Platinum(IV)-assisted [2 + 3] cycloaddition of nitrones to coordinated organonitriles. Synthesis of Δ4-1,2,4-oxadiazolines

Article abstract of DOI:10.1021/ja993564f

[2 + 3] cycloaddition between acetonitrile ligands in the platinum(IV) complex [PtCl₄(MeCN)₂] and the nitrones ^-O⁺N(R³) = C(R¹)(R²) [R¹ = H, R² = Ph, o-C₆H₄OH, p-C₆H₄Me, p-C₆H₄OMe, p-C₆H₄NO₂, p-C₆H₄NMe₂, p-C₆H₄NMe₂·HCl, R³ = Me; R¹ = H, R² = Ph, Bu, R³ = CH₂Ph] proceeds smoothly under mild conditions and gives the first examples of Δ⁴-1,2,4- oxadiazoline complexes, [PtCl⁴{N = C(Me)O-N(R³)-C(R¹)(R²)}₂], as a 1:1 mixture of two diastereoisomers, in 70-90% yields. The heterocyclic ligands were liberated almost quantitatively by reaction at room temperature of the complexes with a slight excess of pyridine in chloroform giving free N = C(Me)O-N(R³)-C(R¹)(R²) and trans-[PtCl₄(pyridine)₂]; subsequent workup allowed the isolation of the novel Δ⁴-1,2,4-oxadiazolines. All prepared compounds were characterized by elemental analyses, FAB or EI mass spectrometry, and IR and ¹H, ¹³C{¹H}, and ¹⁹⁵Pt (metal complexes) NMR spectroscopies; X-ray structure determination was performed for the (R,S) diastereoisomer of trans-[PtCl₄{N=C(Me)ON(Me)-CH(p-C₆H₄OMe)}₂].

Full text of DOI:10.1021/ja993564f

3106
J. Am. Chem. Soc. 2000, 122, 3106-3111
Platinum(IV)-Assisted [2 + 3] Cycloaddition of Nitrones to
Coordinated Organonitriles. Synthesis of ∆4-1,2,4-Oxadiazolines
Gabriele Wagner,† Armando J. L. Pombeiro,*,† and Vadim Yu. Kukushkin*,‡
Contribution from the Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico,
AV. RoVisco Pais, 1049-001 Lisbon, Portugal, and Department of Chemistry,
St. Petersburg State UniVersity, 198904 Stary Petergof, Russian Federation
ReceiVed October 4, 1999
Abstract: [2 + 3] cycloaddition between acetonitrile ligands in the platinum(IV) complex [PtCl4(MeCN)2]
and the nitrones -O+N(R3)dC(R1)(R2) [R1 ) H, R2 ) Ph, o-C6H4OH, p-C6H4Me, p-C6H4OMe, p-C6H4NO2,
t
p-C6H4NMe2, p-C6H4NMe2‚HCl, R3 ) Me; R1 ) H, R2 ) Ph, Bu, R3 ) CH2Ph] proceeds smoothly
under mild conditions and gives the first examples of ∆4-1,2,4-oxadiazoline complexes, [PtCl4{NdC(Me)O-
N(R3)-C(R1)(R2)}2], as a 1:1 mixture of two diastereoisomers, in 70-90% yields. The heterocyclic ligands
were liberated almost quantitatively by reaction at room temperature of the complexes with a slight excess of
pyridine in chloroform giving free NdC(Me)O-N(R3)-C(R1)(R2) and trans-[PtCl4(pyridine)2]; subsequent
workup allowed the isolation of the novel ∆4-1,2,4-oxadiazolines. All prepared compounds were characterized
1
by elemental analyses, FAB or EI mass spectrometry, and IR and H, 13C{1H}, and 195Pt (metal complexes)
NMR spectroscopies; X-ray structure determination was performed for the (R,S) diastereoisomer of trans-
[PtCl4{NdC(Me)ON(Me)-CH(p-C6H4OMe)}2].
Introduction
offers an attractive way to promote or inhibit such reactions or
perform synthetic routes which are not feasible for so-called
pure organic chemistry. Our own research in the field of
reactivity of organonitrile ligands4 has recently got the second
breath when we observed the reaction between the platinum-
(IV) complexes [PtCl4(RCN)2] (R ) Me, CH2Ph, Ph) and
oximes, R1R2CdNOH (R1 ) R2 ) Me; R1R2 ) C4H8, R1R2 )
C5H10, R1R2 ) (H)Ph, R1R2 ) (H)C6H4(OH)-o), which led to
isolation of unusual and unexpectedly stable iminoacylated
compounds [PtCl4(NHdC(R)ONdCR1R2)2], Scheme 1.5
Although the effect of the ligands upon a metal ion is often
relatively well understood and many aspects are fairly well
quantified, similar quantitative theories are unavailable for
investigating the effect of coordination to a metal upon the
ligand. However, qualitatiVe models to justify the changes which
result from coordination of a ligand to a metal allow the
description and sometimes the prediction of metal-mediated
processes which can form the basis for the use of metal
complexes as stoichiometric reagents and homogeneous cata-
lysts in organic chemistry. In this context, ligands containing
double or triple bonds were shown to be the most useful and
versatile materials whose metal-mediated reactions1 give a
tremendous variety of new organic compounds. Qualitative
models describing these, very often, ionic-type processes suggest
polarization of the double and triple bond species and appearance
of new electrophilic or nucleophilic centers which promote
ligand reactions.
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Among these species, organonitriles are of paramount im-
portance in the formation of C-C, C-N, and C-O bonds in
organic chemistry,2 and metal-ion control of their reactivity3
† Instituto Superior Te´cnico.
‡ St. Petersburg State University.
