[PdCl(TeMe2)3](BArF) - The first structurally characterized palladium(II) complex with TeMe2 ligands

Article abstract of DOI:10.1002/zaac.200700575

[PdCl(TeMe₂)₃]BAr^F (4) forms as the major tellurium containing product from the reaction of [(4-Mebti)PdCl] with TeMe ₂ and Na(BAr^F) and is isolated by crystallization from the reaction mixture. At -20°C, the compound forms orange columns from toluene/pentane, space group P1, with Z = 2. In the solid, the cationic [PdCl(TeMe₂)₃]⁺ complex ions show a non-planar PdClTe₃ coordination unit and are associated to dimers via weak Pd...Te interactions.

Full text of DOI:10.1002/zaac.200700575

DOI: 10.1002/zaac.200700575
[PdCl(TeMe2)3](BArF) ؊ The First Structurally Characterized Palladium(II)
Complex with TeMe2 Ligands
Martin Bröring*, and Christian Kleeberg
Marburg, Fachbereich Chemie der Philipps-Universität
Received December 13th, 2007.
Abstract. [PdCl(TeMe2)3]BArF (4) forms as the major tellurium
containing product from the reaction of [(4-Mebti)PdCl] with
TeMe2 and Na(BArF) and is isolated by crystallization from the
reaction mixture. At Ϫ20 °C, the compound forms orange columns
cationic [PdCl(TeMe2)3]ϩ complex ions show a non-planar PdClTe3
coordination unit and are associated to dimers via weak Pd···Te
interactions.
¯
from toluene/pentane, space group P1, with Z ϭ 2. In the solid, the
Keywords: Palladium; Tellurium; Crystal structure
Introduction
lurium derivatives containing additional N-donor sites have
been used for this purpose [4]. To the best of our knowledge
the crown ether complex 1 and the bis(tetrahydrotelluro-
phene) derivative 2 (Fig. 1) are the only structurally charac-
terized PdII compounds with dialkyltellurium ligands
closely related to TeMe2 [5].
Dimethyltellurium [1] is uncommon, but not unknown as
ligand in transition metal coordination compounds, and a
number of structurally characterized TeMe2 complexes with
metal ions of Mn, Fe, Co and Ru has been reported in the
past [2]. As a general rule, TeMe2 binds terminal and in an
arrangement such that the M-Te bond and the CMe-Te-CMe
plane form a steep angle of about 110°. In addition to the
typical CMe-Te-CMe angle of only 91.4Ϫ96.7° this finding
is indicative for the low degree of hybridization at the heavy
main group atom.
Scheme 1 Formation of [PdCl(TeMe2)3](BArF) (4).
During our studies on cationic complexes of pal-
ladium(II) with sterically hindered meridonal-tridentate li-
gands [6] we have now found that the successive treatment
of the complex [(4-Mebti)PdCl] (3) [7] with Na(BArF) and
TeMe2 in toluene does not result in the anticipated ex-
change of the chlorido ligand against a dialkylchalcogene
donor but rather in the displacement of the N,N,N chelate
ligand by three molecules TeMe2. At Ϫ20 °C, the resulting
cationic complex [PdCl(TeMe2)3]ϩ crystallizes from the
reaction mixture in orange columns as the tetrakis[3,5-bis-
(trifluoromethyl)phenyl]boranate 4, accompanied by other
microcrystalline material. The fate of the organic bti ligand
could not be unraveled. Proton NMR examinations of the
reaction mixture show several signals in the aromatic as well
as in the aliphatic region. The spectra indicate the presence
of more than one bti species and of several TeMe2 deriva-
tives in solution. The isolation of one of the bti or TeMe2
containing compounds by selective crystallization was not
successful. All attempted crystallization yielded the above
mentioned crystal mixture.
Fig. 1 Selected examples of palladium complexes with dialkyl-
tellurium ligands.
TeMe2 containing complexes of divalent palladium have
occasionally been reported, although no structural data is
available to date [1, 3]. Pd-Te bonds were established crys-
tallographically in complexes with other tellurium contain-
ing donor ligands. In by far the most cases chelating aryltel-
* Prof. Dr. Martin Bröring
Fachbereich Chemie
Philipps-Universität Marburg
Hans-Meerwein-Straße
D-35043 Marburg, Germany
Fax: int. (0)6421 2825356
E-mail: Martin.Broering@chemie.uni-marburg.de
946
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 634, 946Ϫ949

