064 (vw);
n(CÀH)(CH3)=2984 (w), 2921 (w); n(CÀH)(CH2)=2943 (w), 2852 (w);
n(C=N)oxime and/or n(C=N)imine =1653 (m); n(C=N)imine and/or n(C=
N)oxime and n(C=C)Ar and d(NÀH)=1617 (vs, br); n(C=C)Ar =1564 (m),
1497 (w); n(C=C)Ar and d(CÀH)Et =1462 (m), 1434 (s); d(NamideÀH)=
1406 (s); d(CÀH)Ar =780 (m), 696 (m-s) cmÀ1; HRESI-MS: m/z calcd
for ([M+K]+): 757.010; found: 757.019; ([2M+K]+): 1477.057;
found: 1477.070; ([3M+K]+): 2197.104; found: 2197.129; elemental
analysis (%) calcd for C20H26N6Cl4O2Pt: C 33.39, H 3.64, N 11.68;
found: C 33.55, H 3.66, N 11.44; TLC (eluent: chloroform/acetone=
8:1, 2:0.25 mL), Rf =0.60; crystals suitable for X-ray diffraction were
grown by the slow evaporation of a warm (ca. 458C) solution in
acetone/chloroform.
C 19.94, H 4.09, N 16.73; TLC (eluent: chloroform/acetone=2:1,
2:1 mL) Rf =0.54; crystals suitable for X-ray diffraction were grown
by the slow evaporation in air at RT of a solution in nitromethane.
Compound 16: Yield 80%; m.p. 1658C (decomp); 1H NMR
(300 MHz, [D6]acetone, 208C): d=7.40 (d, br, 2H, o-CH), 7.34–7.21
2
(m, 3H, m-CH + p-CH), 6.15 (s, br, 2H, NH2), 5.02 (s+d, br, JH,Pt
=
34 Hz, 1H, NH), 3.46 (s, 2H, CH2), 3.16 ppm (s, 6H, NMe2); IR (KBr,
selected bonds): n(NamideÀH)=3452 (vs), 3398 (s); n(NimineÀH)=3334
(vs); n(CArÀH)=3062 (vw), 3027 (w); n(CÀH)Alk =2969 (w), 2933 (w),
2902 (w); n(C=N)oxime and/or n(C=N)imine =1653 (s); n(C=N)imine and/
or n(C=N)oxime and d(NÀH) and n(C=C)Ar =1610 (vs, br); n(C=C)Ar =
1494 (m); n(C=C)Ar and d(CÀH)=1471 (m-s, br); d(NamideÀH)=1425
(s); d(CÀH)Ar =753 (m), 708(s); d(CÀH)Alk =630 (m) cmÀ1; HRESI-MS:
m/z calcd for ([MÀ3Cl]+): 671.193; found: 671.190; ([MÀHÀ2Cl]+):
705.154; found: 705.151; ([MÀCl]+): 741.131; found: 799.082; ([M+
Na]+): 799.089; found: 741.127; ([M+Na]+): 1577.190; found:
1577.172; elemental analysis calcd for C22H32N8Cl4O2Pt·2H2O:
C 32.48, H 4.46, N 13.77, found: C 32.64, H 4.31, N 13.87; TLC
(eluent: chloroform/acetone=10:1, 2:0.2 mL) Rf =0.64; crystals
suitable for X-ray diffraction were grown by the slow evaporation
in air at RT of a solution in methanol.
Compound 14: Yield 72%; m.p. 1588C (decomp); 1H NMR
(300 MHz, [D6]acetone, 208C): d=9.72 (s, br, 1H, NH), 8.03 (d, 2H,
o-CH), 7.87 (d, 2H, o-CH), 7.65–7.50 (m, 4H, m-CH + p-CH), 7.45 (t,
2H, m-CH), 7.09 ppm (s, br, 2H, NH2); IR (KBr, selected bonds):
n(NamideÀH)=3494 (m), 3390 (m-s) ; n(NimineÀH···N)=3210 (m, br);
n(CArÀH)=3070 (w), 3058 (w), 3028 (vw); n(C=N)oxime and/or n(C=
N)imine =1654 (m); n(C=N)imine and/or n(C=N)oxime and d(NÀH)=1616
(vs, br); n(C=C)Ar =1598 (s), 1565 (m), 1495 (s); n(C=C)Ar and d(CÀ
H)Et =1450 (m-s); d(NamideÀH)=1428 (s, br) cmÀ1; elemental analysis
(%) calcd for C28H26N6Cl4O2Pt: C 41.24, H 3.21, N 10.31; found:
C 41.16, H 3.42, N 10.30; TLC (eluent: chloroform/acetone=10:1,
2:0.2 mL) Rf =0.61; crystals suitable for X-ray diffraction were
grown by the slow evaporation in air at RT of a solution in nitrome-
thane.
