Preparation and crystal structure of binuclear chloro{6-[[chloro(triphenylphosphine)platinum](mesitylimino)methyl]pyridin-2-yl}bis(triphenylphosphine)platinum(II)

Article abstract of DOI:10.1016/j.poly.2008.09.019

Treatment of N,N′-bis(mesityl)pyridine-2,6-carboxyimidoyl dichloride, 1, in toluene solution with [Pt(PPh₃)₄] at 100 °C afforded a novel platinacyclic compound, 3, in 63% yield, instead of the expected compound 2. The molecular and crystal structures of the title compound, 3, have been determined by the single crystal X-ray diffraction technique. The coordination geometries around the Pt atoms are distorted square-planar. In the crystal structure, the molecules are linked by a pair of C-H···N hydrogen bonds into a centrosymmetric dimer with an R₂² (16) ring, centred at (1/2,1/2,1/2).

Full text of DOI:10.1016/j.poly.2008.09.019

Polyhedron 27 (2008) 3607–3610
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Preparation and crystal structure of binuclear chloro{6-[[chloro-
(triphenylphosphine)platinum](mesitylimino)methyl]pyridin-
2-yl}bis(triphenylphosphine)platinum(II)
b
c
c
d
M. Emin Günay a, , Osman Dayan , Aytaç Gürhan Gökçe , Muhittin Aygün , Bekir Çetinkaya ,
*
Orhan Büyükgüngör e
a Adnan Menderes University, Department of Chemistry, 09010-Aydın, Turkey
b Onsekiz Mart University, Department of Chemistry, 17100-Çanakkale, Turkey
c Dokuz Eylul University, Department of Physics, 35160-Buca, Izmir, Turkey
d Ege University, Department of Chemistry, 35100-Izmir, Turkey
e Ondokuz Mayıs University, Department of Physics, 55139-Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Treatment of N,N0-bis(mesityl)pyridine-2,6-carboxyimidoyl dichloride, 1, in toluene solution with
[Pt(PPh3)4] at 100 °C afforded a novel platinacyclic compound, 3, in 63% yield, instead of the expected
compound 2. The molecular and crystal structures of the title compound, 3, have been determined by
the single crystal X-ray diffraction technique. The coordination geometries around the Pt atoms are dis-
torted square-planar. In the crystal structure, the molecules are linked by a pair of C–HꢀꢀꢀN hydrogen
bonds into a centrosymmetric dimer with an R22ð16Þ ring, centred at (1/2,1/2,1/2).
Article history:
Received 15 January 2008
Accepted 8 September 2008
Available online 3 November 2008
Keywords:
Binuclear platinum complex
Platinalactam
Ó 2008 Elsevier Ltd. All rights reserved.
Centrosymmetric dimer
Imidoyl chlorides
1. Introduction
Heterocyclic ligands containing nitrogen atoms are drawing a
great deal of attention in coordination chemistry and homoge-
neous catalysis [1–3] because of the versatility of their steric and
electronic properties, which can be modified by choosing the
appropriate ring substituents [4]. Recently, planar tridentate pyri-
dine-bridged N,N,N ligands, such as Pydims (A) [5,6] and pyridine-
2,6-dicarboxyimidoyl dichloride (B) have been synthesized and
their reactions have been studied [7].
Cl
R
Cl
R
N
N
N
N
N
N
R
R
A
B
Reactions of imidoyl chlorides with low valent transition metal
complexes (Fig. 1) are known to give
r-bonded oxidative addition
2. Experimental
2.1. Materials and method
products which can be converted into carbene complexes by H–X
addition [8–10]. We report here the synthesis and the crystal
structure of chloro{6-[[chloro(triphenylphosphine)platinum]-
(mesitylimino)methyl-
platinum(II), 3.
j-C]pyridin-2-yl-j-N}bis(triphenylphosphine)-
All manipulations were performed under argon using standard
Schlenk techniques. 1H and 13C NMR spectra were obtained on a
Varian As 400 MHz spectrometer. The C, H and N analyses were
performed using a CHNS-932 (LECO) instrument at the Technical
and Scientific Research Council of Turkey, TUBITAK. Pyridine-2,6-
dicarboxylic acid (Fluka) and 2,4,6-trimethylaniline (Aldrich) were
used as received. [Pt(PPh3)4] and 1 were prepared using a literature
method [11,12]. Solvents were of analytical grade and were dis-
tilled after drying.
* Corresponding author. Tel.: +90 256 2128498 2106; fax: +90 256 2135379.
E-mail address: egunay@hotmail.com (M.E. Günay).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.09.019

