A new access to palladium-phosphine chemistry. Formation of polynuclear palladium compounds via the oxidation of ligands in simple palladium(ii) complexes

Article abstract of DOI:10.1039/a908788e

The reactions of [Pd(dppp)(edt)] 1 or [Pd(dppp)(pdt)] 2 (edt^2- = ethane-1, 2-dithiolate, pdt^2- = propane- 1, 3-dithiolate, dppp = l, 3-bis(diphenylphosphino)propane) with oxygen or elemental Se under different reaction conditions gave rise to a series of polynuclear palladium complexes. The oxidation of 1 by oxygen in alkaline DMF solution yielded a dinuclear complex with sulfinato ligand, [Pd₂(O₂SCH₂CH₂SO ₂)(edt)(dppp)] 3, while that of 2 afforded a hexanuclear complex, [Pd₆(pdt)₆]4. The molecular structure of 3 consists of two fragments [Pd(O₂SCH₂CH₂SO₂)] and [Pd(dppp)]²⁺, which are linked by an edt^2- bridging ligand. The structure of 4 is made up of [Pd(pdt)] nits forming a cyclic neutral complex, of which the Pd₆S₁₂ core possesses pseudo D_6d symmetry and six Pd atoms form a nearly regular six-membered ring with Pd ... Pd distances ranging from 3.050 to 3.090 A. The treatment of 2 with elemental Se in the ratios 1:1 and 1:1 generated [Pd₂(dppp)₂(pdt)]Cl₂ 5 and [Pd₃(dppp)₂(pdt)₂]Cl₂ 6, respectively. The molecular structure of 5 and 6 can be considered as two fragments [Pd(dppp)]²⁺ linked by pdt^2- and [Pd(pdt)₂]^2-, respectively. The reaction of 1 with 0.5 equivalent Se led to formation of [Pd₂(dppp)₂(edt)]Cl₂ 7. The molecular structure of 7 is quite similar to that of 5. All palladium atoms in the complexes are four-co-ordinated with distorted square-planar geometry. The complexes 1, 3-7 have been characterized by NMR, IR and electronic spectra. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a908788e

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A new access to palladium–phosphine chemistry. Formation of
polynuclear palladium compounds via the oxidation of ligands in
simple palladium(II) complexes
Weiping Su, Rong Cao,* Maochun Hong,* Daxu Wu and Jiaxi Lu
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China.
E-mail: hmc@ms.fjirsm.ac.cn
Received 4th November 1999, Accepted 2nd March 2000
Published on the Web 10th April 2000
The reactions of [Pd(dppp)(edt)] 1 or [Pd(dppp)(pdt)] 2 (edt2Ϫ = ethane-1,2-dithiolate, pdt2Ϫ = propane-1,3-dithiolate,
dppp = 1,3-bis(diphenylphosphino)propane) with oxygen or elemental Se under different reaction conditions gave
rise to a series of polynuclear palladium complexes. The oxidation of 1 by oxygen in alkaline DMF solution yielded
a dinuclear complex with sulfinato ligand, [Pd2(O2SCH2CH2SO2)(edt)(dppp)] 3, while that of 2 afforded a
hexanuclear complex, [Pd6(pdt)6] 4. The molecular structure of 3 consists of two fragments [Pd(O2SCH2CH2SO2)]
and [Pd(dppp)]2ϩ, which are linked by an edt2Ϫ bridging ligand. The structure of 4 is made up of [Pd(pdt)] units
forming a cyclic neutral complex, of which the Pd6S12 core possesses pseudo D6d symmetry and six Pd atoms form
a nearly regular six-membered ring with Pd ؒ ؒ ؒ Pd distances ranging from 3.050 to 3.090 Å. The treatment of 2 with
elemental Se in the ratios 2:1 and 1:1 generated [Pd2(dppp)2(pdt)]Cl2 5 and [Pd3(dppp)2(pdt)2]Cl2 6, respectively. The
molecular structure of 5 and 6 can be considered as two fragments [Pd(dppp)]2ϩ linked by pdt2Ϫ and [Pd(pdt)2]2Ϫ
respectively. The reaction of 1 with 0.5 equivalent Se led to formation of [Pd2(dppp)2(edt)]Cl2 7. The molecular
,
structure of 7 is quite similar to that of 5. All palladium atoms in the complexes are four-co-ordinated with distorted
square-planar geometry. The complexes 1, 3–7 have been characterized by NMR, IR and electronic spectra.
formed via the reaction of [Pd2(µ-dppm)2Cl2] with selenium
Introduction
powder in the presence of NaSCH2Ph in DMF,12a eqn. (1). The
Palladium complexes containing phosphine ligands attract
considerable attention owing to their numerous applications in
2[Pd2(µ-dppm)2Cl2] ϩ Se ϩ 2NaSCH2Ph → [Pd4(µ3-Se)2-
organic synthesis and catalysis1–5 and their rich co-ordination
(µ-SCH2Ph)2(µ-dppm)2Cl2] ϩ 2dppmSe ϩ 2NaCl (1)
chemistry.5–11 Owing to the high affinity of palladium for sulfur,
the palladium complexes with phosphine ligands readily react
features of this complex are its novel structure arising from the
with organosulfur compounds3,5,8,9 to give very stable sulfide
asymmetrically co-ordination by phosphorus, selenium, sulfur
and thiolate complexes, which are probably responsible for the
and chlorine atoms and its formation involving considerable
poisoning of palladium catalysts by organosulfur impurities in
rearrangement of the initial components. The notable structure
feedstocks.8e Thus, the studies on the palladium complexes with
as well as the interesting synthetic reaction prompted us to
both phosphine ligands and thiolate ligands are significant
employ other diphosphine ligands such as dppp for studying
in understanding the reaction mechanisms of the poisoning
this kind of reaction.
