The syntheses, 31P{1H} NMR spectra and cyclic voltammetry of trinuclear [Pd2M(μ3-Se)2(dppe)3] 2+ {M = Ni or Pt; dppe = 1,2-bis(diphenylphoshino)ethane}

Article abstract of DOI:10.1016/S0020-1693(01)00504-7

Trinuclear [Pd₂M(μ₃-Se)₂(dppe)₃] ²⁺ (M = Ni or Pt) and pentanuclear [M′{Pd₂(μ₃-Se)₂(dppe)₂} ₂]²⁺ (M′ = Ni, Pd or Pt) clusters have been prepared using a metalloligand [Pd₂(μ-Se)₂(dppe)₂] and characterized by ³¹P{¹H} NMR spectroscopy and cyclic voltammetry. [Pd₂Ni(μ₃-Se)₂(dppe)₃] ²⁺ gives two chemically reversible couples, [Pd₂Pt(μ₃-Se)₂(dppe)₃] ²⁺ exhibits one chemically reversible couple and pentanuclear clusters show three couples in each cyclic voltammogram of the reduction process at 255 K. The redox behavior of the clusters is discussed.

Full text of DOI:10.1016/S0020-1693(01)00504-7

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Inorganica Chimica Acta 321 (2001) 167–170
Note
31
The syntheses, P{1H} NMR spectra and cyclic voltammetry of
trinuclear [Pd2M(m3-Se)2(dppe)3]2+ {M=Ni or Pt;
dppe=1,2-bis(diphenylphoshino)ethane} and pentanuclear
[M%{Pd2(m3-Se)2(dppe)2}2]2+ (M%=Ni, Pd or Pt) clusters with
selenido bridges
Keiji Matsumoto a,*, Naho Kotoku a, Takeshi Shizuka a, Rika Tanaka b, Seichi Okeya c
a Department of Chemistry, Faculty of Science, Osaka City Uni6ersity, Sumiyoshi-ku, Osaka 558-8585, Japan
b Faculty of Engineering, Osaka City Uni6ersity, Sumiyoshi-ku, Osaka 558-8585, Japan
c Department of Material Science and Chemistry, Faculty of System Engineering, Wakayama Uni6ersity, Wakayama 640-8510, Japan
Received 22 January 2001; accepted 4 May 2001
Abstract
Trinuclear [Pd2M(m3-Se)2(dppe)3]2+ (M=Ni or Pt) and pentanuclear [M%{Pd2(m3-Se)2(dppe)2}2]2+ (M%=Ni, Pd or Pt) clusters
have been prepared using a metalloligand [Pd2(m-Se)2(dppe)2] and characterized by 31P{1H} NMR spectroscopy and cyclic
voltammetry. [Pd2Ni(m3-Se)2(dppe)3]2+ gives two chemically reversible couples, [Pd2Pt(m3-Se)2(dppe)3]2+ exhibits one chemically
reversible couple and pentanuclear clusters show three couples in each cyclic voltammogram of the reduction process at 255 K.
The redox behavior of the clusters is discussed. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Trinuclear complexes; Pentanuclear complexes; Palladium complexes; Selenido bridge; Cyclic voltammetry
1. Introduction
reaction of a metalloligand [M2(m-Te)2(dppe)2] (M=Pd
or Pt) with M%2+ (M%=Pd, Pt or Hg) gives pentanu-
clear clusters [6]. On the other hand, a number of
clusters with various structures and nuclearities had
been synthesized previously using [Pt2(m-S)2(PPh3)4] [7].
In this paper we describe 31P{1H} NMR spectra and
cyclic voltammograms of the trinuclear [Pd2M(m3-
Se)2(dppe)3]2+ (M=Ni or Pt) and the pentanuclear
[M%{Pd2(m3-Se)2(dppe)2}2]2+ (M%=Ni, Pd or Pt) clus-
ters with selenido bridges.
Over the last two decades there has been a continuing
interest in the chemistry of metal chalcogenolate cluster
compounds owing to their potential use as synthetic
analogs of biological systems [1], precursors for new
materials [2] and heterogeneous catalysts [3]. The sulfur
containing clusters with a variety of structures and
nuclearities have been studied extensively from these
points of view.
The chemistry of metal selenolate and tellurolate
compounds is a growing area of research [4]. Recent
interest in these compounds results from their possible
use as precursors for semi-conducting materials [5]. In
connection with these investigations we reported that a
2. Experimental
2.1. Reagents
* Corresponding author. Tel.: +81-6-6605-2649; fax: +81-6-6605-
2522.
