PtII versus PdII-assisted [2u202f+u202f3] cycloadditions of nitriles and nitrone. Synthesis of nitrile-derived arylamido platinum(II) and Δ4-1,2,4-oxadiazoline palladium(II) complexes

Article abstract of DOI:10.1016/j.poly.2018.10.057

The reactions of bis(organonitrile) platinum(II) complexes trans-[PtCl₂(N[tbnd]CR)₂] (R = C₆H₄(p-HC[dbnd]O), CH₂C₆H₄(p-CH₃)) with pyrroline N-oxide ^?O⁺N[dbnd]CHCH₂CH₂CMe₂ afford arylamido platinum(II) complexes trans-[PtCl₂{(O[dbnd]CR)N[dbnd]CCH₂CH₂CMe₂NH}₂] (R = C₆H₄(p-HC[dbnd]O) (1), CH₂C₆H₄(p-CH₃) (2)). The spectral data of 1 and 2 show that the oxadiazoline rings in both cases have opened by a spontaneous N–O bond cleavage to form (Z)-p-formyl-N-(5,5-dimethylpyrrolidin-2-ylidene)benzamide or (Z)-N-(5,5-dimethylpyrrolidin-2-ylidene)-2-p-tolylacetamide ligands, respectively, where the N-atoms of the benzamide or acetamide moieties coordinate to platinum(II) metal centre in trans positions. However, the reactions of bis(organonitrile) palladium(II) complexes trans-[PdCl₂(N[tbnd]CR)₂] with pyrroline N-oxide furnish Δ⁴-1,2,4-oxadiazoline palladium(II) complexes trans-[PdCl₂{N[dbnd]C(R)ONC(H)CH₂CH₂CMe₂}₂] (R = C₆H₄(p-HC[dbnd]O) (3), CH₂C₆H₄(p-CH₃) (4)) as the exclusive detected products. Compounds 1–4 have been characterized by IR, ¹H, ¹³C NMR spectroscopy, elemental analyses, ESI⁺-MS and also, in the case of 1, by single crystal X-ray diffraction analysis.

Full text of DOI:10.1016/j.poly.2018.10.057

Accepted Manuscript
PtII versus PdII-assisted [2+3] cycloadditions of nitriles and nitrone. Synthesis
of nitrile-derived arylamido platinum(II) and Δ 4-1,2,4-oxadiazoline palladi-
um(II) complexes
Jamal Lasri, Naser Eltaher Eltayeb, Matti Haukka, Bandar A. Babgi
PII:
S0277-5387(18)30693-4
https://doi.org/10.1016/j.poly.2018.10.057
POLY 13531
DOI:
Reference:
Polyhedron
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Revised Date:
Accepted Date:
25 September 2018
21 October 2018
23 October 2018
Please cite this article as: J. Lasri, N. Eltaher Eltayeb, M. Haukka, B.A. Babgi, PtII versus PdII-assisted [2+3]
cycloadditions of nitriles and nitrone. Synthesis of nitrile-derived arylamido platinum(II) and Δ 4-1,2,4-oxadiazoline
palladium(II) complexes, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.10.057
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PtII versus PdII-assisted [2+3] cycloadditions of nitriles and nitrone.
Synthesis of nitrile-derived arylamido platinum(II) and 4-1,2,4-
oxadiazoline palladium(II) complexes
Jamal Lasria,*, Naser Eltaher Eltayeba, Matti Haukkab, Bandar A. Babgia
aDepartment of Chemistry, Rabigh College of Science and Arts, P.O. Box 344, King
Abdulaziz University, Jeddah, Saudi Arabia
bUniversity of Jyväskylä, Department of Chemistry, University of Jyväskylä, P.O. Box
35, FI-40014, Finland
* Corresponding author.
E-mail address: jlasri@kau.edu.sa (J. Lasri).
ABSTRACT
The reactions of bis(organonitrile) platinum(II) complexes trans-[PtCl2(N≡CR)2] (R =
-
C6H4(p-HC=O), CH2C6H4(p-CH3)) with pyrroline N-oxide O+N=CHCH2CH2CMe2
afford
arylamido
platinum(II)
complexes
trans-
[PtCl2{(O=CR)N=CCH2CH2CMe2NH}2] (R = C6H4(p-HC=O) (1), CH2C6H4(p-CH3)
(2)). The spectral data of 1 and 2 show that the oxadiazoline rings in both cases have
opened by a spontaneous N–O bond cleavage to form (Z)-p-formyl-N-(5,5-
dimethylpyrrolidin-2-ylidene)benzamide or (Z)-N-(5,5-dimethylpyrrolidin-2-ylidene)-2-
p-tolylacetamide ligands, respectively, where the N-atoms of the benzamide or
acetamide moieties coordinate to platinum(II) metal centre in trans positions. However,
the reactions of bis(organonitrile) palladium(II) complexes trans-[PdCl2(N≡CR)2] with
pyrroline N-oxide furnish 4-1,2,4-oxadiazoline palladium(II) complexes trans-
[PdCl2{N=C(R)ONC(H)CH2CH2CMe2}2] (R = C6H4(p-HC=O) (3), CH2C6H4(p-CH3)
(4)) as the exclusive detected products. Compounds 1-4 have been characterized by IR,
13
1H, C NMR spectroscopy, elemental analyses, ESI+-MS and also, in the case of 1, by
single crystal X-ray diffraction analysis.
Keywords: Platinum; Palladium; Nitriles; [2+3] Cycloadditions; N–O bond cleavage.
1.
Introduction