(1) (a) Braterman, P. S. Reactions of Coordinated Ligands; Plenum: New
York, 1989; Vol. 2. (b) ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, 1987. (c)
Kukushkin, Yu. N. ReactiVity of Coordination Compounds [in Russian];
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10.1021/ja993564f CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/22/2000

∆4-1,2,4-Oxadiazolines
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3107
Scheme 1. Addition of Oximes to Coordinated Nitriles
nitrones. Consequently, the latter method allows the preparation
of ∆4-1,2,4-oxadiazolines, but only with strong electron-
withdrawing groups R. Indeed, preparation of the compounds
with the electron-donor group R ) Me was achieved only in
one case when an extremely reactive nitrone was employed and
also harsh reaction conditions (150 °C, neat acetonitrile, 10 days)
were applied.13 In contrast, the platinum(IV)-assisted reaction
we now describe offers broad possibilities for derivatization of
∆4-1,2,4-oxadiazolines. In fact, the electrophilic activation by
the metal center of organonitriles RCN, even with electron-
donor substituents R, such as methyl, is so strong that the
cycloaddition is determined only by the reactivity of a nitrone
and occurs smoothly under mild conditions.
Results and Discussion
Cycloaddition Reaction and Characterization of Products.
Examples of cycloaddition reactions, although these and also
in situ metal-catalyzed processes are well-known in organic
chemistry,18 are rather scarce in coordination chemistry. Among
them attention should be drawn to (i) the cycloaddition of dipolar
reagents to alkynyl Fischer carbene complexes,19 coordinated
CS2,20 or dinuclear metal complexes across the metal-metal
multiple bond;21 (ii) cyclization of metal allyl, allenyl, propargyl,
or related compounds with organic isocyanides, ketenes, SO2,
or S2O;22 (iii) reactions of coordinated organoazides with
This route was then extended to N-alkylated hydroxylamines
to observe unprecedented O-addition of R2NOH to the metal-
bound MeCN6 and to additions of sterically hindered alcohols
which do not react with free nitriles under the Pinner reaction
conditions,7 but they do react with Pt(IV)-bound ones.8 Eventu-
ally, in contrast to the classic substitution processes, we
discovered occurrence of a facile one-end addition of Vic-
dioximes to the nitrile species in [PtCl4(RCN)2] that generated
Pt(IV)-based metallaligands of a novel type.9
All of these iminoacylation reactions, giving rather unusual
metal-bound organic species, proceeded rapidly, typically under
mild conditions and gave final coordination products in high
and sometimes almost quantitative yields. All this together
pointed out that a very reactive starting material containing
highly electrophilically activated RCN ligands is at our disposal,
and we became much interested in initiating the utilization of
[PtCl4(RCN)2] for generation of organic species. We now report
on an extension of the addition reaction to completely different
reagents, i.e., nitrones, that brings about platinum(IV)-assisted
[2 + 3] cycloaddition, followed by liberation of newly formed
ligands by reaction with pyridine, and this opens up an easy
route to ∆4-1,2,4-oxadiazoline heterocyclic species whose
synthesis and further chemistry are still little explored.
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nitrosobenzene with nitrile ylides10 or oxazolinones11 and
reactions of electron-deficient organonitriles,12,13 for example,
Cl3CCN14,15 or NCCH2CN,16 or aryl cyanates, ROCN,17 with
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3108 J. Am. Chem. Soc., Vol. 122, No. 13, 2000
Wagner et al.
isonitriles,23 activated alkynes,24 olefins,25 CS2,26 or isothiocy-
anates;27 (iv) the cycloadditions due to the reaction between
isonitrile complexes and azide ion,28 isocyanates, or isothiocy-
anates;29 (v) formation of metallacycles originating from the
cycloaddition between low-valent metal carbonyls and organo-
nitrile N-oxides;30 (vi) the cycloadditions of free CF3CN to
metallaisonitrile ylides which lead to metal-bound imidazoles.31
As far as the cycloaddition to coordinated organonitrile species
is concerned, to the best of our knowledge, there is only one
example of such a process, i.e., the [2 + 3] addition of azide
ion to cobalt-bound nitriles or, at least formally, the reverse
reaction between azido complexes and RCN giving, in either
case, coordinated tetrazolates.32 The restricted amount of these
reactions described in coordination chemistry is somehow
surprising if one takes into account significant and sometimes
tunable, e.g., by variation of other supporting ligands or of the
overall charge on a complex ion, electrophilic activation of
ligands by their ligation to a metal center making the reactions
with electron-rich dipolar reagents favorable and controllable.
Figure 1. ORTEP view of trans-[PtCl4{NdC(Me)ON(Me)-CH(p-
C6H4OMe)}2] with atomic numbering scheme.
Scheme 2. [2 + 3] Cycloaddition between Coordinated
Acetonitrile and Nitrones (R1 ) H, R2 ) Ph, o-C6H4OH,
p-C6H4Me, p-C6H4OMe, p-C6H4NO2, p-C6H4NMe2,
For this study we addressed the platinum(IV) complex [PtCl4-
(MeCN)2] since it has been proved that the acetonitrile ligands
are highly activated and they are logical candidates for
investigations of cycloaddition reactions with electron-rich
dipoles such as nitrones. The reaction between the complex and
a nitrone in a molar ratio 1:2 proceeds smoothly in a suspension
of CH2Cl2 (with its gradual homogenization) at room temper-
ature and completes after 4-6 h (Scheme 1). The final products
were purified by chromatography on SiO2 and obtained as solids
[(R,S) + (S,S)/(R,R) diastereoisomers] in good yields (70-90%).
All isolated complexes were characterized by elemental analy-
ses, FAB mass spectrometry, and IR and 1H, 13C{1H}, and 195Pt
NMR spectroscopies; X-ray structure determination was per-
t
p-C6H4NMe2‚HCl, R3 ) Me; R1 ) H, R2 ) Ph, Bu, R3 )
CH2Ph)
formed for (R,S)-trans-[PtCl4{NdC(Me)ON(Me)-CH(p-C6H4-
OMe)}2]. The coordination polyhedron of the complex is a
slightly distorted octahedron (Figure 1). The Pt atom is situated
at an inversion center, and all bonds and angles around the
platinum are of normal values.33 The spectroscopic data ad-
ditionally support the formulations and indicate the presence
of two heterocyclic ligands bound to the Pt atom via their imino
nitrogens. Only three structures of uncoordinated ∆4-1,2,4-
oxadiazolines are known,15 and, to the best of our knowledge,
the complexes relevant to this study represent the first example
of ∆4-1,2,4-oxadiazoline species coordinated to a metal center
and, consequently, trans-[PtCl4{NdC(Me)ON(Me)-CH(p-
C6H4OMe)}2] is the first example of a structurally characterized
(∆4-1,2,4-oxadiazoline)metal compound. Surprisingly, geo-
metrical parameters of the ring are almost unaffected by its
ligation to the platinum(IV) center. Indeed, all bond lengths and
angles in the cycle within 3σ correspond to those in the three
purely organic 1,2,4-oxadiazolines.15 However, in contrast to
the envelope conformation found for the organic compounds,15
the coordinated heterocycle is a half-chair that is twisted around
the N2-C2 bond with deviations of 0.307(6) Å for N2 and
-0.209(6) Å for C2 from the plane passed through the atoms
N1, C1, and O1. The methyl group at N2 and the aromatic
substituent at C2 are mutually trans, and both occupy axial
positions on the ring.
