Stepwise phosphine sulfide formation and metal-bridging reaction of tetradentate and tridentate phosphine ligands on palladium(II)

Article abstract of DOI:10.1016/j.jorganchem.2010.02.006

Kinetic studies on the stepwise phosphine sulfide formation reaction of the five-coordinate trigonal-bipyramidal Pd(II) complexes with the tripodal tetradentate phosphine ligand, [PdCl(pp₃)]Cl and [Pd(4-Cltp)(pp₃)](BF₄) (pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine; 4-Cltp = 4-chlorothiophenolate), were carried out, and it was revealed that the reactions proceeded via the intermediate with a pendant dissociated phosphino group. Formation of the intermediate was utilized for the bridging reaction onto Pt(II) to form the phosphine-bridged linear trinuclear and cyclic tetranuclear mixed-metal complexes. Difference in the steric conversion mechanism in the phosphine-bridging reaction between the linear tridentate phosphine (bis[2-(diphenylphosphino)ethyl]phenylphosphine) and pp₃ is also reported.

Full text of DOI:10.1016/j.jorganchem.2010.02.006

Journal of Organometallic Chemistry 695 (2010) 1253–1260
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Note
Stepwise phosphine sulfide formation and metal-bridging reaction
of tetradentate and tridentate phosphine ligands on palladium(II)
b
a
a
Sen-ichi Aizawa a, , Tatsuya Kawamoto , Yuuto Asai , Chie Ishimura
*
a Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
b Department of Chemistry, Faculty of Science, Kanagawa University, Hiratsuka, Kanagawa 259-1293, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Kinetic studies on the stepwise phosphine sulfide formation reaction of the five-coordinate trigonal-bipy-
ramidal Pd(II) complexes with the tripodal tetradentate phosphine ligand, [PdCl(pp3)]Cl and [Pd(4-
Cltp)(pp3)](BF4) (pp3 = tris[2-(diphenylphosphino)ethyl]phosphine; 4-Cltp = 4-chlorothiophenolate),
were carried out, and it was revealed that the reactions proceeded via the intermediate with a pendant
dissociated phosphino group. Formation of the intermediate was utilized for the bridging reaction onto
Pt(II) to form the phosphine-bridged linear trinuclear and cyclic tetranuclear mixed-metal complexes.
Difference in the steric conversion mechanism in the phosphine-bridging reaction between the linear tri-
dentate phosphine (bis[2-(diphenylphosphino)ethyl]phenylphosphine) and pp3 is also reported.
Ó 2010 Elsevier B.V. All rights reserved.
Received 1 December 2009
Received in revised form 1 February 2010
Accepted 5 February 2010
Available online 12 February 2010
Keywords:
Kinetics
Phosphine sulfide formation
Phosphine-bridging reaction
Steric conversion mechanism
1. Introduction
phine-bridging reaction of the square-planar Pd(II) complex with
bis[2-(diphenylphosphino)ethyl]phenylphosphine (p3) to that of
Some phosphine sulfides have been employed as monodentate
or bidentate ligands for some metal ions [1–6], and we have ap-
plied multidentate phosphine sulfide ligands to the Pd(0) catalyzed
CꢀC coupling reaction to stabilize the zerovalent oxidation state of
palladium [7]. However, so far, kinetic study on phosphine sulfide
formation reactions of phosphine complexes has not been
reported.
the trigonal-bipyramidal complex with pp3. As a result, we have
found interesting difference in the isomerization mechanism of
the phosphine-bridged polynuclear complex between the p3 and
pp3 ligand systems.