2
The 1,3-dipolar cycloaddition reactions of organonitriles with nitrones is one of the
most important routes for the preparation of 4-1,2,4-oxadiazolines [1,2]. However,
there are some difficulties associated with the use of nitriles as only organonitriles
bearing an electron acceptor group react with nitrones under harsh reaction conditions
[3,4]. The coordination of organonitriles to a platinum or palladium metal centre
becomes a useful strategy and facile metal-assisted route for the preparation of a variety
of products which are difficult to synthetize directly by pure organic chemistry [1]. The
N–O bond cleavage of the 4-1,2,4-oxadiazoline ligands can be promoted by thermal
heating to afford ketoimine palladium(II) complexes [5]. However, the 4-1,2,4-
oxadiazoline rings have been opened by N–O bond cleavage at room temperature [6] or
under heating [7] to form trans pyrrolylbenzamide palladium(II) complexes. On the
other hand, it was found that the platinum(II) complexes [PtCl2(RCN)2] (R = CH2Cl,
CH2CO2Me) react with a cyclic nitrone to furnish the ketoimino platinum(II) complexes
via one-pot reaction involving spontaneous N–O bond cleavage [8].
In this work, we would like to understand the difference between using platinum(II) and
palladium(II) metal centre as a Lewis acid for the 1,3-dipolar cycloaddition reaction of
pyrroline N-oxide and nitriles such as p-cyanobenzaldehyde and p-tolylacetonitrile.
Hence, we found that the reactions of trans-[PtCl2(N≡CR)2] with pyrroline N-oxide
afford trans-[PtCl2{(O=CR)N=CCH2CH2CMe2NH}2] complexes (R = C6H4(p-HC=O)
(1), CH2C6H4(p-CH3) (2)) as a result of the N–O bond cleavage of the oxadiazoline
rings. In contrast, the reactions of trans-[PdCl2(N≡CR)2] with pyrroline N-oxide furnish
trans-[PdCl2{N=C(R)ONC(H)CH2CH2CMe2}2] complexes (R = C6H4(p-HC=O) (3),
CH2C6H4(p-CH3) (4)) as the exclusive detected products.
2.
Experimental section
2.1. General methods
The bis(p-cyanobenzaldehyde) platinum(II) and palladium(II) complexes trans-
[MCl2(N≡CC6H4(p-HC=O))2] (M = Pt, Pd) and bis(p-tolylacetonitrile) platinum(II) and
palladium(II) complexes trans-[MCl2(N≡CCH2C6H4(p-CH3))2] (M = Pt, Pd) were
previously synthesized by one of us [2b,9]. Moreover, the 4-1,2,4-oxadiazoline
palladium(II) complex (3) was also reported by one of us in our previous work [2b].

