An experimental and theoretical study of the isomerization of mononuclear bis(arylselenolato)bis(triphenylphosphine)platinum complex [Pt(SeR)2(PPh3)2]

Article abstract of DOI:10.1016/S0022-328X(02)02108-3

Mononuclear bis(thienylselenolato)bis(triphenylphosphine)platinum [Pt(SeTh)₂(PPh₃)₂] (Th = 2-thienyl, C₄H₃S) has been prepared by the treatment of cis -[PtCl₂(PPh₃)₂] with NaSeTh. The ³¹P-NMR spectroscopic information indicates that cis-[Pt (SeTh)₂(PPh₃)₂] is initially formed in the reaction. Upon prolonged standing in solution it isomerizes to trans- [Pt(SeTh)₂(PPh₃)₂]. The reaction of cis-[PtCl₂(PPh₃)₂] with LiSeFu (Fu = 2-furyl, C₄H₃O) affords immediately a mixture of cis- and trans-isomers of [Pt(SeFu)₂(PPh₃)₂] with the relative amount of the trans-isomer increasing with time. The recrystallization of the two reaction mixtures yielded cis,anti- and trans,syn-isomers of [Pt(SeTh)₂(PPh₃)₂] as well as cis,syn- and trans,anti-isomers of [Pt(Se-Fu)₂(PPh₃)₂]. Their structures were compared with those of cis,anti - and trans,anti-isomers of [Pt(SePh)₂(PPh₃)₂]. The geometries and relative stabilities of all isomers of [Pt(SeTh)₂(PH₃)₂], [Pt(SeFu)₂(PH₃)₂] and [Pt(SePh)₂(PH₃)₂] were studied by the use of ab initio molecular orbital techniques in order to model the structures and isomerization of the observed mononuclear selenolato complexes.

Full text of DOI:10.1016/S0022-328X(02)02108-3

Journal of Organometallic Chemistry 666 (2003) 111ꢁ120
/
www.elsevier.com/locate/jorganchem
An experimental and theoretical study of the isomerization of
mononuclear bis(arylselenolato)bis(triphenylphosphine)platinum
complexes [Pt(SeR)2(PPh3)2]
Milja S. Hannu-Kuure a, Jarno Komulainen a, Raija Oilunkaniemi a,
Risto S. Laitinen a,*, Reijo Suontamo b, Markku Ahlgre´n c
a Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland
b Department of Chemistry, University of Jyvaskyla, P.O. Box 35, FIN-40350 Jyvaskyla, Finland
¨
¨
¨
¨
c Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland
Received 3 September 2002; accepted 19 November 2002
Abstract
Mononuclear bis(thienylselenolato)bis(triphenylphosphine)platinum [Pt(SeTh)2(PPh3)2] (Thꢀ2-thienyl, C4H3S) has been pre-
/
pared by the treatment of cis-[PtCl2(PPh3)2] with NaSeTh. The 31P-NMR spectroscopic information indicates that cis-
[Pt(SeTh)2(PPh3)2] is initially formed in the reaction. Upon prolonged standing in solution it isomerizes to trans-[Pt(SeTh)2(PPh3)2].
The reaction of cis-[PtCl2(PPh3)2] with LiSeFu (Fuꢀ2-furyl, C4H3O) affords immediately a mixture of cis- and trans-isomers of
/
[Pt(SeFu)2(PPh3)2] with the relative amount of the trans-isomer increasing with time. The recrystallization of the two reaction
mixtures yielded cis,anti- and trans,syn-isomers of [Pt(SeTh)2(PPh3)2] as well as cis,syn- and trans,anti-isomers of [Pt(Se-
Fu)2(PPh3)2]. Their structures were compared with those of cis,anti- and trans,anti-isomers of [Pt(SePh)2(PPh3)2]. The geometries
and relative stabilities of all isomers of [Pt(SeTh)2(PH3)2], [Pt(SeFu)2(PH3)2] and [Pt(SePh)2(PH3)2] were studied by the use of ab
initio molecular orbital techniques in order to model the structures and isomerization of the observed mononuclear selenolato
complexes.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Arylselenolato platinum complexes; X-ray crystallography; NMR spectroscopy; Ab initio MO calculations
1. Introduction
nyl, C4H3S or phenyl) [10,11] resembles that in binary
PdTe thus rationalizing their facile conversion. Whereas
related platinum complexes do not strive for equally
high nuclearity, species like [Pt3Te2(Th)(PPh3)5]Cl [10]
are known. It has been suggested that mononuclear
chalcogenolato complexes play a significant role in the
formation of such polynuclear complexes [11].
The transition metal complexes containing organose-
lenide and telluride ligands [1ꢁ5] may provide an
attractive low-temperature route for binary transition
metal selenides and tellurides, such as palladium and
/
nickel selenides and tellurides [6ꢁ9] that find potential
/
The mononuclear chalcogenolato platinum complexes
applications in materials science. It has been noted by
Brennan et al. [7] that the spatial arrangement of
palladium and tellurium atoms in polynuclear
[Pd6Te8(PEt3)6] [7] and structurally related [Pd6Cl2Te4-
can be exemplified by [Pt(SeR)2(PPh3)2] (Rꢀaryl
/
group) that can be prepared the treatment of cis-
[PtCl2(PPh3)2] with NaSeR, which is obtained through
reduction of R2Se2 with NaBH4 [3], or by the oxidative
addition of diorganodiselenides to Pt(0) centers like
(TeR)2(PPh3)6] and [Pd6Te4(TeR)4(PPh3)6] (Rꢀ2-thie-
/
[Pt(PPh3)4] [12] or [Pt(CH2ꢀCH2)(PPh3)2] [13]. In the
/
solid state [Pt(SeR)2(PPh3)2] complexes give rise to four
possible isomers.
