Genuine examples of tetrahedral tetradentate sulfide ligand bridging four Pd atoms: Controlled formation of [(μ4-S){(μ2-X) Pd2(C∧N)2}2] (X = OH or Cl; HC∧N = p-C2H5OC6H4CH=NC6H 4-p-C2H5) complexes

Article abstract of DOI:10.1021/ic061367t

A smooth reaction of [(μ₃-S)(μ₃-OH)Pd ₃(C∧N)₃] (2) with [(μ₂-X) ₂Pd₂(C∧N)₂] (2:1; HC∧N = p-C ₂H₅OC₆H₄CH=NC₆H ₄-p-C₂H₅, X = OH, Cl) provides [(μ₄-S){(μ₂-OH)Pd₂(C∧N) ₂}₂] (3) and [(μ₄-S)(μ₂-Cl) (μ₂-OH)Pd₄(C∧N)₄] (4). Treatment of 3 with HCl (molar ratio 1:2) leads to the corresponding tetranuclear complex [(μ₄-S)(μ₂-Cl)₂Pd₄(C∧N) ₄] (5). The three complexes contain a (μ₄-S)Pd ₄ core. A density functional theory study of the bonds in 3 supports that the bonding of the S atom can be described in terms of four two-center two-electron S-Pd bonds, in contrast to most other (μ₄-S)M ₄ systems in the literature, where the presence of M-M bonds prevents a bond-localized description of the molecule. The X-ray structures of 2, 3, and 5 are reported.

Full text of DOI:10.1021/ic061367t

Inorg. Chem. 2007, 46, 2035−2040
Genuine Examples of Tetrahedral Tetradentate Sulfide Ligand Bridging
∧
Four Pd Atoms: Controlled Formation of [(
µ
4-S)
{(µ2-X)Pd2(C N)2} ]
2
∧
(X
)
OH or Cl; HC N
)
p-C2H5OC6H4CH
d
NC6H4-p-C2H5) Complexes
Rut Benavente,† Pablo Espinet,*,† Jose´ M. Mart´ın-Alvarez,† Jesu´s A. Miguel,*,† and Gabriel Aullo´n‡
Ä
Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Valladolid, E-47005 Valladolid, Spain,
and Departament de Qu´ımica Inorga`nica, UniVersitat de Barcelona, Diagonal 647, E-08028
Barcelona, Spain
Received July 21, 2006
A smooth reaction of [(
p-C2H5, X OH, Cl) provides [(
of 3 with HCl (molar ratio 1:2) leads to the corresponding tetranuclear complex [(
three complexes contain a ( 4-S)Pd4 core. A density functional theory study of the bonds in 3 supports that the
bonding of the S atom can be described in terms of four two-center two-electron S Pd bonds, in contrast to most
µ3-S)(µ
3-OH)Pd3(C∧N)3] (2) with [(
4-S)
2-OH)Pd2(C∧N)2
µ
}
2-X)2Pd2(C∧N)2] (2:1; HC∧N
2] (3) and [( 4-S)( 2-Cl)(
2-OH)Pd4(C∧N)4] (4). Treatment
4-S)(
2-Cl)2Pd4(C∧N)4] (5). The
) p-C2H5OC6H4CHdNC6H4-
)
µ
{(
µ
µ
µ
µ
µ
µ
µ
−
other (
µ
4-S)M4 systems in the literature, where the presence of M−M bonds prevents a bond-localized description
of the molecule. The X-ray structures of 2, 3, and 5 are reported.
Scheme 1
Introduction
The residual nucleophilicity of the bridging sulfido ligand
in [(µ2-S)2Pt2(PR3)4]2 compounds has provided a significant
number of homo- and heterometallic clusters and aggregates
with (µ3-S) bridging sulfide.1 Sulfido-bridged trinuclear
palladium complexes are much more scarce because of the
absence of a suitable sulfido precursor. Nevertheless, there
are a few examples of complexes with a (µ3-S)Pd3 core.
These have been isolated from reactions with compounds
with a (µ-S)2Pd2 core,2 the reaction of a Pd-Cl complex
with Na2S3 or S(SiMe3)2,4 cleavage of a S-C bond on a
thiocyanate complex,5 thermolysis of a Pd(S2C2O2) complex,6
* To whom correspondence should be addressed. E-mail: espinet@
qi.uva.es.
† Universidad de Valladolid.
‡ Universitat de Barcelona.
or reactions of palladium complexes with SH2, COS,7 or
NaSH.8 The possibility of further exploiting the residual
nucleophilicity of S in a (µ3-S)Pd3 system remains unex-
plored.