2. Experimental
Recently, we have found that two phosphine chalcogenide
groups are selectively formed on the five-coordinate trigonal-bipy-
ramidal Pd(II) complex with tripodal tetradentate phosphine,
tris[2-(diphenylphosphino)ethyl]phosphine (pp3), by the reaction
with excess sulfur or selenium [8], and we have also reported the
stepwise phosphine-bridging reaction to give the trinuclear and
pentanuclear mixed-metal complexes with intended metal se-
quences quantitatively [9]. We have assumed that such success
in selective preparations is attributed to formation of the Pd(II)
intermediate with a pendant dissociated phosphino group. In order
to confirm the reaction mechanism of the phosphine chalcogenide
formation and phosphine-bridging reaction, we have carried out
kinetic studies on the phosphine sulfide formation reaction of the
Pd(II) complexes with pp3 considering that sulfur, which has mod-
erately high solubility in nonpolar solvents, is suitable reactant for
kinetic experiments. Furthermore, we have compared the phos-
2.1. Reagents
Chloroform (Wako, 1 pure) for kinetic measurements were
dried over activated 4A Molecular Sieves. Tris[2-(diphenylphos-
phino)ethyl]phosphine (pp3, Aldrich), bis[2-(diphenylphosphino)-
ethyl]phenylphosphine (p3, Aldrich), sulfur (Wako), tetrakis(aceto-
nitrile)palladium(II) tetrafluoroborate ([Pd(CH3CN)4](BF4)2, Aldrich),
tetra(n-butyl)ammonium chloride (Bu4NCl, Wako), potassium
tetrachloropalladate(II) (K2[PdCl4], Aldrich), potassium tetrachlo-
roplatinate (II) (K2[PtCl4], Aldrich), cis- and trans-bis(benzoni-
trile)dichloroplatinum(II) (cis- and trans-[PtCl2(NCC6H5)2], Aldrich
and Strem, respectively), nickel chloride (Wako), and 4-chlorothi-
ophenol (H-4-Cltp, Wako) were used without further purification.
2.2. Preparation
The mononuclear phosphine complexes [PdCl(pp3)]Cl (1) [10],
[PdCl(pp3)](BF4) (2) [9], [Pd(4-Cltp)(pp3)](BF4) (3) [11], [PdCl(p3)]Cl
* Corresponding author. Tel./fax: +81 76 445 6980.
E-mail address: saizawa@eng.u-toyama.ac.jp (S.-i. Aizawa).
0022-328X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.02.006

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S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
Fig. 1. 31P NMR spectral change of a chloroform solution containing 1 (27 mmol kgꢀ1) and sulfur (420 mmol kgꢀ1) at room temperature. The spectra were recorded at 15 min
(a) and 75 min (b) after the reaction was started and after the reaction was completed (c), respectively. m and d denote the monosulfide and disulfide complexes, respectively.
Table 1
0.5
Activation parameters for phosphine sulfide formation reactions of 1 and 3.
Complex
Reaction
k
D
Hà
(kJ molꢀ1
D
Sà
(J Kꢀ1 molꢀ1
)
0.4
0.3
0.2
0.1
0
(molꢀ1 kg sꢀ1
)
)
1
3
First step
Second step
9.8 ꢁ 10ꢀ3
51.2 1.0
54.0 2.1
ꢀ112
ꢀ96
3
2.1 ꢁ 10ꢀ2
7
7
First step
Second step
2.9 ꢁ 10ꢀ2
55.2 2.0
65.5 2.9
ꢀ89
6.8 ꢁ 10ꢀ5
ꢀ105
9
a
Unit is sꢀ1
.
a
with cis-[PtCl2(NCC6H5)2] (0.038 g, 0.080 mmol) in chloroform
(5 cm3). The reaction solution was concentrated with a rotary
evaporator and to this was added diethyl ether. The mixture was
kept in a refrigerator to give yellow single crystals for an X-ray
analysis.
300
350
400
450
500
550
λ
Fig. 2. Absorption spectral change of
a
chloroform solution containing
at 313.15 K. The spectra were
1
(0.08 mmol kgꢀ1 and sulfur (1.6 mmol kgꢀ1
)
)
recorded at 0.5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150,
160, and 170 min after the temperature was equilibrated. The directions of the
spectral change are denoted by arrows.
2.3. Crystal structure determination
X-ray crystallographic data for trans-[PtCl2{PdCl2(p3)}2] were
collected with the
x scan technique on a Rigaku RAXIS-RAPID
(4) [10], [PtCl(pp3)]Cl (5) [12], and [NiCl(pp3)]Cl (6) [9] were pre-
pared by the reported procedures.