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references therein.
The results obtained (for IR and NMR spectroscopic results
see below) indicate the cycloaddition of the nitrones to the
acetonitrile species to give ∆4-1,2,4-oxadiazolines coordinated
to the platinum(IV), Scheme 2. The newly formed organic
ligands can be easily liberated by reaction of the (∆4-1,2,4-
oxadiazoline)platinum(IV) complexes with a slight excess of
pyridine in chloroform (Scheme 2). The formation of trans-
[PtCl4(pyridine)2],34 highly insoluble in CHCl3, in the course
of the substitution, its separation by filtration, and evaporation
of the solvent to dryness allowed us to obtain individual ∆4-
1,2,4-oxadiazolines. All isolated compounds were characterized
(34) Jo¨rgensen, S. M. J. Prakt. Chem. 1886, 33, 489.

∆4-1,2,4-Oxadiazolines
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3109
by NMR and IR spectroscopies and EI mass spectrometry. The
mass spectra show, in addition to the molecular ions, a typical
fragmentation pattern that indicates loss of CH3CN as a
consequence of retrocycloaddition reaction. In IR spectra, the
heterocycles show strong bands due to ν(CdN) stretch at 1670-
the fact that the success of the metal-mediated reaction is a
consequence of coordination of the nitrile ligand to the platinum
atom in a high oxidation state, i.e., the Pt(IV) ion. Indeed, all
attempts to perform the same reaction with the platinum(II)
acetonitrile compound [PtCl2(MeCN)2]seven under harsh reac-
tion conditionssfailed. Further studies on better understanding
the factors determining the progress of the reaction, on its
extension to other metal ions, and on making the [2 + 3]
cycloaddition metal-catalyzed are on the way in our group.
1
1680 cm-1. In H NMR spectra, the dC(Me)O protons were
detected in the range 2.11-2.68 and the N-CH-N proton
appears in the range 4.72-5.80 ppm. In 13C{1H} NMR spectra,
signals of dC(Me)O and N-CH-N carbons emerge in intervals
from 12.0 to 13.4 and 90.4 to 94.7 ppm, correspondingly, while
carbons of the CdN groups were observed in the very narrow
range 160.0-161.6 ppm.
Experimental Section
Materials and Instrumentation. Aldehydes and N-alkylhydroxy-
lamines were puchased from Aldrich. Solvents were obtained from
commercial sources and used as received. The complex [PtCl4-
(MeCN)2]35 was prepared as previously described. Nitrones were
synthesized by condensation of the corresponding aldehyde and
N-alkylhydroxylamine according to the published methods.36 C, H, and
N elemental analyses were carried out by the Microanalytical Service
of the Instituto Superior Te´cnico. Melting points were determined on
a Kofler table. For TLC, Merck UV 254 SiO2 plates were used. Positive-
ion FAB mass spectra were obtained on a Trio 2000 instrument by
bombarding 3-nitrobenzyl alcohol (NBA) matrixes of the samples with
8 keV (ca. 1.28 × 1015 J) Xe atoms. Mass calibration for data system
We were unable to isolate or to characterize in situ Nd
C(Me)O-N(Me)-CH(p-C6H4NMe2) because the appropriate
complex [PtCl4(NdC(Me)O-N(Me)-CH(p-C6H4NMe2))2] is
rather unstable in solutions and its degradation occurs much
faster than the substitution of the heterocycle by pyridine.
IR and NMR Spectroscopic Results for the Platinum(IV)
Complexes. Comparison of IR spectra of the products with that
of [PtCl4(MeCN)2] shows disappearance of the CtN stretching
vibrations at 2354 cm-1 and appearance of one strong ν(CdN)
band in the range 1597-1612 cm-1. These values are consider-
ably lower than those found for the uncoordinated ∆4-1,2,4-
oxadiazolines (1670 cm-1), indicating a weakening of the Cd
N double bond by coordination to the metal. In the course of
the cycloaddition reaction, a new stereocenter is generated at
the nitrone carbon atom, thus giving rise to two diastereomeric
platinum complexes which display two sets of signals in a ratio
acquisition was achieved using CsI. Infrared spectra (4000-400 cm-1
)
were recorded on a BIO-RAD FTS 3000MX instrument in KBr pellets.
1H, 13C{1H}, and 195Pt NMR spectra were measured on Varian UNITY
300 and Bruker AMX 300 spectrometers at ambient temperature. 195Pt
chemical shifts are given relative to aqueous K2[PtCl4] ) -1630 ppm,
and half-height line widths are shown in parentheses.
X-ray Structure Determination of trans-[PtCl4{NdC(Me)ON-
1
of 1:1 and with small difference in chemical shifts in both H
(Me)-CH(p-C6H4OMe)}2]. Light-yellow plates of the complex were
grown from dichloromethane solution upon addition of diethyl ether.
Diffraction data were collected on an Enraf-Nonius CAD 4 diffracto-
meter. Cell parameters were obtained from 24 centered reflections with
Θ between 10° and 13°. Range of hkl: h ) 0 to 15, k ) 0 to 9, l )
-17 to 17. Standard reflections were measured every 60 min and
showed practically no change with time ((1%). Diffractometer data
were processed by the program PROFIT37 with profile analysis of
reflections. The structures were solved by means of Fourier synthesis
based upon the Pt-atom coordinates obtained from the Patterson
synthesis using the SHELXTL package.38 After that, all reflections with
I < 2σ(I) were excluded from calculations. Refinement was done by
full-matrix least squares based on F2 using the SHELX-97 package.39
All non-H atoms were treated anisotropically. H atoms were located
in a difference Fourier map and refined isotropically. An extinction
correction has been applied. Lorentz, polarization, and absorption
corrections were made.40 Scattering factors are from International
Tables for X-ray Crystallography.41 Crystal data are given in Table 1,
bond distances and angles in Table 2.