3
Infrared spectra (4000-400 cm-1) were recorded on an Alpha Bruker FT-IR instrument
1
13
in KBr pellets and the wavenumbers are in cm-1. H and C NMR spectra (in CDCl3)
were measured on Bruker Avance III HD 600 MHz (Ascend™ Magnet) spectrometer at
ambient temperature. High resolution electrospray ionization mass spectrometry (ESI-
MS) or high resolution electron ionization (EI) mass spectra were recorded using an
impact II mass spectrometer from Bruker or Agilent Q-TOF 6520 instrument,
respectively; all mass spectrometry are reported as m/z.
2.2. Reaction of trans-[PtCl2(N≡CR)2] (R = C6H4(p-HC=O), CH2C6H4(p-CH3)) with
pyrroline N-oxide -O+N=CHCH2CH2CMe2
Pyrroline N-oxide (21.2 mg, 0.187 mmol) was added to a solution of trans-
[PtCl2(N≡CC6H4(p-HC=O))2] (45.0 mg, 0.085 mmol) or trans-[PtCl2(N≡CCH2C6H4(p-
CH3))2] (44.9 mg, 0.085 mmol) in chloroform (10 mL), and the reaction mixture was
stirred at room temperature for 2 h, whereupon the solvent was removed in vacuo. The
crude residue was purified by column chromatography on silica (chloroform as the
eluent, 50 mL), followed by evaporation of the solvent in vacuo to give the final trans-
dichloridobis[(Z)-p-formyl-N-(5,5-dimethylpyrrolidin-2-ylidene)benzamide]
platinum(II) complex (1) [57.7 mg, 90% yield] and trans-dichloridobis[(Z)-N-(5,5-
dimethylpyrrolidin-2-ylidene)-2-p-tolylacetamide] platinum(II) complex (2) [57.1 mg,
89% yield], respectively.
During the crystallization of 1 the free p-cyanobenzaldehyde has been co-crystallized
with the complex 1, and it has been confirmed by electron ionization (EI) mass
spectrometry, m/z: 131 [M]+ (Supplementary data). The presence of free p-
cyanobenzaldehyde in the crystals of 1 is due to its initial existence (in a small amount)
along with its coordinated platinum complex trans-[PtCl2(N≡CC6H4(p-HC=O))2]. After
the [2+3] cycloaddition reaction, we attempted to obtain single crystals directly from the
reaction mixture (before its purification by column chromatography on silica), which
explains the presence of free p-cyanobenzaldehyde in the crystal of complex 1.
2.2.1. Trans-[PtCl2{(O=CC6H4(p-HC=O))N=CCH2CH2CMe2NH}2] (1)
1
IR (cm-1): 1699 υ(NC=O), 1654 υ(N=C), 3258 υ(NH). H NMR (CDCl3), δ: 1.31 (s,
12H, CH3), 1.74 (s, 4H, CH2), 2.98 (s, 4H, CH2), 8.02 (d, JHH 8.1 Hz, 4H, CHaromatic),