The trinuclear phosphine-bridged complex trans-[PtCl2{PdCl2-
(p3)}2] was prepared by the reaction of 4 (0.15 g, 0.16 mmol)
image plate diffractometer with graphite monochromated Mo K
a
(k = 0.71075 Å) radiation at 200 K. Empirical absorption corrections
were applied. The structure was solved and refined using the
SHELXS-97 [13] and SHELXL-97 [14] software. All non-hydrogen atoms

S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
1255
were refined anisotropically and hydrogen atoms were included in
calculated positions.
Ref
3
(a)
2.4. Measurements
m
m
The kinetic measurements for the formation reactions of the
phosphine sulfide complexes in chloroform were performed at
288–333 K under pseudo-first-order conditions where the concen-
trations of sulfur were in large excess (1.5 ꢁ 10ꢀ3–3.75 ꢁ
10ꢀ2 mol kgꢀ1 for 1 and 7.5 ꢁ 10ꢀ3–6.0 ꢁ 10ꢀ2 mol kgꢀ1 for 2) over
those of 1 (7.5 ꢁ 10ꢀ5 mol kgꢀ1) and 2 (1.5 ꢁ 10ꢀ4 mol kgꢀ1). The
temperature of the reaction solution was controlled within 0.1 K.
The absorption spectral changes were recorded on a Perkin–Elmer
Lambda 19 spectrophotometer.
3
m
17 Hz
(b)
36 Hz
m
17 Hz
36 Hz
d
31P NMR spectra were recorded on a JEOL JNM-A400 FT-NMR
spectrometer operating at 160.70 MHz. In order to determine the
chemical shifts of 31P NMR signals, a 3 mm o.d. NMR tube contain-
ing the sample solution was coaxially mounted in a 5 mm o.d. NMR
tube containing deuterated water as a lock solvent and phosphoric
acid as a reference.
m
d
d
m
29 Hz
(c)
29 Hz
d
3. Results and discussion
d
3.1. Kinetics
d
Previously, we reported the formation of the monosulfide and
disulfide complexes by the reactions of 1 with 1 equiv. and excess
sulfur, respectively [8]. As shown in Fig. 1, the sulfide complex for-
mation with excess sulfur was stepwise. The first step showed the
formation of the square-planar monosulfide complex with a pen-
dant phosphine sulfide group and coordinated two terminal and
one central phosphino groups, and the second step gave three coa-
lesced signals of the disulfide complex that exists in a rapid equi-
librium between the square-planar complex with two pendant
phosphine sulfide groups and the five-coordinate complex with
two coordinated phosphine sulfide groups as reported [8]. The
complex 1 exhibits three absorption bands in the visible region,
and the first and second step correspond to disappearance of the
absorption at the shortest wavelength (ca. 370 nm) and subse-
quent decrease of the other two absorption bands, respectively
(Fig. 2). The rate constants for the monosulfide formation were
obtained by the initial slope method following change in the absor-
bance at 425 nm, and the rate constants for the disulfide formation
were obtained by a nonlinear least-square analysis for the expo-
nential time course of the absorbance at 450 nm after complete
disappearance of the absorption at ca. 370 nm. The observed rate
constants (kobs) for both sulfide formation steps are first-order with
respect to the sulfur concentration (Figs. S1 and S2). Temperature
120
80
40
0
ppm
+
S
P
+
+
P
29 Hz
P
P
36 Hz
17 Hz
P
P
S
P
P
P
Pd
SR
P
P
Pd
P
Pd
S
RS
SR = 4-Cltp
SR
disulfide complex
monosulfide complex
1
Fig. 3. 31P NMR spectral change of
a
chloroform solution containing 3
(8.6 mmol kgꢀ1) and sulfur (37 mmol kgꢀ1) at room temperature. The spectra were
recorded at 15 min (a) and 2 h (b) after the reaction was started and after the
reaction was completed (c), respectively. m and d denote the monosulfide and
disulfide complexes, respectively.
dependences of the second-order rate constants were fitted to
the Eyring equation (Fig. S3) to give the activation enthalpies
(D D
Hà) and activation entropies ( Sà) (Table 1). The first-order sul-
fur concentration dependence of kobs and the large negative values
of
D
Sà suggest the associative sulfide formation with pre-dissocia-
tion of the coordinated phosphino groups (Scheme 1). In the case of
S
+
+
P
P
+
P
P
S
S
P
Pd
P
P
P
P
P
Pd
Pd
Cl
Cl
P
P
Cl
monosulfide complex
1
S
S
+
P
P
Pd
Cl
P
P
Cl-
S
S
Cl-
P
P
P
P
P
P
P
P
S
Pd
Pd
Cl
Cl
Cl
Cl
disulfide complex
Scheme 1.

