First structurally characterized triazinyl palladium complexes via oxidative addition of cyanuric chloride derivatives

Article abstract of DOI:10.1016/j.jorganchem.2011.08.004

The reaction of cyanuric chloride and two disubstituted derivatives with [Pd(PPh₃)₄ is described, leading to the trans-triazinyl complexes [(PPh₃)₂Pd(C₃N₃R ₂)Cl 2a-c (R = Ph (a), t-Bu (b), Cl (c)) in good to excellent yield via oxidative addition. The complexes were fully characterized including X-ray structure determination.

Full text of DOI:10.1016/j.jorganchem.2011.08.004

Journal of Organometallic Chemistry 696 (2011) 3580e3583
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Journal of Organometallic Chemistry
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Note
First structurally characterized triazinyl palladium complexes via oxidative
addition of cyanuric chloride derivatives
*
Markus Braun, Walter Frank, Christian Ganter
Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 July 2011
Accepted 12 August 2011
The reaction of cyanuric chloride and two disubstituted derivatives with [Pd(PPh3)4] is described, leading
to the trans-triazinyl complexes [(PPh3)2Pd(C3N3R2)Cl] 2aec (R ¼ Ph (a), t-Bu (b), Cl (c)) in good to
excellent yield via oxidative addition. The complexes were fully characterized including X-ray structure
determination.
Keywords:
Palladium
Ó 2011 Elsevier B.V. All rights reserved.
Cyanuric chloride
Triazine
Oxidative addition
1. Introduction
Recently, we reported a synthesis of the first pyrimidine based N-
heterocyclic carbene complex by oxidative addition of an N-alkyl-
Derivativesof 1,3,5-triazine havefound numerousapplicationsin
chemistry ranging from building blocks in supramolecular chem-
istry [1] to the use as herbicides [2]. Triazines are also used in
medicinal chemistry [3], catalysis [4] and polymer chemistry [5].
Cheap and easily available cyanuric chloride is a convenient source
to get into 1,3,5-triazine chemistry due to the easy displacement of
the three chlorine atoms by a wide range of nucleophilic reagents.
Furthermore, the three chlorine atoms can be subsequently
addressed by carefully controlling the reaction temperature to get
mono- (0 ꢀC), di- (25 ꢀC) or three-substituted (65 ꢀC) compounds [1].
Some C-metallated triazine derivatives are known in the liter-
ature including main group metals like Mg [6] and some transition
metals. Reports about the nucleophilic substitution of C-bonded
halide by carbonyl metallates date back to the mid-1960s [7]. To the
best of our knowledge there are only two reports about the
oxidative addition of triazine derivatives to transition metal frag-
ments: the reaction of s-triazine with Mo(PMe3)6, described by
2-halopyrimidinium cation to [Pd(PPh3)4] [11]. Related oxidative
addition reactions for other ring systems have been reported earlier
[12]. This work inspired us to explore whether oxidative additions
of cyanuric chloride derivatives to Pd(0) proceed analogously and
preliminary results of this study are reported in this paper.
2. Results and discussion
Diphenyltriazine 1a was synthesized by treatment of cyanuric
chloride with 2 equiv. of PheMgeCl [13]. The di(tert-butyl) deri-
vative 1b was prepared by a copper-catalyzed cross-coupling
reaction with t-BuMgCl reported by Hintermann et al. [14]. All
triazine compounds reacted with [Pd(PPh3)4] smoothly in THF at
ambient temperature over night to afford the complexes 2aec as
shown in Scheme 1. All palladium complexes were isolated as white
or yellow powders in good to excellent yield after workup and fully
characterized by spectroscopic methods and elemental analysis.
The 31P{1H}-NMR spectra show only one signal and indicate the
trans orientation of the triphenylphosphine ligands. A cis-isomer is
not observed in the 31P{1H}-NMR spectrum and indicates a fast
reaction, where the thermodynamically more stable trans-complex
is formed rapidly.
Parkin and coworkers, proceeds under CeH activation to a h
2(CN)
molybdenum hydride complex [8] while the oxidative addition of
CeF bonds of a couple of fluorotriazins to low-valent titanium
compounds has been reported by Beckhaus and coworkers [9]. No
triazinyl palladium complexes have been synthesized so far
although a theoretical study has been published lately [10].
The formation of the trans-complexes is also evident from the
13C{1H}-NMR spectrum. The C2 atom of the triazine moiety shows
2
a triplet structure with JCP ¼ 8.2 Hz (2a), 8.2 Hz (2b), 8.7 Hz (2c).
Due to a strong virtual coupling between the two phosphorus
nuclei the phenyl C-atoms of the triphenylphosphine ligands also
* Corresponding author.
E-mail address: christian.ganter@uni-duesseldorf.de (C. Ganter).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.004