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M.E. Günay et al. / Polyhedron 27 (2008) 3607–3610
4
3
2
5
6
Cl
Cl
1
N
7
N
N
1
Pt(PPh3)4 PhMe, 100 ºC
(Ph3P)2(Cl)Pt
Pt(Cl)(PPh3)2
N
N
N
(Ph3P)2(Cl)Pt
N
N
Pt
Cl
PPh3
3
2
Fig. 1. Reaction of imidoyl chlorides with low valent transition metal complexes.
Table 1
2.2. Synthesis of the title complex and analytical characterization
Crystal data and details of the structure refinement for the title complex.
Empirical formula
Formula weight
Crystal system, space group
Unit cell dimensions
a (Å)
C69H59N2P3Cl2Pt2
1470.17
triclinic, P1
2.2.1. Synthesis of 3
A mixture of N,N0-bis(2,4,6-trimethylphenyl)pyridine-2,6-carb-
oxyimidoyl dichloride (88 mg, 0.2 mmol) and [Pt(PPh3)4]
(500 mg, 0.4 mmol) in toluene (20 mL) was stirred under argon
for 2 h at 100 °C. After cooling, the solvent was removed in vacuo
and the waxy residue was suspended in pentane and stirred for
1 h at ambient temperature to form a fine powder. The pentane
was discarded and the residue was extracted with pentane to re-
move the remaining PPh3. The crude product was then recrystal-
lized from CH2Cl2 to precipitate impurities. After filtration,
crystallization of the product was induced by slowly diffusing pen-
tane into the CH2Cl2 solution to afford the complex as a light brown
crystals.
ꢀ
11.9074(5)
12.1059(5)
25.7888(10)
96.294(3)
93.269(3)
117.350(3)
3257.6(3)
2, 1.499
4.485
b (Å)
c (Å)
a
(°)
b (°)
c
0 (°)
V (AÅ3)
Z, Dcalc (g/cm3)
(Mo K
l
a
) (mmꢁ1
)
F(000)
1444
Crystal size (mm3)
0.60 ꢂ 0.36 ꢂ 0.18
Absorption correction
integration
h Range for data collection (°)
Reflections collected/unique (Rint
Data/restrain/parameters
1.60–26.15
58735/12790 (0.045)
10093/0/703
R = 0.0310/Rw = 0.0762
R = 0.0423/Rw = 0.0791
0.993
Yield: 0.210 g (63%). Anal. Calc. for C69H59Cl2N2P3Pt2: C, 56.37;
H, 4.04; N, 1.91. Found: C, 57.06; H, 3.57; N, 2.38%. 1H NMR (d in
ppm, 400 MHz, J in Hz, CDCl3): 1.58 (s, 6H, o-CH3-Mes), 2.14 (s,
3H, p-CH3-Mes), 6.6 (s, 2H, CH-Mes), 7.43 (m, 18H, oH-PPh3), 7.73
(m, pH-PPh3, 9H), 7.82 (m, H-Py and mH-PPh3, 21H) 13C NMR (d
in ppm, 101 MHz, CDCl3): 14.21, 18.74, 127.79, 127.85, 128.37,
128.42, 128.49, 128.54, 129.19, 129.83, 130.73, 131.17, 132.04,
134.12, 134.18, 134.23, 134.75, 134.81, 134.86.
)
Final R indices [I > 2
r(I)]
R indices (all data)
Goodness-of-fit (GoF) on F2
Highest peak/deepest hole (eÅꢁ3
)
2.210/ꢁ1.231
2.3. Crystal structure determination
was solved by SHELXS-97 [14]. The refinement (on F2) was carried
out by full-matrix least square techniques using the SHELXL-97 pro-
gram [15]. All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were treated as riding atoms, with C–H dis-
tances of 0.93 Å for aromatic H atoms and 0.96 Å for methyl H
atoms.
Light brown single crystals suitable for data collection were
mounted on a glass fibre and the diffraction intensity data were
collected at room temperature on a STOE IPDS 2 diffractometer
using graphite-monochromatized Mo
Ka
radiation (k =
0.71073 Å). A summary of crystallographic data and details of the
structure refinement are listed in Table 1. The cell parameters were
determined by using X-AREA software [13] on the setting angles of
58735 reflections [1.60° < h < 26.15°]. Absorption correction was
achieved by the integration method via X-RED software [13]. A total
of 58735 reflections were collected for hmin = ꢁ14, hmax = 14,
kmin = ꢁ14, kmax = 14, lmin = ꢁ31, lmax =31. The crystal structure
Examination of the structure of the title compound with PLATON
[16] showed that there was a solvent-accessible void (380 Å3) in
the region around (1/2, 1/2, 1). The reflection (hkl) data were mod-
ified using the SQUEEZE option of PLATON. Although the empty space
seemed large enough to accommodate small solvent molecules,
the spaces are too constricted to hold any molecule larger than
water. Since no water was present during the synthesis or recrys-