Compound 15: Yield 79%; m.p. 1768C (decomp); 1H NMR
(300 MHz, [D6]DMSO, 208C): d=6.37 (s, br, 2H, NH2), 5.30 (s, br, 1H,
NH), 3.02 (s, 6H, NMe2), 1.76 ppm (s, 3H, CH3); the signals of Et2O
(1.20, t and 3.48 ppm, q) and CHCl3 (8.32 ppm, s) were detected in
the spectrum, their integral intensities are in agreement with the
elemental analyses data; IR (KBr, selected bonds): n(NamideÀH)=
Compound 17: Yield 85%; m.p. 1758C (decomp); 1H NMR
(300 MHz, [D6]acetone, 208C): d=7.9–7.65 (m, br, 2H, o-CH), 7.6–
7.4 (m, 3H, m-CH + p-CH), 6.59 (s, br, 2H, NH2), 5.13 (s, br, 1H, NH),
38
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Coordination Chemistry
3.24 ppm (s, 6H, NMe2); IR (KBr, selected bonds): n(NamideÀH)=3462
(vs), 3400 (s); n(NimineÀH)=3329 (vs); n(CArÀH)=3059(vw),
3030(vw); n(CÀH)NMe =2977 (w), 2932 (w), 2879 (w); n(C=N)oxime
and/or n(C=N)imine =1643 (m); n(C=N)imine and/or n(C=N)oxime and
d(NÀH) and n(C=C)Ar =1617 (vs, br); n(C=C)Ar =1570 (m), 1491 (m),
n(C=C)Ar and d(CÀH)Me =1469 (m-s, br); d(NamideÀH)=1400 (m);
d(CÀH)Ar =764 (m), 701 (s); d(CÀH)Me =606 (m) cmÀ1; HRESI-MS: m/
156.00 (C(Ph)(NH2)(=N)), 132.64 (ipso-C), 131.24 (p-CH), 129.24 (o-
CH), 127.47 (m-CH), 25.91 (CH2), 11.52 ppm (CH3).
Compound 22: 100% yield based on 1H NMR data; half-decay
period is about 6 days. 1H NMR (300 MHz, [D6]DMSO, 208C): d=
8.41 (s, br, 1H, NH), 8.19 (d, 2H, o-CH), 7.84 (d, 2H, o-CH), 7.55–7.40
(m, 6H, m-CH + p-CH), 7.02 ppm (s, br, 2H, NH2); 13C NMR (75 MHz,
[D6]DMSO, 208C): d=162.25 (C(Ph)(O)(=NH)), 162.22 (C(Ph)(NH2)(=
N)), 156.31 (p-CH), 132.68 (p-CH), 131.79 (ipso-C), 131.35 (ipso-C),
129.28 (o-CH), 128.99 (o-CH), 128.57 (m-CH), 127.69 ppm (m-CH).
z
calcd for ([MÀ3Cl]+): 643.162; found: 643.151; ([MÀ2Cl]+):
678.131; found: 678.120; ([MÀCl]+): 713.099; found: 713.086; ([M+
H]+): 749.076; found: 749.063; ([M+Na]+): 771.058; found:
771.040; ([M+K]+): 787.032; found: 784.017; elemental analysis
calcd for C20H28N8Cl4O2Pt: C 32.06, H 3.77, N 14.95; found: C 32.06,
H 4.07, N 14.91; TLC (eluent: chloroform/acetone=10:1, 2:0.2 mL)
Rf =0.54; crystals suitable for X-ray diffraction were grown by the
slow evaporation in air at RT of a solution in acetone or in chloro-
form.