M. Braun et al. / Journal of Organometallic Chemistry 696 (2011) 3580e3583
3581
are in a slightly distorted square-planar environment with trans
angles for C1ePd1eCl1 177.31(8)ꢀ and P1ePd1eP2 177.55(3)ꢀ for
Pd1 and Cl4ePd2eC40 175.25(8)ꢀ and P3ePd2eP4 173.64(3)ꢀ for
Pd2. The two independent molecules feature almost identical bond
distances and angles. The most notable difference is found for the
interplanar angle between the coordination plane around palla-
dium and the triazine ring plane, which is found to be 86.5ꢀ and
73.3ꢀ, respectively. The PdeC bonds of 196.30(2) pm and 197.30(2)
pm are even a bit shorter than in complex 2a and are among the
shortest PdeC bonds observed for related (PPh3)2ClPd-aryl
complexes, including the N-methylpyridinium derived carbene
complexes described recently by Raubenheimer and Schuster [16f],
and Raubenheimer and Herrmann [12d], respectively.
Scheme 1. Synthesis of the triazinyl palladium complexes 2aec.
show a CP coupling (ipso: 1/3JCP ¼ 22.7 Hz (2a), 22.5 Hz (2b), 24.0 Hz
2/4
(2c); ortho:
J
CP
¼ 6.3 Hz (2a), 6.3 Hz (2b), 6.4 Hz (2c); meta:
3/5
3. Conclusion
J
¼ 5.2 Hz (2a), 5.1 Hz (2b), 5.2 Hz (2c)) to the two phosphorus
CP
nuclei. The effect of a strong virtual PP coupling has been demon-
strated before by Nelson and Cary [15].
Oxidative additions of chlorotriazines to [Pd(PPh3)4] were found
to proceed straightforwardly to give the square-planar trans-
(PPh3)2PdCl-triazinyl complexes 2aec in good yield. X-ray crystal
structure determinations for complexes 2a and 2c revealed
geometrical parameters very close to related derivatives, the
comparatively short PdeC bonds being noteworthy exceptions.
Single crystals suitable for X-ray diffraction were obtained by
slow diffusion of n-hexane into a saturated solution of 2a and 2c in
dichloromethane at room temperature. The molecular structures of
the trans-complexes 2a and 2c are shown in Figs. 1 and 2, respec-
tively, together with some representative geometric parameters.
They are the first structurally characterized Pd-triazinyl complexes.
The structure shows the Pd atom of 2a in a slightly distorted
square-planar environment with trans angles for C1ePd1eCl1 of
172.49(5)ꢀ and P1ePd1eP2 of 167.366(16)ꢀ, respectively, and cis
angles for C1-Pd1-P of 97.198(18)ꢀ for P1 and 90.569(18)ꢀ for P2.
The coordination plane around the Pd atom forms a dihedral angle
of 74.5ꢀ with the triazine ring plane. While the PdeP and PdeCl
bond lengths fall in the range observed for (PPh3)2PdCl complexes
with other aryl groups, the Pd1eC1 bond of 198.52(16) pm is
slightly shorter than for the aforementioned derivatives [16].
In contrast to the diphenyltriazinyl derivative 2a, the structure
of the dichloro compound 2c shows two independent molecules in
the chosen asymmetric unit of the crystal structure. Both Pd atoms
4. Experimental section
4.1. General
All manipulations were performed under an inert gas atmo-
sphere of dry nitrogen by using standard vacuum line and Schlenk
techniques. Glassware was dried at 120 ꢀC in an oven for at least
12 h. THF was distilled from sodium/benzophenone and n-hexane
from sodium. All solvents were stored under an atmosphere of
nitrogen. NMR spectra were recorded on Bruker Avance DRX200 or
Bruker Avance DRX500 spectrometers. Chemical shifts are reported
in ppm (d
) compared to TMS (1H and 13C) using the residual peak of
deuterated solvents as internal standard (1H: CDCl3 7.26 ppm; 13C:
CDCl3 77.0 ppm) and 31P{1H} spectra to external H3PO4 (85%).
Coupling constants (J) are quoted in Hz. Elemental analyses were
performed by the institute of pharmaceutical chemistry at the
Heinrich-Heine-Universität Düsseldorf on a Perkin Elmer CHN
2400 series II. For MS data a Thermo Finnigan Trace DSQ (EI) and
a Bruker Ultrafelx I TOF (MALDI) were used.
4.2. Starting materials and reagents
2-Chloro-4,6-diphenyl-1,3,5-triazine [13] and 2-chloro-4,6-di-
tert-butyl-1,3,5-triazine [14] were prepared according to literature
procedures. Cyanuric chloride was purchased from Acros Organics
and used without further purification.
4.3. General procedure for complexation
500 mg of [Pd(PPh3)4] and 1.05 equiv. of 1aec were dissolved in
15 ml of THF and the resulting yellow solution was stirred over
night at ambient temperature. After removal of the solvent, the
crude product was suspended in 10 ml n-hexane and stirred over
night to remove the PPh3. The product was isolated by filtration and
washed with n-hexane (3 ꢁ 5 ml) and dried in vacuo.
4.3.1. Chloro-(2,4-diphenyl)-1,3,5-triazinyl-bis-triphenylphosphan-
palladium(II) (2a)
Obtained as a white powder in 75% yield. 1H-NMR (500 MHz in
Fig. 1. ORTEP representation of complex 2a (ellipsoids drawn at 50% probability level;
H atoms are omitted for clarity). Selected distances (pm) and angles (deg): Pd1eCl1
240.65(5), Pd1eP1 236.44(5), Pd1eP2 235.50(5), Pd1eC1 198.52(16), C1ePd1eCl1
172.49(5), P1ePd1eP2 167.366(16), Cl1ePd1eP1 97.198(18), C1ePd1eP2 90.569(18),
C1ePd1eP1 86.93(5), Cl1ePd1eP2 90.569(18).
CDCl3):
d
¼ 7.13e7.46 (m, 30H, -PPh3), 7.68e8.11 (m,10H, Ph Triazinyl
)
ppm; 13C{1H}-NMR (126 MHz in CDCl3):
d
¼
127.93 (t,
3/5
J
¼ 5.2 Hz, C meta, PPh3), 127.99 (s, C
Ph), 128.49 (s, C
ortho meta
CP