E-mail address: matsumot@sci.osaka-cu.ac.jp (K. Matsumoto).
All operations were carried out under an atmosphere
of dry nitrogen using solvents degassed prior to use.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00504-7

168
K. Matsumoto et al. / Inorganica Chimica Acta 321 (2001) 167–170
Acetonitrile (MeCN) and N,N-dimethyformamide
(DMF) were purified using a standard method.
105 mg). After 20 h NaBPh4 (0.15 mmol, 50 mg) was
mixed. The solution was filtered and the filtrate was
placed in air for 2 days at r.t. Deep brown crystals [8]
were obtained, recrystallized from DMF and air-dried.
Yield was 31% (110 mg). Anal. Found: C, 59.5; H, 4.7.
Calc. for [Ni{Pd2Se2(C26H24P2)2}2][B(C6H5)4]2: C, 60.2;
H, 4.5%.
2.2. Preparations of NaSeH, [NiCl2(dppe)] and
[Pt(dppe)(MeCN)2](ClO4)2
NaSeH was prepared by a reaction of selenium pow-
der (0.7 mmol, 55 mg) with NaBH4 (1.4 mmol, 53 mg)
in ethanol (3 cm3). [NiCl2(dppe)] was prepared by a
reaction between NiCl2 (0.2 mmol, 26 mg) and dppe
(0.2 mmol, 80 mg) in DMF (7 cm3). [Pt(dppe)-
(MeCN)2](ClO4)2 was obtained by reacting [Pt
(MeCN)4](ClO4)2 (0.2 mmol, 110 mg) with dppe (0.2
mmol, 80 mg) in DMF (7 cm3).
2.7. Preparation of [Pd{Pd2(v3-Se)2(dppe)2}2][BPh4]2
(4)
Following a method similar to the preparation of 3,
the deep brown crystals of 4 were obtained by a reac-
tion between [Pd2(m-Se)2(dppe)2] (0.9 mmol, 105 mg),
[PdCl2(CH3CN)2] (0.07 mmol, 18 mg) and NaBPh4
(0.12 mmol, 40 mg) in DMF (7 cm3). Yield 21% (47
mg). Anal. Found: C, 58.9; H, 4.4. Calc. for
[Pd{Pd2Se2(C26H24P2)2}2][B(C6H5)4]2: C, 59.3; H, 4.5%.
2.3. Preparation of [Pd2(v-Se)2(dppe)2]
PdCl2 (0.5 mmol, 90 mg) and dppe (0.5 mmol, 200
mg) were mixed in MeCN (20 cm3). After heating at
70 °C for 4 h, NaSeH was added and the mixture was
reacted for 15 h at room temperature (r.t.). The solu-
tion was filtered and the filtrate was placed at −15 °C
for 3 days. Dark blue crystals of [Pd2(m-Se)2(dppe)2]
were obtained and used to prepare tri- and pentanu-
clear clusters 1–5 without further purification. Yield
was 36% (105 mg). Anal. Found: C, 52.1; H, 4.7. Calc.
for [Pd2Se2(C26H24P2)2]: C, 53.5; H, 4.2%.
2.8. Preparation of [Pt{Pd2(v3-Se)2(dppe)2}2][BPh4]2 (5)
The preparation of 5 is analogous to that used for 3.
The brown crystals of 5 were obtained by a reaction of
[Pd2(m-Se)2(dppe)2] (0.9 mmol, 105 mg) with [Pt-
(MeCN)4](ClO4)2 (0.04 mmol, 22 mg) and NaBPh4
(0.11 mmol, 38 mg) in DMF (7 cm3). Yield 27% (34
mg). Anal. Found: C, 55.9; H, 5.0; N, 2.7. Calc. for
[Pt{Pd2Se2(C26H24P2)2}2][B(C6H5)4]2·7C3H7NO: C, 56.5;
H, 5.1; N, 2.7%.
2.4. Preparation of [Pd2Ni(v3-Se)2(dppe)3][BPh4]2 (1)
[Pd2(m-Se)2(dppe)2] (0.9 mmol, 105 mg) prepared in
Section 2.3 was added to the DMF solution of
[NiCl2(dppe)] (0.2 mmol, 106 mg) obtained in Section
2.2. After stirring for 20 h NaBPh4 (0.3 mmol, 100 mg)
was mixed and the solution was filtered. Brown crystals
were obtained by keeping the filtrate in air for 2 days at
r.t. The product was recrystallized form DMF–MeCN
and air-dried: yield 16% (78 mg). Anal. Found: C, 65.3;
H, 5.2; N, 1.1. Calc. for [Pd2NiSe2(C26H24P2)3]-
[B(C6H5)4]2·2C3H7NO: C, 65.8; H, 5.3; N, 1.2%.
