The oxidative addition of diphenyl diselenide and ditelluride to tetrakis(triphenylphosphine)palladium

Article abstract of DOI:10.1016/S0022-328X(00)00829-9

The oxidative addition of diphenyl diselenide to [Pd(PPh₃)₄] in dichloromethane results in the formation of a dinuclear complex [Pd₂(SePh)₄(PPh₃)₂] (1) and a mononuclear complex [PdCl(SePh)(PPh₃)₂] (2) that have been identified and characterized structurally by X-ray crystallography and ³¹P-NMR spectroscopy. The analogous reaction involving diphenyl ditelluride leads to a mixture of products. [Pd₆Cl₂Te₄(TePh)₂(PPh₃)₆]·1/2CH₂Cl₂ (3) can be isolated and its X-ray structure determined. While the oxidative addition of Ph₂Se₂ mainly involves the clevage of the Se-Se bond, that of Ph₂Te₂ indicates the rupture of both Te-Te and C-Te. Cumulative evidence shows that the choice of the central atom and the solvent also plays an important role in the oxidative addition. The final polynuclear complexes can be conceived to be formed from the mononuclear addition products by sequential condensation steps.

Full text of DOI:10.1016/S0022-328X(00)00829-9

Journal of Organometallic Chemistry 623 (2001) 168–175
www.elsevier.nl/locate/jorganchem
The oxidative addition of diphenyl diselenide and ditelluride to
tetrakis(triphenylphosphine)palladium
Raija Oilunkaniemi a, Risto S. Laitinen a,*, Markku Ahlgre´n b
a Department of Chemistry, Uni6ersity of Oulu, PO Box 3000, FIN-90014 Oulu, Finland
b Department of Chemistry, Uni6ersity of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland
Received 2 October 2000; accepted 27 October 2000
Abstract
The oxidative addition of diphenyl diselenide to [Pd(PPh3)4] in dichloromethane results in the formation of a dinuclear complex
[Pd2(SePh)4(PPh3)2] (1) and a mononuclear complex [PdCl(SePh)(PPh3)2] (2) that have been identified and characterized
structurally by X-ray crystallography and 31P-NMR spectroscopy. The analogous reaction involving diphenyl ditelluride leads to
a mixture of products. [Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) can be isolated and its X-ray structure determined. While the
oxidative addition of Ph2Se2 mainly involves the clevage of the Se–Se bond, that of Ph2Te2 indicates the rupture of both Te–Te
and C–Te. Cumulative evidence shows that the choice of the central atom and the solvent also plays an important role in the
oxidative addition. The final polynuclear complexes can be conceived to be formed from the mononuclear addition products by
sequential condensation steps. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Aromatic diselenides; Aromatic ditellurides; Palladium complexes; X-ray crystallography; NMR spectroscopy
This paper is a part of a systematic investigation of
the factors affecting the pathways of oxidative addition
1. Introduction
of aromatic dichalcogenides to zerovalent palladium
The coordination chemistry of transition metal com-
and platinum centers. The reaction pathway depends
plexes with organoselenide and telluride ligands is a
on the chemical identity of both the chalcogen atom
rapidly developing area of organometallic chemistry
and the Group 10 metal. Whereas dithienyl diselenide
[1–4]. They may provide a low-temperature route for
adds to [M(PPh3)4] mainly with the cleavage of Se–Se
binary transition metal selenides and tellurides, such as
bond forming mononuclear (M=Pt) or dinuclear
PdTe and NiTe [5–7] that find potential applications in
materials science. One way to prepare chalcogenolato
complexes involves the oxidative addition of diorgan-
(M=Pd, Pt) complexes [12], the reaction of dithienyl
ditelluride involves the cleavage of both C–Te and
Te–Te bonds [13,14] resulting in the formation of
odichalcogenides to low-valent transition metal centers
complexes with more complicated structures. The
that often results in the cleavage of the chalcogen–
choice of solvent also seems to affect the reaction
chalcogen bond and the formation of mono- or dinu-
pathway.
clear complexes with anionic bridging or terminal RE−
We report the reaction of diphenyl diselenide and
ligands [3]. In some cases the addition of diaryl
ditelluride with tetrakis(triphenylphosphine)palladium
dichalcogenides to zerovalent Group 10 metals has
in dichloromethane in order to explore the effect of the
been found to lead to the cleavage of the carbon–
aromatic group on the oxidative addition1. The main
chalcogen bond [8–14]. The oxidative addition of
products are identified by NMR spectroscopy and
organochalcogen compounds to low-valent transition
structurally characterized by X-ray crystallography.
metal centers may also be an initial step in homoge-
neous catalysis [15].
