The NMR spectroscopic and X-ray crystallographic study of the oxidative addition of bis(2-thienyl) diselenide to zerovalent palladium and platinum centers

Article abstract of DOI:10.1016/S0022-328X(99)00319-8

The pathway of the reaction of dithienyl diselenide with tetrakis(triphenylphosphine)palladium(0) and -platinum(0) has been explored by the use of NMR spectroscopy and X-ray diffraction. The oxidative addition of dithienyl diselenide to [Pd(PPh₃)₄] mainly results in the formation of two isomers of dinuclear [Pd₂(SeTh)₄(PPh₃)₂] (Th = 2-thienyl, C₄H₃S) complex. The workup of the solution produced X-ray-quality crystals of trans-[Pd₂(SeTh)₄(PPh₃)₂]. The corresponding reaction with [Pt(PPh₃)₄], however, affords isomers of mononuclear [Pt(SeTh)₂(PPh₃)₂]. Upon recrystallization from dichloromethane a small amount of crystals of dinuclear [Pt₂(SeTh)₄(PPh₃)₂] is obtained together with those of trans-[Pt(SeTh)₂(PPh₃)₂]. While the products from both reactions imply that the oxidative addition takes place with the cleavage of the Se-Se bond, a small amount of trans-[PdCl(Th)(PPh₃)₂] is formed in the reaction of [Pd(PPh₃)₄] and Th₂Se₂ in dichloromethane indicating that C-Se cleavage may also take place during the oxidative addition.

Full text of DOI:10.1016/S0022-328X(99)00319-8

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Journal of Organometallic Chemistry 587 (1999) 200–206
The NMR spectroscopic and X-ray crystallographic study of the
oxidative addition of bis(2-thienyl) diselenide to zerovalent
palladium and platinum centers
Raija Oilunkaniemi a, Risto S. Laitinen a,*, Markku Ahlgre´n b
a Department of Chemistry, Uni6ersity of Oulu, PO Box 3000, FIN-90401 Oulu, Finland
b Department of Chemistry, Uni6ersity of Joensuu, PO Box 111, FIN-90801 Joensuu, Finland
Abstract
The pathway of the reaction of dithienyl diselenide with tetrakis(triphenylphosphine)palladium(0) and -platinum(0) has been
explored by the use of NMR spectroscopy and X-ray diffraction. The oxidative addition of dithienyl diselenide to [Pd(PPh3)4]
mainly results in the formation of two isomers of dinuclear [Pd2(SeTh)4(PPh3)2] (Th=2-thienyl, C4H3S) complex. The workup of
the solution produced X-ray-quality crystals of trans-[Pd2(SeTh)4(PPh3)2]. The corresponding reaction with [Pt(PPh3)4], however,
affords isomers of mononuclear [Pt(SeTh)2(PPh3)2]. Upon recrystallization from dichloromethane a small amount of crystals of
dinuclear [Pt2(SeTh)4(PPh3)2] is obtained together with those of trans-[Pt(SeTh)2(PPh3)2]. While the products from both reactions
imply that the oxidative addition takes place with the cleavage of the SeꢀSe bond, a small amount of trans-[PdCl(Th)(PPh3)2] is
formed in the reaction of [Pd(PPh3)4] and Th2Se2 in dichloromethane indicating that CꢀSe cleavage may also take place during
the oxidative addition. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Aromatic diselenides; Palladium complex; Platinum complex; X-ray crystallography; NMR spectroscopy
or
1. Introduction
The last decade has seen a rapid growth of interest in
the coordination chemistry of transition metal com-
plexes with organoselenide and -telluride ligands [1–4]
because of their potential utility as precursors for bi-
nary transition metal selenides and tellurides, such as
PdTe and NiTe [5–7], which could have applications in
the fabrication of new electronic materials [4]. The
preparation of these complexes characteristically in-
volves the oxidative addition of the organochalcogen
compounds to low-valent transition metal centers most
often resulting in the cleavage of the chalco-
genꢀchalcogen bond and the formation of mono- or
dinuclear complexes with anionic bridging or terminal
RE− (E=Se, Te) ligands:
An extensive list of examples is given by Gysling [3] in
his comprehensive review on the ligand chemistry of
organic selenium and tellurium species. It has, however,
also been reported that the reaction of aryl ditellurides
with Ni(0), Pd(0), and Pt(0) may result in the cleavage
of the carbonꢀchalcogen bond [8–11]. The oxidative
addition of organochalcogen compounds to low-valent
transition metal centers is considered a key step in
homogeneous catalysis [12].