of palladium catalysts by organosulfur impurities and recover-
In this paper we report the condensation reactions of mono-
ing catalytic activity of poisoned palladium catalysts. How-
nuclear palladium() complexes with mixed diphosphine and
ever, the studies on palladium–phosphine complexes, especially
those with diphosphine ligands, have mainly been focused
thiolate ligands, [Pd(dppp)(SRS)] (SRS2Ϫ = edt2Ϫ 1 or propane-
1,3-dithiolate 2, through oxidation of the ligands with oxygen
or elemental Se, and the crystal structures of a series of poly-
nuclear palladium complexes isolated from the condensation
reactions along with their spectroscopic properties.
on the complexes of palladium in lower oxidation state of 0
and ϩ1,5–7,9 such as [Pd2(dppm)2]2ϩ, [Pd2(dppm)3],7f [Pd3-
(dppm)3(µ3-S)H]PF6,7g,h [Pd4(dppm)4(H)2]X2,7e and {[Pd(µ-
6c
SC6F5)(µ-dppm)Pd](µ-SC6F5)}4
(dppm = bis(diphenylphos-
phino)methane). The palladium() complexes blending both
phosphine and thiolate ligands have received attention only in
recent years.10
Results and discussion
Synthesis
Reactions11 performed in our laboratory revealed that the
oxidation of [Ni(edt)(PR3)2] (edt = ethane-1,2-dithiolate) by
oxygen results in the cleavage of the C–S bond of edt2Ϫ and
the condensation of two edt2Ϫ groups into tpdt (tpdt = 3-thia-
pentane-1,5-dithiolate), or the condensation of mononuclear
complexes into dinuclear complexes via oxidation of PR3. As a
part of the systematic investigation of the chemical properties
and stereochemistry of transition metal complexes with mixed
thiolate and phosphine ligands, more recently we reported
a tetranuclear complex [Pd4(µ3-Se)2(µ-SCH2Ph)2(µ-dppm)2Cl2]
The reactions of [Pd(dppp)(SRS)] (SRS = pdt2Ϫ or edt2Ϫ) with
oxygen or elemental Se have been carried out under different
conditions. As shown in Scheme 1, these reactions depended on
the conditions and yielded a series of di-, tri- and hexa-nuclear
palladium complexes. The oxidation of [Pd(dppp)(edt)] 1 by O2
in alkaline solution gave rise to a binuclear complex containing
sulfinato ligand, [Pd2(O2SCH2CH2SO2)(edt)(dppp)] 3. The oxid-
ation of [Pd(dppp)(pdt)] 2 by O2 in neutral solution led to the
formation of a hexanuclear complex [Pd6(pdt)6] 4. These results
DOI: 10.1039/a908788e
J. Chem. Soc., Dalton Trans., 2000, 1527–1532
This journal is © The Royal Society of Chemistry 2000
1527

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Scheme 1
indicate that the products of the reactions [Pd(dppp)(SRS)]/O2
depend on the basicity of the media, although we failed to
characterize the reactions of [Pd(dppp)(edt)] with O2 in neutral
solution and [Pd(dppp)(pdt)] with O2 in alkaline solution due
to the poor quality of the crystals obtained. Our results agree
well with those for nickel thiolate complexes in the literature, for
example the reaction of [Ni(S2C2Ph2)2]2Ϫ with oxygen in neutral
solution gave a complex [Ni(S2C2Ph2)2], however in alkaline
solution, the system generated an irreversible oxidation product
Fig. 1 Structure of complex 1.
The reaction of [Pd(dppp)(pdt)] or [Pd(dppp)(edt)] with
elemental Se may first lead to detachment of ligands from
complexes due to oxidation to form fragments such as solv-
ated [Pd(dppp)]2ϩ species. These species undergo further dis-
placement of ligated solvent and are linked by bridging ligands
(edt2Ϫ or pdt2Ϫ) in other species to form the resultant products.
As shown in Scheme 2, the reaction of [Pd(SRS)(dppp)]
(SRS2Ϫ = edt2Ϫ or pdt2Ϫ) with 0.25 equivalent elemental Se
may primarily produce the solvated [Pd(dppp)(sol)2]2ϩ species
and (SRS)2, then the solvated species combines with initial
[Pd(SRS)(dppp)] to give [Pd2(SRS)(dppp)2]2ϩ. When the amount
of Se is raised to 1 equivalent, dppp may be further oxidized
and [Pd2(SRS)(dppp)2]2ϩ is converted into [(dppp)Pd(SRS)Pd-
(sol)2]2ϩ (sol = solvent) species and dpppSe2; the combination
of [(dppp)Pd(SRS)Pd(sol)2]2ϩ with [Pd(dppp)(SRS)] results in
[Ni(O2S2C2Ph)2]2Ϫ 13,14
.
The reaction of [Pd(dppp)(pdt)] 2 and [Pd(dppp)(edt)] 1 with
0.25 equivalent of elemental Se in the presence of Me4NCl
afforded two analogous products, [Pd2(dppp)2(pdt)]Cl2 (5) and
[Pd2(dppp)2(edt)]Cl2 (7), respectively. However, the reaction
of 2 with 1 equivalent elemental Se gave a trinuclear complex
[Pd3(dppp)2(pdt)2]Cl2 6. Complex 6 can also be obtained from
the stoichiometric reaction of 5 and Se followed by the addition
of 1 equivalent of 2 in DMF. Thus, the amount of selenium
powder used controlled the formation of products in reactions
with [Pd(dppp)(SRS)]. The results are somewhat similar to
those of the oxidation reactions of simple metal thiolate
complexes by elemental S or Se,15–17 which give polynuclear
complexes through the oxidation and release of thiolate ligands.