(1) (a) Fong, S.-W. A.; Hor, T. S. A. J. Chem. Soc., Dalton Trans. 1999,
639. (b) Li, Z.; Liu, H.; Mok, K. F.; Batsanov, A. S.; Howard, J. A.
K.; Hor, T. S. A. J. Organomet. Chem. 1999, 575, 223. (c) Mas-
Balleste´, R.; Aullo´n, G.; Champkin, P. A.; Clegg, W.; Me´gret, C.;
Gonza´lez-Duarte, P.; Lledo´s, A. Chem.sEur. J. 2003, 9, 5023.
(2) (a) Yeo, J. S. L.; Li, G.; Yip, W. H.; Mak, T. C. W.; Hor, T. S. A. J.
Chem. Soc., Dalton Trans. 1999, 435.
(3) (a) Narayan, S.; Jain, V. K.; Butcher, R. J. Polyhedron 1998, 17, 2037.
(b) Capdevila, M.; Clegg, W.; Coxall, R. A.; Gonza´lez-Duarte, P.;
Hamidi, M.; Lledo´s, A.; Ujaque, G. Inorg. Chem. Commun. 1998, 1,
466. (c) Wirth, S.; Fenske, D. Z. Anorg. Allg. Chem. 1999, 625, 2064.
(d) Tzeng, B.-C.; Chan, S.-C.; Chan, M. C. W.; Che, C.-M.; Cheung,
K.-K.; Peng, S.-M. Inorg. Chem. 2001, 40, 6699.
(5) Ferguson, G.; Lloyd, B. R.; Manojlovic-Muir, L.; Muir, K. W.;
Puddephatt, R. J. Inorg. Chem. 1986, 25, 4190.
(6) Cowan, R. L.; Pourreau, D. B.; Rheingold, A. L.; Geib, S. J.; Trogler,
W. C. Inorg. Chem. 1987, 26, 259.
(7) (a) Werner, H.; Bertleff, W.; Schubert, U. Inorg. Chim. Acta 1980,
43, 199. (b) Tarlton, S. V.; Choi, N.; McPartlin, M.; Mingos, D. M.;
Vilar, R. J. Chem. Soc., Dalton Trans. 1999, 653.
(4) Fenske, D.; Fleischer, H.; Krautscheid, H.; Magull, J. Z. Naturforsch.,
B: Chem. Sci. 1990, 45, 127.
(8) Matsumoto, K.; Takahashi, K.; Nakao, Y. Polyhedron 1999, 18, 1811.
10.1021/ic061367t CCC: $37.00
Published on Web 02/10/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 6, 2007 2035

Benavente et al.
In the present study, we report the results arising from a
change of the imine in the starting complex [(µ-OH)2Pd2-
(C∧N)2] (to HC∧N ) p-C2H5OC6H4CHdNC6H4-p-C2H5)
looking for better single crystals. This change not only
afforded the synthesis of a new trinuclear palladium ortho-
metalated complex with asymmetrical bridges, (µ3-S)(µ3-
OH), for which the crystal structure could be solved, but
also provided the controlled formation of unprecedented (µ4-
S)Pd4 complexes, also supported by a crystal structure.
Results and Discussion
Synthesis and Characterization. The reaction of [(µ-
OH)2Pd2(C∧N)2] (1) with the HC∧N in CH2Cl2, with 3 mol
equiv of carbon disulfide at room temperature for 2 h,
produced a mixture of two complexes (Scheme 1; molar ratio
2:3 ) 48:52), which could be characterized in the 1H NMR
spectrum of the mixture in CDCl3. The trinuclear complex
Figure 1. Molecular structure of 2 with thermal ellipsoids (30% prob-
ability).
1
[(µ3-S)(µ3-OH)Pd3(C∧N)3] (2) displays a set of H NMR
resonances for the orthopalladated imine and a singlet at
-2.55 ppm, with the intensity corresponding to one µ3-OH
group for three imines. The other compound, [(µ4-S){(µ2-
OH)Pd2(C∧N)2}2] (3), shows just one set of 1H NMR
resonances, proving the chemical equivalence of the four
orthopalladated imine ligands. Worth noting are the doublet
observed for H3 at very low field (9.28 ppm) and a singlet
at -3.82 ppm, with intensity OH:imine ) 1:2. This is
consistent with a tetranuclear palladium compound made of
two (C∧N)Pd(µ2-OH)Pd(C∧N) moieties linked by one µ4-
bridging sulfide. A trans arrangement of the sulfide and the
iminic N atoms is expected in the thermodynamically
preferred isomer.10
Figure 2. Molecular structure of 3 with thermal ellipsoids (30%
probability).