1 The formation of dinuclear [Pd2(SePh)4(PPh3)2] from Ph2Se2 and
[Pd(PPh3)4] in benzene has been reported, but no structural informa-
* Corresponding author.
tion has been given [16].
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00829-9

R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 623 (2001) 168–175
169
2. Experimental
360 frames via €-rotation (D€=1°; two times 20–60 s
per frame). Crystal data and the details of the structure
determinations are given in Table 1.
2.1. General
All structures were solved by direct methods using
SHELXS-97 [17] and refined using SHELXL-97 [18]. After
the full-matrix least-squares refinement of the non-hy-
drogen atoms with anisotropic thermal parameters, the
hydrogen atoms were placed in calculated positions in
Synthetic work was carried out under a dry argon
atmosphere. Dichloromethane was distilled on CaH2
and purged with argon before use. Tetrakis-
(triphenylphosphine)palladium [Pd(PPh3)4], diphenyl di-
selenide Ph2Se2, and diphenyl ditelluride Ph2Te2
(Aldrich) were used as supplied.
,
the aromatic rings (C–H=0.93 A). In the final refine-
ment the hydrogen atoms were riding with the carbon
atom they were bonded to. The isotropic thermal
parameters of the hydrogen atoms were fixed at 1.2
times to that of the corresponding carbon atom. The
scattering factors for the neutral atoms were those
incorporated with the programs. Fractional coordinates
of all atoms, anisotropic thermal parameters, and the
full listing of bond parameters are available as supple-
mentary material as CIF files.
2.2. The reaction of [Pd(PPh3)4] with Ph2Se2
Ph2Se2 (0.064 g, 0.21 mmol) was dissolved in 5 ml of
dichloromethane, added into 20 ml of
a
dichloromethane solution of [Pd(PPh3)4] (0.237 g, 0.21
mmol), and stirred overnight. The solution was concen-
trated by the partial evaporation of dichloromethane.
Upon addition of hexane a red precipitate was formed.
The precipitate was filtered off, washed with hexane,
and dried. The recrystallization from dichloromethane
afforded red, tabular crystals of [Pd2(SePh)4(PPh3)2] (1).
Yield 0.105 g (75%). Anal. Calc. for C60H50P2Pd2Se4: C
52.93, H 3.70; Found: C 52.76, H 3.39.
3. Results
3.1. General
Upon a slow evaporation of the filtrate a few violet
crystals of [PdCl(SePh)(PPh3)2] (2) were formed.
The reaction of diphenyl diselenide and [Pd(PPh3)4]
in dichloromethane affords [Pd2(SePh)4(PPh3)2] (1) with
good yields. [PdCl(SePh)(PPh3)2] (2) is obtained as a
minor side product. Both 1 and 2 are air-stable and
soluble in most organic solvents. Trans-isomers of both
[Pd2(SePh)4(PPh3)2] and [PdCl(SePh)(PPh3)2] crystallize
from dichloromethane or chloroform to yield X-ray
quality single crystals.
The oxidative addition of diphenyl ditelluride to
[Pd(PPh3)4] is similar to that of thienyl ditelluride [13]
and affords several products. Hexanuclear, air-stable
[Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) complexes
could be isolated among other, yet unidentified species.
2.3. The reaction of [Pd(PPh3)4] with Ph2Te2
The reaction of Ph2Te2 (0.075 g, 0.18 mmol) and
[Pd(PPh3)4] (0.205 g, 0.18 mmol) was carried out in
dichloromethane as described above. The reaction mix-
ture was allowed to stand at room temperature for a
week. During this time dark black–red crystals of
[Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) (ca. 0.019 g;
20%) were obtained. The variable, nonstoichiometric
amount of solvent in the crystals of the product pre-
cluded accurate elemental analysis.