* Corresponding author.
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 2 1 0 8 - 3

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M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ120
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In solution the existence of only a cis- and trans-
isomers is expected, since the organoselenolato ligands
can undergo facile rotation about the PtÃSe bond.
Indeed, the solution NMR spectroscopic information
of different [Pt(SeR)2(PR3)2] complexes has been as-
signed in terms of the presence of cis- and trans-isomers
mers that have been characterized previously [13,17]. We
also discuss the solution equilibria of the complexes in
dichloromethane and benzene. The geometries and
relative stabilities of all isomers of [Pt(SeFu)2(PH3)2],
[Pt(SeTh)2(PH3)2], and [Pt(SePh)2(PH3)2] were calcu-
lated by ab initio MO techniques in order to model
the experimental data.
/
[12ꢁ16]. It has also been suggested that the reactions
/
starting from cis-[PtCl2(PPh3)2] initially afford the cis-
isomer, but the product slowly isomerizes to the trans-
isomer [12,13]. With the exception of ca-
[Pt(SePh)2(PPh3)2] the X-ray structure of which has
recently been reported [17], all structurally characterized
[Pt(SeR)2(PR3)2] species with non-chelating ligands
2. Experimental
2.1. General
exhibit
a trans,anti structure in the solid state
All preparations were carried out under a dry argon
atmosphere. As the metal complexes themselves are not
sensitive to air they could be manipulated in air. cis-
[PtCl2(PPh3)2] (Aldrich) and n-buthyl lithium (Aldrich)
were used as supplied. Thiophene and furan (Aldrich)
were dried on CaCl2 and distilled prior to use. Th2Se2
was prepared according to the literature procedure
[21,22]. Tetrahydrofuran (THF) was distilled under an
argon atmosphere over Na/benzophenone. Dichloro-
methane, benzene, and hexane were degassed with
argon.
[12,13,17]. The X-ray structure of a related mononuclear
[Pd(SePh)2{P(n-Bu)3}2] also indicates a ta-isomer [18].
In the present work we report a systematic study on
the structural and chemical properties of a series of
[Pt(SeR)2(PPh3)2] (Rꢀaryl group) complexes in light of
/
their significance as synthons for more complicated
species. While it could be expected that the structural
characteristics and chemical properties of all members
of the series are relatively similar regardless of the
identity of the aryl group, this is not self-evident.
Indeed, we have recently observed that in case of
mononuclear selenoether and telluroether complexes
2.2. X-ray crystallography
[MCl2{(C4H3E)E?CH3}2] (Mꢀ
/
Pd, Pt; Eꢀ
/
S, O; E?ꢀ
/
Se, Te) the isomerism and the structures of the
complexes are affected by the nature of both chalcogen
atoms and aryl group both in solution and in the solid
state [19]. Furthermore, whereas the crystallization of
[PdCl2{(C4H3S)SeCH3}2] from acetone afforded the
trans-isomer of the mononuclear complex, that of
[PdCl2{(C4H3O)SeCH3}2] yielded a dinuclear complex
[Pd2Cl2(m-SeCH3)2{CH3Se(C4H2O)}2C(CH3)2] resulting
from the condensation of the furyl groups with the
solvent [20]. The reaction routes and products in the
Diffraction data of cs-[Pt(SeFu)2(PPh3)2] (1cs), ta-
[Pt(SeFu)2(PPh3)2] (1ta), and ca-[Pt(SeTh)2(PPh3)2]
(2ca)1 were collected on a Nonius Kappa CCD diffract-
ometer using graphite monochromated Moꢁ
/
Ka radia-
0.71073 A) by recording 360 frames via 8-
18; twice 20ꢁ60 s per frame). Crystal
˚
tion (lꢀ
rotation (D8ꢀ
/
/
/
data and details of structure determinations are given in
Table 1.
The structures were solved by direct methods using
SHELXS-97 [23] and refined using SHELXL-97 [24]. After
the full-matrix least-squares refinement of non-hydro-
gen atoms with anisotropic thermal parameters, the
hydrogen atoms were placed in calculated positions in
oxidative addition of diaryl dichalcogenides R2E2 (Eꢀ
Se, Te) to [M(PPh3)4] (MꢀPd, Pt) are also dependent
on the metal, chalcogen, aryl group, and solvent [10ꢁ
12].