Complexes 2 and 3 could be separated by recrystallization
from CH2Cl2/toluene. Their analytical and spectroscopic data
(see the Experimental Section) were consistent with the
formulation given in Scheme 1. Both structures were
unambiguously confirmed by single-crystal X-ray diffraction
analyses (see below).11
In order to obtain information on the possible pathways
of the generation of the tetrametallic compound 3, the
reaction of 1 with a large excess of CS2 (Pd:CS2 ) 1:30)
was studied. This resulted in the formation of 2 as the main
product (molar ratio 2:3 ) 91:9) after 25 min of reaction.
On the other hand, when the proportion of CS2 was reduced
to Pd:CS2 ) 1:0.5, complex 1 gave, after 24 h, a mixture
where the tetrapalladium complex was the major product
(molar ratio 2:3 ) 20:80). These results suggest a reaction
pathway where 2 is generated initially. Then, its reaction
with still unreacted 1 affords 3, in a rearrangement where
the lone pair of the sulfido in 2 would act as a nucleophile
to split the OH bridges in 1. In effect, the reaction of 2 with
1 in dichloromethane (molar ratio 1:0.5) for 6 h at room
Figure 3. Molecular structure of 5 with thermal ellipsoids (30% prob-
ability).
Recently, we discovered a new synthetic route that affords
trinuclear palladium orthometalated complexes [(µ3-S)(µ3-
OH)Pd3(C∧N)3] (HC∧N ) p-CnH2n+1OC6H4CHdNC6H4O-
p-CnH2n+1, n ) 2, 10) by the reaction of [(µ-OH)2Pd2(C∧N)2]
with CS2.9 The complexes contain unprecedented (µ3-S)(µ3-
OH) bridges holding together the three metal atoms. These
asymmetric bridges induce an all-cis arrangement of the three
orthometalated ligands. Their structure could not be perfectly
assessed by X-ray diffraction methods because of the poor
quality of the crystals obtained, but a partial resolution
confirmed the arrangement of the molecular core.
(10) For examples of the antisymbiotic behavior and transphobia concepts,
see references in: (a) Pearson, R. Inorg. Chem. 1973, 12, 712. (b)
Vicente, J.; Abad, A.; Mart´ınez-Viviente, E.; Jones, P. G. Organo-
metallics 2002, 21, 4454.
(11) Only two other structures with a µ3-OH group bridging three Pd atoms
have been reported: Braunstein, P.; Fischer, J.; Matt, D.; Pfeffer, M.
J. Am. Chem. Soc. 1984, 106, 410. Gogoll, A.; Toom, L.; Greenberg,
H. Angew. Chem., Int. Ed. 2005, 44, 4729.
(9) Espinet, P.; Herna´ndez, C.; Mart´ın-Alvarez, J. M.; Miguel, J. A. Inorg.
Chem. 2004, 43, 843.
2036 Inorganic Chemistry, Vol. 46, No. 6, 2007

Tetrahedral Tetradentate Sulfide Ligand Bridging Pd Atoms
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Compound 2
S(2)-Pd(1)
S(2)-Pd(2)
S(2)-Pd(3)
O(4)-Pd(1)
O(4)-Pd(2)
O(4)-Pd(3)
Pd(1)-Pd(2)
Pd(2)-Pd(3)
Pd(1)-Pd(3)
2.3029(17)
2.3037(16)
2.2941(16)
2.139(3)
2.175(4)
2.139(4)
2.943(2)
2.992(2)
3.137(2)
Pd(1)-S(2)-Pd(2)
Pd(1)-S(2)-Pd(3)
Pd(2)-S(2)-Pd(3)
Pd(1)-O(4)-Pd(2)
Pd(1)-O(4) -Pd(3)
Pd(2)-O(4)-Pd(3)
79.40(5)
86.05(5)
81.18(5)
86.02(13)
94.30(14)
87.82(14)
Figure 4. Partial representation of the Laplacian function for the modeled
compound 3 (left) and [Pd4(µ-S)(η3-allyl)2(PH3)4] (right) in a plane of Pd2S.