M.E. Günay et al. / Polyhedron 27 (2008) 3607–3610
3609
Table 2
tallization, and since little electron density in the area of the void
Selected geometrical parameters (Å, °) for the title complex.
was found, we conclude that the voids are empty.
Pt1–Cl1
Pt1–C1
Pt1–N1
N1–C6
2.374(1)
1.984(5)
2.105(3)
1.367(6)
1.423(6)
98.86(10)
97.17(4)
163.58(10)
165.16(12)
95.3(3)
Pt2–Cl2
Pt2–C2
N2–C1
C1–C6
2.381(1)
1.992(5)
1.278(5)
1.486(6)
1.324(5)
89.77(13)
90.58(13)
90.10(5)
89.20(4)
177.25(4)
172.62(12)
125.0(3)
118.3(3)
3. Results and discussion
Pyridine-2,6-dicarboxyimidoyl dichloride (1) is an interesting
diimidoyl chloride that has been reported recently. Keeping the
above mentioned facts in mind and in continuation of our study
with aminocarbene complexes [17], we treated 1 with tetrakis(tri-
phenylphosphine)platinum(0) in toluene at 100 °C for 2 h with the
hope of obtaining 2. The easy cleavage of the C2–C7 bond implies
that this bond is probably the weakest bond in 1. However, 1H
NMR solution studies on the crystalline light brown solid revealed
the presence of a pyridine skeleton with one mesityl substituent. In
order to determine the atom connectivity we performed a crystal-
lographic study which confirmed unequivocally the structure de-
picted as 3. The mechanistic details of the cleavage reaction are
not fully understood.
N2–C7
N1–C2
N1–Pt1–Cl1
P1–Pt1–Cl1
N1–Pt1–P1
C1–Pt1–Cl1
C6–C1–Pt1
C6–N1–Pt1
N2–C1–Pt1
C2–N1–Pt1
C1–N2–C7
C2–Pt2–P3
C2–Pt2–P2
P3–Pt2–Cl2
P2–Pt2–Cl2
P3–Pt2–P2
C2–Pt2–Cl2
N1–C2–Pt2
C3–C2–Pt2
94.0(2)
134.0(3)
143.0(3)
122.3(4)
The Pt–P and Pt–N coordination distances are in the expected
range and are in accordance with other reported Pt structures
[19,22–24]. Selected interatomic distances, bond and torsion an-
gles for the title complex are listed in Table 2.
The mesityl ring is rotated with respect to the platinalactam
ring (Pt1/N1/C1/C6) plane by 89.5(3)°. The Pt2-P2 and Pt2-P3
bonds [2.298(1) and 2.297(1) Å] are significantly longer than the
Pt1–P1 bond trans to the platinalactam N atom [2.216(1) Å]. This
difference appears to be a result of a stronger trans influence of
the P atom.
In the crystal structure, the molecules of the title compound are
linked by C–HꢀꢀꢀN weak hydrogen bonds into centrosymmetric dim-
mers, as shown in Fig. 3. The C113 atom in the molecule at (x,y,z)
acts as a weak hydrogen-bond donor, via atom H113, to the N2
atom at (1 ꢁ x,1 ꢁ y,1 ꢁ z), thus forming a dimer characterized by
an R22ð16Þ motif [25] with an inversion centre at (1/2,1/2,1/2) with
In summary, pyridine-2,6-dicarboxyimidoyl dichloride (1)
experiences complex transformations when reacted with
[Pt(PPh3)4]. The mechanistic aspect of this process remains to be
elucidated.
An ORTEP3 [18] view of the title complex is shown in Fig. 2. The
ꢀ
title compound crystallizes in the triclinic space group P1.
The asymmetric unit contains one neutral binuclear complex.
The coordination environments of the Pt centres are different.
The coordination geometry around Pt1 atom is distorted square-
planar, formed by the C and N atoms of the platinalactam ring, Cl
atom and P atom from the triphenylphosphine group. The N1–
Pt1–C1 angle is acute, with a value of 66.68(15)°, but is comparable
to those found in similar metallalactam complexes [19–21]. The
Cl1–Pt1–P1 angle is more obtuse [97.17(4)°] to accommodate the
steric bulk of the PPh3 ligand. The maximum deviation of the coor-
dination plane formed by the Pt1/Cl1/C1/N1/P1 atoms is ꢁ0.050 Å
for Pt1. The Pt2 atom has the expected square-planar geometry,
involving one Cl atom, the coordinating C atom of the pyridine ring
and two P atoms from the triphenylphosphine groups, with no
atom deviating by more than 0.077 Å [for Pt2] from the coordina-
tion plane defined by Pt2/Cl2/P2/P3/C2. The coordination planes
are almost perpendicular to each other [88.12(5)°].
Fig. 3. Part of the crystal structure of the title compound showing the centrosym-
metric dimer containing the R22ð16Þ ring. For the sake of clarity, all H atoms except
H113 have been omitted.
Fig. 2. An ORTEP3 view of the title compound. Displacement ellipsoids are shown
at the 20% probability level and hydrogen atoms have been omitted for clarity.

3610
M.E. Günay et al. / Polyhedron 27 (2008) 3607–3610
dimensions H113ꢀꢀꢀN2a = 2.62 Å, C113ꢀꢀꢀN2a = 3.505(7) Å and
\C113–H113ꢀꢀꢀN2a = 160° (a: 1 ꢁ x,1 ꢁ y,1 ꢁ z).
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4. Supplementary data
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CCDC 666496 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
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Acknowledgements
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The authors acknowledge the Faculty of Arts and Sciences, Ond-
okuz Mayıs University, Turkey, for the use of the Stoe IPDS-II dif-
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