Chia and McWhinnie [13] deduced in 1978 that the
oxidative addition of Th2Te2 (Th=thienyl, C4H3S) to
[Pd(PPh3)4] in benzene solution produces dinuclear
[Pd2(TeTh)4(PPh3)2] with two terminal and two bridg-
ing ThTe− ligands. Fukukawa et al. [14] have also
reported the formation of an analogous complex
* Corresponding author. Fax: +358-8-5531608.
E-mail address: risto.laitinen@oulu.fi (R.S. Laitinen)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00319-8

R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 587 (1999) 200–206
201
[Pd2(SePh)4(PPh3)2] from Ph2Se2 and [Pd(PPh3)4] in
benzene. Detailed structural information on the reac-
tion products, however, is missing in both cases.
Analogous dinuclear complexes in which two bridging
RE− (E=S, Se) ligands link two palladium or plat-
Upon slow evaporation of the filtrate a small amount
of green crystals of [PdCl(Th)(PPh3)2] (2) (0.01 g, yield
5%) was formed.
The preparation was repeated by using toluene as a
solvent instead of dichloromethane. The same main
product 1 was obtained also in this case.
inum
[Pt2I2(SCH2CMeꢁCH2)2(PPh3)2]
Et)2(PEt3)2] [16], [Pd2(C3H5)2{Ph2P(O)NP(Se)Ph2-
centers
together
are
exemplified
by
[15], [Pt2Cl2(Se-
2.2.2. [Pt(SeTh)2(PPh3)2] (3) and [Pt2(SeTh)4(PPh3)2]
(4)
Se}2]·2CHCl3 [17], [Pd2{Se2C8H12}2(PPh3)2] [18], and
[Pd2Cl2(SeMe)2{SeMe(C4H2O)}2CMe2] [19].
The preparation of 3 was performed in dichloro-
methane in a similar fashion to that described above for
1 by using 0.065 g (0.20 mmol) of dithienyl diselenide
and 0.250 g (0.20 mmol) of [Pt(PPh3)4]. The product
was separated as an orange–yellow precipitate, yield
0.120 g (55%). Anal. Calc. for C44H36P2S2Se2Pt: C,
50.63; H, 3.48; S, 6.14. Found: C, 50.80; H, 3.36; S,
6.56%. Recrystallization from dichloromethane by a
slow evaporation of the solvent yielded yellow crystals
of 3·12CH2Cl2 suitable for X-ray analysis. M.p. (dec.)
156–158°C.
We are undertaking a systematic investigation of the
oxidative addition of aromatic dichalcogenides to ze-
rovalent palladium and platinum centers. The scope is
to gain insight into the factors affecting the actual
reaction pathways and product distribution by varying
the chemical nature of the chalcogen atom, aromatic
substituent, and the solvent. This paper is concerned
with the reaction of bis(2-thienyl) diselenide with te-
trakis(triphenylphosphine)palladium and -platinum.
The reaction products are identified and characterized
by X-ray diffraction and NMR spectroscopy.
In addition to 3 a small amount of yellow crystals of
4 was separated upon recrystallization from dichloro-
methane.