4
13
8.18 (d, JHH 8.1 Hz, 4H, CHaromatic), 10.13 (s, 2H, HC=O). C NMR (CDCl3), δ: 28.3
(CH3), 128.8, 129.9, 137.1, 145.4 (Caromatic), 174.5 (NC=O), 191.7 (HC=O). The other
13
signals cannot be detected by C NMR even after a long accumulation period. Anal.
Calcd for C28H32N4O4Cl2Pt (753.14): C, 44.57; H, 4.27; N, 7.43. Found: C, 44.81; H,
4.63; N, 7.78. ESI+-MS, m/z: 753.12 [M]+.
2.2.2. Trans-[PtCl2{(O=CCH2C6H4(p-CH3))N=CCH2CH2CMe2NH}2] (2)
1
IR (cm-1): 1669 υ(NC=O), 1577 υ(N=C), 3417 υ(NH). H NMR (CDCl3), δ: 1.36 (s,
12H, CH3), 1.99 (m, 4H, CH2), 2.37 (m, 6H, CH3), 4.00 (t, JHH 7.4 Hz, 4H, CH2), 5.09
13
(s, 4H, CH2), 7.15-7.22 (m, 8H, CHaromatic), 10.89 (bs, 2H, NH). C NMR (CDCl3), δ:
21.1 (CH3), 28.7 (CH3), 32.9 (CH2), 47.2 (CH2), 65.1 (C-NH), 129.1, 130.0, 131.9,
136.6 (Caromatic), 173.6 (N=C), 184.6 (NC=O). Anal. Calcd for C30H40N4O2Cl2Pt
(753.22): C, 47.75; H, 5.34; N, 7.42. Found: C, 48.10; H, 5.55; N, 7.68. ESI+-MS, m/z:
753.16 [M]+.
2.3. Reaction of trans-[PdCl2(N≡CCH2C6H4(p-CH3))2] with pyrroline N-oxide
-O+N=CHCH2CH2CMe2
Pyrroline N-oxide (21.2 mg, 0.187 mmol) was added to a solution of trans-
[PdCl2(N≡CCH2C6H4(p-CH3))2] (37.4 mg, 0.085 mmol) in chloroform (10 mL), and the
reaction mixture was stirred at room temperature for 2 h, whereupon the solvent was
removed in vacuo. The crude residue was purified by column chromatography on silica
(chloroform as the eluent, 50 mL), followed by evaporation of the solvent in vacuo to
give the final 4-1,2,4-oxadiazoline palladium(II) complex (4) as the exclusive detected
product [45.3 mg, 80% yield].
2.3.1. Trans-[PdCl2{N=C(CH2C6H4(p-CH3))ONC(H)CH2CH2CMe2}2] (4)
IR (cm-1): 1659 υ(C=N). 1H NMR (CDCl3), δ: 0.98 and 1.01 (two s, 6H, two CH3), 1.07
and 1.09 (two s, 6H, two CH3), 1.26-1.32 (m, 2H, CH2), 1.55-1.70 (m, 6H, three CH2),
2.29 and 2.31 (two s, 6H, two CH3), 2.93-2.97 (m, 2H, CH2), 4.21-4.27 (m, 2H, CH2),
5.46 (t, JHH 5.4 Hz, 2H, N-CH-N), 7.12-7.22 (m, 4H, CHaromatic), 7.34-7.39 (m, 4H,
CHaromatic). 13C NMR (CDCl3), δ: 21.1, 22.2 and 27.2 (CH3), 30.2, 33.5 and 33.9 (CH2),
69.9 (Me2C-N), 88.4 (N-CH-N), 127.8, 129.4, 129.7 and 137.3 (Caromatic), 167.5 and

5
167.6 (C(O)=N). Anal. Calcd for C30H40N4O2Cl2Pd (664.16): C, 54.10; H, 6.05; N,
8.41. Found: C, 54.25; H, 6.17; N, 8.55. ESI+-MS, m/z: 663.02 [M-H]+.
2.4. X-ray structure determinations
The crystals of 1 were obtained by slow evaporation of its chloroform solution. The
crystals were measured on a D8 QUEST Bruker Diffractometer. The Apex3 [10]
program package was used for cell refinements and data reductions. Multi-scan
absorption correction (SADABS) [11] was applied to the intensities before structure
solution. The structure was solved using the SHELXT [12] software. Structural
refinement was carried out using SHELXL-2017 [12]. The NH hydrogen atom was
located from the difference Fourier map and refined isotropically. Other hydrogen
atoms were positioned geometrically and constrained to ride on their parent atoms, with
C—H = 0.95–1.00 Å, and Uiso = 1.2–1.5 Ueq (parent atom). The crystallographic
details are summarized in Table 1.
Table 1. Crystal Data of 1.
1
empirical formula C28H32Cl2N4O4Pt, C8H5NO,
2(CHCl3)
Fw
1124.43
temp (K)
115(2)
0.71073
Triclinic
P-1
8.981(5)
10.468(5)
13.049(8)
100.680(15)
(Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
α(
(
(
V (Å3)
Z
105.685(15)
103.623(14)
1106.5(11)
1
1.688
3.701
25321
4054