3.2. Crystal structures of [Pd2(SePh)4(PPh3)2],
2.4. NMR spectroscopy
[PdCl(SePh)(PPh3)2], and [Pd6Cl2Te4(TePh)2(PPh3)6]
The 31P{1H}-NMR spectra were recorded on a
Bruker DPX400 spectrometer operating at 161.98
MHz. The spectral width was 58.480 kHz and the pulse
width 8.55 ms corresponding to the nuclear tip angle of
ca. 45°. The pulse delay was 1.0 s. The accumulations
contained ca. 5000–10000 transients. d-Chloroform
The molecular structures and the numbering of the
atoms of trans-[Pd2(SePh)4(PPh3)2] (1) and the
mononuclear side product trans-[PdCl(SePh)(PPh3)2]
(2) are shown in Figs.
1
and 2. Those of
[Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) are shown in
Fig. 3. The selected bond distances and angles are listed
in Tables 2 and 3.
2
was used as an internal H lock and orthophosphoric
acid (85%) as an external standard. The 31P chemical
shifts are reported relative to the external standard.
All species 1–3 form discrete complexes. The dinuc-
lear complex 1 shows a similar molecular structure to
trans-[Pd2(SeTh)4(PPh3)2] and trans-[Pt2(SeTh)4(PPh3)2]
(Th=thienyl, C4H3S) [12], as well as to trans-
[Pt2(SePh)4(PPh3)2] [19] with which it is isostructural.
The palladium atoms in all complexes 1–3 show
expectedly a slightly distorted square-planar coordina-
tion geometry (for the individual bond parameters in
2.5. X-ray crystallography
Diffraction data for 1–3 were collected on a Nonius
Kappa CCD diffractometer using graphite monochro-
,
mated Mo–Ka radiation (u=0.71073 A) by recording

170
R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 623 (2001) 168–175
Table 1
Details of the structure determination of [Pd2(SePh)4(PPh3)2] (1), [PdCl(SePh)(PPh3)2] (2) and [Pd6Cl2Te4(TePh)2(PPh3)6] (3)
1
2
3·1/2CH2Cl2
Empirical formula
Relative molecular mass
Crystal system
C30H25PPdSe2
680.79
Monoclinic
C2/c
C42H35ClP2PdSe C60.25H50.50Cl1.50P3Te3Pd3
822.45
Monoclinic
P21/c
1622.59
Monoclinic
C2/c
Space group
,
a (A)
28.014(6)
9.545(2)
22.570(3)
118.43(3)
5307.4(5)
293
17.533(4)
10.900(2)
19.832(4)
109.32(3)
3576.8(1)
120
22.820(5)
22.176(4)
23.912(5)
104.98(3)
11690(4)
293
,
b (A)
,
c (A)
i (°)
V (A )
T (K)
3
,
Z
8
4
8
F(000)
2672
1.704
3.520
2176
1.527
1.730
6212
1.844
2.569
Dcalc (g cm−3
)
v(Mo–Ka) (mm−1
Crystal size (mm)
Theta range (°)
)
0.20×0.15×0.10 0.25×0.15×0.15 0.30×0.15×0.10
2.80–24.92
19 085
4569
3237
307
0.1550
0.0742
0.1425
0.1139
0.1586
0.476
2.12–27.49
40 542
7924
5911
425
0.0655
0.0342
0.0666
0.0584
0.0729
1.077
2.55–23.50
15 395
8558
4075
638
0.1291
0.0735
0.0975
0.1893
0.1234
0.995
Number of reflections collected
Number of unique reflections
Number of observed reflections a
Number of parameters
Rint
b
R1
b
wR2
R1 (all data)
wR2 (all data)
GOF
−3
,
Max. and min. heights in final difference Fourier synthesis (e A
)
0.448, −0.634
0.449, −0.632
0.837, −0.631
a I\2|(I).
b R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ, wR2=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwF2o]1/2
.
a hinged arrangement in the Pd{m-SeR}2Pd fragment
with the respective angles of 104.4 and 124.5° between
the two neighbouring coordination planes.