The different isomers of [Pt(SeFu)2(PPh3)2] (Fuꢀ
furyl, C4H3O) (1) and [Pt(SeTh)2(PPh3)2] (Thꢀ2-thie-
/
/
/
/2-
1
A
following abbreviated notation is used to describe the
/
complexes: the bold arabic numeral refers to the molecular
composition followed by two alphabets describing the isomer. In the
solid state two letters are needed, i.e. 1ta refers to trans,anti-
[Pt(SeFu)2(PPh3)2]. In solution only one alphabet is required, i.e. 1t
refers to trans-[Pt(SeFu)2(PPh3)2].
nyl, C4H3S) (2) were prepared and structurally char-
acterized by X-ray crystallography and NMR
spectroscopy. Their structures were compared with
those of two [Pt(SePh)2(PPh3)2] (Phꢀphenyl) (3) iso-
/

M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ
/120
113
Table 1
Details of the structure determination of cis,syn-[Pt(SeFu)2(PPh3)2] (1cs), trans,anti-[Pt(SeFu)2(PPh3)2]×
/
2CH2Cl2 (1ta×/2CH2Cl2), and cis,anti-
[Pt(SeTh)2(PPh3)2] (2ca) (Fuꢀ
/
2-furyl, C4H3O; Thꢀ
/
2-thienyl, C4H3S)
1cs
1ta×/2CH2Cl2
2ca
Empirical formula
Relative molecular mass
Crystal system
C44H36O2P2Se2Pt
1011.68
Monoclinic
P21/n
C23H20OPCl2SePt1/2
590.77
C44H36P2S2Se2Pt
1043.80
Monoclinic
P21/n
Monoclinic
P21/c
Space group
˚
a (A)
˚
11.227(2)
15.765(3)
21.499(4)
100.37(3)
3743(1)
150(2)
11.522(2)
12.966(3)
15.823(3)
110.19(3)
2218.6(8)
150(2)
11.5651(2)
15.5078(3)
21.6574(4)
101.49(3)
3806.3(1)
120(2)
b (A)
˚
c (A)
b (8)
3
V (A )
˚
T (K)
Z
4
1968
4
1152
4
2032
F(000)
Dcalc (g cmꢂ3
)
1.795
5.817
1.769
5.154
1.821
5.825
m(Moꢁ
/
Ka) (mmꢂ1
Crystal size (mm)
)
0.15ꢄ
/
0.15ꢄ
/
0.08
0.20ꢄ/0.15ꢄ/0.05
0.15ꢄ
/
0.15ꢄ0.10
/
u Range (8)
2.31ꢁ25.00
/
2.74ꢁ28.30
/
1.86ꢁ26.00
/
Number of reflections collected
Number of unique reflections
Number of observed reflections
Number of parameters
Rint
48 181
6558
5257
34 655
5337
4665
31 395
7477
5631
a
461
260
461
0.0737
0.0426
0.0714
0.0613
0.0763
1.127
0.0645
0.0375
0.0783
0.0479
0.0814
1.130
0.0747
0.0370
0.0779
0.0598
0.0873
1.013
b
R1
b
wR2
R1 (all data)
wR2 (all data)
GOOF
ꢂ3
˚
Max and min heights in final difference Fourier synthesis (e A
)
0.843, ꢂ
/0.607
1.445, ꢂ
/
1.494
1.347, ꢂ1.084
/
a
I ꢀ
R1ꢀ
/
2s(I).
b
/
ajjFojꢂ
/
jFcjj/SjFoj, wR2ꢀ
/
[aw(F2oꢂ
/
F2c)2/awF4o]1/2
.
˚
0.95 A). In the final refine-
the aromatic rings (CÃ
/
Hꢀ
/
D2O solution of selenium dioxide, and the D2O solution
of [PtCl6]2ꢂ were used as external standards. The 31P
and 195Pt chemical shifts are reported relative to the
external standards and the 77Se chemical shifts relative
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.
to neat Me2Se [d(Me2Se)ꢀ
/
d(SeO2)ꢃ1302.6) [25]. All
/
spectra were measured unlocked.
One of the thienyl groups in ca-[Pt(SeTh)2(PPh3)2]
(2ca) is disordered. The disorder was resolved by
constraining the atoms C(22) and S(2) together, giving
them common anisotropic temperature factors, and
refining the site occupational factor. Fractional coordi-
nates, anisotropic thermal parameters, and the full
listing of bond parameters are available as Supplemen-
tary material.
2.4. Preparation of [Pt(SeR)2(PPh3)2]
2.4.1. [Pt(SeFu)2(PPh3)2]
Two milliliters (5.00 mmol) of n-BuLi was added to a
solution of 0.36 ml (5.09 mmol) of furan in 5.5 ml of
THF. Selenium powder (0.395 g, 5.00 mmol) was added
into the reaction solution after 30 min. After the
reaction mixture was stirred at room temperature (r.t.)
for further 40 min, 0.95 ml of the resulting FuSeLi
solution (0.60 mmol) was added to a solution of cis-
[PtCl2(PPh3)2] (0.200 g, 0.25 mmol) in 20 ml of
dichloromethane. After stirring of 60 min the reaction
mixture was filtered and concentrated by a partial
removal of the solvent. [Pt(SeFu)2(PPh3)2] was precipi-
tated by adding n-hexane to the solution. The yellow
product was filtered off, washed with hexane and dried.