The studies on the formation mechanisms of polynuclear
nickel complexes with chelating thiolate ligands17–19 suggest
that solvated nickel thiolate fragments are basic intermediates.
Accordingly, as illustrated in Scheme 2, possible routes to our
[Pd3(dppp)2(SRS)2]2ϩ
.
It should be mentioned that some side products isolated from
the reaction systems, such as dpppSe, dppp(O)2, and dppp(Se)2
have also been characterized structurally and support to some
extent our speculation in Scheme 2.
Description of the structures
The structure of complex 1, as shown in Fig. 1, is a mono-
nuclear neutral molecule. The palladium atom is co-ordinated
by two phosphorus atoms from dppp ligand and two sulfur
atoms from edt2Ϫ ligand in a slightly distorted square-planar
geometry. The Pd atom is 0.06 Å above the least squares plane
S(1)S(2)P(1)P(2). The dppp ligand chelates to Pd forming a six-
memebred ring [P(1)C(1)C(2)C(3)P(2)Pd] in a chair form, while
ligand edt2Ϫ chelates to Pd to give a five-membered ring
[S(1)C(01)C(02)S(2)Pd] in a twist conformation. Two bite
angles P(1)–Pd–P(2) and S(1)–Pd–S(2) are 91.60 and 89.22Њ,
respectively (Table 1). The latter is 5Њ smaller than that of
[Pd(dppp)(pdt)].12c The Pd–P and Pd–S bond lengths are
2.280(1) and 2.315(1) Å, respectively, which are comparable to
those of palladium thiolate complexes with phosphine ligands
reported previously.20,21
The molecular structure of complex 3 is shown in Fig. 2. The
structure consists of two fragments [Pd(O2SCH2CH2SO2)] and
[Pd(dppp)]2ϩ, which are bridged by an edt2Ϫ ligand. The struc-
ture may be also viewed as two square-planar co-ordination
units PdP2S2 and PdS4 sharing a common edge. Thus, two kinds
of environment of palladium atoms are present: Pd(1) is co-
ordinated by four sulfur atoms from edt2Ϫ and sulfinato ligands,
being 0.11 Å above the least squares plane S(1)S(2)S(3)S(4),
while Pd(2) is surrounded by two phosphorus and two sulfur
atoms in a distorted square-planar arrangement being 0.10 Å
out of the least squares plane. The molecule is folded along
the S ؒ ؒ ؒ S vector of the two bridging-sulfur atoms with the
dihedral angle between the mean planes S(1)S(2)S(3)S(4) and
S(1)S(2)P(1)P(2) being 108.5Њ. The Sb–Pd–Sb angles with an
average value of 79.4Њ are smaller than St–Pd–St angles (average
Scheme 2
palladium complexes have been deduced to understand their
formation. For the formation of 3, first 1 is oxidized by O2 in
alkaline DMF solution to give solvated [Pd(O2SCH2CH2SO2)]
species and phosphate. Then, the condensation of solvated
[Pd(O2SCH2CH2SO2)] species and a [Pd(dppp)(edt)] molecule
generates 3. The formation of [Pd6(pdt)6] probably proceeds
through a complicated multistep mechanism, in which the oxid-
ation of [Pd(dppp)(pdt)] by O2 produces solvated [Pd(pdt)]
species and phosphate in the initial reaction step. In the
subsequent steps these species combine to yield [Pd6(pdt)6].
1528
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Table 1 Bond lengths (Å) and angles (Њ) for complexes 1 and 3–6
Compound
1
Pd–P(2)
Pd–P(1)
Pd–S(2)
Pd–S(1)
2.2797(9)
P(2)–Pd–P(1)
91.60(3)
88.84(4)
178.12(4)
173.48(4)
90.14(4)
89.22(4)
2.2810(10) P(2)–Pd–S(2)
2.3096(11) P(1)–Pd–S(2)
2.3184(11) P(2)–Pd–S(1)
P(1)–Pd–S(1)
S(2)–Pd–S(1)
3
Pd(1)–P(2)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–S(2)
Pd(1) ؒ ؒ ؒ Pd(2)
Pd(2)–S(4)
Pd(2)–S(3)
Pd(2)–S(1)
Pd(2)–S(2)
S(3)–O(2)
S(3)–O(1)
S(4)–O(4)
S(4)–O(3)
S(4)–C(4)
2.285(2)
2.285(2)
2.374(2)
2.381(2)
3.0297(9)
2.266(2)
2.274(2)
2.361(2)
2.373(2)
1.451(6)
1.445(6)
1.458(6)
1.464(6)
1.826(8)
P(2)–Pd(1)–P(1)
P(2)–Pd(1)–S(1)
P(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
S(4)–Pd(2)–S(3)
S(3)–Pd(2)–S(1)
S(4)–Pd(2)–S(2)
S(1)–Pd(2)–S(2)
Pd(2)–S(1)–Pd(1)
Pd(2)–S(2)–Pd(1)
O(2)–S(3)–O(1)
O(2)–S(3)–C(3)
O(1)–S(3)–C(3)
O(4)–S(4)–O(3)
O(4)–S(4)–C(4)
O(3)–S(4)–C(4)
89.89(7)
93.93(7)
96.92(7)
79.21(7)
87.57(7)
96.35(7)
96.41(7)
79.63(6)
79.56(6)
79.18(6)
114.3(4)
105.3(4)
105.1(4)
114.7(4)
104.9(4)
105.0(4)
Fig. 3 Structure of complex 5.