The bridging phenylselenolato ligands in 1 are not
equidistant from the two palladium atoms. The two
the coordination sphere, see Tables 2 and 3). The sums
of the four bond angles around the metal atom are
360.1, 359.2 and 360.1–360.2° for 1–3, respectively,
well in accord with the virtually planar coordination.
The respective rms deviations of the metal atom and
four donor atoms from the coordination planes are
0.0737, 0.0339 and 0.0586–0.0841 for 1–3, respectively.
The two square-planar coordination spheres in dinuc-
lear Pd(II) and Pt(II) complexes can adopt either copla-
nar or hinged arrangement [3]:
1 exhibits the coplanar arrangement (see Fig. 1) that
seems to be a more common feature in dinuclear palla-
dium or platinum centers involving bridging chalcogen
donors than the hinged arrangement [12,13,20–23]. It
should be noted, however, that the hinged arrangement
is also known for these types of complexes, as exem-
Fig. 1. The molecular structure of [Pd2(SePh)4(PPh3)2] (1) indicating
the numbering of the atoms. The thermal ellipsoids have been drawn
at 30% probability.
plified
by
[Pd2{Se2C8H12}2(PPh3)2]
[24]
and
[Pd2Cl2(SeMe)2{SeMe(C4H2O)}2CMe2}] [25] that show

R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 623 (2001) 168–175
171
[25]. The shorter bridging Pd–Se bonds in
[Pd2{Se2C8H12}2(PPh3)2] [23] and [Pd2Cl2(SeMe)2-
{SeCH3(C4H2O)}2CMe2}] as compared to those in 1
are probably due to the hinged arrangement of the two
square-planar coordination planes of the neighbouring
palladium atoms, since the lone-pair repulsions between
the two selenium atoms are likely to be smaller than in
the case of coplanar arrangement (see Fig. 4).
The mononuclear [PdCl(SePh)(PPh3)2] (2) shows a
,
Pd–Se bond length of 2.4200(6) A. It falls within the
,
range 2.401–2.560 A of Pd–Se distances observed in
mononuclear palladium complexes [27–30]. The differ-
ences in the bond lengths can be attributed to the
relative effects of the trans-influence. The Pd–Se bonds
in hexacoordinated palladium complexes containing
PhSe− ligands are exemplified by 2.479–2.506 A re-
Fig. 2. The molecular structure of [PdCl(SePh)(PPh3)2] (2). The
thermal ellipsoids have been drawn at 30% probability.
,
ported for a series of trans-[PdMe2(SePh)2L2] (L=Me
or L2=H2CCH2CH2CH2) complexes [31].
The hexanuclear complex [Pd6Cl2Te4(TePh)2(PPh3)6]
(3) has a similar structure to [Pd6Cl2Te4(TeTh)2(PPh3)6]
and [Pd6Te4(TeTh)4(PPh3)6] [13]. It is in fact isostruc-
Table 2
,
Selected bond lengths (A) and bond angles (°) for [Pd2(SePh)4(PPh3)2]
(1) and [PdCl(SePh)(PPh3)2] (2)
Fig. 3. [Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) indicating the num-
bering of the atoms. The thermal ellipsoids have been drawn at 30%
probability.
