Crystal structure of cis-[PdCl2(CNMes)2]

Article abstract of DOI:10.1134/S0022476616040302

The interaction between PdCl₂(CH₃CN)₂ and 2,4,6-Me₃C₆H₂NC (MesNC) proceeds with the substitution of acetonitrile ligands and leads to the synthesis of a cis-[PdCl₂(MesNC)₂

Full text of DOI:10.1134/S0022476616040302

Journal of Structural Chemistry. Vol. 57, No. 4, pp. 822-825, 2016.
Original Russian Text © 2016 M. A. Kinzhalov, A. A. Zolotarev, V. P. Boyarskiy.
CRYSTAL STRUCTURE OF cis-[PdCl2(CNMes)2]
M. A. Kinzhalov, A. A. Zolotarev,
and V. P. Boyarskiy
UDC 546.98
The interaction between PdCl2(CH3CN)2 and 2,4,6-Me3C6H2NC (MesNC) proceeds with the substitution of
acetonitrile ligands and leads to the synthesis of a cis-[PdCl2(MesNC)2] complex. The structure of this
compound is determined by single crystal X-ray diffraction (XRD). The complex has a slightly distorted
square-planar structure of the metal center with two cis-positioned isocyanide ligands. In both CN
isocyanide moieties the triple bonds have lengths similar to the lengths of the respective bonds in other
isocyanide complexes. In the structure, the cis-[PdCl2(MesNC)2] complexes are bound by weak С–H⋯Cl
hydrogen bonds and π-stacking interactions.
DOI: 10.1134/S0022476616040302
Keywords: palladium complexes, isocyanides.
In the recent decade, palladium complexes with acyclic diaminocarbene ligands are widely used as catalysts in the
cross-coupling reactions [1, 2]. There are different methods of the synthesis of diaminocarbene complexes of palladium
[1, 3, 4], while the most efficient and universal method is the coupling of isocyanide ligands in bis(isocyanide) complexes of
palladium with NH-nucleophiles [1, 3, 5]. This, in its turn, determines the growth of the interest to the synthesis and study of
the structure of bis(isocyanide) complexes of palladium(II) [6, 7].
Previously in the scientific literature, the syntheses of a series of complexes of palladium with isocyanide ligands
were described, whose structure was determined on the basis of the studying of the data of IR and NRM spectroscopy. At the
same time, now it is important to study not only the composition, but also the stereochemistry of these compounds, because
the behaviors of cis- and trans-complexes differ relative to the reaction with N-nucleophiles. In this connection it is necessary
to refine the spectral data on the structure of the above described bis(isocyanide) complexes of palladium(II) by the XRD
method. So, in this article we report on the complete characterization (by spectroscopy and by the single crystal XRD
method) of one of such derivatives (cis-[PdCl2(CNMes)2] complex).
The synthesis of the cis-[PdCl2(CNMes)2] complex was carried out by the substitution of nitrile ligands for
isocyanide ones (Scheme 1) under the conditions proposed in the literature for other isocyanide complexes of the formula cis-
[PdCl2(CNAr)2] [8-10].
1
13
1
Experimental. The H and C{ H} NMR spectra were recorded on a Bruker 400 MHz Avance spectrometer at
room temperature. The chemical shifts (in ppm) were determined relative to the signal of internal standard tetramethylsilane
(TMS), with the following signal shapes: s for a singlet, d for a doublet, t for a triplet, and m for a multiplet. The infrared
–1
spectra were recorded on a Shimadzu FTIR-8400S spectrophotometer (4000-400 cm samples pelleted with KBr). The mass-
spectra were obtained on a Bruker micrOTOF spectrometer with electrospray ionization; the solvent was МеОН, MeCN or
a MeOH/DMSO mixture, the region of m/z = 50-3000. The values of m/z are given for the signals of isotopologues with the
St. Petersburg State University, Russia; m.kinzhalov@spbu.ru. Translated from Zhurnal Strukturnoi Khimii, Vol. 57,
No. 4, pp. 861-864, May-June, 2016. Original article submitted August 13, 2015.
822
0022-4766/16/5704-0822 © 2016 by Pleiades Publishing, Ltd.