2. Experimental
2.3. NMR spectroscopy
2.1. General
The 31P{1H}-, 77Se- and 195Pt-NMR spectra were
recorded on a Bruker DPX400 spectrometer operating
at 161.98, 76.31, and 85.60 MHz, respectively. The
typical respective spectral widths were 58.480, 68.493,
and 42.735 kHz. The pulse widths were 8.55, 7.30 and
9.20 ms, the two former corresponding to a nuclear tip
angle of ca. 45°, and the last to a tip angle of ca. 25°.
The 31P pulse delay was 1.0 s, that for 77Se was 1.6 s,
and that for 195Pt was 0.5 s. The 31P accumulations
contained ca. 5000–10 000 transients, those for 77Se
30 000–50 000 transients, and for 195Pt 10 000 tran-
Synthetic work was carried out under a dry argon
atmosphere. Tetrahydrofuran and toluene were distilled
under nitrogen from Na/benzophenone. Dichloro-
methane was distilled over CaH2 and purged with
argon before use. Tetrakis(triphenylphosphine)-
palladium and -platinum (Aldrich) were used without
further purification. Dithienyl diselenide was prepared
by modifying the literature methods [20].
2
sients. Chloroform-d or benzene-d6 was used as a H
2.2. Syntheses
lock. Orthophosphoric acid (85%), a saturated D2O
solution of selenium dioxide, and the D2O solution of
PtCl26− were used as external standards. The 31P and
195Pt chemical shifts are reported relative to the external
standard and the 77Se chemical shifts relative to neat
Me2Se [l(Me2Se)=l(SeO2)+1302.6].
2.2.1. [Pd2(SeTh)4(PPh3)2] (1) and [PdCl(Th)(PPh3)2]
(2)
Dithienyl diselenide (0.100 g, 0.30 mmol) was dis-
solved in 5 ml of dichloromethane and the resulting
solution was added into 20 ml of a dichloromethane
solution of [Pd(PPh3)4] (0.355 g, 0.30 mmol) and stirred
overnight. The solution was concentrated by the partial
evaporation of dichloromethane. The reaction product
was precipitated by adding n-hexane to the solution.
The red precipitate was filtered off, washed with hexane
and dried. Recrystallization from dichloromethane by
slow evaporation of the solvent yielded red crystals
suitable for X-ray analysis. M.p. (dec.) 152–154°C,
yield 0.199 g (95%). Anal. Calc. for C52H42P2Pd2S4Se4:
C, 45.07; H, 3.06; S, 9.26. Found: C, 45.73; H, 2.93; S,
9.29%.
2.4. X-ray crystallography
Diffraction data for 1–4 were collected on a Nonius
Kappa CCD diffractometer at 293 K using graphite
,
monochromated Mo–Ka radiation (u=0.71073 A) by
recording 360 frames via 8-rotation (D€=1°; twice
10–20 s per frame). Crystal data and the details of the
structure determinations are given in Table 1.
All structures were solved by direct methods using
SHELXS-97 [21] and refined using SHELXL-97 [22]. The
terminal ThSe− ligands in 1 and 4 were found to be

202
R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 587 (1999) 200–206
orientationally disordered, as were both selenium-con-
taining ligands in 3. It was also observed that the six
phenyl rings in 4 could each assume two different orien-
tations. In the refinement the disorder was taken into ac-
count, and the site occupation factors of each disordered
pair were refined by constraining their sums to unity.
Since the site occupation factors and thermal parameters
of the disordered atoms correlate with each other, the
thermal parameters of the corresponding pairs of atoms
were restrained to be equal.
(PPh3)2] (1) with good yields. In dichloromethane [Pd-
Cl(Th)(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(SeTh)4(PPh3)2] and
[PdCl(Th)(PPh3)2] crystallize from dichloromethane or
chloroform to yield X-ray quality single crystals.
Dithienyl diselenide reacts with [Pt(PPh3)4] in a
slightly different fashion. The main product in
dichloromethane is a mixture of cis- and trans-isomers
of mononuclear [Pt(SeTh)2(PPh3)2] (see discussion be-
low). Upon recrystallization from dichloromethane
trans-[Pt(SeTh)2(PPh3)2] (3) is obtained with a small
amount of dinuclear trans-[Pt2(SeTh)4(PPh3)2] (4).