2.9. Measurements
Cyclic voltammograms were recorded at 29391 and
25591 K with a Yanaco P-1100 system equipped with
a Rikadenki RW201K x–y recorder. The working and
counter electrodes were a glassy carbon disk and a
platinum wire, respectively. The Ag ꢀ AgCl reference
electrode was used. Potentials are reported against the
ferrocenium/ferrocene (Fc+/Fc) couple used as an in-
ternal standard. The Fc+/Fc potentials (E1/2) were
+0.46 V at 293 K and +0.41 V at 255 K in DMF
relative to a SCE. Tetrabutylammonium perchlorate
(TBAP) was used as a supporting electrolyte.
2.5. Preparation of [Pd2Pt(v3-Se)2(dppe)3][BPh4]2 (2)
Following a method similar to the preparation of 1,
a reaction between [Pd2(m-Se)2(dppe)2] (0.9 mmol, 105
mg), the DMF solution of [Pt(dppe)(MeCN)2](ClO4)2
(0.2 mmol, 175 mg) and NaBPh4 (0.3 mmol, 100 mg)
gave yellow crystals of 2: yield 10% (48 mg). Anal.
Found: C, 62.9; H, 4.9; N, 0.75. Calc. for
[Pd2PtSe2(C26H24P2)3][B(C6H5)4]2·C3H7NO: C, 62.7; H,
4.9; N, 0.57%.
Controlled potential coulometry of 1 and 2 was
carried out at 29391 K in a standard H-type cell with
a Hokuto HA-501 potentiostat and a Rikadenki RW-
11T x–y recorder using the t–y mode to obtain the
total charge consumed. The working electrode was of
reticulated vitreous carbon and the counter electrode
was a platinum wire. The Ag ꢀ AgCl reference electrode
was used in a DMF solution.
31P{1H} NMR spectra were measured in a DMF
2.6. Preparation of [Ni{Pd2(v3-Se)2(dppe)2}2][BPh4]2 (3)
solution on a JEOL FX-60Q spectrometer at 300 K. 31
P
chemical shifts are reported with respect to external
H3PO4. Positive values are downfield of the reference.
To a stirred solution of NiCl2 (0.1 mmol, 13 mg) in
DMF (7 cm3) was added [Pd2(m-Se)2(dppe)2] (0.9 mmol,

K. Matsumoto et al. / Inorganica Chimica Acta 321 (2001) 167–170
169
Chemical shifts obtained from 31P{1H} NMR spectra
for 1–5 are listed in Table 1. The spectra indicate the
presence of one magnetic environment in solution for
the phosphorus atoms of dppe bound to Ni, Pd or Pt.
The NMR spectrum of cluster 1 gives one triplet-like
signal at l=55.5 and one doublet-like signal at l=
48.5 owing to the phosphorus atoms (PꢀNi) bound to
the Ni atom and those (PꢀPd) bound to the Pd atoms,
respectively. These two resonances have relative intensi-
ties in the ratio 1:2. The chemical shift value of PꢀNi
(l=55.5) is larger than that of PꢀNi (l=50.2) found
in [Ni3(m3-Se)2(dppe)3][BPh4]2 [9], while this value of
PꢀPd (l=48.5) is smaller than that (l=50.6) observed
for [Pd3(m3-Se)2(dppe)3][BPh4]2 [9]. In the NMR spec-
trum of cluster 2 one double triplet signal at l=49.4 is
ascribed to PꢀPd and one triplet signal at l=42.4 is
attributed to PꢀPt. The former intensity is two times
larger than the latter. The chemical shift value (l=
49.4) of PꢀPd for 2 is small compared with that for
[Pd3(m3-Se)2(dppe)3][BPh4]2 [9], but this value (l=42.4)
of PꢀPt is larger than that (l=38.4) for [Pt3(m3-
Se)2(dppe)3][BPh4]2 [9]. In order to estimate the NMR
parameters, computer simulation of the 31P{1H} NMR
spectrum for 2 was carried out following the analogous
method described previously [9]. The coupling con-
Fig. 1. Sketches of the cluster compounds: (a) trinuclear cluster and
(b) pentanuclear cluster.