Yield 0.198 g (78%). Anal. Calc. for C44H36P2O2Se2Pt:
C, 52.23; H, 3.59. Found: C, 51.54; H, 3.31%. The X-
2.3. NMR spectroscopy
The 31P{1H}, 77Se and 195Pt{1H} spectra were re-
corded on a Bruker DPX 400 operating at 161.98, 76.31
and 85.60 MHz, respectively. The typical respective
spectral widths were 48.543, 53.333 and 51.282 kHz and
the pulse widths 7.5, 6.7 and 10.0 ms. The pulse delays
were 1.0, 2.0 and 0.8 s for 31P, 77Se and 195Pt,
respectively. Orthophosphoric acid (85%), a saturated

114
M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ120
/
ray-quality crystals of both cs-[Pt(SeFu)2(PPh3)2] (1cs)
and ta-[Pt(SeFu)2(PPh3)2] (1ta) were obtained by re-
crystallization from dichloromethane.
4. Results and discussion
4.1. General
2.4.2. [Pt(SeTh)2(PPh3)2]
NaSeTh (0.62 mmol; prepared in situ by the reduction
of 0.100 g (0.31 mmol) of Th2Se2 in dichloromethane
with a methanolic solution of NaBH4) was added to a
solution of 0.245 g (0.31 mmol) of cis-[PtCl2(PPh3)2] in
dichloromethane. The reaction mixture was stirred for 2
h at r.t., filtered, and concentrated by partial evapora-
tion of the solvent. [Pt(SeTh)2(PPh3)2] was precipitated
by adding n-hexane to the solution. The orange product
was filtered off, washed with hexane and dried. Yield
0.264 g (81%). Anal. Calc. for C44H36P2O2Se2Pt: C,
50.63; H, 3.48; S, 6.14. Found: C, 48.97; H, 3.13; S,
5.79%. The X-ray quality crystals of ca-
[Pt(SeTh)2(PPh3)2] (2ca) were obtained by recrystalliza-
tion from dichloromethane.
The reaction of FuSeLi with cis-[PtCl2(PPh3)2] in
dichloromethane produces a mixture of cis- and trans-
[Pt(SeFu)2(PPh3)2] with a good combined yield. The
isomers were identified by use of NMR spectroscopy.
Recrystallization from dichloromethane afforded crys-
tals of cs- and ta-[Pt(SeFu)2(PPh3)2] that were structu-
rally characterized by X-ray crystallography.
Mixtures of isomers of [Pt(SeR)2(PPh3)2] (Rꢀ
/
Th,
Ph) were formed by reducing R2Se2 (RꢀTh, Ph) with
/
NaBH4 to afford RSeꢂ, which was followed by treat-
ment with cis-[PtCl2(PPh3)2] in dichloromethane or
benzene. The isomers were identified by NMR spectro-
scopy and structurally characterized in the solid state by
X-ray crystallography. The crystal structure of ca-
[Pt(SeTh)2(PPh3)2] has been determined in this work.
Those of ts-[Pt(SeTh)2(PPh3)2] [12], ca-[Pt(SePh)2-
(PPh3)2] [17], and ta-[Pt(SePh)2(PPh3)2] [13,17] have
been reported previously.
3. Computational details
Ab initio MO calculations of the twelve [Pt(SeR)2-
(PH3)2] (Rꢀ
carried out using the Stuttgart relativistic large core
effective core potential approximation (RLC ECP) [26ꢁ
/Fu, Th, Ph; see Table 2) isomers were
/
28] by augmenting the double-zeta quality basis sets of
the valence orbitals by two polarization functions for all
other non-hydrogen atoms [29] except platinum for
which no polarization was used (denoted below as
ECP** basis). Full geometry optimizations were com-
pleted at the HF level of theory using gradient techni-
ques. Relative energies of all isomers were explored by
calculating the total energies of the molecules at the
DFT level of theory involving Becke’s three parameter
hybrid functionals with the Perdew/Wang 91 correlation
(B3PW91) [30ꢁ36] and using the HF-optimized geome-
/
tries. All calculations were performed with the GAUS-
SIAN 98 series of programs [37].
Table 2
The abbreviated notation for [Pt(SeR)2(PH3)2] (Rꢀ
isomers
/Fu, Th, Ph)
a
cs-[Pt(SeFu)2(PH3)2]
cs-[Pt(SeTh)2(PH3)2]
cs-[Pt(SePh)2(PH3)2]
ca-[Pt(SeFu)2(PH3)2]
ca-[Pt(SeTh)2(PH3)2]
ca-[Pt(SePh)2(PH3)2]
ts-[Pt(SeFu)2(PH3)2]
ts-[Pt(SeTh)2(PH3)2]
ts-[Pt(SePh)2(PH3)2]
ta-[Pt(SeFu)2(PH3)2]
ta-[Pt(SeTh)2(PH3)2]
ta-[Pt(SePh)2(PH3)2]
4cs
5cs
6cs
4ca
5ca
6ca
4ts
5ts
6ts
4ta
5ta
6ta
Fig. 1. The molecular structures of (a) cs-[Pt(SeFu)2(PPh3)2] (1cs) and
ca-[Pt(SeTh)2(PPh3)2] (2ca), and (b) ca-[Pt(SePh)2(PPh3)2] (3ca)
(adapted from data in Ref. [17]) indicating the numbering of the
atoms. The thermal ellipsoids have been drawn at 50% probability
level.
a
cs, cis,syn; ca, cis,anti; ts, trans,syn; ta, trans,anti.