(∆δ ca. 0.01 ppm) and 13C{1H} NMR spectra (∆δ ca. 0.05
ppm). The N-CH-N group appears in 1H NMR typically at a
chemical shift of 5.25-6.75 ppm and displays a coupling (3JPtH
of 12-13 Hz), whereas the corresponding 13C signal is in the
2
range 87.3-94.3 ppm with JPtC from 20 to 21 Hz. For the d
1
C(Me)O group, a H chemical shift of 2.80 to 3.06 ppm (4JPtH
of 3.0-4.5 Hz) was observed, while the 13C signal appears in
the range 15.0-17.4 ppm (3JPtC of 3.0-4.2 Hz). The fact that
both groups display coupling constants to platinum and also
the values of the coupling constants indicate that the heterocyclic
ligands in all complexes are coordinated to platinum via their
iminoacyl nitrogens. An additional argument in favor of
coordination by the imino N atom is the chemical shift of the
NdC carbon itself (174.6-177.5 ppm), which appears at
considerably lower field than the corresponding carbon in the
free ligands (160.0-161.6 ppm).
The 195Pt NMR spectra of the diastereoisomers, in contrast
1
to the H and 13C{1H} ones, show only one broad signal with
Preparation of the Oxadiazoline Platinum(IV) Complexes. A
mixture of [PtCl4(MeCN)2] (42 mg, 0.10 mmol) and the corresponding
nitrone (0.20 mmol) in CH2Cl2 (2.0 mL) was stirred for 4 h at room
temperature, whereupon the initial suspension became a homogeneous
a half-height peak width in the range 520-800 Hz. The chemical
shifts range from -98 to -190 ppm, depending on the structure
of the heterocyclic ligand and solvent employed for NMR
measurements. This interval agrees well with that observed for
trans-[PtCl4(iminoacyl)2] complexes,5,6,9 thus giving additional
arguments in favor of trans arrangement of the oxadiazoline
ligands. No evidence for the presence of the other geometrical
isomer was obtained from the NMR data.
Concluding Remarks. Our results show that nonactivated
organonitriles can be readily activated toward [2 + 3] cycload-
dition reactions with nitrones by coordination to a platinum-
(IV) center, thus giving easy access to ∆4-1,2,4-oxadiazoline
complexes, from which the oxadiazoline ligands can be liberated
almost quantitatively under mild conditions using pyridine, and
providing a novel and simple synthetic route for such a rare
type of heterocycle. Attention additionally should be drawn to
(35) Kukushkin, V. Yu.; Tkachuk, V. M. Z. Anorg. Allg. Chem. 1992,
613, 123.
(36) Houben Weyl, Methoden der Organischen Chemie; 4. Aufl. Vol. E
14b; Thieme Verlag: Stuttgart, Germany.
(37) Strel’tsov, V. A.; Zavodnik, V. E. Kristallografia 1989, 34, 1369.
(38) Sheldrick, G. M. SHELXTL User Manual, Rev. 3; Nicolet XRD
Corp.: Madison, WI, 1981.
(39) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(40) Axelrud, L. G.; Grin, Yu. N.; Zavalii, P. Yu.; Pecharsky, V. K.;
Fundamensky, V. S. CSD-universal program package for single crystal and/
or powder structure data treatment. Collected Abstracts, XII-th European
Crystallographic Meeting, Moscow, August 1989; USSR Academy of
Sciences: Moscow, 1989; p 155.
(41) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV.

3110 J. Am. Chem. Soc., Vol. 122, No. 13, 2000
Wagner et al.
Table 1. Crystal Data and Structure Refinement for
trans-[PtCl4{NdC(Me)ON(Me)-CH(p-C6H4OMe)}2]
[PtCl4(NdC(Me)O-N(CH2Ph)-C(H)Ph)2] (Two Diastereoiso-
mers, 1:1). Yield: 81%. Anal. Calcd for C32H32N4Cl4O2Pt: C, 45.67;
H, 3.83; N, 6.66. Found: C, 45.47; H, 3.76; N, 6.45. FAB+-MS, m/z:
771 [M - 2Cl]+, 698 [M - 4Cl - 2H]+. Mp: 176 °C. TLC on SiO2:
Rf ) 0.85 (eluent CH2Cl2). IR spectrum (selected bands), cm-1: 1607
s ν(CdN). 1H NMR spectrum in CDCl3, δ: 3.04 and 3.06 (s + d each,
4JPtH 4.5 Hz, 3H each, dC(Me)O), 4.19, 4.20, 4.30, and 4.31 (four d,
empirical formula
fw
temp, K
wavelength, Å
cryst syst
space group
a, Å
C22H28Cl4N4O4Pt
749.36
293(2)
0.71073
monoclinic
P21/a (No. 14)
12.6010(10)
7.572(5)
3
12.3 Hz, 1H each, CH2Ph), 6.52 and 6.55 (two s + d, JPtH 12.0 Hz,
1H each, N-CH-N), 7.00 (m, 2H) and 7.32 (m, 3H) (Ph), 7.40 (m,
3H) and 7.53 (m, 2H) (CH2Ph). 13C{1H} NMR spectrum in CDCl3, δ:
15.60 and 15.67 (3JPtC 4.2 Hz, NdC(Me)O), 60.84 and 60.92 (CH2-
Ph), 87.98 and 88.08 (2JPtC 20.6 Hz, N-CH-N), 125.79 and 125.83
(o-Ph), 128.3 (m-Ph), 128.5 and 128.6 (p-Ph and p-PhCH2), 128.7
(PhCH2), 130.0 (PhCH2), 132.93 and 132.97 (ipso-PhCH2), 137.74 and
137.78 (ipso-Ph), 175.25 and 175.38 (CdN). 195Pt NMR spectrum
CDCl3, δ: -180 (775 Hz).