Complete graphics of the Laplacian function and the electron densities are
available as the Supporting Information.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 3a
S(1)-Pd(1)
S(1)-Pd(2)
S(1)-Pd(3)
S(1)-Pd(4)
O(1)-Pd(1)
O(1)-Pd(2)
O(2)-Pd(3)
O(2)-Pd(4)
Pd(1)-Pd(2)
Pd(3)-Pd(4)
2.2889(14)
2.2881(14)
2.2946(14)
2.2915(16)
2.119(3)
2.117(4)
2.103(5)
2.098(4)
3.346(3)
Pd(1)-S(1)-Pd(2)
Pd(1)-S(1)-Pd(3)
Pd(1)-S(1)-Pd(4)
Pd(2)-S(1)-Pd(3)
Pd(2)-S(1)-Pd(4)
Pd(4)-S(1)-Pd(3)
Pd(2)-O(1)-Pd(1)
Pd(4)-O(2)-Pd(3)
93.93(5)
123.35(6)
115.54(6)
119.55(6)
112.59(6)
93.34(5)
Chart 1
104.33(16)
105.16(18)
3.336(2)
a For the sake of comparison, the distance Pd‚‚‚Pd in the optimized
structure is 3.424 Å and those in [(µ4-S){(µ2-η3-C3H5)Pd2(PH3)2}2] are 2.668
and 2.669 Å.
bridging hydroxo groups, and a cis arrangement of the three
imine moieties is found. The three Pd atoms describe an
isosceles triangle with distances that do not suggest signifi-
cant intermetallic interaction [2.943(1)-3.137(1) Å]. The
distortion observed from the ideal equilateral to an isosceles
triangle might originate from a second-order Jahn-Teller
effect12 or more probably from packing effects.2e
The X-ray structures of 3 and 5 confirm that these
molecules contain four Pd(C∧N) moieties connected by two
µ2-hydroxo bridging ligands (in compound 3) or two µ2-
chloro bridging ligands (in compound 5) and by a central
µ4-sulfide. The two Pd(C∧N) moieties linked by a µ2 ligand
are coplanar. The two planes, each containing two Pd(C∧N)
moieties, are arranged perfectly perpendicular to each other
in compound 3 [the angle between these two planes is 89.7-
(5)°], but they form an angle of 81.9(5)° in compound 5.
The coordination of the central µ4-sulfide is distorted
tetrahedral. The angles Pd-S-Pd are 93.64° on average for
Pd atoms linked additionally by the µ2-hydroxo group in
compound 3 and 98.27° on average when they are linked
by the µ2-chloro ligand in compound 5. The angles Pd-S-
Pd range from 112.59° to 123.35° when they are not bridged
by OH in compound 3 and from 107.67° to 125.13° when
they are not bridged by Cl in compound 5.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 5
S(1)-Pd(1)
S(1)-Pd(2)
S(1)-Pd(3)
S(1)-Pd(4)
Cl(1)-Pd(1)
Cl(1)-Pd(2)
Cl(2)-Pd(3)
Cl(2)-Pd(4)
Pd(1)-Pd(2)
Pd(3)-Pd(4)
2.3189(19)
2.3196(19)
2.3067(19)
2.3092(18)
2.434(2)
2.466(2)
2.459(2)
2.432(2)
3.505(2)
Pd(1)-S(1)-Pd(2)
Pd(1)-S(1)-Pd(3)
Pd(1)-S(1)-Pd(4)
Pd(2)-S(1)-Pd(3)
Pd(2)-S(1)-Pd(4)
Pd(3)-S(1)-Pd(4)
Pd(1)-Cl(1)-Pd(2)
Pd(3)-Cl(2)-Pd(4)
98.17(7)
107.67(7)
125.13(9)
116.35(8)
112.24(8)
98.37(7)
91.33(6)
91.17(6)
3.494(2)
temperature does afford cleanly the tetranuclear complex 3.
Moreover, 2 also reacts with [Pd(C∧N)(µ-Cl)]2 (molar ratio
1:0.5), affording [{Pd2(C∧N)2(µ2-OH)}{Pd2(C∧N)2(µ2-Cl)}2-
(µ4-S)] (4). The 1H NMR spectrum of 4 showed the expected
1
two sets of H NMR resonances for the two nonequivalent
types of orthometalated imine and a singlet at -3.63 ppm
(with intensity 1 for four imines) due to the presence of the
µ-OH group.
Treatment of 3 with HCl (molar ratio 1:2) led to the
displacement of the two bridging hydroxo ligands by chloro,
giving the corresponding tetranuclear complex [(µ4-S)(µ2-
1
Cl)2Pd4(C∧N)4] (5). Its H NMR spectrum shows just one
Density Functional Theory (DFT) Studies. Distorted
tetrahedral coordination of sulfides is not uncommon. It is
found in the infinite structure of PdS.13 It can be found also
in many sulfide-containing molecular clusters of a variety
of metals. However, a closer look at all of the X-ray
structures available with the help of a search in the
Cambridge Crystallographic Database reveals that, with very
few exceptions, these sulfides are always connecting two
metals bonded by a metal-metal bond, which leads to an
acute M-S-M angle and distorts the ideal tetrahedron. For
set of 1H NMR signals for the orthopalladated imine ligand,
proving the chemical equivalence of the imine ligands and
the isomeric purity of the complex. The expected ligand
arrangement with the sulfide trans to the iminic N atoms, as
found for 3, was unambiguously confirmed for 5 by single-
crystal X-ray diffraction.