M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ
/120
115
Table 3
˚
Selected bond lengths (A) and angles (8) of cs-[Pt(SeFu)2(PPh3)2] (1cs), ta-[Pt(SeFu)2(PPh3)2] (1ta), ca-[Pt(SeTh)2(PPh3)2] (2ca), ts-
[Pt(SeTh)2(PPh3)2] (2ts), ca-[Pt(SePh)2(PPh3)2] (3ca), and ta-[Pt(SePh)2(PPh3)2] (3ta)
a
b
b
1cs
1ta×/2CH2Cl2
2ca
2ts×/1/2CH2Cl2
3ca×/C6H6
3ta
Bond lengths
Pt(1)Ã
Pt(1)Ã
Pt(1)Ã
Pt(1)Ã
/
Se(1)
Se(2)
P(1)
2.5119(9)
2.4675(8)
2.278(2)
2.268(2)
2.4535(6)
2.306(1)
2.5070(6)
2.4623(6)
2.269(1)
2.271(2)
2.4629(1)
2.4651(1)
2.311(2)
2.320(2)
2.4885(3)
2.4506(3)
2.2900(6)
2.2937(6)
2.4525(5)
2.4548(5)
2.325(1)
2.314(1)
/
/
/
P(2)
Bond angles
Se(1)ÃPt(1)Ã
Se(1)ÃPt(1)Ã
Se(1)ÃPt(1)Ã
Se(2)ÃPt(1)Ã
Se(2)ÃPt(2)Ã
P(1)ÃPt(1)Ã
/
/
Se(2)
P(1)
P(2)
P(1)
P(2)
80.29(4)
94.75(5)
159.34(4)
166.20(4)
84.38(5)
103.19(6)
180.00
78.22(2)
169.15(3)
84.02(4)
96.29(4)
158.84(4)
103.03(5)
179.60(4)
83.88(4)
96.62(4)
95.94(4)
83.57(4)
178.20(6)
95.097(9)
174.73(2)
82.21(2)
85.85(2)
173.20(2)
97.40(2)
177.63(2)
93.93(3)
86.81(3)
84.13(3)
95.21(3)
176.41(4)
/
/
96.26(2)
83.74(2)
83.74(2)
96.26(2)
180.00
/
/
/
/
/
/
/
/
P(2)
a
Ref. [12].
Ref. [17].
b
4.2. Crystal structures
coordination plane of platinum but is slightly deviated.
The difference in the relative signs of the torsional
angles indicates that in 1cs the two selenolato ligands lie
on the same side of the coordination plane (a cis,syn
isomer), whereas in 2ca they are on the opposite sides (a
cis,anti isomer).
4.2.1. cis-Isomers of [Pt(SeR)2(PPh3)2] (Rꢀ
Ph)
The molecular structures of cs-[Pt(SeFu)2(PPh3)2]
(1cs), ca-[Pt(SeTh)2(PPh3)2] (2ca), and ca-
[Pt(SePh)2(PPh3)2] (3ca) [17] are shown in Fig. 1.
Selected bond distances and angles are listed in Table 3.
The coordination environment around platinum in
cs-[Pt(SeFu)2(PPh3)2] (1cs) and ca-[Pt(SeTh)2(PPh3)2]
/
Fu, Th,
ca-[Pt(SePh)2(PPh3)2] (3ca) is clearly a cis,anti-iso-
mer, as seen in Fig. 1(b). The torsional angles Se(1)Ã
/
Pt(1)ÃSe(2)ÃC(21) and Se(2)ÃPt(1)ÃSe(1)ÃC(11) show
/
/
/
/
/
values of 61.4(8) and 65.8(2)8, respectively [17]. The
same sign of the two torsional angles again imply an anti
isomer. The molecular structure of 3ca also differs from
those of 1cs and 2ca by exhibiting a close contact
(2ca) is a slightly distorted square-plane (a aPtꢀ
and 361.68 for 1cs and 2ca, respectively). The respective
Se bond lengths for 1cs and 2ca [2.4675(8), 2.5119(9)
/
362.1
PtÃ
/
between the phenyl rings of the cis-phenylselenolato
˚
3.334(2) A] [17]. In the case of
˚
and 2.4623(6), 2.5070(6) A] are typical for single bond
lengths (the sum of covalent radii of platinum and
ligands [C(11)ꢀ ꢀ ꢀC(21)ꢀ
/
1cs and 2ca there are no close contacts between the two
aryl groups of cis-selenolato ligands.
˚
selenium is 2.46 A [38]). They are in agreement with the
PtÃSe bonds in ca-[Pt(SePh)2(PPh3)2] (3ca) [2.4506(3),
2.4885(3)
/
˚
A
[17]; see Table 3] and in cis-
˚
[Pt(SePh)2(dppm)] [2.4340(9), 2.4610(10) A [39], and
are slightly longer than those in cis-[Pt(Se2CH2)(PPh3)2]
4.2.2. trans-Isomers of [Pt(SeR)2(PPh3)2] (Rꢀ
Th, Ph)
/
Fu,
˚
(2.4177(8) and 2.4352(11) A, [40]).
PtÃP lengths also show typical single bond values in
1cs [2.268(2), 2.278(2) A], 2ca [2.269(1), 2.271(1) A], and
The molecular structures of ta-[Pt(SeFu)2(PPh3)2]
(1ta), ts-[Pt(SeTh)2(PPh3)2] (2ts) [12], and ta-
[Pt(SePh)2(PPh3)2] (3ta) [17] are shown in Fig. 2.