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S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
+
S
P
+
P
P
+
P
P
S
P
Pd
P
P
P
P
Pd
Pd
RS
RS
P
P
SR
2
monosulfide complex
P
+
S
+
+
P
P
P
S
S
P
Pd
P
P
S
P
P
P
Pd
Pd
RS
S
P
SR
disulfide complex
RS
S
P
Scheme 2.
0.7
0.6
0.5
0.4
(b)
(a) 2.0
1.5
1.0
0.5
0.0
350
450
550
650
400
420
λ /nm
440
460
λ
/nm
Fig. 4. Absorption spectral change of a chloroform solution containing 3 (0.15 mmol kgꢀ1) and sulfur (14.7 mmol kgꢀ1) at 298.15 K. The spectra were recorded at 0, 5, 10, 15,
20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, and 75 min (a) and at 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 360, 375, 390, 405, 420, 435, 450, 465, and 480 min (b)
after the temperature was equilibrated. The directions of the spectral changes are denoted by arrows.
Fig. 5. ORTEP diagram of trans-[PtCl2{PdCl2(p3)}2].
2 having BFꢀ4 counter ion instead of Clꢀ, the disulfide complex was
not formed to give only the monosulfide one even though excess
sulfur was used. This fact indicates that coordination of a chloride
ion is necessary for the pre-dissociation of the coordinated phos-
phino group in the second step (Scheme 1).
In contrast with the chloro complex 2, the thiolato complex 3,
which has also BFꢀ4 as a counter anion, gave the disulfide complex
by the reaction with excess sulfur. The 31P NMR spectra in Fig. 3
shows the formation of the square-planar monosulfide complex
similar to the first step for 1 and 2 followed by the formation of

S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
1257
Fig. 6. 31P NMR spectrum of trans-[PtCl2{PdCl2(p3)}2] in chloroform.
the five-coordinate disulfide complex without any equilibrium for
centration dependence of kobs and the large negative value of D
Sà
the second step. Considering that BFꢀ4 does not participate in the
substitution reaction as shown in the reaction of 2, it is apparent
that the second step proceeds with the intramolecular substitution
of the coordinated phosphino group for the pendant phosphine
sulfide group in the square-planar monosulfide complex (Scheme
suggest that the first step proceeds via the associative sulfide for-
mation similar to that of 1 and 2 (Scheme 2). On the other hand,
from the fact that kobs for the second step is independent of the sul-
fur concentration giving the large negative value of
D
Sà, the rate-
determining step for the disulfide formation is assumed to be asso-
ciative intramolecular substitution of the coordinated phosphino
group for the pendant phosphine sulfide group on palladium(II)
followed by the sulfide formation of the dissociated phosphino
group (Scheme 2).
2). The sulfur–phosphorus
and consequently the unoccupied
p
bonding orbital is not so stabilized,
*
p orbital is moderately low
and can be a good
Since the thiolato sulfur atom in 3 is a strong
pared with chloride ion, it is reasonable to assume that
p
-accepting orbital for the metal center [15].
and donor com-
-accepting
r
p
p
P@S coordination is stabilized in the intermediate for 3 compared
with 1. As shown in Fig. 4, the first and second steps correspond to
decrease in absorbance in the visible region (Fig. 4a) and subse-
quent increase in absorbance in the wavelength region longer than
422 nm, at which the isosbestic point is observed (Fig. 4b), respec-
tively. The rate constants for the monosulfide and disulfide forma-
tions were obtained by nonlinear least-square analyzes for the
exponential time courses of the absorbances at 540 and 450 nm,
respectively. While kobs for the monosulfide formation is propor-
tional to the excess sulfur concentration (Fig. S4), kobs for the disul-
fide formation is independent of the sulfur concentration (Fig. S5).