87.6Њ). Grouping the Pd–S bonds, i.e. Pd–St and Pd–Sb, gives
the average bond lengths 2.373(2) and 2.270(2) Å, respect-
ively. The Pd–St bond length of 2.272(2) Å is shorter than those
in most of the palladium() thiolate complexes reported previ-
ously10c,22 and those in 1 and 2; this may be illustrated by the
π-back bond, in which the electron density is shifted from the
higher density d orbitals of the palladium atom to the empty
π-acceptor orbitals of the sulfur atoms in sulfinato ligands due
to the increased Lewis acidity of the sulfur atoms caused by the
electronegative oxygen atoms, resulting in the strengthened Pd–
St bond. The fact that the Pd–Sb bond length is 0.05 Å longer
than those in complexes 1 and 2 results from trans influences
exerted by the terminal thiolate and phosphine ligands.10a The
average S–O bond length of the sulfinato ligands is 1.456(6) Å
4
Pd(1)–S(1)
Pd(1)–S(6)
Pd(1)–S(2)
Pd(1)–S(3)
Pd(1) ؒ ؒ ؒ Pd(3A)
Pd(1) ؒ ؒ ؒ Pd(2)
Pd(2)–S(1)
Pd(2)–S(5)
Pd(2)–S(2)
Pd(2)–S(4)
Pd(2) ؒ ؒ ؒ Pd(3)
Pd(3)–S(4)
Pd(3)–S(3A)
Pd(3)–S(6A)
Pd(3)–S(5)
2.332(4)
2.332(4)
2.331(4)
2.340(4)
3.052(2)
3.152(2)
2.327(3)
2.327(4)
2.329(4)
2.338(3)
Pd(3)–Pd(1)–Pd(2)
Pd(3)–Pd(2)–Pd(1)
Pd(1)–Pd(3)–Pd(2)
S(1)–Pd(1)–S(2)
S(6)–Pd(1)–S(2)
S(1)–Pd(1)–S(3)
S(6)–Pd(1)–S(3)
S(1)–Pd(2)–S(5)
S(1)–Pd(2)–S(2)
S(5)–Pd(2)–S(4)
119.42(4)
123.33(4)
117.25(4)
81.98(13)
98.73(13)
99.33(13)
79.83(13)
98.18(13)
82.11(12)
79.99(13)
99.73(13)
79.99(13)
85.14(11)
85.00(12)
83.40(12)
83.45(12)
3.0902(14) S(2)–Pd(2)–S(4)
2.307(4)
2.311(3)
2.315(4)
2.316(3)
S(4)–Pd(3)–S(5)
Pd(2)–S(1)–Pd(1)
Pd(2)–S(2)–Pd(1)
Pd(3)–S(4)–Pd(2)
and corresponds to that in free S᎐O (1.48 Å),22 suggesting that
᎐
the S–O bonds in 3 adopt typical S᎐O double bond characters,
᎐
Pd(3) ؒ ؒ ؒ Pd(1A)
3.0520(20) Pd(3)–S(5)–Pd(2)
consistent with the IR result (ν(S᎐O) 1035.6, 1139.7 cmϪ1).
The cation structure of comp᎐lex 5 is depicted in Fig. 3. The
[Pd2(dppp)2(pdt)]2ϩ cations occupy a crystallographic twofold
axis. The complex may be viewed as two [Pd(dppp)]2ϩ frag-
ments sharing a common pdt2Ϫ ligand. It may also be con-
sidered as a [Pd(dppp)(pdt)] unit to which the [Pd(dppp)]2ϩ is
bonded in a cis fashion. As a result, each of the two sulfur
atoms of pdt2Ϫ bridges two Pd atoms, and the Pd2S2 moiety is
folded along its S ؒ ؒ ؒ S vector, different from those reported
in related complexes [(dppe)M(µ-SC5H9NMe)2M(dppe)]10c
(M = Pd or Pt) in which the central M2S2 ring is exactly planar.
The Pd–P bond lengths of 5 (2.289 Å) are similar to those of
other Pd-dppp complexes in this paper. The average Pd–S bond
length (2.35 Å) is approximately 0.04 Å longer than those in 1
and 2 owing to the existence of steric hindrance.
5
6
Pd–P(2)
Pd–P(1)
Pd–S
2.2889(11) P(2)–Pd–P(1)
2.2897(12) P(2)–Pd–S
2.3741(12) P(1)–Pd–S
S–Pd–S
90.47(4)
170.60(4)
92.61(4)
81.87(4)
86.23(4)
Pd–S–Pd
Pd(1)–P(2)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(1)–S(2)
Pd(1) ؒ ؒ ؒ Pd(2)
Pd(2)–S(1)
Pd(2)–S(2)
2.277(3)
2.288(3)
2.361(3)
2.370(3)
3.0932(8)
2.326(2)
2.320(2)
P(2)–Pd(1)–P(1)
P(2)–Pd(1)–S(1)
P(1)–Pd(1)–S(1)
P(2)–Pd(1)–S(2)
P(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
Pd(2)–S(1)–Pd(1)
Pd(2)–S(2)–Pd(1)
91.98(11)
92.13(10)
171.13(10)
172.85(10)
92.15(10)
83.00(10)
82.59(8)
82.31(8)
The cation [Pd3(dppp)2(pdt)2]2ϩ complex 6 is depicted in Fig.
4. The structure possesses a crystallographic inversion center.
As a consequence, the three metal atoms are strictly linear and
the structure may be viewed as two [Pd(dppp)]2ϩ sharing a
[Pd(pdt)2]2Ϫ subunit. Alternatively, it may be viewed as a central
palladium chelated by two identical [Pd(dppp)(pdt)] fragments.