b, Å
c, Å
14.497(2)
90
102.83(3)
90
1348.7(9)
2
1.845
R, deg
â, deg
γ, deg
V, Å3
Z
F
calcd, Mg m-3
µ(Mo KR), mm-1
5.634
[PtCl4(NdC(Me)O-N(Me)-C(H)(p-C6H4Me))2] (Two Diastereo-
isomers, 1:1). Yield: 70%. Anal. Calcd for C22H28N4Cl4O2Pt: C, 36.83;
H, 3.93; N, 7.80. Found: C, 36.68; H, 3.90; N, 7.79. FAB+-MS, m/z:
669 [M - 2Cl + Na]+, 646 [M - 2Cl]+, 611 [M - 3Cl]+, 575 [M -
4Cl - 2H]+. Mp: 190 °C (dec). TLC on SiO2, Rf ) 0.73 (eluent CH2-
reflns collected/unique
data/restraints/params
goodness-of-fit on F 2
final R indices [I > 2σ(I)]
1934/1844 [R(int) ) 0.053]
1844/0/205
1.155
R1 ) 0.0287
wR2 ) 0.0755
1
Cl2). IR spectrum (selected bands), cm-1: 1606 s ν(CdN). H NMR
spectrum in CDCl3, δ: 2.30 (s, 6H, C6H4Me), 2.87 and 2.89 (two s,
3H each, C-N(Me)-O), 2.93 and 2.94 (s + d each, JPtH 4.2 Hz, 3H
Table 2. Bond Lengths (Å) and Angles (deg) for
trans-[PtCl4{NdC(Me)ON(Me)-CH(p-C6H4OMe)}2]
4
each, dC(Me)O), 6.38 (s + d, 3JPtH 11.9 Hz, 2H, N-CH-N), 7.05 (d,
8.1 Hz, 4H) and 7.13 (d, 8.1 Hz, 4H) (C6H4Me). 13C{1H} NMR
spectrum in CDCl3, δ: 15.54 and 15.58 (3JPtC 4 Hz, NdC(Me)O), 21.2
(C6H4Me), 46.0 (C-N(Me)-O), 90.59 and 90.64 (2JPtC 20 Hz, N-CH-
N), 125.70 and 125.90 (CH), 129.2 (CH), 134.83 and 134.86 (Cq),
138.7 (Cq) (C6H4Me), 174.65 (CdN). 195Pt NMR spectrum in CDCl3,
δ: -194 (700 Hz).
Pt-Cl(1)
2.305(2)
2.321(2)
2.047(6)
1.265(9)
1.350(7)
1.488(7)
1.473(9)
1.499(9)
1.480(10)
1.473(10)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
C(8)-C(3)
C(6)-O(2)
O(2)-C(9)
1.513(9)
1.399(10)
1.381(11)
1.367(10)
1.386(10)
1.382(10)
1.374(9)
1.367(8)
1.393(15)
Pt-Cl(2)
Pt-N(1)
N(1)-C(1)
C(1)-O(1)
O(1)-N(2)
N(2)-C(2)
C(2)-N(1)
C(1)-C(10)
N(2)-C(11)
[PtCl4(NdC(Me)O-N(Me)-C(H)(p-C6H4OMe))2] (Two Di-
astereoisomers, 1:1). Yield: 67%. Anal. Calcd for C22H28N4Cl4O4Pt:
C, 35.26; H, 3.77; N, 7.48. Found: C, 35.75; H, 3.86; N, 7.33. FAB+-
MS, m/z: 701 [M - 2Cl + Na]+, 678 [M - 2Cl]+, 643 [M - 3Cl -
H]+, 607 [M - 4Cl - 2H]+. Mp: 176 °C. TLC on SiO2: Rf ) 0.77
(eluent CH2Cl2). IR spectrum (selected bands), cm-1: 1612 s ν(Cd
N(1)#1-Pt-N(1)a
N(1)-Pt-Cl(1)
180.00
O(1)-C(1)-C(10)
112.6(6)
89.77(17) O(1)-N(2)-C(11) 105.8(6)
N(1)-Pt-Cl(2)
88.55(16) C(2)-N(2)-C(11)
90.23(17) N(2)-C(2)-C(3)
91.45(16) N(1)-C(2)-C(3)
113.6(6)
109.6(5)
112.9(5)
122.8(6)
119.9(6)
121.3(7)
119.4(6)
119.3(7)
122.0(6)
119.0(6)
115.4(6)
125.2(6)
119.6(7)
1
N). H NMR spectrum in CDCl3, δ: 2.86 and 2.87 (two s, 3H each,
N(1)#1-Pt-Cl(1)
N(1)#1-Pt-Cl(2)
Cl(1)-Pt-Cl(2)
Cl(1)#1-Pt-Cl(2)
4
C-N(Me)-O), 2.92 and 2.93 (s + d each, JPtH 3.0 Hz, 3H each, d
C(Me)O), 3.75 (s, 6H, OMe), 6.35 (s + d, 3JPtH 11.7 Hz, 2H, N-CH-
N), 6.84 (d, 8.8 Hz, 4H) and 7.10 (d, 8.8 Hz, 4H) (C6H4OMe). 13C{1H}
NMR spectrum in CDCl3, δ: 15.59 and 15.64 (3JPtC 4 Hz, NdC(Me)O),
45.9 (C-N(Me)-O), 55.2 (OMe), 90.38 and 90.46 (2JPtC 21 Hz,
N-CH-N), 113.8 (CH), 127.17 and 127.19 (CH), 129.85 and 129.90
(Cq), 159.9 (Cq), 174.7 (CdN). 195Pt NMR spectrum in CDCl3, δ:
-190 (600 Hz).
91.36(6)
88.64(6)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(7)-C(8)-C(3)
C(8)-C(3)-C(2)
C(5)-C(6)-O(2)
C(7)-C(6)-O(2)
C(6)-O(2)-C(9)
Cl(1)#1-Pt-Cl(1) 180.00
Pt-N(1)-C(1)
130.8(5)
122.7(4)
115.1(6)
105.7(5)
100.2(5)
102.7(5)
106.1(5)
Pt-N(1)-C(2)
N(1)-C(1)-O(1)
C(1)-O(1)-N(2)
O(1)-N(2)-C(2)
N(2)-C(2)-N(1)
C(2)-N(1)-C(1)
[PtCl4(NdC(Me)O-N(Me)-C(H)(p-C6H4NO2))2]. Yield: 91%.