Temperature dependences of the second- and first-order rate con-
stants for both steps were fitted to the Eyring equation (Fig. S6) to
give the activation parameters (Table 1). The first-order sulfur con-
3.2. Bridging reaction
Previously, we reported the quantitative formation reactions of
the Pd(II)–Pt(II)–Pd(II) and Ni(II)–Pt(II)–Ni(II) trinuclear and
Rh(III)–Pd(II)–Pt(II)–Pd(II)–Rh(III) pentanuclear complexes by the
stepwise phosphine-bridging reactions of 1, 3, and 6 [9]. From
the present kinetic results, such a success of the quantitative prep-
aration can be attributed to the existence of the intermediates with
a dissociated phosphino group of the bound pp3 ligand. Because
the second steps of the sulfide formation and the phosphine-bridg-
ing reaction of the pp3 complexes correspond to the reactions for
the square-planar complexes with the linear tridentate p3 ligand,
the phosphine-bridging reactions of the p3 complex 4 was com-
pared with those of 1.

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S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
Reaction of 1 with trans-[PtCl2(NCC6H5)2]
Cl
NCC H
6
5
Pt
C H CN
+
6 5
Cl
2+
P
P
P
Cl
P
Cl
Pd
+
P
trans
P
P
Pt
P
P
P
P
P
P
2
P
Pd
Cl
P
Pd
2
Pd
Cl
Cl
Cl
P
Cl
-
trans
Cl
1
P
+
2+
P
P
Cl
P
Cl
P
Cl
P
P
P
Pd
Pd
Pd
P
P
P
P
P
Pt
Pt
P
P
Cl
P
Cl
Pd
Cl
Cl
Cl
trans
cis
Reaction of 1 with cis-[PtCl2(NCC6H5)2]
NCC H
6
5
NCC H
Cl
6
5
Pt
+
Cl
P
2+
+
P
P
P
Cl
P
P
P
P
cis
P
P
Pd
Pd
P
P
P
P
Cl
Pd
Cl
P
Pd
2
2
Pt
Cl
P
Cl
Cl
cis
1
Reaction of 4 with cis-[PtCl2(NCC6H5)2]
C H CN
NCC H
6
6
5
5
NCC H
Cl
6
5
Pt
-
Cl
Cl
+
-
cis
P
Cl
P
P
P
P
Cl
P
P
P
P
NCC H
Pd
6
5
Pd
Pd
Pt
Cl
Cl
Cl
Cl
Cl
Cl
cis
(trans effect of P)
Cl
P
Cl
P
Pd
P
Cl
P
P
P
P
Pd
P
P
Cl
Cl
P
Pt
Pd
Cl
NCC H
Cl
P
Cl
Pt
Cl
Cl
Pd
Cl
P
Cl
6
5
trans
trans
Scheme 3.
The trinuclear structure with a Pd(II)–Pt(II)–Pd(II) metal ion se-
quence was confirmed by an X-ray analysis of a crystal obtained by
the reaction of cis-[PtCl2(NCPh)2] with 2 equiv. of 4 (Fig. 5). The
crystal structure revealed that the cis geometry of the starting Pt(II)
complex was converted to the trans one by the bridging reaction,
and the racemic isomer with the same chirality of the two central
phosphorus atoms was crystallized. The 31P NMR spectrum of the
crude product in chloroform showed two sets of the signals for
the Pd(II)–Pt(II)–Pd(II) trinuclear complex with the terminal phos-
phorus atoms coordinated to Pd(II) at 65.1 and 65.3 ppm (3JP–
P = 10 Hz), the central phosphorus atom at 74.4 and 75.6 ppm,
and the terminal phosphorus atom bridging to the central Pt(II)
at 14.4 and 15.0 ppm, corresponding to the racemic and meso iso-
tual 2JP–P coupling through Pt(II) center should be observed. The 31
P
NMR spectral simulation [17] for the bridging phosphorus atom
actually gave a large 2JP–P value (650 Hz) characteristic of the trans
geometry (Fig. S7) [9]. Since one set of the signals at the higher
field agreed with the signals for the crystallizing racemic isomer,
the other set of signals at the lower field was reasonably assigned
to the meso isomer.