Selected bond distances and angles are listed in Table 3.
The platinum atom shows approximate square-planar
/
˚
˚
˚
3ca [2.2900(6), 2.2937(6) A [17]]. They can be compared
with the bond lengths in cis-[Pt(Se2CH2)(PPh3)2] and
cis-[Pt(SePh)2(dppm)] {2.274(2), 2.290(2) [40] and
coordination in each complex (a aPtꢀ
/
360.0, 360.0 [12],
˚
2.253(2), 2.257(2) A [22], respectively}.
and 360.68 [17] for 1ta, 2ts, and 3ta, respectively). The
˚
Se bond length in 1ta [2.4535(6) A] is consistent with
those determined previously for 2ts and 3ta {2.4629(1),
Whereas 1cs and 2ca are nominally different isomers,
they are in fact isomorphous. It can be seen in Fig. 1
that one of the selenolato groups lies approximately on
the coordination plane of platinum [the torsional angle
C(21) shows a value of 178.2(2) and
176.1(2)8 in 1cs and 2ca, respectively], while the other
bond is almost perpendicular to the plane [the respective
PtÃ
/
˚
2.4651(1) [12] and 2.4525(5), 2.4548(5) A [17], respec-
tively}. These bond lengths are also consistent with
other mononuclear selenolato complexes [22,40], as
discussed above.
Se(1)Ã
/
Pt(1)Ã
/
Se(2)Ã
/
The PtÃ
/
P bond lengths in the trans-complexes
˚
{2.306(1) A in 1ta, 2.311(2), 2.320(2) A in 2ts [12], and
˚
torsional angles Se(2)Ã
and ꢃ91.7(2)8]. The SeÃ
ligand in 1cs and 2ca does not lie exactly on the
/
Pt(1)Ã
/
Se(1)Ã
/
C(11) are ꢂ
/
91.2(2)
C bond of the coplanar RSeꢂ
˚
2.314(1), 2.325(1) A in 3ta [17]} are slightly longer than
those in cis-complexes. This is consistent with a slightly
/
/

116
M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ120
/
{ŽP(1)Ã
is
trans,syn-isomer {ŽP(1)Ã
118.94(4)ꢁ122.7(5); ŽP(1)Ã
57.4(13)ꢁ[ꢂ60.6(3)8]} [12].
/
Pt(1)Ã
/
Se(2)Ã
/
C(21)} for 3ta [17]. By contrast 2ts
Pt(1)ÃSe(1)ÃC(11)ꢀ
Pt(1)ÃSe(2)ÃC(21)ꢀ
a
/
/
/
/
/
/
/
/
/
ꢂ
/
/
/
4.3. Optimized geometries and relative energies of the
[Pt(SeR)2(PH3)2] (RꢀFu, Th, Ph) isomers
/
The geometries and energetics of all possible isomers
of [Pt(SeR)2(PH3)2] (see Table 2) were computed by ab
initio MO techniques to explore the factors affecting the
structural trends and stabilities of the observed isomers
of [Pt(SeR)2(PPh3)2] (RꢀFu, Th, Ph). The selected
/
optimized bond parameters of the different isomers of
[Pt(SeR)2(PH3)2] are shown in Table 4, and their
optimized molecular geometries are shown in Fig. 3.
It is noteworthy that no local energy minimum was
obtained for the cis,syn-isomers of [Pt(SeFu)2(PH3)2] (4)
and [Pt(SeTh)2(PH3)2] (5). The optimization with differ-
ent starting geometries always resulted in a cis,anti-
isomer. In the case of [Pt(SePh)2(PH3)2] local minima for
both 6cs and 6ca isomers were obtained (see Fig. 3). The
existence of local minimum for the cis,syn-isomer can be
attributed to the p-stacking of the phenyl rings of the
two cis-phenylselenolato ligands. Such a p-stacking is
missing both in the case of [Pt(SeFu)2(PH3)2] and
[Pt(SeTh)2(PH3)2]. The same difference has also been
observed experimentally. The X-ray structure of 3ca
exhibits a close contact between the two phenyl rings of
the cis-phenylselenolato ligands, but similar close con-
tacts are not observed in case of 1cs and 2ca.
Fig. 2. The molecular structures of (a) ta-[Pt(SeFu)2(PPh3)2] (1ta), (b)
ts-[Pt(SeTh)2(PPh3)2] [10], and (c) ta-[Pt(SePh)2(PPh3)2] [17] indicating
the numbering of the atoms. The thermal ellipsoids have been drawn at
50% probability level.
The calculated bond parameters are generally in
agreement with those obtained from the crystal structure
determinations (see Tables 3 and 4). The most signifi-
cant deviations between the observed and calculated
structures are displayed by the orientations of the
selenolato ligands with respect to the plane of coordina-
tion. This can be attributed to packing effects in the
stronger trans-influence of PPh3 compared with that of
the RSeꢂ ligand.