Anal. Calcd for C20H22N6Cl4O6Pt: C, 30.82; H, 2.85; N, 10.78.
Found: C, 30.96; H, 2.75; N, 10.41. FAB+-MS in NBA matrix shows
no signals characteristic for the compound. The compound has no
defined melting point: on heating, it decomposes above 270 °C. TLC
on SiO2: Rf ) 0.60 (eluent CH2Cl2). IR spectrum (selected bands),
cm-1: 1603 s ν(CdN), 1524 s νas(NO2), 1350 νs(NO2). In 300 MHz
NMR spectra we observed only one set of signals and were unable to
distinguish diastereoisomers. 1H NMR spectrum in CDCl3, δ: 2.76 (s,
3H, C-N(Me)-O), 2.80 (s + d, 4JPtH 3.9 Hz, 3H, dC(Me)O), 6.32 (s
+ d, 3JPtH 12.3 Hz, 1H, N-CH-N), 7.26 (d, 8.5 Hz, 2H) and 8.00 (d,
8.6 Hz, 2H) (C6H4). 13C{1H} NMR spectrum in CDCl3, δ: 15.0 (3JPtC
4 Hz, NdC(Me)O), 45.6 (C-N(Me)-O), 88.9 (2JPtC 21 Hz, N-CH-
N), 122.9 (CH), 126.9 (CH), 144.2 (Cq) and 147.5 (Cq) (C6H4), 175.4
(CdN). 195Pt NMR spectrum in CDCl3, δ: -198 (600 Hz).
N(1)-C(1)-C(10) 132.2(6)
a Symmetry transformations used to generate equivalent atoms: #1,
-x + 1, -y + 1, -z + 1.
yellow solution. After chromatography on SiO2/CH2Cl2 and evaporation
of the solvent, the product was obtained as a pale yellow powder.
[PtCl4(NdC(Me)O-N(Me)-C(H)Ph)2] (Two Diastereoisomers,
1:1). Yield: 72%. Anal. Calcd for C20H24N4Cl4O2Pt: C, 34.85; H, 3.51;
N, 8.13. Found: C, 34.82; H, 3.40; N, 7.83. FAB+-MS, m/z: 689 [M]+,
619 [M - 2Cl]+, 583 [M - 3Cl - H]+, 547 [M - 4Cl - 2H]+. Mp:
173 °C. TLC on SiO2: Rf ) 0.77 (eluent CH2Cl2). IR spectrum (selected
bands), cm-1: 1604 s ν(CdN). 1H NMR spectrum in CDCl3, δ: 2.93
and 2.94 (two s, 3H each, C-N(Me)-O), 2.98 and 2.99 (s + d each,
3
4JPtH 4.2 Hz, 3H each, dC(Me)O), 6.45 (s + d, JPtH 12.1 Hz, 2H,
[PtCl4(NdC(Me)O-N(Me)-C(H)(o-C6H4OH))2] (Two Diastereo-
isomers, 1:1). Yield: 94%. Anal. Calcd for C20H24N4Cl4O4Pt: C, 33.30;
H, 3.35; N, 7.77. Found: C, 31.22; H, 3.35; N, 7.22. FAB+-MS, m/z:
722 [M + H]+, 651 [M - 2Cl]+, 615 [M - 3Cl - H]+, 579 [M - 4Cl
- 2H]+. Mp: 157 °C dec. TLC on SiO2: Rf ) 0.50 (eluent 9:1 CH2-
Cl2:acetone). IR spectrum (selected bands), cm-1: 3367 s ν(OH), 1610
s ν(CdN). 1H NMR spectrum in acetone-d6, δ: 2.85 and 2.86 (two s,
N-CH-N), 7.22 (m, 4H) and 7.36 (m, 6H) (Ph). 13C{1H} NMR
spectrum in CDCl3, δ: 15.50 and 15.54 (3JPtC 4 Hz, NdC(Me)O), 46.0
(C-N(Me)-O), 90.57 and 90.62 (2JPtC 20 Hz, N-CH-N), 125.81 and
125.83 (o-Ph), 128.4 (m-Ph), 128.79 and 128.82 (p-Ph), 137.66 and
137.69 (ipso-Ph), 174.83 and 174.90 (CdN). 195Pt NMR spectrum in
CDCl3, δ: -192 (800 Hz).

∆4-1,2,4-Oxadiazolines
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3111
4
1
3H each, C-N(Me)-O), 2.96 (s + d, JPtH 4.1 Hz, 6H, dC(Me)O),
6.75 (m, 2H, N-CH-N), 6.75 (m, 2H), 6.85 (ddd, 7.8 Hz, 3.3 Hz, 1.2
Hz, 2H), 6.96 (d, 7.5 Hz, 2H) and 7.11 (m, 2H) (C6H4O). 13C{1H}
NMR spectrum in acetone-d6, δ: 15.80 and 15.85 (3JPtC 4 Hz, Nd
C(Me)O), 45.8 (C-N(Me)-O), 87.3 (broad, N-CH-N), 115.9, 119.6,
125.9, 127.3, 130.1, and 154.8 (C6H4OH), 176.3 (CdN). 195Pt NMR
spectrum in acetone-d6, δ: -142 (520 Hz).
cm-1: 1677 s ν(CdN). H NMR spectrum in CDCl3, δ: 2.12 (s, 3H,
dC(Me)O), 4.14 (d, 12.6 Hz, 1H) and 4.29 (d, 12.9 Hz, 1H) (CH2Ph),
5.80 (s, 1H, N-CH-N), 7.31-7.42 (m, 10H, Ph and CH2Ph). 13C-
{1H} NMR spectrum in CDCl3, δ: 12.1 (NdC(Me)O), 63.3 (CH2Ph),
90.4 (N-CH-N), 126.4, 128.4, 128.5, and 140.2 (Ph), 128.2, 128.6,
129.4 and 135.3 (CH2Ph), 161.6 (CdN).