As reported previously, while the trans isomer of the Pd(II)–
Pt(II)–Pd(II) trinuclear complex is initially formed by the reaction
of trans-[PtCl2(NCPh)2] with 1, the trans-to-cis geometrical con-
version on the Pt(II) center proceeds to give the cis isomer as a
final product (Scheme 3a) [9]. In contrast with the reaction of
cis-[PtCl2(NCPh)2] with 4 above-mentioned, the cis isomer was
directly formed without the geometrical conversion by the reac-
tion of cis-[PtCl2(NCPh)2] with 1 (Scheme 3b) [9]. These facts
indicate that the cis geometry of the Pt(II) center is thermody-
namically more stable than the trans one due to the ‘‘trans influ-
ence” of the phosphorus donor atoms. Because the chelate-ring
mers (Fig. 6). Disappearance of the 195Pt satellite signals in the 31
P
NMR spectrum arises from relaxation of 195Pt via the chemical shift
anisotropy mechanism [16]. Since the AA0XX0 spin system is made
up of the two chemically equivalent bridging phosphorus atoms (A
and A0) and the two central phosphorus atoms (X and X0), the vir-

S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
1259
Fig. 7. 31P NMR spectrum of the cyclic tetranuclear complex in chloroform.
opening of the p3 ligand in 4 is probably very slow and the pre-
dissociation equilibrium lies so far to the left compared with the
pp3 ligand in 1, it is assumed that cis-to-trans conversion by
the ‘‘trans effect” of the initially bridging phosphorus atom to
the chloro ligand in the trans position proceeds prior to the
subsequent substitution of benzonitrile for the phosphorus atom
in the second bridging step (Scheme 3c). Previously, we proposed
the mechanism of the trans-to-cis conversion of the Pd(II)–Pt(II)–
Pd(II) trinuclear complex with the pp3 ligand, in which the
chelate-ring opening of the tridentate-type pp3 ligand on the
Pd(II) terminal moiety by coordination of Clꢀ followed by an
attack on the Pt(II) center with the dissociated phosphino group
are necessary instead of an attack of the Clꢀ onto the Pt(II) center
(Scheme 3a). This mechanism was confirmed by the fact that the
trans-to-cis conversion of the trinuclear complex with the p3
ligand, which acts as bidentate on the terminal Pd(II), does not
proceeds even though Bu4NCl was added to provide excess Clꢀ.
This is consistent with the fact that the further bridging reaction
of the bidentate-type phosphine moiety of pp3 in the Rh(III)–
Pd(II)–Pt(II)–Pd(II)–Rh(III) pentanuclear complex does not proceed
[9], and the two terminal phosphine chalcogenide groups are
selectively formed on [PdCl(pp3)]Cl by the reaction with excess
sulfur or selenium [8].
reaction solution showed the 31P NMR signal of the trans-Pt(II)
3
moiety at 12.6 ppm (2JP–Pt = 550 Hz and JP–P = 45 Hz) besides the
signal for the originally observed cis-Pt(II) central moiety at
3
2
14.9 ppm (2JP–Pt = 15 Hz and JP–P = 67 Hz), where the JP–Pt and
3JP–P values were obtained by the spectral simulation (Fig. S8)
[17]. Furthermore, the two sets of signals for the racemic and meso
isomers was changed to one set with the symmetric central phos-
phorus atoms, showing the signals for the terminal and central
phosphino groups coordinated to the Pd(II) terminals at 66.0
(3JP–P = 11 Hz) and 81.5 ppm, respectively (Fig. 7). This spectrum
indicates formation of the cyclic tetranuclear complex with the
cis- and trans-Pt(II) bridges (Scheme 4). Broadening of the 195Pt
satellite signals in the 31P NMR spectrum arises from relaxation
of 195Pt via the chemical shift anisotropy mechanism [16]. The
cis-to-trans conversion of cis-[PtCl2(NCPh)2] accompanied by the
second bridging step is consistent with the mechanism of the cis-
to-trans conversion for the p3 bridged trinuclear complex. Interest-
ingly, the trans–cis bridging structure in the cyclic tetranuclear
complex was further converted to the trans–trans bridging struc-
ture (Scheme 4). Such a subsequent steric conversion may be
attributable to steric instability of the trans–cis and cis–cis bridging
structures. The subsequent steric conversion was not observed by
the similar reaction of the corresponding Pt(II) complex 5 instead
of 1 with cis-[PtCl2(NCPh)2] to give the trans–cis tetranuclear com-
plex as a final product, and use of the corresponding Ni(II) complex
6 gave the trans–trans tetranuclear complex directly. This differ-
ence in reactivity depends on the inertness of the metal ions in
[MCl(pp3)]Cl (M = Pd(II) (1), Pt(II) (5), Ni(II) (6)).