Table 1
31P chemical shifts (l)
Cluster
lP (ppm)
[Pd2Ni(m3-Se)2(dppe)3][BPh4]2 (1)
[Pd2Pt(m3-Se)2(dppe)3][BPh4]2 (2)
55.5 (PꢀNi)
48.5 (PꢀPd)
49.4 (PꢀPd)
42.4 (PꢀPt)
42.0
1
3
stants are estimated as J(PtꢀP)=3158 Hz, J(PtꢀP)=
4
2
−32 Hz, J(PꢀP)=6 Hz and J(PꢀP)=3 Hz. Clusters
3 and 4 show one singlet at l=42.0 and l=44.4,
respectively. Cluster 5 gives one resonance at l=40.7
with two satellites [4J(PtꢀP)=37 Hz]. All phosphorus
atoms of clusters 3–5 are magnetically equivalent in
solution. The 31P chemical shift for the metals follows
the order M%=Pd (4)\Ni (3)\Pt (5) for the
[M%{Pd2(m3-Se)2(dppe)2}2][BPh4]2 clusters.
[Pd4Ni(m3-Se)4(dppe)4][BPh4]2 (3)
[Pd5(m3-Se)4(dppe)4][BPh4]2 (4)
[Pd4Pt(m3-Se)4(dppe)4][BPh4]2 (5)
44.4
40.7
3. Results and discussion
Numerical data from cyclic voltammograms of clus-
ters 1–5 are summarized in Table 2. Fig. 2 gives cyclic
voltammograms of 1, 2 and 5. Cluster 1 shows two
chemically reversible couples, while 2 exhibits one
chemically reversible couple at 255 K. The ipc/ipa ratio
of each couple for both clusters is close to unity at the
Two trinuclear clusters have been synthesized by a
reaction of the metalloligand [Pd2(m-Se)2(dppe)2] with
M(dppe)2+ (M=Ni or Pt) and three pentanuclear
clusters have been obtained by a reaction between
[Pd2(m-Se)2(dppe)2] and M%2+ (M%=Ni, Pd or Pt) (Fig.
1). The clusters are soluble in MeCN and DMF.
Table 2
Peak potential values a for the reduction of clusters 1–5 in DMF solution (supporting electrolyte TBAP 0.1 mol dm−3; scan rate 50 mV s−1
)
Cluster
Epc (V)
Epa (V)
[Pd2Ni(m3-Se)2(dppe)3][BPh4]2 (1)
[Pd2Pt(m3-Se)2(dppe)3][BPh4]2 (2)
[Pd4Ni(m3-Se)4(dppe)4][BPh4]2 (3)
[Pd5(m3-Se)4(dppe)4][BPh4]2 (4)
[Pd4Pt(m3-Se)4(dppe)4][BPh4]2 (5)
−1.65
(−1.68)
−1.88
(−1.87)
−1.98
(−1.99)
−2.01
(−2.04)
−2.00
−2.05
(−2.04)
−1.60
(−1.62)
−1.83
(−1.83)
−1.00
(−1.05)
−1.03
(−1.01)
−1.03
−1.98
(−1.98)
−2.32
(−2.33)
−2.18
(−2.21)
−2.17
−2.46
(−2.45)
−2.39
(−2.40)
−2.37
(−1.94)
−1.95
(−1.98)
−1.95
(−2.26)
−2.11
(−2.15)
−2.10
(−2.40)
−2.32
(−2.31)
−2.28
(−2.02)
(−2.19)
(−2.36)
(−1.05)
(−1.98)
(−2.13)
(−2.28)
a Values at 293 K; those in parentheses refer to 255 K.

170
K. Matsumoto et al. / Inorganica Chimica Acta 321 (2001) 167–170
255 K. The small anodic peaks at −1.05 and −1.01 V
for 3 and 4 are not exhibited after cathodic scanning to
−2.12 V at 255 K. We, therefore, concluded that Pd2+
of the metalloligand [Pd2(m-Se)2(dppe)2] is reduced, al-
though the reduction potential of each cluster is some-
what lower than that for [Pd3(m3-Se)2(dppe)3][BPh4]2
[10].
References
[1] (a) I.G. Dance, Polyhedron 5 (1986) 1037;
(b) P.J. Blower, J.R. Dilworth, Coord. Chem. Rev. 76 (1987)
121;
(c) G. Henkel, B. Krebs, Angew. Chem., Int. Ed. Engl. 30 (1991)
769.
[2] S.A. Sunshine, D.A. Keszler, J.A. Ibers, Acc. Chem. Res. 20
(1987) 395.
[3] R.R. Chianelli, T.A. Pecoraro, T.R. Halbert, W.H. Pan, E.I.
Stiefel, J. Catal. 86 (1986) 226.