It can be seen from Fig. 2(a) and (c) that 1ta and 3ta
are trans,anti-isomers with pertinent torsional angles
being 53.8(1)8 {ŽP(1)Ã
/
Pt(1)Ã
/
Se(1)Ã
/
C(1)}for 1ta, and
151.0(5)8
ꢂ
/
24.7(5)8 {ŽP(2)ÃPt(1)Ã
/
/
Se(1)Ã
/
C(11)} and ꢂ
/
Table 4
Selected bond parameters of HF/ECP** optimized geometries of the different isomers of [Pt(SeR)2(PH3)2] (Rꢀ
/
Fu, Th, Ph)
[Pt(SeFu)2(PH3)2]
[Pt(SeTh)2(PH3)2]
[Pt(SePh)2(PH3)2]
4ca
4ts
4ta
5ca
5ts
5ta
6cs
6ca
6ts
6ta
Bond lengths
Pt(1)Ã
Pt(1)Ã
Pt(1)Ã
Pt(1)Ã
/
Se(1)
Se(2)
P(1)
2.51
2.51
2.34
2.34
2.51
2.54
2.35
2.34
2.53
2.53
2.34
2.34
2.51
2.51
2.34
2.34
2.51
2.53
2.35
2.35
2.53
2.53
2.35
2.35
2.53
2.53
2.34
2.34
2.54
2.54
2.34
2.34
2.52
2.52
2.35
2.35
2.53
2.53
2.35
2.35
/
/
/
P(2)
Bond angles
Se(1)ÃPt(1)Ã
Se(1)ÃPt(1)Ã
Se(1)ÃPt(1)Ã
Se(2)ÃPt(1)Ã
Se(2)ÃPt(2)Ã
P(1)ÃPt(1)Ã
/
/
Se(2)
P(1)
P(2)
P(1)
P(2)
83.2
173.6
90.0
177.6
87.1
95.7
91.0
86.2
176.9
180.0
87.7
92.3
92.3
87.7
180.0
82.8
173.4
90.6
178.7
87.4
94.5
91.5
86.7
178.1
180.0
87.0
93.0
93.0
87.0
180.0
96.0
175.7
81.9
95.0
177.0
82.1
178.8
86.7
93.3
93.3
86.7
178.1
180.0
87.0
93.0
93.0
87.0
180.0
/
/
/
/
/
/
90.5
90.6
81.9
82.1
/
/
173.2
96.3
173.4
96.0
175.7
100.1
177.0
100.8
/
/
P(2)

M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ
/120
117
Fig. 3. The optimized HF/ECP** geometries of all isomers of [Pt(SeR)2(PH3)2] (RꢀFu, Th, Ph).
/
solid state, since the NMR spectroscopic information
indicates that in solution the selenolato groups can
every case the cis,syn-isomer is least stable. This is most
pronounced for 4 and 5 neither of which show a local
minimum for this isomer. The existence of a local
minimum of cs-[Pt(SePh)2(PH3)2] (6cs) is probably due
to the p-stacking of the selenolato phenyl rings.
We note that at B3PW91/ECP**//HF/ECP** level of
theory the cis-isomers are predicted to be more stable
relative to the trans-isomer than at the HF/ECP** level.
The relative B3PW91/ECP**//HF/ECP** energies indi-
cate that the cis,anti-isomers lie only ca. 5 kJ molꢂ1
above the two trans-isomers in both 4 and 5. The
difference is more pronounced in the case of
undergo virtually unhindered rotation about the PtÃ
/Se
bond [12ꢁ16].
/
The total HF/ECP** and B3PW91/ECP**//HF/
ECP** energies of the ten isomers of [Pt(SeR)2(PH3)2]
are listed in Table 5. They have been used to compute
the relative energies of the different isomers that are
shown in Fig. 4 both at HF/ECP** and B3PW91/
ECP**//HF/ECP** levels of theory. It can be seen that
the cis-isomers of all three complexes lie at a higher
energy than the trans-isomers at both levels of theory. In

118
M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ120
/
Table 5
Total HF/ECP** and B3PW91/ECP**//HF/ECP** energies (in a.u.) of
esting to note that these computed results are in a
qualitative agreement with the X-ray structures of the
isolated trans-isomers of the three [Pt(SeR)2(PPh3)2]
complexes: [Pt(SeFu)2(PPh3)2] appears as a trans,anti-
isomer, [Pt(SeTh)2(PPh3)2] as a trans,syn-isomer, and
[Pt(SePh)2(PPh3)2] as a trans,anti-isomer.
the [Pt(SeR)2(PH3)2] (Rꢀ
/
Fu, Th, Ph) isomers
Isomer
HF/ECP**
B3PW91/ECP**
//HF/ECP**
ca-[Pt(SeFu)2(PH3)2] (4ca)
ts-[Pt(SeFu)2(PH3)2] (4ts)
ta-[Pt(SeFu)2(PH3)2] (4ta)
ca-[Pt(SeTh)2(PH3)2] (5ca)
ts-[Pt(SeTh)2(PH3)2] (5ts)
ta-[Pt(SeTh)2(PH3)2] (5ta)
cs-[Pt(SePh)2(PH3)2] (6cs)
ca-[Pt(SePh)2(PH3)2] (6ca)
ts-[Pt(SePh)2(PH3)2] (6ts)
ta-[Pt(SePh)2(PH3)2] (6ta)
ꢂ
/
232.06570
232.07591
232.07530
220.53630
220.54573
220.54552
224.94943
224.95663
224.97341
224.97292
ꢂ
/
236.22137
236.22307
236.22364
224.57268
224.57472
224.57455
229.30722
229.31323
229.32288
229.32305
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
4.4. Isomerization of [Pt(SeR)2(PPh3)2]
4.4.1. NMR spectroscopic identification of
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
[Pt(SeR)2(PPh3)2] (RꢀFu, Th, Ph)
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
NMR spectroscopic information of the [Pt(SeR)2-
(PPh3)2] isomers is presented in Table 6. Assignment of
the 31P, 77Se, and 195Pt resonances of the isomers of
[Pt(SeTh)2(PPh3)2] (2) and [Pt(SePh)2(PPh3)2] (3) was
based on the trends of the chemical shifts and coupling
constants, as discussed previously [12,13,17]. The reso-
nances of [Pt(SeFu)2(PPh3)2] (1) could be assigned on
the basis of the spectroscopic information from these
other complexes. The assignments could be verified by
redissolving the isomerically pure crystalline samples.