calc (Mg/m3)
(K) (mm-1)
No. reflns.
Unique reflns.
GOOF (F2)
Rint
1.07
0.040
0.0198
0.0424
R1a (I  2)
wR2b (I  2)
a R1 = ||Fo| – |Fc||/|Fo|. b wR2 = [[w(Fo2 – Fc2)2]/ [w(Fo ) ]]1/2.
2 2

6
3.
Results and discussion
3.1. Synthesis of platinum(II) complexes (1) and (2)
The reaction of bis(p-cyanobenzaldehyde) platinum(II) complex trans-
-
[PtCl2(N≡CC6H4(p-HC=O))2] with pyrroline N-oxide O+N=CHCH2CH2CMe2, in
CHCl3 at room temperature for 2 h, affords trans-dichloridobis[(Z)-p-formyl-N-(5,5-
dimethylpyrrolidin-2-ylidene)benzamide]
platinum(II)
complex
trans-
[PtCl2{(O=CC6H4(p-HC=O))N=CCH2CH2CMe2NH}2] (1) as the exclusive detected
product (Scheme 1, reaction a), instead of the expected 4-1,2,4-oxadiazoline
platinum(II) complex trans-[PtCl2{N=C(C6H4(p-HC=O))ONC(H)CH2CH2CMe2}2]
which has never been detected by NMR spectroscopy (Scheme 1, reaction b). Complex
1
13
1 has been characterized by IR, H, C NMR spectroscopy, elemental analysis, ESI+-
MS, and also by single crystal X-ray diffraction analysis which shows that the 4-1,2,4-
oxadiazoline rings have opened by spontaneous N–O bond cleavage to form (Z)-p-
formyl-N-(5,5-dimethylpyrrolidin-2-ylidene)benzamide ligands where both N-atoms of
the benzamide moieties coordinate to platinum(II) metal centre in trans positions.
The IR spectrum of complex 1 showed strong (NC=O) and (N=C) vibrations at 1699
13
and 1654 cm–1, respectively, and υ(NH) at 3258 cm–1. In the C NMR spectrum, the
NC=O resonances are detected at δ 174.5 ppm and confirm the N–O ring cleavage.

7
R
Cl
N
Pt
+
N
+
N
Cl
-
O
R
CHCl3
r.t., 2 h
(a)
(b)
R
R
R
R
Cl
Cl
O
N
O
O
N
O
Pt
Cl
Pt
Cl
N
N
N
N
H
N
H
N
1: R = C6H4(p-HC=O)
2: R = CH2C6H4(p-CH3)
Not detected
Ring opening by N-O bond cleavage
Scheme 1
On the other hand, the reaction of bis(p-tolylacetonitrile) platinum(II) complex trans-
[PtCl2(N≡CCH2C6H4(p-CH3))2] with pyrroline N-oxide, in CHCl3 at room temperature
for 2 h, furnishes trans-dichloridobis[(Z)-N-(5,5-dimethylpyrrolidin-2-ylidene)-2-p-
tolylacetamide]
platinum(II)
complex
trans-[PtCl2{(O=CCH2C6H4(p-
CH3))N=CCH2CH2CMe2NH}2] (2) as the exclusive detected product (Scheme 1,
reaction a). Also in this case, the expected 4-1,2,4-oxadiazoline platinum(II) complex
trans-[PtCl2{N=C(CH2C6H4(p-CH3))ONC(H)CH2CH2CMe2}2] has never been observed
by NMR spectroscopy (Scheme 1, reaction b). Complex 2 has been characterized by IR,
13
1H, C NMR spectroscopy, elemental analysis and ESI+-MS which shows that the 4-
1,2,4-oxadiazoline rings have opened by spontaneous N–O bond cleavage to form (Z)-
N-(5,5-dimethylpyrrolidin-2-ylidene)-2-p-tolylacetamide ligands.
The IR spectrum of complex 2 showed strong (NC=O) and (N=C) vibrations at 1669
1
and 1577 cm–1, respectively, and υ(NH) at 3417 cm–1. In the H NMR spectrum, the
proton NH resonance is detected at δ 10.9 ppm. In the 13C NMR spectrum, the N=C and