[Pd2(SePh)4(PPh3)2] (1)
[PdCl(SePh)(PPh3)2] (2)
Bond lengths
Pd–P
,
Pd–Se(1) distances are 2.463(1) and 2.494(1) A (see
Table 2). The terminal Pd–Se(2) bond in 1 shows a
2.284(2)
Pd–P(1)
Pd–P(2)
Pd–Se
2.3485(9)
Pd–Se(1)
Pd–Se(2)
Pd–Se(1) a
Se(1)–C(11)
Se(2)–C(21)
2.463(1)
2.461(1)
2.494(1)
1.925(10)
1.919(11)
2.3130(9)
2.4200(6)
2.3468(9)
,
length of 2.461(1) A. All these values are close to single
bond lengths {the sum of the covalent radii of palla-
dium and selenium is 2.45 A [26]}. The bridging Pd–Se
bonds in [Pd2{Se2C8H12}2(PPh3)2] are shorter than
Pd–Cl
,
those in 1, but exhibit similar asymmetry (2.413–2.419
Bond angles
P–Pd–Se(1)
96.24(7)
87.90(7)
174.69(4)
175.85(4)
84.11(4)
91.80(4)
95.89(4)
98.7(3)
P(1)–Pd–P(2)
P(1)–Pd–Se
P(2)–Pd–Se
P(1)–Pd–Cl
P(2)–Pd–Cl
Se–Pd–Cl
175.91(3)
94.23(3)
82.61(3)
89.71(3)
93.69(3)
173.36(2)
,
and 2.481–2.489 A) [24] each selenium being closer to
P–Pd–Se(2)
the palladium atom to which it is chelating. The termi-
P–Pd–Se(1) a
,
nal
Pd–Se
distances
(2.382–2.387
A)
in
Se(1)–Pd–Se(2)
Se(1)–Pd–Se(1) a
Se(2)–Pd–Se(1) a
Pd–Se(1)–Pd(1) a
C(11)–Se(1)–Pd
C(11)–Se(1)–Pd a
C(21)–Se(2)–Pd
[Pd2{Se2C8H12}2(PPh3)2] are also shorter than in 1. In
contrast, the Pd(m–SeR)2Pd unit in [Pd2(SeTh)4(PPh3)2]
is symmetric with all bridging and terminal bonds
showing virtually equal lengths [2.466(1) and 2.461(1)
97.5(3)
101.8(3)
,
A,
respectively]
[12].
[Pd2Cl2(SeMe)2{SeCH3-
(C4H2O)}2CMe2}] is also symmetric, the bridging Pd–
Se distances spanning a narrow range of 2.396–2.420 A
a Symmetry operation −x, 2−y, −z.
,

172
R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 623 (2001) 168–175
ing PhTe− ligands seem to be somewhat longer
Table 3
,
Selected bond lengths (A) and bond angles (°) in
[Pd6Cl2Te4(TePh)2(PPh3)6] (3)
,
(2.629(2)–2.647(2) A) in agreement with 2.6286(10)–
,
2.6452(9) A in [Pd6Cl2Te4(TeTh)2(PPh3)6], 2.6137(7)–
,
2.6594(7)
A
in [Pd6Te4(TeTh)4(PPh3)6] [13], and
2.630(1)–2.636(1) A in [Pd6Te6(PEt3)8] [6].
There is a close Te(1)···Te(2) contact of 3.164(1) A in
3 (the sum of van der Waals’ radii of two tellurium
Bond lengths
Te(1)–Pd(3)
Te(1)–Pd(1)
Te(1)–Pd(2)
Te(1)–Te(2)
Te(2)–Pd(3)
Te(2)–Pd(1)
Te(2)–Pd(2)
Te(3)–C(1)
2.591(2)
2.603(1)
2.600(1)
3.164(1)
2.560(1)
2.597(2)
2.602(2)
2.154(2)
Te(3)–Pd(2) a
Te(3)–Pd(1)
Pd(1)–P(1)
Pd(2)–P(2)
Pd(2)–Te(3) a
Pd(3)–P(3)
Pd(3)–Cl(1)
2.629(2)
2.647(2)
2.310(4)
2.302(4)
2.629(2)
2.311(4)
2.422(4)
,
,
,
atoms is 3.6 A [26]). This kind of chalcogen–chalcogen
interaction has also been observed in other complexes
containing a similar M3E2 core (M=Ni, Pd, Pt; E=S,
Se, Te) [6,13,33–39].