Scheme 1. Synthesis of cis-[PdCl2(CNMes)2].
highest content. Organic and inorganic reagents and solvents were obtained from commercial sources and used without any
further purification.
Synthesis of cis-[PdCl2(CNMes)2] complex. 1.12 g (7.7 mmol) of solid CNMes were added to the suspension of
1.0 g (3.85 mmol) of PdCl2(CH3CN)2 in 50 ml of CHCl3. The reaction mixture was boiled at stirring for 3 h and then cooled
till room temperature, and the solvent was evaporated. The produced colorless substance was washed with Et2O (in 3 portions
of 20 ml each) and dried in the air. The yield was 1.7 g (94 %). The analytical sample for XRD was prepared by gaseous
diffusion of Et2O into the solution of the complex in CH2Cl2 at 20 °С. The copper–copper(II) sulfate reference anode (70 V,
+
MeOH)was used: calculated for C20H22Cl2N2PdNa : 489.0087, found: m/z 489.0072 [M+Na] . The IR spectrum (KBr, some
+
–1
1
selected bands, cm ): ν(C–H) 2950, 2920 (m), ν(N≡C) 2214 (s). The H NMR spectrum (CDCl3, δ, ppm): 2.34 (s, 6H, CH3),
13
1
2.44 (s, 12H, CH3), 6.97 (s, 4H, CHarom). The C{ H} NMR spectrum (CDCl3, δ, ppm): 18.5 (4C, CH3), 21.4 (2C, CH3),
122.4 (2C, CN), 127.5 (2C, C ipso), 129.1 (4C, CH meta), 136.0 (4C, C ortho), 141.8 (2C, C para).
Single crystal X-ray diffraction analysis. For the X-ray diffraction analysis, the crystal was fixed by a micromount
and placed on an Agilent Technologies Excalibur Eos diffractometer equipped with a plane X-ray CCD detector. The
measurements were carried out at temperature of 100 K using monochromatic MoKα radiation. The unit cell parameters were
refined by the least-square method on the 2θ values of 35860 reflections in the range of 5.348-54.996°. The structure was
solved by the direct method and refined to R1 = 0.0286 (wR2 = 0.0595) for 7585 independent reflections with |F0| ≥ 4σF using
the SHELX software package [11] embedded in the OLEX2 complex [12]. The absorption correction was introduced
empirically in the program CrysAlisPro program [13] by means of spheric harmonics, implemented in the SCALE3
ABSPACK scaling algorithm. The hydrogen atoms were included in the refinement with the fixed positional and temperature
parameters. The CCDC no. 1413220 contains additional crystallographic data for this work and can be obtained free of
charge from the Inorganic Crystal Structure Database via the web-site: www.ccdc.cam.ac.uk/data_request/cif. The
crystallographic data are as follows: 2(C20H22Cl2N2Pd) M = 935.39, monoclinic crystal symmetry, P21/n space group,
3
a = 13.4639(3) Å, b = 22.0592(5) Å, c = 13.7830(4) Å, α = 90°, β = 101.265(3)°, γ = 90°, V = 4014.73(17) Å , Z = 8 (4 pairs),
3
–1
calc = 1.464 g/cm , μ = 1.195 mm , crystal size (mm) 0.25×0.15×0.12, the total number of reflections 35860, independent
D
reflections with I > 2σ(I) 9214 (Rint = 0.0408), R1(|F0| ≥ 4σF)/R1 (all data) = 0.0286/0.0412, wR2(|F0| ≥ 4σF)/wR2 (all data) =
3
= 0.0595/0.0649, S = 1.054, ρmin, ρmax, e/Å = –0.60, 0.62.
–1
Results and discussion. The stretching bands ν(C≡N) are observed at 2214 cm in the IR spectrum of the complex.
The increase in the frequency of vibration absorption ν(CN) at the transformation of the isocyanide from the free state
–1
(ν(CN) in MesNC 2114 cm [14]) to the coordination state indicates the increase in the electrophilic character of the
13
isocyanide carbon atom and, thus, indirectly proving an increase in the reactivity to nucleophiles [15-17]. In the C NMR
spectrum, the coordination of isocyanide to the palladium atom is accompanied with a sharp change in the chemical shift of
the end carbon atom to the lower frequency region (δC in MesNC is 166.9 ppm [14], δC in cis-[PdCl2(CNMes)2] is
122.4 ppm), which is characteristic for other isocyanide complexes [7, 18].
In order to prove the structure of the complex in the solid phase, we used the XRD method which made it possible to
determine the cis-configuration of isocyanide ligands.
The C20H22Cl2N2Pd organometallic complexes constitute the base of the crystal structure of the cis-[PdCl2(CNMes)2]
compound (Fig. 1). The crystallographic independent part of the structure consists of two such complexes (the atomic
823

Fig. 1. Structure of the product with atomic numbering.
Fig. 2. Arrangement of molecules in the cell.
numbering is uniform for the complexes using the letter “А” for the second complex). The XRD data show that the complex
has a slightly distorted square-planar structure of the metal center with the angles between the planes (in which the С10H11N
and PdCl2 radicals are located) in the range of 5.43(4)-6.13(4)° and 8.18(4)-9.66(4)° for the two С10H11N radicals
respectively. The ligands consist of two cis configurated isocyanide fragments (the Pd–C bond lengths are in the range of
1.934(3)-1.945(3) Å) and two chlorine atoms (the Pd–Cl bond lengths in the range of 2.3016(6)–2.3091(6) Å). The C–N–C–
Pd fragments are nearly linear (the values of the Pd–C–N and C–N–C angles are in the range of 174.0(2)-179.5(2)°). In both
CN isocyanide fragments, the triple bonds have the lengths (1.141(3)-1.150(3) Å) similar to the lengths of the like bonds in
other isocyanide complexes of palladium (1.142(9) Å and 1.127(9) Å in cis-[PdCl2(CNCy)2] [19]; 1.145(8) Å and 1.157(9) Å
in cis-[PdCl2(CNXyl)2] [20]). In the structure, the cis-[PdCl2(MesNC)2] complexes are bound by weak С–H⋯Cl hydrogen
bonds and π-stacking interactions (Fig. 2).
824

The studies were carried out using the equipment of the following Resource Centers of the Saint-Petersburg State
University: Research Center for X-ray Diffraction Studies, Chemical Analysis and Materials Research Center, and Center for
Magnetic Resonance. The work was carried out with the financial support of RFBR (grants Nos. 14-03-31204 mol_a, 14-03-
00297-a and 16-33-60123 mol_a_dk).
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