The average Pd–S bond length within these fragments is 2.367
Å, and is 0.04 Å longer than that of the central Pd (2.326 Å),
which may be explained by trans influences exerted by the
phosphine ligands, as in other complexes in this paper. The
planarity of the central PdS4 unit is required by symmetry and
only a small distortion from planarity is observed for the two
PdP2S2 entities. The two PdP2S2 and one PdS4 units are con-
densed through opposite edges in a trans fashion to form the
Pd3P4S4 core of 6. The Pd ؒ ؒ ؒ Pd distance is 3.0935(8) Å, indi-
cating no direct metal–metal interaction.
The molecular structure of complex 4 is shown in Fig. 5. The
molecule possesses a crystallographic twofold axis. The Pd6
Fig. 2 Structure of complex 3.
J. Chem. Soc., Dalton Trans., 2000, 1527–1532
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Table 2 UV-Vis Spectral data and 31P NMR chemical shifts (CDCl3)
of complexes 1, 3, 5–7
Absorption peak
(λmax/nm)
Chemical
shifts δ
Complex
1 [Pd(dppp)(edt)]
235, 275
3.08
5.84
7.15
6.91
3 [Pd(O2SCH2CH2SO2)(edt)(dppp)]
5 [Pd2(dppp)2(pdt)]Cl2
6 [Pd3(dppp)2(pdt)2]Cl2
7 [Pd2(dppp)2(edt)]Cl2
dppp25
235, 275, 320, 400
255, 280, 340
255, 285, 310, 380
240, 285, 325
Ϫ16.7
here. In the case of the complexes with edt2Ϫ ligands, the spec-
trum of 7 shows a strong band at λmax 325 nm, while that of 3
exhibits a strong band at 320 nm and a shoulder at 400 nm.
An obvious difference was observed when one ligand changed
from dppp to sulfinate. In the case of the complexes with pdt2Ϫ
ligands, the electronic spectrum of 5 reveals an absorption peak
at 340 nm. The spectrum of 6 is characterized by two bands at
310 and 380 nm. The spectrum of 1 shows two peaks at 275 and
235 nm which appear in the electronic spectra of 3 and are
comparable to peaks at 240 and 285 nm for 7, but no peaks
in the region λ > 300 nm. Since the difference between the
co-ordination environment of palladium of 1 and those of 7
and 3 mainly comes from the coordination mode of the edt2Ϫ
ligand, it is likely that the absorptions at 325 nm for 7, 320 nm
for 3, 340 nm for 5, 310 and 380 nm for 6 arise from sulfur-to-
palladium LMCT transition. For complex 6 the two bands at
380 and 310 nm may belong to the absorption of 6 and another
complex from dissociation of 6 in CH2Cl2 The shoulder at 400
nm in the electronic spectrum of 3 should originate from sulfur-
to-palladium LMCT transition in the PdS4 moiety.
Fig. 4 Cation structure of complex 6.
31P NMR spectra
Table 2 includes the 31P NMR data of all the complexes
described in this paper and the related free diphosphine except
for 7 whose spectrum could not be determined due to poor
solubility. The spectra of 1–3, 5 and 6 show a single resonance
peak in the range δ 7.15–3.08, indicating that their configur-
ations in solution are consistent with their solid-state structures.
The chemical shifts of these compounds increase as the ratio
of Pd2ϩ :edt2Ϫ or pdt2Ϫ increases, suggesting that their entire
core structures influence the electron density around the P
nucleus.
Fig. 5 Structure of complex 4.
core is similar to that of a cyclic complex with twelve mono-
thiolate ligands, [Pd6(SCH2CH2CH3)12.23 The molecular struc-
ture may be derived from a hypothetical [Pd(pdt)2]2Ϫ anion, to
which palladium() and [Pd(pdt)] fragments are linked in a cis
fashion, giving a [Pd3(pdt)3] subunit. Two [Pd3(pdt)3] subunits
connect head to tail in a cis fashion by sharing two common
pdt2Ϫ ligands to form a cyclic hexanuclear structure [Pd6(pdt)6].
Each of the palladium atoms is surrounded by four sulfur
atoms in a slightly distorted square-planar arrangement, and
lies 0.11 Å above the corresponding S4 least squares planes. The
dihedral angles between PdS2 planes fall in the range 159.42–
165.03Њ. Of six pdt2Ϫ ligands, four act as both chelating and
bridging ligands bound to three Pd atoms and the other two as
bridges between two Pd atoms. There are three six-membered
rings in the Pd6S12 core unit, i.e. two sulfur rings and one
palladium ring, which form a sandwich in an antiprismatic
configuration. The Pd ؒ ؒ ؒ Pd and Pd–Sb distances vary in the
ranges 3.050–3.090 and 2.300–2.343 Å, respectively.
Conclusion
We have systematically investigated the condensation reactions
of mononuclear palladium() complexes [Pd(dppp)(edt)] and
[Pd(dppp)(pdt)] through the oxidation of the ligands by oxygen
and elemental Se under different reaction conditions. The
results obtained illustrate that the reactions depend on the
media or the molar ratio of the reactants. It is suggested that
the oxidation of ligands in simple complexes leads to detach-
ment of ligands to form solvated active fragments, and the
combination of the latter through the displacement of ligated
solvent molecules gives rise to di- and poly-nuclear complexes.
Braunstein et al.6a have reported that the reaction of [Pd2-
(dppm)2Cl2] with copper() ions gives a Pd4 cluster, which is
ascribed to dimerization of Pd2 active fragments resulting from
abstraction of ClϪ from [Pd2(dppm)2Cl2] by CuI. In spite of
the difference in synthetic method, the condensation reactions
presented by us correspond with Braunstein’s reaction in terms
of the assembly of active fragments. Therefore, in a sense, the
chemistry described here has presented insight into the form-
ation of polynuclear complexes in general. Our synthetic
method used has opened a new way to palladium–phosphine
chemistry.