The Pd–P distances in 1–3 [2.284(2), 2.3130(9)–
2.3485(9), and 2.302(4)–2.311(4), respectively] and the
Bond angles
Pd(3)–Te(1)–Pd(1)
Pd(3)–Te(1)–Pd(2)
Pd(1)–Te(1)–Pd(2)
Pd(3)–Te(1)–Te(2)
Pd(1)–Te(1)–Te(2)
Pd(2)–Te(1)–Te(2)
Pd(3)–Te(2)–Pd(1)
Pd(3)–Te(2)–Pd(2)
Pd(1)–Te(2)–Pd(2)
Pd(3)–Te(2)–Te(1)
Pd(1)–Te(2)–Te(1)
Pd(2)–Te(2)–Te(1)
85.28(5)
92.20(5)
80.89(4)
51.66(3)
52.43(4)
52.56(4)
86.05(5)
92.89(5)
80.99(5)
52.55(4)
52.62(3)
52.53(3)
Te(2)–Pd(1)–Te(1)
P(1)–Pd(1)–Te(3)
Te(2)–Pd(1)–Te(3) 167.47(5)
74.95(5)
92.5(1)
,
,
Pd–Cl distances of 2.3468(9) A in 2 and 2.422(4) A in
3 indicate normal single bonds. The small differences
can again be explained by the effects of the relative
trans-influence. The bond lengths within the ligands are
also quite normal.
Te(1)–Pd(1)–Te(3)
P(2)–Pd(2)–Te(2)
P(2)–Pd(2)–Te(1)
Te(2)–Pd(2)–Te(1)
94.41(5)
96.2(1)
170.9(1)
74.91(4)
P(2)–Pd(2)–Te(3) a 100.7(1)
Te(2)–Pd(2)–Te(3) a 162.69(5)
Te(1)–Pd(2)–Te(3) a 88.37(4)
3.3. NMR specroscopy
P(3)–Pd(3)–Cl(1)
P(3)–Pd(3)–Te(2)
Cl(1)–Pd(3)–Te(2) 168.2(1)
P(3)–Pd(3)–Te(1)
Cl(1)–Pd(3)–Te(1)
Te(2)–Pd(3)–Te(1)
94.4(1)
97.3(1)
The reaction of Ph2Se2 and [Pd(PPh3)4] in
dichloromethane produces a mixture exhibiting two
major 31P resonances at 28.9 and 27.9 ppm. In addition
there are weak resonances at 27.1, 27.0, and a very
weak signal at 25.3 ppm. The weak resonances at 30.2
and −3.4 ppm were assigned to Ph3PO and PPh3,
respectively [12,13].
C(1)–Te(3)–Pd(2) a 109.6(4)
C(1)–Te(3)–Pd(1) 97.6(4)
Pd(2) a–Te(3)–Pd(1) 110.83(5)
P(1)–Pd(1)–Te(2)
P(1)–Pd(1)–Te(1)
171.4(1)
92.5(1)
75.79(4)
98.3(1)
173.0(1)
a Symmetry transformation: −x+1/2, −y+1/2, −z+1.
We have assigned previously two 31P resonances at
29.9 and 29.3 ppm to cis- and trans-isomers of
[Pd2(SeTh)4(PPh3)2] [12]. The two strongest resonances
at 28.9 and 27.9 ppm can therefore be assigned to the
two isomers of [Pd2(SePh)4(PPh3)2]. The trans-isomer is
obtained as the main product upon recrystallization.
The weaker resonances at 27.1 and 27.0 ppm can be
assigned tentatively to either the two isomers of
[Pd(SePh)2(PPh3)2] or those of [PdCl(SePh)(PPh3)2].
The former can be expected to act as intermediates
along the reaction coordinate to the dinuclear complex
1, and traces of trans-[PdCl(SePh)(PPh3)2] have been
obtained upon recrystallization. The weak resonance at
25.2 ppm is probably due to trans-[PdCl(Ph)(PPh3)2]
that can be expected to be formed in small amounts.
The analogous trans-[PdCl(Th)(PPh3)2] has been ob-
tained as a minor product upon the reaction of Th2Se2
and [Pd(PPh3)4] in dichloromethane and has been struc-
turally characterized by X-ray crystallography [13]. Its
31P chemical shift in dichloromethane lies at 25.0 ppm.
The reaction of Ph2Te2 and [Pd(PPh3)4] affords sev-
eral products exhibiting a rich 31P-NMR spectrum.