[4] (a) M. Bochmann, K. Webb, M. Harman, M.B. Hursthouse,
Angew. Chem., Int. Ed. Engl. 29 (1990) 638 (and references
therein);
Fig. 2. Cyclic voltammograms of 5×10−4 mol dm−3 clusters (a) 1,
(b) 2 and (c) 5 in a DMF solution containing 0.1 mol dm−3 TBAP at
a scan rate of 50 mV s−1 at 255 K. A small oxidation peak at −1.05
V is not shown for 5 in the figure. The peak is not exhibited after
cathodic scanning to −2.27 V, but is observed only after cathodic
scanning to −2.5 V.
(b) D.R. Cary, G.E. Ball, J. Arnold, J. Am. Chem. Soc. 117
(1995) 3492 (and references therein);
(c) C.P. Gerlach, V. Christou, J. Arnold, Inorg. Chem. 35 (1996)
2758 (and references therein);
(d) A.L. Seligson, J. Arnold, J. Am. Chem. Soc. 115 (1993) 8214
(and references therein).
scan rate of 50 mV s−1 and a similar ratio is obtained
at the scan rate of 100, 200 and 500 mV s−1. Cluster 1,
[NiPd2(m3-Se)2(dppe)3]2+, exhibits two couples at −
1.65 and −2.01 V at 255 K. The controlled potential
coulometry for 1 at 1.80 V indicates that each process is
a one-electron transfer. Because the reduction poten-
tials of 1 are close to those observed for [Ni3(m3-
Se)2(dppe)3][BPh4]2 (−1.64 and −1.90 V) [10], cluster
1 is considered to be reduced to [Ni0Pd2(m3-Se)2(dppe)3]0
after cathodic scanning to −2.20 V: the process con-
tains the two-step reduction of Ni2+. Accordingly, it is
possible that the reduction of [Ni3(m3-Se)2(dppe)3]-
[BPh4]2 previously reported produces [Ni0Ni2II(m3-
Se)2(dppe)3]0 although we suggested that its reduction
product may contain [NiINiINiII(m3-Se)2(dppe)3]0 [9].
Cluster 2, [Pd2Pt(m3-Se)2(dppe)3]2+, shows one couple
at −1.85 V at 255 K which is also very close to the
[5] J. Arnold, Prog. Inorg. Chem. 43 (1995) 353.
[6] C. Nishitani, T. Shizuka, K. Matsumoto, S. Okeya, H. Kimoto,
Inorg. Chem. Commun. 1 (1998) 325.
[7] S.W.A. Fong, T.S.A. Hor, J. Chem. Soc., Dalton Trans. (1999)
639.
[8] The X-ray structure of the pentanuclear cluster 3 was determined
and the square planar coordination around the central Ni atom
was confirmed. The NiꢀSe bond lengths range from 2.347(2) to
,
2.363(2) A. Crystal data: C152H136B2P8Pd4NiSe4·2H2O, FW=
(
3068.3, triclinic, space group P1, a=20.1715(3), b=24.0987(7),
,
c=19.0765(3) A, h=99.359(3), i=105.407(2), k=92.133(2)°,
V=8789.4(3) A , Dc=1.16 g cm−3, v(Mo Ka)=14.49 cm−1
,
3
,
F(000)=3092. The R (Rw) factor was 0.086 (0.141) for 22 073
[I\2|(I)] observed reflections with 950 parameters.
[9] K. Matsumoto, K. Takahashi, M. Ikuzawa, H. Kimoto, S.
Okeya, Inorg. Chim. Acta 281 (1998) 174.
[10] K. Matsumoto, M. Ikuzawa, M. Kamikubo, S. Ooi, Inorg.
Chim. Acta 217 (1994) 129.
[11] The cyclic voltammogram of [Pt2Pd(m3-Te)2(dppe)3][BPh4]2 con-
taining tellurido bridges gives one chemically reversible couple at
−1.76 V at 255 K. The process involves a two-electron transfer.
As the reduction potential (−1.76 V) is the same as that for
[Pd3(m3-Te)2(dppe)3][BPh4]2 (−1.76 V) [10], the reduction
product of [Pt2Pd(m3-Te)2(dppe)3][BPh4]2 is possibly [Pt2Pd0(m3-
Te)2(dppe)3]0. 31P{1H} NMR spectrum shows two signals at
l=43.3 (PꢀPt) and at l=44.5 (PꢀPd) with relative intensities in
the ratio 2:1.
reduction potential of −1.84
V
for [Pd3(m3-
Se)2(dppe)3][BPh4]2 [10]. The process involves a two-
electron reduction. In this case the reduction product of
2 may also contain [Pd0PdIIPtII(m3-Se)2(dppe)3]0 [11].
The cyclic voltammograms of the pentanuclear clusters
3–5 are similar to each other and have three couples at
.