Electronic spectra
Electronic spectral data of complexes 3, 5, 6, and 7 in CH2Cl2
are provided in Table 2. All spectra are dominated by strong
charge-transfer bands between 200 and 400 nm trailing out into
regions of higher wavelengths. The bands in the regions λ < 300
nm are due to the diphosphine ligands and will not be discussed
1530
J. Chem. Soc., Dalton Trans., 2000, 1527–1532

View Article Online
Table 3 Crystallographic data for complexes 1, 3–6
1
3
4
5
6
Formula
M
Crystal system
Space group
C29H30P2PdS2
611.0
Monoclinic
P21/n
C31H35O4.5P2Pd2S4
882.57
Orthorhombic
Aba2
C18H36OPd6S12
1293.7
Monoclinic
P21/c
C57H58Cl2P4Pd2S2
1214.73
Monoclinic
C2/c
C63H75Cl2NO3P4Pd3S4
1536.46
Monoclinic
C2/c
a/Å
b/Å
c/Å
10.354(2)
25.041(5)
11.332(2)
107.87(3)
2796.3(9)
4
15.905(3)
22.848(5)
18.904(4)
10.506(2)
16.789(3)
10.837(2)
99.83(3)
1883.4(6)
2
22.5683(7)
11.6585(4)
20.5798(5)
27.118(5)
14.987(3)
20.477(4)
β/Њ
V/Å3
6870(3)
8
1.420
298
5363.3(3)
4
1.005
298
6677
4
1.149
298
Z
µ/mmϪ1
0.944
298
3.484
298
T/K
Reflections measured
Unique reflections
Rint
R
Rw
5285
5010
0.022
0.036
13643
5790
0.054
0.047
0.080
8794
3269
0.054
0.064
10133
4613
0.045
0.054
0.070
11457
5962
0.086
0.071
0.149
0.100
0.151
[Pd6(pdt)6] 4. Solid complex 2 (1.25 g, 2 mmol) was dissolved
in DMF (15 ml). Oxygen was bubbled into the solution at
ambient temperature and then the temperature was raised to
90 ЊC whilst maintaining a slow stream of O2. After 10 h the
mixture was cooled to room temperature. During this period
reaction solution gradually turned dark red from orange. It
was filtered. After cooling the filtrate was mixed with MeOH
(20 ml), and then kept at 4 ЊC for ten days to give dark red cubic
crystals of 4ؒH2O, yield 0.11 g (26%). Calc. for C18H36OPd6S12:
C, 16.7; H, 2.96. Found: C, 16.3; H, 3.07%. IR (KBr): 2900w,
Experimental
Syntheses
All syntheses and manipulations were performed under a puri-
fied dinitrogen atmosphere using standard Schlenk techniques
except as noted otherwise. The solvents were degassed prior to
use. All common chemicals were of reagent grade. The solvents,
PdCl2 and elemental Se (amorphous red selenium) were pur-
chased from Shanghai Chemical Reagents Factory, the other
reagents from Aldrich chemical Co. The salts Na2edt and
Na2pdt were prepared from the reaction of dithiol and sodium
metal in absolute ethanol and precipitated by addition of
diethyl ether in small portions to the solution. The products
were collected by filtration, washed thoroughly with ether and
dried in vacuum. The complex [Pd(dppp)(pdt)]12c 2 was pre-
pared by the literature method. All elemental analyses were
carried out by the Elemental Analysis Laboratory in this
Institute.
1
1670s, 1261m, 1085w, 993w, 661w, 509w and 487w cmϪ1. H
NMR (CDCl3): δ 3.37 (m, 4H, SCH2) and 1.83 (m, 2H,
SCCH2).
[Pd2(dppp)2(pdt)]Cl2 5. To a solution of complex 2 (0.63 g,
1 mmol) and Me4NCl (0.11 g, 1 mmol) in CH3CN (20 ml) was
added elemental Se (0.02 g, 0.25 mmol). After stirring for 3 h
the yellow precipitate formed was collected by filtration and
washed with distilled water and ethanol, giving 0.11 g crystals
of 5 (20%) on recrystallization from CH2Cl2. Calc. for C57H58-
Cl2P4Pd2S2: C, 56.3; H, 4.81. Found: C, 55.4, H, 4.81%. IR
(KBr) 3068w, 3014w 2925w, 1434s, 1272w, 1103m, 977m, 756m,
[Pd(dppp)(edt)] 1. A mixture of PdCl2 (0.90 g, 5 mmol) and
dppp (2.10 g, 5 mmol) in MeCN (20 ml) was stirred for 1 h at
room temperature to yield a white precipitate. Upon addition
of Na2edt (0.70 g, 5 mmol) in EtOH (30 ml) the white precipi-
tate immediately dissolved and the reaction solution turned
orange-red. After stirring for 2 h, the solution was filtered
and the filtrate kept at 4 ЊC for 2 days to yield orange crystals,
which were collected by filtration, washed with water, ethanol
and finally diethyl ether, and dried in vacuum, affording 1.89 g
(62%). Calc. for C29H30P2PdS2: C, 57.0; H, 4.95. Found: C, 59.5;
H, 4.96%. IR (KBr): 3048w, 2883w, 1434s, 1099m, 744m, 700s,
1
709m, 692s, 513s and 493m cmϪ1. H NMR (CDCl3): δ 7.78–
7.19 (40H, PC6H5), 3.54, 3.32 (m, 4H, SCH2) 2.80, 2.35 (m, 8H,
PCH2), 1.94 (m, 2H, SCCH2) and 1.73 (m, 4H, PCCH2).