Furthermore, the spectrum of the redissolved crystals of
[Pd6Cl2Te4(TePh)2(PPh3)6] (3) is also complicated im-
plying decomposition of the hexanuclear framework in
solution, as also observed earlier in the case of
[Pd6Cl2Te4(TeTh)2(PPh3)6] and [Pd6Te4(TeTh)4(PPh3)6]
[13]. Up to present it has not been possible to make a
meaningful assignment of the spectra.
tural with the former complex. The complex 3 also
shows an analogous molecular framework as
[Pd6Te6(PPh3)8] [6].
The structure is composed of two Pd3Te2 fragments
that are similar to those found in pentanuclear cations
[M{Pd2Te2(dppe)2}2]2+ (M=Pd, Pt) [32,33]. The same
geometry is also observed in [Pt3Te2(PEt3)6]2+ [34] and
[Pt3Te2(dppe)3]2+ [35]. It is also worth noting that
Fenske et al. [36–38] have shown the existence of a
similar Pd3Se2 framework in a series of multinuclear
palladium complexes.
The two Pd3Te2 units in 3 are joined together into a
cyclic hexanuclear complex by two bridging PhTe−
ligands. The hexanuclear framework seems to provide
an inherently stable structure. Indeed, it has been dis-
cussed by Brennan et al. [6] that there is a direct
relationship between the Pd6Te6 framework and the
lattice of binary PdTe.
The Pd–(m3-Te) bond lengths in 3 span a range of
,
,
2.561(1)–2.603(1) A (average 2.592 A). This is expect-
edly in good agreement with the Pd–(m3-Te) distances
found in [Pd6Cl2Te4(TeTh)2(PPh3)6] (2.5615(9)–
,
2.6113(8) A) and [Pd6Te4(TeTh)4(PPh3)6] (2.5909(7)–
[Pd{Pd2Te2(dppe)2}2]2+
,
2.6361(7)
A)
[13],
,
{2.595(2)–2.619(2)
2.591(1)–2.637(1) A [6]}. The Pd–Te distances involv-
A
[32]; and [Pd6Te6(PEt3)8]
,

R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 623 (2001) 168–175
173
center mainly leads to a mixture of isomers of mononu-
clear [Pt(SeR)2(PPh3)2] [12,44] and the dinuclear
[Pt2(SeTh)4(PPh3)2] complex is only formed in small
amounts, that with palladium affords [Pd2(SeR)4-
(PPh3)2] (R=Th, Ph) as the main product. This indi-
cates that some Se–C(aryl) bond cleavage also takes
place during the reaction. Some [PdCl(SePh)(PPh3)2] (2)
is also formed upon addition of Ph2Se2 to [Pd(PPh3)4]2.
Furthermore, [Pd(SePh)2(PPh3)2] might also be present
in the reaction mixture.
The presence of monomeric chlorine-containing com-
plexes might also lead to dinuclear complexes contain-
ing bridging chloro ligands in addition to bridging
arylselenolato ligands. While such complexes have not
been observed in the present reaction mixtures, some
examples have been prepared, isolated, and structurally
characterized by related reaction routes [19,39,40].
Several products are formed during the reaction of
diaryl ditelluride and [M(PPh3)4] (M=Pt, Pd). There is
clear cumulative evidence that the cleavage of the C–Te
bond takes place much more readily than that of the
C–Se bond (see Table 4 and Refs. [8–14]).
Fig. 4. The pp lone-pair interactions in the ꢀM(m-SeR)2Mꢁ unit (a)
coplanar arrangement (R=Ph) and (b) hinged arrangement (R=
Me; molecular conformation taken from Ref. [25]).
4. Discussion
The reaction of R2Te2 (R=Th) with platinum in
dichloromethane affords [Pt3Te2(Th)(PPh3)5]Cl and [Pt-
Cl(Th)(PPh3)2] in equimolar amounts [13]. That with
palladium leads to hexanuclear [Pd6Cl2Te4(TeR)2-
(PPh3)6] {R=Ph, Th [13]}. When [Pd(PPh3)4] was
treated with dithienyl ditelluride in toluene,
[Pd6Te4(TeTh)4(PPh3)6] containing the same framework
was formed. The solvent apparently plays an active role
in the C–Te bond cleavage, as has recently been dis-
cussed by Khanna et al. [11]. This kind of interaction
The pathway of the oxidative addition reaction of
diaryl dichalcogenides to zerovalent platinum and pal-
ladium centers is dependent on the choice of the metal,
the chalcogen element, the aryl group, and the solvent.