ꢂ/
ꢂ/
4.4.2. Isomerization
The immediate reaction products from the reactions
involving cis-[PtCl2(PPh3)2] seems to be, expectedly, cis-
[Pt(SeR)2(PPh3)2]. Upon prolonged standing in solution
the concentration of the cis-isomer decreased and that
of the trans-isomer increased. This is exemplified for
[Pt(SeTh)2(PPh3)2] (2) in Fig. 5.
Fig. 4. Relative energies of the different isomers of [Pt(SeR)2(PH3)2].
The white columns represent HF/ECP** energies, and the grey
columns represent B3PW92/ECP**//HF/ECP** energies.
The calculated relative concentration of cis-
[Pt(SeTh)2(PPh3)2] (2c) is based on the ratio of inten-
sities of the 31P resonances due to cis- and trans-
isomers. Initially the reaction mixture shows the pre-
sence of only the cis-isomer, but isomerization to the
trans-isomer proceeds quickly in the early stages of the
reaction. With time the reaction becomes slower. It
appears that the reaction is faster in benzene than in
dichloromethane (see Fig. 5). After 500 h the CH2Cl2
and C6H6 solutions contain ca. 40 and 25 mol.% of cis-
[Pt(SeTh)2(PPh3)2], respectively. The isomerization of
[Pt(SePh)2(PH3)2] (6) with the cis,syn-isomer lying at 42
kJ molꢂ1 and the cis,anti-isomer at 26 kJ molꢂ1 above
the trans,syn- and trans,anti-isomers.
The trans,syn- and trans,anti-isomers show close-
lying relative energies. The most stable isomers of the
three complexes are ta-[Pt(SeTh)2(PH3)2], ts-
[Pt(SeTh)2(PH3)2], and ta-[Pt(SePh)2(PH3)2]. It is inter-
Table 6
NMR data for cis- and trans-isomers of [Pt(SeR)2(PPh3)2] (Rꢀ
/
Fu, Th, Ph)
a
a
a
Solvent
31P{1H}(d)
95Pt{1H}(d)
1J(PtÃ
/P) (Hz)
77Se (d)
cis-[Pt(SeFu)2(PPh3)2] (1c)
trans-[Pt(SeFu)2(PPh3)2] (1t)
CH2Cl2
CH2Cl2
C6H6
17.4
22.3
18.0
21.6
19.1
20.8
ꢂ
/
4856
4952
4863
4957
4904
5040
3114
2855
3041
2873
2968
2840
143
69
ꢂ
/
b
cis-[Pt(SeTh)2(PPh3)2] (2c)
trans-[Pt(SeTh)2(PPh3)2] (2t)
ꢂ
/
187
84
c
C6H6
C6H6
ꢂ
/
d
cis-[Pt(SePh)2(PPh3)2] (3c)
trans-[Pt(SePh)2(PPh3)2] (3t)
ꢂ
/
299
176
d
C6H6
ꢂ/
a
In ppm.
b
The 13P chemical shift of 2c in CH2Cl2 is 17.9 ppm [1J(PtÃ
/
P)ꢀ
P)ꢀ2864 Hz] [12].
For 31P and 195Pt-NMR spectroscopic information, see Ref. [17].
/
3070 Hz] [12].
c
The 13P chemical shift of 2t in CH2Cl2 is 21.5 ppm [1J(PtÃ
/
/
d

M.S. Hannu-Kuure et al. / Journal of Organometallic Chemistry 666 (2003) 111ꢁ
/120
119
192292, 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: ꢃ44-
/
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Acknowledgements
Financial support from Academy of Finland, Finnish
Cultural Foundation, Emil Aaltonen Foundation, and
Tauno Tonning Foundation is gratefully acknowledged.
¨
Fig. 5. Isomerization of cis-[Pt(SeTh)2(PPh3)2] in CH2Cl2 (m) and
C6H6 ('). The relative content of the cis-isomer xcis (mol.%) has been
determined from the relative intensities of the 31P resonances of cis-
and trans-[Pt(SeTh)2(PPh3)2].
References
cis-[Pt(SeFu)2(PPh3)2] (1c) and cis-[Pt(SePh)2(PPh3)2]
(3c) follows qualitatively the same route as that of 2c.
The observed isomerization from the cis-isomer to the
trans-isomer is consistent with the relative energies of
the different [Pt(SeR)2(PH3)2] isomers (see Fig. 4).
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