NdC(Me)O-N(Me)-C(H)(p-C6H4Me). Yield: 88%. Oil. EI-MS,
m/z: 189 [M - 1], 148 [M - 1 - CH3CN], 131 [M - CH3CN -
H2O]. TLC on SiO2: Rf ) 0.28 (eluent 9:1 CH2Cl2:Et2O). IR spectrum
(selected bands), cm-1: 1676 s ν(CdN). 1H NMR spectrum in CDCl3,
δ: 2.11 (s, 3H, dC(Me)O), 2.35 (s, 3H, C6H4Me), 2.88 (s, 3H,
C-N(Me)-O), 5.52 (s, 1H, N-CH-N), 7.18 (d, 7.8 Hz, 2H), 7.29
(d, 7.8 Hz, 2H) (C6H4Me). 13C{1H} NMR spectrum in CDCl3, δ: 12.1
(NdC(Me)O), 21.2 (C6H4Me), 47.0 (C-N(Me)O), 93.4 (N-CH-N),
125.8, 126.2, 129.2 and 138.1 (C6H4Me), 161.1 (CdN).
[PtCl4(NdC(Me)O-N(Me)-C(H)(p-C6H4NMe2)•HCl)2] (Two Di-
astereoisomers, 1:1). This complex precipitates directly from the
reaction mixture. It is washed with 10 mL of CH2Cl2 and 5 mL of
ether and dried in air. Yield: 98%. Anal. Calcd for C24H36N6Cl6O2Pt:
C, 33.98; H, 4.28; N, 9.91. Found: C, 33.35; H, 4.24; N, 9.00. FAB+-
MS, m/z: 704 [PtCl4(NC(Me)ON(Me)C(H)C6H4NHMe2)2 - 2Cl]+.
Mp: 141 °C dec. IR spectrum (selected bands), cm-1: 1597 s ν(Cd
N). 1H NMR spectrum in DMSO-d6, δ: 2.84 and 2.91 (two s, 3H each,
3
C-N(Me)-O and dC(Me)O), 2.98 (s, 6H, NMe2), 6.40 (s + d, JPtH
NdC(Me)O-N(Me)-C(H)(p-C6H4OMe). Yield: 73%. Oil. EI-
MS, m/z: 206 [M], 164 [M - 1 - CH3CN], 146 [M - 1 - CH3CN
- H2O]. TLC on SiO2: Rf ) 0.28 (eluent 9:1 CH2Cl2:Et2O). IR
spectrum (selected bands), cm-1: 1674 s ν(CdN). 1H NMR spectrum
in CDCl3, δ: 2.11 (s, 3H, dC(Me)O), 2.87 (s, 3H, C-N(Me)-O),
3.79 (s, 3H, C6H4OMe), 5.50 (s, 1H, N-CH-N), 6.89 (d, 8.7 Hz, 2H),
7.31 (d, 8.4 Hz, 2H) (C6H4OMe). 13C{1H} NMR spectrum in CDCl3,
δ: 12.1 (NdC(Me)O), 47.0 (C-N(Me)O), 55.3 (C6H4OMe), 93.3 (N-
CH-N), 113.9, 123.8, 127.6 and 149.8 (C6H4Me), 160.0 (CdN).
11.8 Hz, 1H, N-CH-N), 7.23 (m, 4H, C6H4NMe2). The complex is
rather unstable in DMSO-d6 and poorly soluble in most other common
deuterated solvents to measure the 13C{1H} NMR spectrum. 195Pt NMR
spectrum in DMSO-d6, δ: -98 (560 Hz).
[PtCl4(NdC(Me)O-N(Me)-C(H)(p-C6H4NMe2))2]. The complex
is liberated from the corresponding hydrochloride adduct by stirring a
suspension of [PtCl4(NdC(Me)O-N(Me)-C(H)(p-C6H4NMe2)‚HCl)2]
and Na2CO3 in CH2Cl2, followed by filtration and evaporation of the
solvent. Yield: 70%. The complex is very unstable, even in the solid
state, and its degradation is already significant within 1 h after isolation.
Elemental analyses obtained were unsatisfactory. However, spectrosopy
data presented below give arguments in favor of the proposed structure.
NdC(Me)O-N(Me)-C(H)(p-C6H4NO2). Yield: 65%. Oil. EI-MS,
m/z: 221 [M], 180 [M - CH3CN]. TLC on SiO2: Rf ) 0.26 (eluent
9:1 CH2Cl2:Et2O). IR spectrum (selected bands), cm-1: 1672 s ν(Cd
1
N), 1519 s νas(NO2), 1346 νs(NO2). H NMR spectrum in CDCl3, δ:
2.11 (s, 3H, dC(Me)O), 2.91 (s, 3H, C-N(Me)-O), 5.64 (s, 1H,
N-CH-N), 7.61 (d, 9.0 Hz, 2H) and 8.23 (d, 8.7 Hz, 2H) (C6H4).
13C{1H} NMR spectrum in CDCl3, δ: 12.0 (NdC(Me)O), 47.0 (C-
N(Me)-O), 92.2 (N-CH-N), 127.3 (CH), 129.2 (CH), 139.2 (Cq)
and 147.1 (Cq) (C6H4), 160.2 (CdN).
:
IR spectrum (selected bands), cm-1 1611 s ν(CdN). 1H NMR
spectrum in CDCl3, δ: 2.86 (s, 3H, C-N(Me)-O), 2.91 (s, 6H, NMe2),
3
2.96 (s, 3H, dC(Me)O), 6.33 (s + d, JPtH 12.0 Hz, 1H, N-CH-N),
6.73 (m, 2H) and 7.04 (d, 7.2 Hz, 2H) (C6H4NMe2). The complex is
rather unstable in CDCl3 to measure the 13C{1H} NMR spectrum. 195Pt
NMR spectrum in CDCl3, δ: -173 (650 Hz).