The main products in these reactions are summarized in
Table 4.
The most significant single factor affecting the
product distribution is the chemical identity of the
chalcogen atoms in the starting dichalcogenide. The
oxidative addition of R2Se2 (R=Ph, Th) to [M(PPh3)4]
(M=Pd, Pt) mainly leads to the cleavage of the Se–Se
bond with the formation of mononuclear and dinuclear
complexes the latter of which are probably formed
through condensation of the mononuclear complexes
[13]. While the reaction with the zerovalent platinum
2 Khandelwal and Gupta [45] have proposed on the basis of
elemental analysis and molecular weight determination that 2 is also
formed upon the reaction of polymeric [PdCl(SePh)]n with an excess
of PPh3.
Table 4
The main products in the oxidative addition reactions of R2E2 (E=Se, Te; R=Th, Ph) to [M(PPh3)4] (M=Pd, Pt) in dichloromethane (side
products are shown in italics)
Se
Te
Tha
Ph
Thb
Ph
Pd
Pt
[Pd2(SeTh)4(PPh3)2]c
[Pd2(SePh)4(PPh3)2]d
[PdCl(SePh)(PPh3)2]
[Pd2(TeTh)4(PPh3)2]e
[Pd6Cl2Te4(TeTh)2(PPh3)2]
[Pd6Te4(TeTh)4(PPh3)2]f
[Pt3Te2(Th)(PPh3)5]Cl
[PtCl(Th)(PPh3)2]
[Pd6Cl2Te4(TePh)2(PPh3)2]
[PdCl(Th)(PPh3)2]c
[Pt(SeTh)2(PPh3)2]
[Pt2(SeTh)4(PPh3)2]
[Pt(SePh)2(PPh3)2]g
a Ref. [12].
b Ref. [13].
c When the reaction is carried out in toluene, only [Pd2(SeTh)4(PPh3)2] is formed.
d It has been proposed that [Pd2(SePh)4(PPh3)2] is also formed in benzene. There is no structural data; see Ref. [16].
e The reaction has been carried out in benzene. The identity of the product is based on elemental analysis; see Ref. [43].
f The reaction has been carried out in toluene.
g The product is obtained upon the oxidative addition of Ph2Se2 to [Pt(H2C=CH2)(PPh3)2]; see Ref. [44].

174
R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 623 (2001) 168–175
finds support in the preparation and structural charac-
terization of [PdCl(CH2Cl)(PPh3)2] in dichloromethane
[41]. Species like [MCl(R)(PPh3)2] have been suggested
to be an important factor in the catalytic activity of
palladium and platinum complexes [42].
Acknowledgements
Financial support from Neste Oy Foundation,
Academy of Finland, and Tauno To¨nning Foundation
is gratefully acknowledged.
The more complicated polynuclear complexes are
probably formed from mono- and dinuclear complexes
by successive condensation reactions [13], as initially
suggested by Brennan et al. [6], who formulated a
pathway for the formation on hexanuclear [Pd6Te6-
(PEt3)8] with a dinuclear intermediate [Pd2Te4(PEt3)4]
[6,7]. Because [Pd6Te4(TeR)2(PPh3)6] contains the same
framework as [Pd6Te6(PEt3)8], their formation probably
goes through similar stages. The suggested formation of
[Pd2(TeTh)4(PPh3)2] from Th2Te2 and [Pd(PPh3)4] in
benzene [43] lends credibility to this reaction pathway.
The use of [Pt(PPh3)4] as a reagent with R2Te2 again
leads to complexes of lower nuclearity than that of
[Pd(PPh3)4]. In an analogous manner, the addition of
organic disulfides to the zerovalent platinum center
mainly affords mononuclear complexes, while that with
Pd(0) results in the formation of dinuclear complexes
[46]. Mononuclear palladium complexes could be sta-
blized with strongly electronwithrawing aryl groups.
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