Crystal Structures. Detailed crystallographic data are
summarized in Table 4. ORTEP drawings of the molecules
2, 3, and 5 are shown in Figures 1-3, respectively, and
selected bond distances and angles are listed in Tables 1-3.
The molecule of 2 consists of three Pd(C∧N) moieties
linked by one µ3-sulfide and one µ3-hydroxo ligand. The
cyclometalated C is coordinated trans to the O atoms of the
(12) Fackler, J. P., Jr. Prog. Inorg. Chem. 1976, 21, 55.
(13) Brese, N. E.; Squattrito, P. J.; Ibers, J. A. Acta Crystallogr., Sect. C:
Cryst. Struct. Commun. 1985, C41, 1829.
Inorganic Chemistry, Vol. 46, No. 6, 2007 2037

Benavente et al.
Table 4. Crystal and Structure Refinement Data for 2, 3, and 5
2
3
5
empirical formula
fw
T (K)
C
102H110N6O8Pd6S2
C68H64N4O6Pd4S
1490.89
298(2)
C68H72Cl2N4O4Pd4S
1537.86
298(2)
2250.48
298(2)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.71073
triclinic
P1h
0.71073
triclinic
P1h
0.71073
monoclinic
P2(1)/c
18.395(4)
16.080(3)
22.437(5)
90
104.752(5)
90
6418(2)
4
9.123(4)
15.099(6)
18.519(7)
69.010(9)
86.773(9)
76.679(9)
2316.5(16)
1
10.4576(17)
13.229(2)
23.965(4)
85.723(3)
81.829(4)
72.474(4)
3127.7(9)
2
Z
D
calc (g cm-3
)
1.613
1.245
1136
1.583
1.219
1496
1.592
1.269
3096
abs coeff (mm-1
F(000)
)
cryst size (mm)
θ range for data collection (deg)
reflns collcd
0.22 × 0.11 × 0.03
1.18-23.38
10936
0.14 × 0.14 × 0.05
0.86-23.26
14871
0.13 × 0.08 × 0.03
1.14-23.29
30661
indep reflns
6675
8952
9214
abs correction
SADABS
1.000000, 0.779657
6675/0/568
1.002
SADABS
1.000000, 0.851928
8952/1/774
1.025
SADABS
1.000000, 0.843978
9214/28/825
1.003
max, min transmn factor
data/restraints/param
GOF on F 2
R1 [I > 2σ(I)]
wR2 (all data)
0.0348
0.1012
0.0368
0.0982
0.0382
0.1294
instance, bis(µ-η3-allyl)-µ4-sulfidotetrakis(triphenylphosphine)-
tetrapalladium (two Pd-Pd), corresponding to the structural
type A in Chart 1, shows two short Pd-Pd interactions at
2.625 and 2.639 Å associated with two acute Pd-S-Pd
angles, 68.2° and 68.5°. The other four angles defining the
distorted tetrahedron around the S atom are 144.0°, 140.47°,
123.5°, and 119.01°.14 The degree of distortion can be
estimated by the ST parameter.15 The only molecular com-
pound containing a sulfide ligand fairly close to a tetrahedral
arrangement yet involving a M-M bond is [S(AuPPh3)2-
{Au(C6F5)3}2]. In spite of the fact that this gold compound
corresponds to the structural type B, in Chart 1, the Au-Au
bond is very long (3.224 Å), which makes it compatible with
an Au-S-Au bond angle of 87.75° in front of the Au-Au
bond (the values for the other five angles around S are
104.84°, 108.14°, 115.70°, 116.50°, and 119.67°).16 The
angle between the two Au-S-Au planes (with and without
the Au-Au bond) is 82.48°, but still all of these distortions
lead to a very high degree of tetrahedricity (ST ) 1.63). Only
two compounds were found that, exceptionally, contain
tetrahedrally coordinated sulfide connected to four metal
atoms not involved in M-M bonds. These are [Cr4S(O2-
(PEt3)3(CO)6Cl] (obtained in 0.9% yield; ST ) 0.94),18 for
which the metal coordination environment and the oxidation
state of the metal prevent M-M interaction (Chart 1, C).