Compounds 7, 8, and 11–17 are air stable at RT in the solid state
and in the most common organic solvents. These species are also
stable in nitromethane at reflux for at least 2 h (11–17), meanwhile
7 and 8 decompose under these conditions for 2 h. Complex 10
degrades in common organic solvents after three weeks at 20–
258C or after 45 min in nitromethane at reflux to produce a broad
range of yet unidentified species. Complex 9 could not be crystal-
lized and it decomposes within 6 h at RT to form oily residues.
Complex 9 could not be purified from the hydrolysis products and
was characterized in a mixture. No molecular ion of 14 or its frag-
mentation was observed in the mass spectrum despite running
the experiment in a wide interval of voltage at capillary exit and
using different solvents (MeOH, CH2Cl2, and MeCN) and mixtures of
them.
Compound 23: 100% yield based on 1H NMR data; half-decay
1
period is about 7 min. H NMR (300 MHz, [D6]DMSO, 208C): d=7.02
(s, br, 1H, NH), 6.54 (s, br, 1H, NH), 5.65 (s, br, 1H, NH), 3.29 (s, 6H,
NMe2), 1.82 ppm (s, 3H, CH3); 13C NMR was not obtained because
of fast decomposition of the imine in solution.
Compound 24: 100% yield based on 1H NMR data; half-decay
period is about 7 min. 1H NMR (300 MHz, [D6]DMSO, 208C): d=
7.40–7.17 (m, 5H, Ph), 6.69 (s, br, 1H, NH), 6.36 (s, br, 1H, NH), 5.72
(s, br, 1H, NH), 3.45 (s, 2H, CH2), 3.29 ppm (s, 6H, NMe2); 13C NMR
was not obtained because of fast decomposition of the imine in
solution.
Compound 25: 100% yield based on 1H NMR data; half-decay
1
period is about 7 min. H NMR (300 MHz, [D6]DMSO, 208C): d=7.74
(d, 2H, o-CH), 7.66–7.35 (m, 3H, m-CH + p-CH), 7.18 (s, br, 2H,
NH2), 5.86 (s, br, 1H, NH), 3.36 ppm (s, 6H, NMe2); 13C NMR was not
obtained because of fast decomposition of the imine in solution.
Acknowledgements
We thank the Federal Targeted Program “Scientific and Scientific-
Pedagogical Personnel of the Innovative Russia in 2009–2013”
(contract no. P1294 from 09/06/2010), the Russian Fund for Basic
Research (grants nos. 11–03–00262 and 11–03–90417), the RAS
Presidium Subprogram coordinated by academic N. T. Kuznetsov.
We acknowledge Saint Petersburg State University for a research
grant (2011–2013). Dr. P. S. Lobanov and Dr. S. A. Miltsov are
thanked for stimulating discussions.
Liberation of the iminoacylated amidoximes
A mixture of an imino complex (11–17; 0.06 mmol) and NaCN
(17.7 mg, 0.36 mmol) were dissolved in [D6]DMSO (0.56 mL) at RT
to produce 19–25, respectively. The completeness of the liberation
was monitored by 1H NMR spectroscopy. The product was detected
1
by H NMR spectroscopy after 5 min, whereupon it was character-
ized by 13C{1H} NMR technique (total acquisition time is ca. 2 h). Be-
sides [D6]DMSO signals, high resolution ESI-MS spectra exhibited
signals of quasimolecular ions of amidoximes 6, 5, and 4 (for 19–
21 and 23–25, respectively; and 4 for 22) and dimethyl urea (for
23–25).
Keywords: amidoximes · nitriles · nucleophilic addition ·
1,2,4-oxadiazoles · platinum
Compound 19: 100% yield based on 1H NMR data; half-decay
period is about 8 days; 1H NMR (300 MHz, [D6]DMSO, 208C): d=
7.57 (s, br, 1H, NH), 6.31 (s, br, 2H, NH2), 2.16 (q, 2H, CH2), 1.76 (s,
3H, CH3), 1.08 ppm (t, 3H, CH3); 13C NMR (75 MHz, [D6]DMSO,
208C): d=167.51 (C(Et)(O)(=NH)), 158.23 (C(CH3)(NH2)(=N)), 26.17
(CH2), 20.17 (CH3), 11.05 ppm (CH3).
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ChemPlusChem 2012, 77, 31 – 40
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: November 14, 2011
Published online on January 4, 2012
40
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