[Pd3(dppp)2(pdt)2]Cl2 6. To a solution of complex 2 (0.62 g,
1 mmol) in DMF (15 ml) were added elemental Se (0.08 g,
1 mmol) and Me4NCl (0.11 g, 1 mmol). After stirring for 2 h at
room temperature the solution was filtered. The final dark red
solution was mixed with 2-propanol (15 ml), and kept at 4 ЊC
for one week to give yellow crystals of 7ؒDMFؒ2H2O, yield
0.24 g (50%). Calc. for C63H75Cl2NO3P4Pd3S4: C, 49.24; H, 4.92.
Found: C, 51.4; H, 5.03%. IR (KBr): 3047w, 2900w, 1664s,
692s, 659m, 511s, 491m and 428w cmϪ1. H NMR (CDCl3):
δ 7.5–7.2 (20H, PC6H5), 2.93 (m, 4H, SCH2), 2.51 (m, 4H,
PCH2) and 1.63 (, 2H, PCCH2).
1
1
[Pd2(O2SCH2CH2SO2)(edt)(dppp)] 3. To a solution of com-
plex 1 (1.20 g, 2 mmol) in DMF (15 ml) was added solid
MeONa (0.04 g, 1 mmol) under vigorous stirring. Oxygen was
bubbled into the reaction mixture at ambient temperature and
then the temperature was raised to 90 ЊC when maintaining a
slow stream of O2. After 8 h the mixture was cooled to room
temperature, then 20 ml MeOH were added. The solution was
filtered and kept at 4 ЊC for one week to give yellow block crys-
tals of 3ؒ0.5H2O, yield 0.35 g (30%). Calc. for C31H35O4.5P2-
Pd4S4: C, 42.16; H, 4.00. Found: C, 43.77; N, 3.88%. IR (KBr):
3052w, 2915w, 1627m, 1434s, 1193s, 1064m, 1035s, 997m, 970m,
1434s, 1157w, 1101m, 703m, 511s and 487m cmϪ1. H NMR
(CDCl3): δ 8.02–7.13 (40H, PC6H5), 3.66, 3.47 (m, 8H, SCH2),
2.962, 2.889 (s, 6H, (CH3)2NCHO), 2.68, 2.66, 2.46, 2.40, 2.32
(s, 8H, OCH2), 1.87 (m, 4H, SCCH2) and 1.75 (m, 4H, PCCH2).
Complex 6 can also be prepared from the stoichiometric
reaction of 5 and Se followed by the addition of 1 equivalent
of 2 in DMF.
[Pd2(dppp)2(edt)]Cl2 7. The preparation was similar to that of
complex 5 described above except for the use of 1 as starting
material. Recrystallization from DMF/MeOH afforded 0.08 g
crystals of 7 (14%). Calc. for C28H28ClP2PdS: C, 56.0; H, 4.70.
Found: C, 57.5; H, 4.55%. IR (KBr): 3047w, 2987w, 1664w,
1434s, 1315w, 1151m, 1101s, 948w, 744m, 793s, 671m, 514s and
916m, 833w, 690s, 524w and 513s cmϪ1. H NMR (CDCl3):
δ 7.6–7.2 (20H, PC6H5), 3.59 (m, 4H, O2SCH2), 3.01, 2.96 (m,
4H, SCH2), 2.57, 2.56, 2.55 (s, 4H, PCH2) and 1.57 (m, 2H,
PCCH2).
1
497m cmϪ1
.
J. Chem. Soc., Dalton Trans., 2000, 1527–1532
1531

View Article Online
and H. Kurosawa, J. Am. Chem. Soc., 1998, 120, 4536; (c) J. Dupont,
Physical measurements
M. Pfeffer, M. A. Rotteveel, A. De Cian and J. Fischer,
Organometallics, 1989, 8, 1116; (d) A. L. Balch, J. R. Boehm,
H. Hope and M. M. Olmstead, J. Am. Chem. Soc., 1976, 98, 7431;
(e) I. Gautheron, J. Gagnon, T. Zhang, D. Rivard, D. Lucas,
Y. Mugnier and P. D. Harvey, Inorg. Chem., 1998, 37, 1112; ( f ) R. V.
Kiress and R. Eisenberg, Inorg. Chem., 1989, 28, 3372; (g) M. C.
Jennings, N. C. Payne and R. J. Puddephatt, J. Chem. Soc., Chem.
Commun., 1986, 1809; (h) M. C. Jennings, N. C. Payne and
R. J. Puddephatt, Inorg. Chem., 1987, 26, 3776; (i) M. T. Reetz,
E. Bohres, R. Goddard, M. C. Holthausen and W. Thiel, Chem.
Eur. J., 1999, 5, 2101.
Infrared spectra in the range 4000–400 cmϪ1 were recorded on
a Magna 750 IR spectrometer with the use of pressed KBr
pellets, electronic absorption spectra in CH2Cl2 solution on a
ShimadzuUV-3000spectrophotometerand1HNMRspectrafor
all compounds on a Varian Unity-500 spectrometer. Chemical
shifts are quoted in ppm relative to the signal of TMS. All
spectra were acquired at room temperature.