In the present work, we carried out the reaction of the cis-
Pd(II)–Pt(II)–Pd(II) trinuclear complex bridged by the pp3 ligand
with 1 equiv. of cis-[PtCl2(NCPh)2] in chloroform for comparison
with the bridging reaction to form the Rh(III)–Pd(II)–Pt(II)–
Pd(II)–Rh(III) pentanuclear complex [9]. As shown in Fig. 7, the

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S.-i. Aizawa et al. / Journal of Organometallic Chemistry 695 (2010) 1253–1260
P
2+
+
-
P
P
Cl
P
P
P
P
P
P
Pd
P
P
Cl
P
Cl
Pt
Cl
P
Pd
Pd
P
Cl
Pt
P
Cl
Cl
Cl
Pd
P
Cl
Cl
P
cis
cis
NCC H
6
5
Cl
NCC H
C H CN
6
5
NCC H
Cl
6
5
Pt Cl
P
Pt
Pt
6
5
Cl
Cl
Cl
P
cis
cis
+
trans
+
P
P
P
P
Cl
P
P
P
P
Cl
Pd
P
Cl
P
Pt
Pd
Cl
P
Cl
Pd
Pt
Cl
Pd
Cl
Cl
P
Cl
Cl
P
cis
cis
Cl
Pt
Cl
Cl
NCC H
Pt
P
6
5
P
P
P
Cl
P
trans
-
tranns
Cl
P
P
P
P
P
P
P
Cl
Pd
P
Pd
Pd
P
Cl
Pt
Cl
Cl
Pd
P
Cl
P
Cl
Cl
Cl
Cl
Cl
Pt
Cl
cis
Cl
cis
Cl
P
P
P
Pt
Cl
P
P
tranns
Cl
P
P
Pd
Pd
Cl
Cl
Cl
Cl
P
Pt
Cl
tranns
Scheme 4.
[4] A.N. Skvortsov, A.N. Reznikov, D.A. de Vekki, A.I. Stash, V.K. Belsky, V.N. Spevak,
N.K. Skvortsov, Inorg. Chim. Acta 359 (2006) 1031.
Appendix A. Supplementary material
[5] D.K. Dutta, P. Chutia, J.D. Woollins, A.M.Z. Slawin, Inorg. Chim. Acta 359 (2006)
877.
[6] P. Sekar, J.A. Ibers, Inorg. Chim. Acta 359 (2006) 2751.
[7] S. Aizawa, A. Majumder, Y. Yokoyama, M. Tamai, O. Maeda, A. Aitamura,
Organometallics 28 (2009) 6067.
[8] S. Aizawa, T. Hase, T. Wada, J. Organomet. Chem. 692 (2007) 813.
[9] S. Aizawa, K. Saito, T. Kawamoto, E. Matsumoto, Inorg. Chem. 45 (2006) 4859.
[10] S. Aizawa, T. Iida, S. Funahashi, Inorg. Chem. 35 (1996) 5163.
[11] S. Aizawa, T. Kawamoto, K. Saito, Inorg. Chim. Acta 357 (2004) 2191.
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[13] G.M. Sheldrick, SHELXS97, Program for Crystal Structure Solution, University of
Göttingen, Germany, 1997.
CCDC 755765 contains the supplementary crystallographic data
for the trinuclear complex trans-[PtCl2{PtCl2(P3)}2]. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2010.02.006.
References
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