3582
M. Braun et al. / Journal of Organometallic Chemistry 696 (2011) 3580e3583
Fig. 2. ORTEP representation of complex 2c (ellipsoids drawn at 50% probability level; H atoms are omitted for clarity). Selected distances (pm) and angles (deg): Pd1eCl1 236.76(7),
Pd1eP1 233.78(7), Pd1eP2 233.00(7), Pd1eC1 196.30(2), C1ePd1eCl1 177.31(8), P1ePd1eP2 177.55(3), Cl1ePd1eP2 88.15(2), C1ePd1eP2 89.41(7), C1ePd1eP1 90.97(7),
Cl1ePd1eP1 91.41(2); Pd2eCl4 237.56(8), Pd2eP3 235.69(7), Pd2eP4 234.57(7), Pd2eC40 197.30(2), Cl4ePd2eC40 175.25(8), P3ePd2eP4 173.64(3), Cl4ePd2eP3 93.18(3),
Cl4ePd2eP4 89.91(3), C40ePd2eP3 89.38(7), C40ePd2eP4 87.94(7).
Ph), 130.79 (t, 1/3JCP ¼ 22.7 Hz, C
PPh3), 131.14 (s, C
PPh3),
para
microscope and investigated on an STOE Imaging Plate Diffraction
System and an Oxford Diffraction Excalibur Diffractometer, respec-
ipso
134.61 (t, 2/4JCP ¼ 6.3 Hz, C ortho PPh3), 136.47 (s, C ipso Ph), 165.15 (s,
2
CePh), 206.88 (t, JCP ¼ 8.2 Hz, C
CePd) ppm; 31P{1H}-NMR
tively, using graphite monochromatized MoK
a
radiation
ipso
(81 MHz in CDCl3):
d
¼ 19.87 (s) ppm; MS (MALDI): m/z (%) ¼ 862.2
(
l
¼ 0.71073 Å). Unit cell parameters were determined by least-
(MþeClꢂ, 30%), 600.0 (MþeClꢂePPh3, 50%); elemental analysis
calcd. (%) for C51H40ClN3P2Pd (898.72): C 68.16, H 4.49, N 4.68;
found: C 65.09, H 4.44, N 4.48.
squares refinements on the positions of 8000 and 84 265 reflec-
tions, respectively. For 2a the anorthic crystal system is consistent
Table 1
Details of the crystal structure determinations.
4.3.2. Chloro-(2,4-di-tert-butyl)-1,3,5-triazinyl-bis-
triphenylphosphan-palladium(II) (2b)
Compound
2a
2c
Obtained as a pale yellow powder in 85% yield. 1H-NMR
CCDC number
Empirical formula
Formla weight
Temperature
Wavelength
Crystal system
Space group
Unit cell
833624
C51H40ClN3P2Pd
898.65
833625
C39H30Cl3N3P2Pd
815.35
291(2) K
0.71073 Å
Monoclinic
P21/c
a ¼ 26.1701(6) Å
b ¼ 11.29530(10) Å
c ¼ 25.5013(6) Å
(500 MHz in CDCl3):
d
¼ 0.86 (s, 18H, C(CH3)3), 7.17e7.20 (m, 12H,
ePPh3), 7.25e7.26 (m, 6H, ePPh3), 7.54e7.58 (m, 12H, ePPh3) ppm;
13C{1H}-NMR (126 MHz in CDCl3):
d
¼ 28.61 (s, C(CH3)3), 38.26 (s,
291(2) K
0.71073 Å
triclinic
C(CH3)3), 128.00 (t, 3/5JCP ¼ 5.1 Hz, C metaePh), 129.85 (s, C paraePh),
1/3
131.47 (t,
J
CP
Hz ¼ 22.5 Hz, C ipsoePh), 134.56 (t, 2/4JCP ¼ 6.3 Hz, C
ꢀ
P1
2