Crystallographic studies
8 (a) A. L. Balch, L. S. Benner and M. M. Olmstead, Inorg. Chem.,
1979, 18, 2996; (b) C. T. Hunt and A. L. Balch, Inorg. Chem., 1981,
20, 2267; (c) A. L. Balch, C. T. Hunt, C. L. Lee, M. M. Olmstead
and T. P. Farr, J. Am. Chem. Soc., 1981, 103, 3764; (d) M. Ebner,
H. Otto and H. Werner, Angew. Chem., Int. Ed. Engl., 1985, 24, 518;
(e) G. Ferguson, B. R. Lloyd, L. Manojloic´-Muir, K. W. Muir
and R. J. Puddephatt, Inorg. Chem., 1986, 25, 4190; ( f ) S. Okeya,
H. Kameda, H. Kawashima, H. Shimomura, T. Nishioka and
K. Isobe, Chem. Lett., 1995, 501.
9 M. J. H. Russel and C. F. J. Barnard, in Comprehensive Coordination
Chemistry, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty,
Pergamon Press Ltd., Oxford, 1987, vol. 5, p. 1103.
10 (a) D. L. Reger and J. E. Collins, Inorg. Chem., 1995, 34, 2473;
(b) S. P. Kaiwar, J. K. Hsu, L. M. Liable-Sands, A. L. Rheingold
and R. S. Pilato, Inorg. Chem., 1997, 36, 4234; (c) M. Capdevila,
W. Clegg, P. Gonzalez-Duarte, B. Harris, L. Mira, J. Sola and
I. C. Taylor, J. Chem. Soc., Chem. Commun., 1992, 2817; (d) K. A.
Van Houten, D. C. Heath, C. A. Barringer, A. L. Rheingold and
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For compounds 1, 3–7, cell dimension measurements and data
collections were performed on a Siemens smart CCD diffract-
ometer with graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å) at 23 1Њ. For the structure analyses, all calcu-
lations were performed on an HP/586 computer with the
SHELXL PC program.24 Crystallographic data are listed in
Table 3. In the case of 1, 3 and 4 all non-hydrogen atoms were
refined anisotropically. The C02 atom of edt2Ϫ for 1, β-carbon
atom of pdt2Ϫ ligand for 5, and the atoms in two DMF solvent
molecules for 6ؒDMF were treated for disorder in two positions
by refining the site occupancies. Owing to the poor structural
data, the R value of structure 7 is rather high. Crystal dimen-
sions 0.12 × 0.20 × 0.30 mm, C56H56Pd2Cl2P2S2, M = 1200.8,
monoclinic, space group C2/c (no. 15), a = 22.300(7), b =
11.649(4), c = 20.307(6) Å, β = 96.99(2)Њ, V = 3890(1) Å3, Z = 4,
isotropic refinement of all non-hydrogen atoms on Fo for
2366 observations (F ≥ 2.0σ(F)) and 173 variables, R(Rw) =
0.166(0.217). Considering its structure is similar to that of 5,
the detailed structure is not discussed in this paper.
11 R. Cao, M. Hong, F. Jiang, X. Xie and H. Liu, J. Chem. Soc.,
Dalton Trans., 1994, 3459.
12 (a) R. Cao, W. Su, M. Hong, W. Zhang, W. T. Wong and J. X. Lu,
Chem. Commun., 1998, 2083; (b) R. Cao, M. Hong, F. Jiang, X. Xie
and H. Liu, Polyhedron, 1996, 15, 2661; (c) W. Su, R. Cao, M. Hong,
Z. Zhou, F. Xie, H. Liu and T. Mak, Acta Crystallogr., Sect. C,
1996, 52, 2691; (d) W. Su, R. Cao, M. Hong, Z. Zhou, F. Xie, H. Liu
and T. Mak, Polyhedron, 1997, 14, 2531.
CCDC reference number 186/1882.
See http://www.rsc.org/suppdata/dt/a9/a908788e/ for crystal-
lographic files in .cif format.
13 G. N. Schrauzer, C. Zhang and R. Chadha, Inorg. Chem., 1990, 29,
4104.
14 T. Nicholson and J. Zubieta, Inorg. Chem., 1987, 26, 2094.
15 G. Christou and C. D. Garner, J. Chem. Soc., Dalton Trans., 1979,
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Trans., 1978, 1423; K. S. Hagen, J. G. Reynolds and R. H. Holm,
J. Am. Chem. Soc., 1981, 103, 4054.
16 I. G. Dance, A. Choy and M. L. Scudder, J. Am. Chem. Soc., 1984,
106, 6285.
17 R. J. Mereinik, Rev. Inorg. Chem., 1979, 1, 11.
18 B. S. Snyder, C. P. Rao and R. H. Holm, Aust. J. Chem., 1986, 39,
963.
19 W. Tremel, M. Kriege, B. Krebs and G. Henkel, Inorg. Chem., 1988,
27, 3886.
20 W. L. Steffen and G. J. Palenik, Inorg. Chem., 1976, 15, 2432.
21 K. Osakada, Y. Ozawa and A. Yamamoto, Bull. Chem. Soc. Jpn.,
1991, 64, 2002; R. H. Fenn and G. R. Segrott, J. Chem. Soc.,
Dalton Trans., 1972, 330; I. Hakanishi, S. Tanaka, K. Matsamoto
and S. Ooi, Acta Crystallogr., Sect. C, 1994, 50, 58.
22 F. X. Power and D. R. Lide, J. Chem. Phys., 1964, 41, 1413;
L. Markó, B. M. Monostory, T. Madach and H. Vahrenkamp,
Angew. Chem., Int. Ed. Engl., 1980, 19, 226; P. Lorenz,
J. Messlhäuser, W. Hiller and K. Haug, Angew. Chem., Int. Ed.
Engl., 1985, 24, 228; G. Besenyei, C. Lee, J. Gaulinski, S. J. Rettig,
B. R. James, D. A. Nelson and M. A. Lilga, Inorg. Chem., 1987, 26,
3622.
Acknowledgements
This work was supported by grants from the National Science
Foundation of China, the Natural Science Foundation of
Fujian Province and the Youth Fund of Chinese Academy of
Sciences.
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