8
NC=O resonances are detected at δ 173.6 and 184.6 ppm, respectively, and confirm the
N–O ring cleavage.
3.2. X-ray structure crystallography
In the crystal structure, trans-dichloridobis[(Z)-p-formyl-N-(5,5-dimethylpyrrolidin-2-
ylidene)benzamide] platinum(II) complex 1 the central PtII metal atom displays a
distorted square-planar coordination (Fig. 1, Table 2). The two Cl atoms and the two N
atoms of imine groups forming the square-planar coordinated to the central PtII atom. In
1, the two Cl atoms and the two N atoms are trans with respect to each other.
The TELP Figure of structure 1 is shown in Fig. 1. The key non-covalent intermolecular
interactions involving the platinum complex were located by using a Hirschfeld surface
analysis. The Hirschfeld surface (dnorm) [13] is shown in Fig. 2. In structure 1, two
neighbouring platinum molecules are connected via two equivalent N-HO hydrogen
bonds (contact A in Fig. 2. Structural details are given in Table 2). The CH2-group of
the five-membered ring (C14) is acting as a weak H-bond donor for the chloride of
CHCl3 (contact E in Fig. 2). Simultaneously, the H-atom of the CHCl3 molecule is
acting as a donor for the O(2) oxygen of the Pt molecule (D). One of the methyl groups
on the five-membered ring (C12) is involved in two CH- interactions. The methyl
group is contacted both with the p-formylbenzamide group of the neighbouring Pt
complex (B) and with the free p-cyanobenzaldehyde molecule (C). The solvent of
crystallization i.e. CHCl3, is acting also as halogen bond donor for the platinum
coordinated Cl(1) ligand (F). The ClCl distance of 3.295(2) Å is equal to 5.9%
contraction of the contact compared to the sum of the Bondi’s van der Waals radii [14].
Such a small value is indicative for relatively weak halogen bond.

9
Fig. 1. The TELP drawing (50% probability level) of 1. The halogen bond contact
between the metal complex and CHCl3 solvent molecule: Cl(1)Cl(3): 3.295(2) Å,
C(15)-Cl(3)Cl(1): 166.82(11), Pt(1)-Cl(1)Cl(3): 141.61(4).
Fig. 2. Hirschfeld surface (dnorm) of 1. The figure is generated by CrystalExplorer
software [13]. Contacts: A: Hydrogen bond between N(2) and O(1), B: CH- interaction