orthoePh), 179.12 (s, C metaeTriazinyl), 207.10 (t, JCP ¼ 8.2 Hz, C
a ¼ 9.3352(6) Å
b ¼ 11.2620(8) Å
c ¼ 21.4646(14) Å
ipso
CePd) ppm; 31P{1H}-NMR (81 MHz in CDCl3):
d
¼ 19.62 (s) ppm;
dimensions
MS (MALDI): m/z (%) ¼ 822.2 (MþeClꢂ, 60%), 560.1 (MþeClꢂePPh3,
100%); elemental analysis calcd. (%) for C47H48ClN3P2Pd (858.74): C
65.74, H 5.63, N 4.89; found: C 65.85, H 5.52, N 4.65.
a
b
g
¼ 97.069(8)ꢀ
¼ 101.217(7)ꢀ
¼ 93.088(8)ꢀ
a
b
g
¼ 90ꢀ
¼ 100.297(2)ꢀ
¼ 90ꢀ
Volume
Z
2189.7(3) Å3
2
7416.8(3) Å3
8
4.3.3. Chloro-(2,4-dichloro)-1,3,5-triazinyl-bis-triphenylphosphan-
palladium(II) (2c)
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for
data collection
Index ranges
1.363 mg/m3
0.596 mmꢂ1
920
1.460 mg/m3
0.835 mmꢂ1
3296
Obtained as a yellow powder in 95% yield. 1H-NMR (500 MHz in
0.2 ꢁ 0.2 ꢁ 0.2 mm3
0.54 ꢁ 0.23 ꢁ 0.21 mm3
CDCl3):
d
¼ 7.34e7.37 (m, 12H, ePPh3), 7.40e7.43 (m, 6H, ePPh3),
7.68e7.72 (m, 12H, -PPh3) ppm; 13C{1H}-NMR (126 MHz in CDCl3):
2.49e25.00ꢀ
2.97e25.00ꢀ
3/5
1/3
d
¼ 128.28 (t,
J
¼ 5.2 Hz, C metaePh), 129.79 (t,
J
CP
2/
CP
ꢂ10 < ¼ h < ¼ 11,
ꢂ13 < ¼ k < ¼ 13,
ꢂ25 < ¼ l < ¼ 25
28751
ꢂ31 < ¼ h < ¼ 31,
ꢂ13 < ¼ k < ¼ 11,
ꢂ30 < ¼ l < ¼ 30
54559
Hz ¼ 24.0 Hz, C ipsoePh), 130.69 (s, C paraePh), 134.47 (t,
4JCP ¼ 6.4 Hz, C orthoePh), 164.52 (s, C metaeTriazinyl), 211.75 (t,
2JCP ¼ 8.7 Hz, C
CePd) ppm; 31P{1H}-NMR (81 MHz in CDCl3):
Reflections collected
Independent reflections
Refinement method
ipso
d
¼ 20.81 (s) ppm; MS (MALDI): m/z (%) ¼ 779.9 (MþeClꢂ, 45%),
7526 [R(int) ¼ 0.0312] 13 038 [R(int) ¼ 0.0481]
Full-matrix
least-squares
on F2
Full-matrix least-squares
517.8 (MþeClꢂePPh3, 35%); elemental analysis calcd. (%) for
C39H30Cl3N3P2Pd (815.41): C 57.45, H 3.71, N 5.15; found: C 57.52, H
3.78, N 4.86.
on F2
Data/restraints/parameters 7526/0/523
13038/0/865
1.094
Goodness-of-fit on F2
0.978
Final R indices [I > 2
s
(I)] R1 ¼ 0.0241,
wR2 ¼ 0.0637
R1 ¼ 0.0278,
R1 ¼ 0.0325, wR2 ¼ 0.0673
5. Crystal structure determinations
R indices (all data)
R1 ¼ 0.0359, wR2 ¼ 0.0685
wR2 ¼ 0.0647
Crystals of compounds C51H40ClN3P2Pd (2a) andC39H30Cl3N3P2Pd
(2c) suitable for X-ray study were selected by means of a polarization
Largest diff. peak and hole 0.572 and ꢂ0.202 e.Åꢂ3 0.404 and ꢂ0.390 e.Åꢂ3

M. Braun et al. / Journal of Organometallic Chemistry 696 (2011) 3580e3583
3583
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