The structures and identities of the reaction products
1–4 are established by NMR spectroscopy and X-ray
crystallography.
After the full-matrix least-squares refinement of the
non-hydrogen atoms with anisotropic thermal parame-
ters, the hydrogen atoms were placed in calculated posi-
,
tions in the aromatic rings (CꢀH=0.93 A). In the final
refinement the hydrogen atoms were riding with the car-
bon atom they were bonded to. The isotropic thermal
parameters of the hydrogen atoms were fixed at 1.2 times
that of the corresponding carbon atom. The scattering
factors for the neutral atoms were those incorporated
within the programs. Fractional coordinates, anisotropic
thermal parameters, and the full listing of bond parame-
ters are available as supplementary material.
3.2. X-ray crystallography
The molecular structures and the numbering of the
atoms of trans-[Pd2(SeTh)4(PPh3)2] (1) and trans-[Pd-
Cl(Th)(PPh3)2] (2) are shown in Figs. 1 and 2. Those of
trans-[Pt(SeTh)2(PPh3)2] (3) and trans-[Pt2(SeTh)4-
(PPh3)2] (4) are shown in Figs. 3 and 4. The selected
bond distances and angles are listed in Table 2.
3. Results and discussion
All species 1–4 form discrete complexes. The dinu-
clear complexes 1 and 4 have similar molecular struc-
tures, though they are not isostructural. In every
complex the palladium or platinum atoms show a
3.1. General
The reaction of dithienyl diselenide and [Pd(PPh3)4] in
dichloromethane or toluene produces [Pd2(SeTh)4-
Table 1
Details of the structure determination of [Pd2(SeTh)4(PPh3)2] (1), [PdCl(Th)(PPh3)2] (2), [Pt(SeTh)2(PPh3)2] (3), and [Pt2(SeTh)4(PPh3)2] (4)
1
2
3·12CH2Cl2
4
Empirical formula
Relative molecular mass
Crystal system
C26H21PS2Se2Pd
692.84
Monoclinic
P21/c
13.279(3)
16.949(3)
12.518(3)
C40H33ClP2SPd
749.51
Triclinic
C44.5H36ClP2S2Se2Pt
1085.25
Monoclinic
C2/c
11.209(2)
34.471(7)
C26H21PS2Se2Pt
781.53
Monoclinic
P21/c
14.452(3)
10.671(2)
18.030(4)
(
Space group
P1
,
a (A)
12.2220(5)
12.7082(5)
13.3445(5)
90.598(5)
115.039(5)
108.842(5)
1750.9(1)
2
,
b (A)
,
c (A)
22.435(4)
h (°)
i (°)
k (°)
111.42(3)
101.98(3)
111.81(3)
3
,
V (A )
2623(1)
4
8480(3)
8
2581.5(9)
4
Z
F(000)
1352
1.755
3.716
0.25×0.25×0.10
2.04–28.29
2521
764
1.422
0.785
0.40×0.15×0.08
2.62–26.42
4114
4224
1.700
5.294
0.40×0.25×0.20
2.41–25.00
5470
1480
2.011
8.492
0.30×0.15×0.10
2.97–26.34
3767
Dcalc (g cm−3
)
v (Mo–Ka) (mm−1
Crystal size (mm)
q Range (°)
Number of observed reflections
[I]2|(I)]
)
Number of parameters/restraints
306/15
0.0642
0.1126
402/0
0.0543
0.0804
505/40
0.0377
0.1017
372/79
0.0451
0.1158
a
R1
a
wR2
Goodness-of-fit
0.912
1.069
1.011
1.022
Max./min. heights in final difference
0.914, −1.552
0.714, −0.382
1.486, −1.298
1.194, −1.257
−3
,
Fourier synthesis (e A
)
a R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ, wR2=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwF2o]1/2
.