10
between C(12) and the coordinated p-formylbenzamide group from the neighboring
metal complex. C: CH- interaction between C(12) and the noncoordinated p-
cyanobenzaldehyde molecule. D: Weak H-bond between CHCl3 (donor) and O(2) of the
noncoordinated molecule. E: Weak H-bond between C(14) and Cl(4). F: Halogen bond
between the chloroform (Cl(3) as donor) and the Cl(1) ligand.
Table 2. The intermolecular non-covalent contacts involving complex 1.
Contact
d(D-H) (Å)
0.78(3)
1.00
d(HA) (Å)
2.25(3)
2.19
d(DA) (Å)
2.990(3)
<DHA ()
159(3)
N(2)-H(2)O(1)#1
C(15)-H(15)O(2)#2
C(14)-H(14B) )Cl(4)#3
Contact
H-Bond A
H-Bond D
H-Bond E
3.180(4)
171.8
0.99
2.84
3.647(3)
138.6
d(C-H) (Å)
0.98
d(HC) (Å)
2.790
d(CC) (Å)
3.769
<C-HC ()
178.2
CH- B
CH- C
C(12)-H(12C)C(2)#4
C(12)-H(12C)C(7)#4
C(12)-H(12A)C(17)#5
C(12)-H(12A)C(18)#5
Contact
0.98
2.691
3.584
151.7
0.98
2.844
3.819
173.0
0.98
2.854
3.782
158.1
Pt(1)-Cl(1)
C(15)-
Cl(1)Cl(3)
Pt(1)-Cl(1)Cl(3)
Cl(3)Cl(1)
166.82(11)
Halogen bond F
2.3031(12)
3.295(2)
141.61(4)
Pt(1)-Cl(1) )Cl(3)
Symmetry transformations used to generate equivalent atoms: #1: -x+2,-y+2,-z+1, #2: x+1,y,z+1, #3: -
x+2,-y+1,-z+2, 4: x, -1+y, z, #5: 2-x, 1-y, 1-z.
3.3. Synthesis of palladium(II) complexes (3) and (4)
In our previous work [2b], we have shown that the reaction of pyrroline N-oxide with
bis(p-cyanobenzaldehyde) palladium(II) complex trans-[PdCl2(N≡CC6H4(p-HC=O))2]
afforded 4-1,2,4-oxadiazoline palladium(II) complex trans-[PdCl2{N=C(C6H4(p-
HC=O))ONC(H)CH2CH2CMe2}2] (3). Hence, the reaction of bis(p-tolylacetonitrile)
palladium(II) complex trans-[PdCl2(N≡CCH2C6H4(p-CH3))2] with pyrroline N-oxide, in
CHCl3 at room temperature for 2 h, furnishes 4-1,2,4-oxadiazoline palladium(II)
complex trans-[PdCl2{N=C(CH2C6H4(p-CH3))ONC(H)CH2CH2CMe2}2] (4) as the
exclusive detected product (Scheme 1, reaction a). In this case, the cleavage of the N–O
bond has not observed, and trans-dichloridobis[(Z)-N-(5,5-dimethylpyrrolidin-2-
ylidene)-2-p-tolylacetamide] palladium(II) complex trans-[PdCl2{(O=CCH2C6H4(p-

11
CH3))N=CCH2CH2CMe2NH}2] has never been detected by NMR spectroscopy
(Scheme 1, reaction b).
1
Complex 4 has been characterized by IR, H, 13C NMR spectroscopy, elemental
analysis and ESI+-MS which shows that the trans 4-1,2,4-oxadiazoline rings have been
formed without further N–O bond cleavage. The IR spectrum of complex 4 showed
1
strong (N=C) vibration at 1659 cm–1. In the H NMR spectrum, the proton N-CH-N
resonance is detected at δ 5.46 ppm. In the 13C NMR spectrum, the C(O)=N resonances
are detected at δ 167.5 and 167.6 ppm, and confirm the formation of the 4-1,2,4-
oxadiazoline rings.
In contrast with the oxadiazoline complexes formed by reaction of acyclic nitrones with
coordinated organonitriles, which exhibit two sets of signals corresponding to 1:1
diastereoisomeric mixtures [2d,15], complex 4 displays only one set of NMR signals
which indicate that the [2+3] cycloaddition reactions proceed with high
diastereoselectivity leading to the formation of a pair of enantiomers [(R,R)/(S,S)],
whereas in case of complex 4 two signals with very close chemical shift values (Δδ ~
0.11 ppm) were observed, which belong to two oxadiazoline moieties with a different
[(R,S)/(S,R)] configuration [6]. The structure of the cyclic nitrone (pyrroline N-oxide)
-O+N=CHCH2CH2CMe2 offers a more rigid conformation (E) than in the case of the
acyclic ones –O+N(Me)=C(H)(Ar) preventing one of the nitrone sides from the reaction,
thus promoting the selectivity [2b,6,16].