The bonding in compounds of type A and B cannot be
described in a simple way as containing a sp3-hybridized
sulfide involved in four two-center S-M bonds. Only type
C (or D in our case if other bridging ligands are represented)
can be described that way. A closer view of the electronic
structure of compounds 3 (type D) and [(µ4-S){(µ2-η3-C3H5)-
Pd2(PPh3)2}2] (type A) was achieved using DFT calculations
with appropriate models, including a topological analysis of
the electron density for their optimized geometries,19 together
with an analysis of Continuous Symmetry Measures of
tetrahedral shape, ST (more details in the Supporting Infor-
mation).
The coordination of the S atom in 3 is tetrahedral, having
a low distortion from the ideal shape by only ST ) 2.3. Its
Laplacian function (Figure 4) shows clearly that the four-
membered ring S-Pd-O-Pd has bond critical points
between the Pd and S atoms and between the Pd and O
atoms, indicative of the presence of a chemical bond, with
electron densities r ) 0.080 and 0.073 for the Pd-S and
Pd-O bonds, respectively. These four maxima are situated
at 1.23 Å from S and are very near a tetrahedral disposition
(ST ) 2.2). Consequently, the bonding in this compound can
be adequately described in terms of a sp3-hybridized sulfide
giving rise to four M-S localized bonds, as illustrated in
Figure 5.
CCH3)8(H2O)4](BF4)2·H2O (obtained in 20% yield; ST
)
0.18)17 and [Fe(DMF)Cl(Cl4-cat)2Mo2Fe2S4(PEt3)2ClFe4S4-
(14) Bogdanovic, B.; Goddard, R.; Rubach, M. Acta Crystallogr., Sect. C:
Cryst. Struct. Commun. 1989, 45, 1511.
(15) The Continuous Symmetry Measures provide quantitative information
of how much the environment deviates from an ideal polyhedron. A
zero value of ST would indicate a perfect match to the ideal tetrahedron;
larger values reflect increasing deviations from the ideal tetrahedral
shape. Thus, a distortion of a tetrahedron to reach a square plane
corresponds to ST ) 33.3. Cirera, J.; Alemany, P.; Alvarez, S. Chem.s
Eur. J. 2004, 10, 190.
In contrast, compound [(µ4-S){(µ2-η3-C3H5)Pd2(PH3)2}2]
with two Pd-Pd bonds shows an important loss of tetrahe-
(16) Canales, F.; Gimeno, M. C.; Laguna, A.; Jones, P. G. Organometallics
1996, 15, 3412.
(17) Bino, A.; Johnston, D. C.; Goshorn, D. P.; Halbert, T. R.; Stiefel, E.
I. Science 1988, 241, 1479.
(18) Han, J.; Coucouvanis, D. J. Am. Chem. Soc. 2001, 123, 11304.
(19) (a) Bader, R. F. W. Chem. ReV. 1991, 91, 893. (b) Bader, R. F. W.
Atoms in Molecules: A Quantum Theory; Clarendon Press: Oxford,
U.K., 1995.
2038 Inorganic Chemistry, Vol. 46, No. 6, 2007

Tetrahedral Tetradentate Sulfide Ligand Bridging Pd Atoms
7.60 (d, J ) 2.1 Hz, 3H), 7.23 (d, J ) 8.1 Hz, 3H), 6.83, 6.72
(AA′BB′ system, J ) 8.2 Hz, 12H), 6.44 (dd, J ) 8.4 and 2.1 Hz,
3H), 4.15 (q, J ) 6.9 Hz, 6H), 2.64 (q, J ) 7.5 Hz, 6H), 1.46 (t,
J ) 7.5 Hz, 9H), 1.26 (t, J ) 7.5 Hz, 9H) -2.40 (s, 1H). IR (Nujol,
cm-1): ν(O-H) 3622w.
[(µ4-S){(µ2-OH)Pd2(C∧N)2}2] (3). Anal. Calcd for C68H74N4O6-
Pd4S: C, 54,41; H, 4.97; N, 3.73; S, 2.14. Found: C, 54.16; H,
4.84; N, 3.85; S, 2.51. 1H NMR (300 MHz, CDCl3): 9.28 (d, J )
2.2 Hz, 4H), 7.85 (s, 4H), 7.11 (s, AA′BB′ system, 16H), 7.09 (d,
J ) 8.2 Hz, 4H), 6.45 (dd, J ) 8.2 and 2.2 Hz, 4H), 4.17 (q, J )
6.9 Hz, 8H), 2.69 (q, J ) 7.1 Hz, 8H), 1.28 (t, J ) 7.5 Hz, 12H),
0.97 (t, J ) 7.0 Hz, 12H), -3.82 (s, 2H).