NdC(Me)O-N(Me)-C(H)(o-C6H4OH). Yield: 72%. Oil. EI-MS,
m/z: 191 [M - 1], 151 [M - CH3CN]. TLC on SiO2: Rf ) 0.13 (eluent
9:1 CH2Cl2:Et2O). IR spectrum (selected bands), cm-1: 3374 s ν(OH),
1675 s ν(CdN). 1H NMR spectrum in CDCl3, δ: 2.06 (s, 3H,
dC(Me)O), 2.93 (s, 3H, C-N(Me)-O), 5.92 (s, 1H, N-CH-N), 6.93
(m, 1H), 7.03 (m, 1H) and 7.32 (m, 2H) (C6H4O). 13C{1H} NMR
spectrum in CDCl3, δ: 13.3 (NdC(Me)O), 46.5 (C-N(Me)-O), 88.9
(N-CH-N), 117.6, 120.5, 125.2, 126.9, 130.8, and 153.7 (C6H4OH),
160.0 (CdN).
[PtCl4(NdC(Me)O-N(CH2Ph)-C(H)tBu)2] (Two Diastereoiso-
mers, 1:1). Yield: 50%. Anal. Calcd for C28H40N4Cl4O2Pt: C, 41.96;
H, 5.03; N, 6.99. Found: C, 40.98; H, 4.41; N, 6.65. FAB+-MS, m/z:
753 [M - 2Cl + Na]+, 731 [M - 2Cl]+. Mp: 214 °C dec. TLC on
SiO2: Rf ) 0.90 (eluent CH2Cl2). IR spectrum (selected bands), cm-1
:
1
1567 s ν(CdN). H NMR spectrum in CDCl3, δ: 1.03 and 1.04 (two
t
4
s, 9H each, Bu), 2.85 and 2.87 (s + d each, JPtH 3.5 Hz, 3H each,
dC(Me)O), 4.11 (d, 13.1 Hz, 2H), 4.20 (d, 13.1 Hz, 1H) and 4.21 (d,
3
13.1 Hz, 1H) (CH2Ph), 5.25 and 5.26 (two s + d, JPtH 13.0 Hz, 1H
NdC(Me)O-N(CH2Ph)-C(H)tBu. Yield: 53%. Oil. EI-MS,
m/z: 232 [M], 191 [M - CH3CN], 173 [M - CH3CN - H2O]. TLC
on SiO2: Rf ) 0.31 (eluent 9:1 CH2Cl2:Et2O). IR spectrum (selected
bands), cm-1: 1670 s ν(CdN). 1H NMR spectrum in CDCl3, δ: 1.08
each, N-CH-N), 7.38 (m, 3H) and 7.51 (m, 2H) (CH2Ph). 13C{1H}
NMR spectrum in CDCl3, δ: 17.36 and 17.42 (3JPtC 3.0 Hz, Nd
C(Me)O), 27.67 and 27.72 ((CH3)3C), 37.8 ((CH3)3C), 61.30 and 61.37
(CH2Ph), 94.20 and 94.34 (2JPtC 20.2 Hz, N-CH-N), 128.0 (p-PhCH2),
128.4 (PhCH2), 129.72 and 129.75 (PhCH2), 134.1 (ipso-PhCH2), 177.5
(CdN). 195Pt NMR spectrum CDCl3, δ: +107 (775 Hz).
t
(s, 9H, Bu), 2.68 (s, 3H, dC(Me)O), 3.82 (dd, 13.2 Hz, 2.1 Hz, 1H)
and 4.72 (d, 13.2 Hz, 1H) (CH2Ph), 4.72 (s, 1H, N-CH-N), 7.30-
7.40 (m, 5H, Ph). 13C{1H} NMR spectrum in CDCl3, δ: 13.4 (Nd
C(Me)O), 25.3 (C(CH3)3), 35.6 (C(CH3)3), 62.9 (CH2Ph), 94.7 (N-
CH-N), 128.2, 129.0, 130.2 and 134.4 (CH2Ph), 160.0 (CdN).
Liberation of Coordinated ∆4-1,2,4-Oxadiazolines by Reaction
with Pyridine. A solution of the corresponding platinum(IV) complex
(0.060 mmol) and pyridine (10.4 mg, 0.13 mmol) in CHCl3 (2.0 mL)
was stirred for 6 h at room temperature. In the course of reaction the
[PtCl4(pyridine)2] precipitates from the starting yellow solution as a
yellow powder. After filtration, the filtrate is evaporated to dryness in
vacuo and the residue formed analyzed without further purification.
Acknowledgment. G.W. is grateful to the PRAXIS XXI
program for a fellowship (BPD11779/97). A.J.L.P. thanks the
FCT (Foundation for Science and Tecnology) and the PRAXIS
XXI program for financial support. V.Yu.K. is very much
obliged to the Russian Fund for Basic Research (Grant 97-03-
33626a) and the PRAXIS XXI program (Grant BCC16428/98)
for financial support of this study.
NdC(Me)O-N(Me)-C(H)Ph. Yield: 78%. Oil. EI-MS, m/z: 175
[M - 1], 134 [M - 1 - CH3CN], 118 [M - 1 - CH3CN - O]. TLC
on SiO2: Rf ) 0.32 (eluent 9:1 CH2Cl2:Et2O). IR spectrum (selected
bands), cm-1: 1673 s ν(CdN). 1H NMR spectrum in CDCl3, δ: 2.11
(s, 3H, dC(Me)O), 2.89 (s, 3H, C-N(Me)-O), 5.55 (s, 1H, N-CH-
N), 7.32-7.39 (m, 5H, Ph). 13C{1H} NMR spectrum in CDCl3, δ: 12.0
(NdC(Me)O), 47.5 (C-N(Me)O), 93.5 (N-CH-N), 126.3, 128.3,
128.5 and 140.0 (Ph), 161.2 (CdN).
Supporting Information Available: Tables of crystal data
and refinement, atomic coordinates, bond length, angles, and
anisotropic parameters (PDF) and an X-ray crystallographic file
(CIF). This material is available free of charge via the Internet
at http://pubs.acs.org.
NdC(Me)O-N(CH2Ph)-C(H)Ph. Yield: 89%. Oil. EI-MS, m/z:
252 [M], 211 [M - CH3CN], 193 [M - CH3CN - H2O]. TLC on
SiO2: Rf ) 0.32 (eluent 9:1 CH2Cl2:Et2O). IR spectrum (selected bands),
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