Palladium(II) Complex with TeMe2 Ligands
˚
A well-developed column of 4 was picked from the mix-
ture and investigated by single crystal X-ray diffraction. The
compound crystallizes in the triclinic system, space group
from the said plane by 0.37 A. The Te1-Pd-Te3 angle devi-
ates from 180° mainly by an in-plane distortion of about
10° such that the binding sphere of the smaller chlorido
ligand is sterically restricted by the larger tellurium donor
atoms.
Unexpected, on the other hand, is the unsymmetric
orientation of the methyl substituents of the TeMe2 ligands
in 4. One of the methyl groups of each dialkyltellurium moi-
ety is situated close to the mean squares PdClTe3 plane
while the other methyl groups point to the same side of this
plane. As a result, the complex cation presents one sterically
blocked and one open and accessible side. The reason for
this conformational peculiarity is revealed by an analysis of
the crystal packing.
¯
P1, with Z ϭ 2. The unit cell contains a disordered mol-
ecule of toluene which has been removed from the data
using the SQUEEZE program [8]. One of the CF3 groups
of the (BArFϪ) anion shows rotational disorder and was
refined using a split atom model with a 64:36 site occu-
pancy. Figure 2 provides a view on the structure of the mo-
lecular ion [PdCl(TeMe2)3]ϩ and gives selected bond lengths
and angles.
Fig. 3 Illustration of the association of two [PdCl(TeMe2)3]ϩ units
via weak Pd···Te1Ј interactions (ellipsoids set at 50 % probability;
hydrogen atoms removed for clarity).
As shown in Figure 3 the cationic palladium(II) com-
plexes of 4 form weakly associated dimers in the crystal
lattice. As such the methyl group orientation discussed
above appears ideally suited for attractive interactions. The
bonding between the monomeric subunits of these associ-
ates, however, is not straightforward and requires some dis-
cussion. The atom group Pd-Cl···PdЈ shows bond distances
Fig. 2 Details of the molecular structure of the [PdCl(TeMe2)3]ϩ
cation of 4 (ellipsoids set at 50 % probability; hydrogen atoms
removed for clarity). Top: Complex ion with orientation of the
methyl groups of the TeMe2 ligands. Bottom: mean squares plane
representation of the PdClTe3 coordination unit.
˚
Selected bond lengths /A and angles /°: Pd-Cl 2.359(2), Pd-Te1 2.5938(7),
Pd-Te2 2.5409(7), Pd-Te3 2.6004(8), Cl-Pd-Te1 80.42(5), Cl-Pd-Te2
171.34(5), Cl-Pd-Te3 94.49(5), Te1-Pd-Te2 92.30(2), Te1-Pd-Te3 169.34(2),
Te2-Pd-Te3 93.44(2).
˚
of 2.359/3.750 A and an angle of 77.17° while the group
˚
Pd-Te1···PdЈ is characterized by distances of 2.594/3.700 A
and an angle of 75.57°. Thus, neither attractive Pd···ClЈ nor
Pd···Te1Ј contacts can unambigously be assigned, although
the metrics point to the latter scenario as the more probable
one (Figure 3). The distance between the mean square
planes of the juxtaposed PdClTe3 coordination units is
In 4, the bond distances along Cl-Pd-Te2 fit well with
those of the sterically similar telluro crown ether complex 1
˚
which displays bond lengths of Pd-Cl: 2.362/2.348 A and
˚
Pd-Te: 2.540/2.557 A [5(a)]. The longer Pd-Te1 and Pd-Te2
˚
distances on the other hand appear more typical for trans
situated dialkyltellurium compounds like 2 [5(b)], where Pd-
found at 3.364 A, so that attractive multipole interactions
are present and add to the dimer stability.
˚
Te bonds of 2.593 and 2.591 A have been observed. The
The (BArFϪ) counterions of 4 also show some particular
association. The aryl moieties are rotated in such a way as
to form two different binding pockets. One of these pockets
displays an angle of 100.59° between the mean squares
planes of the six-membered aryl rings and binds the cation
dimer via van-der-Waals interactions. The other pocket is
compressed to an angle as small as 85.17° and binds to the
same site of an adjacent (BArFϪ) moiety (Figure 4). Thus
the dimeric cationic entities are connected linearly to each
other in the crystallographic b direction by dimeric anionic
entities, and the crystal is build up by packing the so-
formed one-dimensional strands.
C2Te planes of the chalcogeno ligands of 4 form the antici-
pated steep angles with the mean squares PdClTe3 plane of
95.96° (Te1), 93.77° (Te2), and 91.00° (Te3), and the re-
spective angles CMe-Te-CMe- are found close to rectangular
at 93.52°, 96.53°, and 93.91°. All these data fit very well
with the structural properties of the other Pd-bonded di-
alkyltellurium complexes 1 and 2. The palladium(II) ion in
4 is found in a distorted square-planar environment. While
for the tellurium atoms the positional deviation with respect
˚
to the PdClTe3 mean squares plane is small (max. 0.081 A
for Te1 and Te3) the chlorido ligand is severely displaced
Z. Anorg. Allg. Chem. 2008, 946Ϫ949
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
947