R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 587 (1999) 200–206
203
Fig. 1. The molecular structure of [Pd2(SeTh)4(PPh3)2] (1) indicating
the numbering of the atoms. The terminal thienyl rings are disor-
dered. The more favored orientation (A) is shown in the figure (site
occupation factor is 0.51). The thermal ellipsoids have been drawn at
30% probability.
Fig. 3. The molecular structure of [Pt(SeTh)2(PPh3)2] (3) indicating
the numbering of the atoms. The more favored orientation A of the
disordered thienyl rings is shown in the figure (site occupation factor
is 0.71). The thermal ellipsoids have been drawn at 30% probability.
slightly distorted square-planar coordination geometry
(for the individual bond parameters in the coordination
sphere, see Table 2).
H12)2(PPh3)2] [18], [Pd{N(SePPh2)2-Se,Se%}2] [25],
[Pd2Cl2(PPrn3)2(SeC5H4N)2] [26], and [Pd(C3S3Se2)2]−
[27].
In 1 and 4 the two symmetry-related neighboring
coordination planes are linked together through two
bridging ThSe− ligands (see Figs. 1 and 4). This kind
of planar [M(m-SeR)2M] (M=Pd, Pt) arrangement is
well established [15–17,23]. While both [Pd2(Se2-
C8H12)2(PPh3)2] [18] and [Pd2Cl2(SeMe)2{SeMe-
(C4H2O)}2CMe2] [19] contain a similar [Pd{m-SeR}2Pd]
fragment, there is an angle of 104.4 [18] and 124.5° [19]
between the two neighboring coordination planes.
The lengths of the bridging and terminal PdꢀSe
PtꢀSe distances in 3 and 4 are 2.4629(1)–2.4651(1)
,
and 2.440(1)–2.508(6) A, respectively. They are slightly
longer than the PtꢀSe bonds in [Pt(SeR)2L2] (R=Ph,
py, L=PPh3, or L2=dppe, dppm) (the average bond
,
lengths range from 2.418 to 2.466 A; Refs. [28,29]),
,
[Pt2Cl2(SeEt)2(PEt3)2] (average 2.430 A; Ref. [16]),
,
[Pt2Se2(PPh3)4] (average 2.449 A; Ref. [23]), and
,
[Pt(Se2CH2)(PPh3)2] (average 2.426 A; Ref. [30]).
,
bonds (2.463(1)–2.466(1) A) in 1 are close to single
bond lengths (the sum of the covalent radii of palla-
,
dium and selenium is 2.45 A [24]) and can be compared
,
to the PdꢀSe distances of 2.382–2.560
A
in
[Pd(C9H12N){N(SePPh2)2-Se,Se%}] [17], [Pd2(Se2C8-
Fig. 4. The molecular structure of [Pt2(SeTh)4(PPh3)2] (4) indicating
the numbering of the atoms. The more favored orientation (A) of the
terminal thienyl rings is shown in the figure (site occupation factor is
0.81). The full disorder scheme of both the thienyl and phenyl rings
is shown in the insert. The site occupation factors of the two
orientations of the phenyl rings are 0.55 and 0.45 for the orientations
A and B, respectively. The thermal ellipsoids have been drawn at 30%
probability.
Fig. 2. The molecular structure of [PdCl(Th)(PPh3)2] (2) indicating
the numbering of the atoms. The thermal ellipsoids have been drawn
at 30% probability.