[(µ4-S){(µ4-OH)Pd2(C∧N)2}2] (3). To a solution of 2 (0.050 g,
0.044 mmol) in dichloromethane (25 mL) was added [(µ2-OH)2-
Pd2(C∧N)2)] (0.016 g, 0.022 mmol). The mixture was stirred for 6
h at room temperature. The solvent was evaporated off, and the
yellow-orange residue was washed with diethyl ether (2 × 5 mL),
collected on a frit, and dried in a vacuum. Yield: 0.045 g.
[(µ4-S)(µ2-Cl)(µ2-OH)Pd4(C∧N)4] (4). To a solution of 2 (0.050
g, 0.044 mmol) in dichloromethane (25 mL) was added [(µ2-Cl)2-
Pd2(C∧N)2)] (0.0018 g, 0.023 mmol). The mixture was stirred for
6 h at room temperature. The solvent was evaporated off, and the
yellow-orange residue was washed with diethyl ether (2 × 5 mL),
collected on a frit, and dried in a vacuum. Yield: 0.050 g. Anal.
Calcd for C68H73ClN4O5Pd4S: C, 53,75; H, 4.84; N, 3.69. Found:
C, 53.50; H, 4.47; N, 3.55. 1H NMR (300 MHz, CDCl3): 9.54 (d,
J ) 2.3 Hz, 2H), 8.93 (d, J ) 2.3 Hz, 2H), 7.83 (s, 2H), 7.80 (s,
2H), 7.13 (br, AA′BB′ system, 8H), 7.05 (m, 12H), 6.50 (m, 4H),
4.19 (q, J ) 7.0 Hz, 4H), 4.04 (q, J ) 7.0 Hz, 4H), 2.69 (m, 8H),
1.29 (t, J ) 7.6 Hz, 6H), 1.24 (t, J ) 7.6 Hz, 6H), 1.10 (t, J ) 7.0
Hz, 6H), 0.95 (t, J ) 7.0 Hz, 6H), -3.63 (s, 1H).
Figure 5. Localization of the critical points around a bridging sulfido
ligand. The bond critical points are represented by black circles and the
ring critical points by white circles.
dricity around the sulfido bridge (ST ) 13.5). The electronic
structure is further characterized by bond critical points,
corresponding to the presence of Pd-Pd interactions in
addition to Pd-S ones (r ) 0.047 and 0.069, respectively).
At variance with complex 3, the two maxima in each Pd2S
plane overlap. Consequently, the bonds in [(µ4-S){(µ2-η3-
C3H5)Pd2(PH3)2}2] surround a ring critical point at the center
of the Pd-S-Pd triangle, r ) 0.040 (compared to r ) 0.020
for 3), and are far from a sp3 hybridization for the sulfide or
from a localized two-center bond conception of the molecule.
Conclusion
In summary, although structures containing S surrounded
by four M atoms are not uncommon, 3-5 are rare examples
of metal sulfides with nondistorted tetrahedral coordination
of S, the first of its kind in palladium chemistry. Their
existence seems to be helped by the ligands sterically
preventing the metals from getting close enough to make
M-M interactions. The sulfide uses its four electron pairs
in an apparently simple coordination to four Pd acidic centers.
Thus, compounds 3-5 are genuine examples of sulfide acting
as a simple tetradentate ligand to four transition metals.
[(µ4-S)(µ2-Cl)2Pd4(C∧N)4] (5). To a solution of 3 (0.05 g, 0.033
mmol) in dichloromethane (10 mL) was added 65 µL of HCl (1 M
in diethyl ether). The mixture was stirred for 1 h at room
temperature. The solvent was evaporated off, and the residue was
crystallized from dichloromethane/diethyl ether. Yield: 0.037 g.
Anal. Calcd for C68H72Cl2N4O4Pd4S: C, 53,11; H, 4.72; N, 3.64.
1
Found: C, 52.85; H, 4.56; N, 3.58. H NMR (300 MHz, CDCl3):
9.05 (d, J ) 2.3 Hz, 1H), 7.77 (s, 1H), 6.54 (dd, J ) 2.12 and 6.1
Hz, 1H), 7.11 (d, J ) 6.4 Hz, 1H), 7.05, 6.96 (AA′BB′ system, J
) 8.2 Hz, 4H), 4.09 (q, J ) 6.7 Hz, 2H), 1.22 (t, J ) 7.8 Hz, 3H),
2.65 (q, J ) 7.3 Hz, 2H), 1.07 (t, J ) 6.9 Hz, 3H). IR (Nujol,
cm-1): ν (Pd-Cl) 269w.