12
R
Cl
N
Pd
+
N
+
N
Cl
-
O
R
CHCl3
r.t., 2 h
(a)
(b)
R
R
R
R
Cl
Pd
Cl
Cl
Pd
Cl
O
O
O
N
O
N
N
N
H
N
H
N
N
N
Not detected
3: R = C6H4(p-HC=O)
4: R = CH2C6H4(p-CH3)
Scheme 2
4.
Conclusions
The results of this work show that the facile PtII-assisted [2+3] cycloaddition reaction of
cyclic nitrone (pyrroline N-oxide) with organonitrile RCN ligands (R = C6H4(p-HC=O),
CH2C6H4(p-CH3)), at room temperature, occurs with N–O bond rupture to give new PtII
complexes via a single-pot reaction. Hence, we succeeded to prepare trans-
[PtCl2{(O=CR)N=CCH2CH2CMe2NH}2] complexes (R
=
C6H4(p-HC=O) (1),
CH2C6H4(p-CH3) (2)). However, the expected 4-1,2,4-oxadiazoline platinum(II)
complexes trans-[PtCl2{N=C(R)ONC(H)CH2CH2CMe2}2] (R = C6H4(p-HC=O),
CH2C6H4(p-CH3)) have never been detected by NMR spectroscopy or X-ray
crystallography. On the other hand, using palladium(II) metal centre instead of
platinum(II), under the same experimental conditions, we succeeded to isolate 4-1,2,4-
oxadiazoline palladium(II) complexes trans-[PdCl2{N=C(R)ONC(H)CH2CH2CMe2}2]
(R = C6H4(p-HC=O) (3), CH2C6H4(p-CH3) (4)) as the exclusive products. Hence the

13
metal centre plays a key role in obtaining products with or without N–O bond cleavage.
The obtained results when using PtII centre are in good agreement with those observed
by other groups [8]. However, except in the case of 2-cyanopyridine [17], the use of PdII
centre for [2+3] cycloaddition of cyclic nitrone with nitriles, at room temperature,
affords in all cases 4-1,2,4-oxadiazoline palladium(II) complexes [2b,5,6].
Appendix A. Supplementary data
CCDC 1864425 contains the supplementary crystallographic data for complex 1. These
data
can
be
obtained
free
of
charge
the
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or
from
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgment
This project was funded by the Deanship of Scientific Research (DSR) at King
Abdulaziz University, Jeddah, under grant no. (G-100-662-37). The authors, therefore,
acknowledge with thanks DSR for technical and financial support.
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16
PtII versus PdII-assisted [2+3] cycloadditions of nitriles and nitrone.
Synthesis of nitrile-derived arylamido platinum(II) and 4-1,2,4-
oxadiazoline palladium(II) complexes
Jamal Lasri*, Naser Eltaher Eltayeb, Matti Haukka, Bandar A. Babgi
Graphical abstract
R
R
Cl
O
O
M = Pt
Pt
Cl
N
N
H
H
N
N
R
+
N
-
Cl
N
O
M
N
Cl
R
R
Cl
Pd
Cl
R
O
N
O
N
M = Pd
N
N
M = Pt or Pd

17
PtII versus PdII-assisted [2+3] cycloadditions of nitriles and nitrone.
Synthesis of nitrile-derived arylamido platinum(II) and 4-1,2,4-
oxadiazoline palladium(II) complexes
Jamal Lasri*, Naser Eltaher Eltayeb, Matti Haukka, Bandar A. Babgi
Synopsis
The reactions of trans-[PtCl2(N≡CR)2] with pyrroline N-oxide afford arylamido
platinum(II) complexes trans-[PtCl2{(O=CR)N=CCH2CH2CMe2NH}2] via one-pot
reaction involving spontaneous N–O bond cleavage. However, the reactions of trans-
[PdCl2(N≡CR)2] with pyrroline N-oxide furnish 4-1,2,4-oxadiazoline palladium(II)
complexes trans-[PdCl2{N=C(R)ONC(H)CH2CH2CMe2}2].