204
R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 587 (1999) 200–206
Table 2
,
Selected bond lengths (A) and angles (°) for [Pd2(SeTh)4(PPh3)2] (1), [PdCl(Th)(PPh3)2] (2), [Pt(SeTh)2(PPh3)2] (3) and [Pt2(SeTh)4(PPh3)2] (4)
[Pd2(SeTh)4(PPh3)2] (1)
[PdCl(Th)(PPh3)2] (2)
[Pt(SeTh)2(PPh3)2] (3)
[Pt2(SeTh)4(PPh3)2] (4)
PdꢀSe(1)
PdꢀSe(2)
PdꢀSe(1) a
PdꢀP
2.4661(11)
2.4634(12)
2.4657(12)
2.297(2)
PdꢀCl
2.3812(12)
PtꢀSe(1)
PtꢀSe(2)
PtꢀP(1)
PtꢀP(2)
2.4629(1)
PtꢀSe(1)
PtꢀSe(2A)
PtꢀSe(2B)
PtꢀSe(1) b
PtꢀP
2.4715(10)
2.4395(13)
2.508(6)
2.4461(10)
2.273(2)
PdꢀP(1)
PdꢀP(2)
PdꢀC(1)
2.3438(12)
2.3301(12)
2.014(3)
2.4651(1)
2.3114(17)
2.3204(16)
Se(1)ꢀPdꢀSe(2)
Se(1)ꢀPdꢀSe(1) a
Se(1) aꢀPdꢀSe(2)
Se(1)ꢀPdꢀP
92.81(4)
83.10(4)
172.44(4)
177.42(6)
96.60(7)
87.77(7)
96.90(4)
ClꢀPdꢀP(1)
ClꢀPdꢀP(2)
ClꢀPdꢀC(1)
P(1)ꢀPdꢀP(2)
P(1)ꢀPdꢀC(1)
P(2)ꢀPdꢀC(1)
93.26(4)
88.73(4)
174.78(10)
176.07(5)
88.47(8)
89.27(8)
Se(1)ꢀPtꢀSe(2)
Se(1)ꢀPtꢀP(1)
Se(1)ꢀPtꢀP(2)
Se(2)ꢀPtꢀP(1)
Se(2)ꢀPtꢀP(2)
P(1)ꢀPtꢀP(2)
179.6(1)
83.88(4)
96.62(4)
95.94(4)
83.57(4)
178.20(6)
Se(1)ꢀPtꢀSe(2A)
Se(1)ꢀPtꢀSe(2B)
Se(1)ꢀPtꢀSe(1) b
Se(1)ꢀPtꢀP
92.66(4)
93.99(14)
81.39(4)
178.37(6)
173.51(4)
160.9(2)
88.77(7)
87.62(15)
97.15(6)
98.61(4)
Se(1) aꢀPdꢀP
Se(2)ꢀPdꢀP
Se(2A)ꢀPtꢀSe(1) b
Se(2B)ꢀPtꢀSe(1) b
Se(2A)ꢀPtꢀP
PdꢀSe(1)ꢀPd a
Se(2B)ꢀPtꢀP
PꢀPtꢀSe(1) b
PtꢀSe(1)ꢀPt b
a Symmetry operation: −x+1, −y+1, −z+1.
b Symmetry operation: −x+1, −y, −z+2.
The PdꢀP distances in 1 and 2 (2.297(2) and
2.330(1)–2.344(1), respectively) as well as the PtꢀP dis-
these resonances are due to the cis- and trans-isomers
of [Pd2(SeTh)4(PPh3)2]. The recrystallization afforded
trans-[Pd2(SeTh)4(PPh3)2] (1).
,
tances in 3 and 4 (2.311(2)–2.320(2) and 2.273(2) A) are
normal for palladiumꢀphosphorus or platinumꢀ
phosphorus bonds. The small differences can be ex-
plained by the effects of relative trans-influence. The
bond lengths within the ligands are also normal.
The terminal thienyl rings in 1 and 4, and both
thienyl rings in 3 are disordered (see Figs. 1, 3 and 4).
In the case of 1 the rings assume two different orienta-
tions at the ca. 50% level of probability. In 3 and 4 one
orientation is more favored than the other. The thienyl
rings of the bridging ligands, on the other hand, are not
disordered either in 1 or 4. The difference may be
explained by weak hydrogen bonds that fix the orienta-
tion. There are no such close contacts in the terminal
ligands, and the thienyl ring assumes two different
orientations with almost an equal probability. The
thienyl ring in 2 also finds itself in a fixed orientation
with no indication of disorder due to the weak hydro-
gen bonds.