X-ray Structures. Crystal and structure refinement data for 2,
3, and 5 are collected in Table 4. Data in common: Bruker AXS
SMART 1000 CCD diffractometer, φ and ω scans, Mo KR radiation
(λ ) 0.71073 Å), graphite monochromator, T ) 295 K. Raw frame
data were integrated with the SAINT21 program. Structures were
solved by direct methods with SHELXTL.22 Semiempirical absorp-
tion correction was done with SADABS.23 All non-H atoms were
refined anisotropically. H atoms were set in calculated positions
and refined as riding atoms, with a common thermal parameter.
All calculations were made with SHELXTL.
Experimental Section
General Procedures. Literature methods were used to prepare
[(µ2-OH)2Pd2L2] (1).20 C, H, N, and S analyses were carried out
on a Perkin-Elmer 2400 microanalyzer. IR spectra were recorded
on a Perkin-Elmer FT-1720X spectrometer using Nujol mulls
between polyethylene plates. 1H NMR spectra were recorded on a
Bruker AC-300 or ARX-300 MHz spectrophotometer.
Reaction of 1 with CS2. To a suspension of 1 (0.500 g, 0.665
mmol) in dichloromethane (60 mL) was added carbon disulfide
(0.120 mL, 2.00 mmol). The mixture was stirred for 2 h at room
temperature. The solvent was evaporated off, and the yellow-orange
residue, consisting of a mixture of 2 and 3, was washed with acetone
(3 × 5 mL), collected on a frit, and dried in a vacuum. Yield: 0.35
g. The two compounds could be separated by fractional crystal-
lization from CH2Cl2/toluene (1:1). In this mixture, 2 is practically
insoluble upon cooling to -20 °C, and 3 is very soluble.
Refinement of the structure of compound 2 proceeded smoothly
to give R1 ) 0.0348 based on the reflections with I > 2σ(I). The
ORTEP diagram is represented in Figure 1, and selected distances
and angles are collected in Table 1.
[(µ3-S)(µ3-OH)Pd3(C∧N)3] (2). Anal. Calcd for C51H55N3O4-
Pd3S: C, 54.43; H, 4.93; N, 3.73; S, 2.85. Found: C, 54.59; H,
4.76; N, 3.75; S, 3.08. 1H NMR (300 MHz, CDCl3): 7.95 (s, 3H),
(21) SAINT+. SAX area detector integration program, version 6.02; Bruker
AXS, Inc.: Madison, WI, 1999.
(22) Sheldrick, G. M. SHELXTL, An integrated system for solVing, refining,
and displaying crystal structures from diffraction data, version 5.1;
Bruker AXS, Inc.: Madison, WI, 1998.
(20) D´ıez, L.; Espinet, P.; Miguel, J. A. J. Chem. Soc., Dalton Trans. 2001,
(23) Sheldrick, G. M. SADABS, Empirical Absorption Correction Program;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
1189.
Inorganic Chemistry, Vol. 46, No. 6, 2007 2039

Benavente et al.
Disorder of two ethyl groups was modeled in the refinement of
3. An occupancy of 74% was found for C15A and an occupancy
of 46% for C57A. H atoms of the disordered parts of 3 (C14, C15A,
C15B, C56, C57A, and C57B) were not included in the calculations.
A fixed distance of 1.5 Å between C14 and C15B was included as
a restraint and the refinement converged to give R1 ) 0.0368. The
ORTEP diagram is represented in Figure 2, and selected distances
and angles are collected in Table 2.
The 4-ethylphenyl group attached to N(2) in compound 5 is
disordered and has been modeled with an occupancy of 78% for
part A. Part B refinement has been restrained with an instruction
SAME (with part A as the reference) and with SIMU and DELU
instructions to avoid nonpositive definites. The refinement con-
verged to give R1 ) 0.0382. The ORTEP diagram is represented
in Figure 3, and selected distances and angles are collected in
Table 3.
(Project CTQ2005-08727/BQU) and the Junta de Castilla y
Leo´n (Project VA099A05). This paper is dedicated to
Professor V. Riera on the occasion of his 70th birthday.
Supporting Information Available: X-ray crystallographic data
in CIF format and complete graphics of the Laplacian functions
and the electron densities for the modeled compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as Supplementary publications with
the following deposition numbers: CCDC 256155, 256156, and
624863 for complexes 2, 3, and 5, respectively. Copies of the data
can be obtained free of charge upon application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. [fax (int.) +44-1223/336-033;
e-mail deposit@ccdc.cam.ac.uk].
Acknowledgment. This work was supported by the
Spanish Comisio´n Interministerial de Ciencia y Tecnolog´ıa
IC061367T
2040 Inorganic Chemistry, Vol. 46, No. 6, 2007