M. Bröring, C. Kleeberg
observed with I > 2σ(I), 647 parameters, R1 (I > 2σ(I)) ϭ 0.0427,
Ϫ3
˚
wR2 (all data) ϭ 0.0938, max./min. peak ϭ 1.026/Ϫ0.970 eA
.
Acknowledgements. We gratefully acknowledge financial support
for this work by the Deutsche Forschungsgemeinschaft (DFG).
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Materials and Methods: TeMe2 [1], [(4-Mebti)PdCl] (3) [7] and
Na(BArF) [9] were prepared according to published procedures.
Solvents were dried by standard procedures and distilled from ap-
propriate drying agents. 1H NMR spectra were obtained on a
Bruker DRX 400 instrument in CD2Cl2.
Chloridotris(dimethyltellurium)palladium(II) as tetrakis[3,5-bis-
(trifluoromethyl)-phenyl]boranate [PdCl(TeMe2)3](BArF) (4). Under
a blanket of argon, [(4-Mebti)PdCl] (3) (10 mg, 21 μmol) and
Na(BArF) (18.7 mg, 21 μmol) are suspended in dry toluene (2 mL),
stirred for 5 min, and treated with dimethyltellurium (1.8 μL,
22 μmol) for 16 h at ambient temperature. After filtration through
a plug of celite and addition of pentane (10 mL) the reaction mix-
ture is left at Ϫ20 °C for 3 days. A non uniform solid forms con-
taining microcrystalline material and several larger yellow-orange
columns. The title compound can be found in these columns.
Collection and Reduction of X-ray Data. A single crystal of 4 was
mounted on the tip of a capillary using perfluoropolyether oil.
Intensity data was collected at 153(2) K, using a Stoe IPDS-2
X-ray diffractometer. Graphite monochromated Mo KͰ radiation
˚
(0.71073 A) was used. The structure was solved by the Patterson
method with SHELXS-86 [10]. Refinements were carried out by
full-matrix least-squares techniques against F2 using SHELXL-97
[11]. All non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were assigned to idealized positions. Crystallographic
data (excluding structure factors) for the structures reported in this
paper has been deposited at the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-670410. Copies of
the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [Fax: ϩ44(1223) 336-033;
E-mail: deposit@cam.ac.uk].
Crystal data for 4: C38H30BClF24PdTe3, 881.29, triclinic, space
˚
¯
group P1, a ϭ 12.628(2), b ϭ 13.529(2), c ϭ 16.238(2) A, Ͱ ϭ
3
˚
70.854(10)°, β ϭ 89.043(11)°, γ ϭ79.682(10)°, V ϭ 2575.6(6) A ,
Z ϭ 2, ρcalc ϭ 1.906 g cmϪ3, μ(Mo-Kα) ϭ 2.191 cmϪ1, θmin ϭ 1.62°,
θmax ϭ 25.91°, 22308 reflections measured, 9893 independent, 6615
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Z. Anorg. Allg. Chem. 2008, 946Ϫ949

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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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