The 77Se-NMR spectrum of the redissolved precipitate
exhibited two resonances at 203 and 198 ppm due to
terminal ThSe− ligands and three resonances at −163,
−180 and −182 ppm due to bridging ligands. cis-
[Pd2(SeTh)4(PPh3)2] is expected to exhibit three reso-
nances at the intensity ratio of 2:1:1 The first resonance
corresponds to two equivalent terminal ligands. The
two latter signals each correspond to one independent
bridging ligand. In the trans-isomer both terminal and
bridging ligands are mutually symmetry-equivalent, and
only two resonances are expected in the intensity ratio
of 1:1.
The strongest signal at 198 ppm has approximately
twice the intensity of the other four resonances and is
assigned to two terminal ligands of cis-
[Pd2(SeTh)4(PPh3)2]. The signal at 203 ppm must then
be due to the trans-isomer. The assignment of the
remaining signals to the bridging ligands of the two
isomers can be carried out by considering the effects of
the trans-influence on the chemical shifts and on the
coupling information (see Ref. [31]).
3.3. NMR spectroscopy
3.3.1. The reaction of [Pd(PPh3)4] and Th2Se2
The reaction of [Pd(PPh3)4] and Th2Se2 in
dichloromethane rapidly produces a mixture exhibiting
three major 31P resonances at 29.9, 29.3, and −3.6
ppm. Upon prolonged standing a new resonance ap-
pears at 25.0 ppm.
The workup of the reaction mixture produced a
precipitate that upon redissolution exhibited only two
resonances at 29.9 and 29.3 ppm. It was inferred that
It can be concluded that cis-[Pd2(SeTh)4(PPh3)2] ex-
hibits three resonances at 198, −163 (2JPse=137 Hz),

R. Oilunkaniemi et al. / Journal of Organometallic Chemistry 587 (1999) 200–206
205
and −182 ppm with the intensity ratio of 2:1:1. trans-
[Pd2(SeTh)4(PPh3)2] shows two resonances of equal in-
tensity at 203 and −180 ppm.
The filtrate after the hexane precipitation was found
to exhibit two 31P-NMR resonances at 25.0 and −3.6
ppm. The former is due to the mononuclear complex
[PdCl(Th)(PPh3)2] (2), and latter is due to free PPh3.
When the reaction of [Pd(PPh3)4] and Th2Se2 was
carried out in toluene, the 31P-NMR spectrum of the
reaction mixture exhibited the two resonances due to
the isomers of the dinuclear palladium complex 1 to-
gether with free PPh3.
3.3.2. The reaction of [Pt(PPh3)4] and Th2Se2
The 31P spectrum of the reaction mixture of
[Pt(PPh3)4] and Th2Se2 in dichloromethane shows two
major 31P-NMR resonances at 21.5 and 17.9 ppm with
satellites due to coupling to 195Pt. The respective cou-
pling constants are 2864 and 3070 Hz that are typical
4. Conclusions
This paper reports the reactions of tetrakis-
(triphenylphosphine)palladium and -platinum with
bis(thienyl) diselenide as part of a systematic investiga-
tion of the factors affecting the pathways of oxidative
addition of aromatic dichalcogenides to zerovalent pal-
ladium and platinum centers. The oxidative addition to
both [Pd(PPh3)4] and [Pt(PPh3)4] results in the cleavage
of the SeꢀSe bond. The main products in the reaction
of [Pd(PPh3)4] and Th2Se2 are dinuclear cis- and trans-
[Pd2(SeTh)4(PPh3)2], which could be identified by
31P- and 77Se-NMR spectroscopy. Recrystallization af-
forded trans-[Pd2(SeTh)4(PPh3)2], which could be char-
acterized by X-ray crystallography. When the reaction
is carried out in dichloromethane, a small amount of
[PdCl(Th)(PPh3)2] is formed. This implies that the sol-
vent plays an active role in the reaction and that the
cleavage of a CꢀSe bond may also occur during the
oxidative addition. A number of analogous palladium
and platinum complexes are formed in different oxida-
tive addition reactions (see Refs. [11,33–36]). It has
been suggested by Xie et al. [37] that the formation of
species like 2 plays an important role in the catalytic
activity of palladium and platinum complexes.
The reaction of [Pt(PPh3)4] also results in the cleav-
age of the SeꢀSe bond in Th2Se2, but in this case the
reaction mixture contained the cis- and trans-isomers
of the mononuclear complex [Pt(SeTh)2(PPh3)2]. Crys-
tals of trans-[Pt(SeTh)2(PPh3)2] were obtained upon
recrystallization from dichloromethane. Simulta-
neously, small amounts of dinuclear trans-[Pt2(Se-
Th)4(PPh3)2] were obtained.
The route of the oxidative addition of aromatic
diselenides proceeds somewhat differently, depending
on whether [Pd(PPh3)4] or [Pt(PPh3)4] is used as a
reagent. The different behavior of analogous palladium
and platinum complexes has very recently been noted
for the reactions of [MCl2(PhCN)2] (M=Pd, Pt) with
cyclohepteno-1,4-diselenin [18,38]. The reaction with
1
for JPtP [4]. In addition the solution contains some
Ph3PSe (37 ppm), Ph3PO (30 ppm), and free PPh3.
Yellow crystals of trans-[Pt(SeTh)2(PPh3)2] (3) show
one resonance at 21.5 ppm (1JPtP=2864 Hz). The reso-
nance at 17.9 ppm (1JPtP=3070 Hz) is assigned to
cis-[Pt(SeTh)2(PPh3)2]. This is consistent with the re-
ported chemical shifts of trans- and cis-[Pt(SePh)2-
(PPh3)2] in benzene-d6 (20.6 ppm (1JPtP=2831 Hz) and
18.4 ppm (1JPtP=2969 Hz), respectively) [32]. It was
observed that upon prolonged standing in
dichloromethane, the intensity of the resonance at
17.9 ppm decreases with respect to the resonance at
21.5 ppm. The 195Pt chemical shift of cis-[Pt(Se-
Th)2(PPh3)2] is −4859 ppm (1JPtP=3068 Hz) and that
of trans-[Pt(SeTh)2(PPh3)2] −4937 ppm (1JPtP=2858
Hz).
The 77Se-NMR spectrum of the initial reaction mix-
ture of [Pt(PPh3)4] and Th2Se2 in dichloromethane ex-
hibits two resonances at 171 and 80 ppm with an
approximate intensity ratio of 1:2. The intensity of the
resonance at 171 ppm decreases with time. The reso-
nance at 80 ppm due to trans-[Pt(SeTh)2(PPh3)2] (3)
shows two 195Pt satellites (1JPtSe=117 Hz). All three
components are further split into triplets (2JPSe=14
Hz). The coupling information is well in accord with
1
that reported for [Pt(SeC5H4N)2(dppe)] [26]: JPtP
=
1
2
2968, JPtSe=220, JPSe(cis)=12 Hz. The resonance at
171 ppm is assigned to cis-[Pt(SeTh)2(PPh3)2].
Upon recrystallization of 3, a small amount of crys-
talline trans-[Pt2(SeTh)4(PPh3)2] (4) was simultaneously
obtained. These crystals were hand-picked under a mi-
croscope (31P resonance at 20.4 ppm (1JPtP=3422 Hz);
77Se resonances at 163 and −169 ppm) and were
structurally characterized (see Section 3.2). 4 is proba-
bly slowly formed either from two trans- or two cis-iso-
mers of [Pt(SeTh)2(PPh3)2]:

206
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Crystallographic information for complexes 1–4 (ex-
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supplementary publication numbers CSD-118899–
118902, respectively. Copies of the data can be obtained
free of charge on application to The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-
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Financial support from Neste Oy Foundation,
8
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