Bridging pseudohalides in palladacycles as a source of different assemblies

Article abstract of DOI:10.1002/ejic.201200247

The reaction of [Pd{CH₂SiPh₂(CH₂NC ₅H₁₀)-κ²C,N}(μ-Cl)]₂ (CH₂NC₅H₁₀ = piperidinomethyl) with KSCN led to the centrosymmetric dimer [Pd{CH₂SiPh₂(CH ₂NC₅H₁₀)-κ²C,N}(μ-SCN- κ¹S,κ¹N)]₂, which features side-on bridging thiocyanate ligands. However, the analogous reaction of the chlorido-bridged starting material with NaN₃ yielded the dimer [Pd{CH₂SiPh₂(CH₂NC₅H ₁₀)-κ²C,N}(μ-N₃-κ ¹κ¹N)]₂, in which the azido ligands exhibit end-on coordination. This complex persists as a mixture of cis and trans isomers in solution. Lastly, the square tetrametallic complex [Pd{CH ₂SiPh₂(CH₂NC₅H₁₀)- κ²C,N}(μ-CN-κ¹C,κ¹N)] ₄ was obtained from the reaction between the parent chlorido-bridged complex and AgCN. In solution, this compound forms an equilibrium between the tetra- and trimetallic species. Thermodynamic data (equilibrium constants and free energies in CDCl₃ and C₆D₆, and enthalpy and entropy in CDCl₃) were determined and show that the formation of the trimetallic isomer is thermodynamically disfavored [K_eq = (1.93±0.07)× 10^-4 molL^-1 and G_eq = 20.83±0.11 kJmol^-1 in CDCl₃, K_eq = (4.5±0.2)× 10^-5 molL^-1 and G_eq = 24.40±0.14 kJmol^-1 in C₆D₆] and that the variation in the enthalpy and entropy are positive (H = 75±5 kJmol ^-1 and S = 186±15 Jmol^-1K^-1 in CDCl ₃). Coordination of pseudohalides to the soft metal center of a silapalladacycle leads to different bridging modes depending on the pseudohalide. With cyanide, a molecular square is formed, which in solution is in equilibrium with the corresponding triangular species.

Full text of DOI:10.1002/ejic.201200247

FULL PAPER
DOI: 10.1002/ejic.201200247
Bridging Pseudohalides in Palladacycles as a Source of Different Assemblies
Marta Arroyo,[a] Patricia Gómez-Iglesias,[a] José Santos Melero,[a] Daniel Schildbach,[b]
Christian Unkelbach,[b] Carsten Strohmann,*[b] and Fernando Villafañe*[a]
Keywords: Self-assembly / Bridging ligands / Palladium / Metallacycles / Silanes
The reaction of [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-Cl)]2
(CH2NC5H10 = piperidinomethyl) with KSCN led to the cen-
trosymmetric dimer [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-
SCN-κ1S,κ1N)]2, which features side-on bridging thiocyanate
ligands. However, the analogous reaction of the chlorido-
bridged starting material with NaN3 yielded the dimer
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-N3-κ1κ1N)]2, in which
the azido ligands exhibit end-on coordination. This
complex persists as a mixture of cis and trans isomers in
solution. Lastly, the square tetrametallic complex
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-CN-κ1C,κ1N)]4 was ob-
tained from the reaction between the parent chlorido-
bridged complex and AgCN. In solution, this compound
forms an equilibrium between the tetra- and trimetallic spe-
cies. Thermodynamic data (equilibrium constants and free
energies in CDCl3 and C6D6, and enthalpy and entropy in
CDCl3) were determined and show that the formation of the
trimetallic isomer is thermodynamically disfavored [Keq
=
(1.93Ϯ0.07)ϫ 10–4 molL–1 and ΔGeq = 20.83Ϯ0.11 kJmol–1
in CDCl3, Keq
= =
(4.5Ϯ0.2)ϫ 10–5 molL–1 and ΔGeq
24.40Ϯ0.14 kJmol–1 in C6D6] and that the variation in the
enthalpy and entropy are positive (ΔH = 75Ϯ5 kJmol–1 and
ΔS = 186Ϯ15 Jmol–1 K–1 in CDCl3).
The presence of a silicon atom in the (piperidinomethyl)-
silylmethyl cyclopalladated complexes is expected to play a
Introduction
In coordination chemistry, pseudohalides are interesting dual role: stabilizing the metallated carbon atom by polar-
polyatomic ligands due to their ability to induce a variety ization effects and preventing β-elimination. The palladacy-
of structural motifs. They often act as bridging ligands giv- cle is made possible by the presence of a nitrogen donor in
ing rise to different structures that may be discrete moieties, the side-arm that can coordinate to the PdII center, thereby
such as dimers, trimers, or tetramers, infinite assemblies, forming the five-membered palladacycle. This chelating
such as monodimensional chains, either ladder or helicoid side-arm is an often employed tool, for example, in activa-
type, or even two- or three-dimensional cages. The final ting alkylsilanes towards metallation and in stabilizing the
structure depends both on the electronic and structural configuration of diastereomerically enriched α-lithiated alk-
requirements of both the pseudohalide and the metal frag- ylsilanes in the case of chiral amine ligands.[3]
ment used. The donor atoms and the directionality of the
frontier orbital determine the coordination mode of the
pseudohalide.[1]
Results and Discussion
Following our studies on the reactivity of (piperidino-
methyl)silylmethyl cyclopalladated complexes,[2] we decided
to explore the behavior of this soft metallic center with two
coordinating sites available in cis geometry towards pseu-
dohalides such as cyanide, thiocyanate, or azide, which
present several possible coordination modes and give rise
to different assemblies, as described herein.
Chlorido-bridged dimer [Pd{CH2SiPh2(CH2NC5H10)-
κ2C,N}(μ-Cl)]2 (1) served as the starting material for the
synthesis of new pseudohalido-bridged complexes. The
pseudohalides employed were thiocyanate, azide, and cya-
nide and were introduced by the reaction of 1 with metal
salts of the corresponding pseudohalide (Scheme 1).
[a] IU CINQUIMA/Química Inorgánica, Facultad de Ciencias,
Universidad de Valladolid,
47005 Valladolid, Spain
Fax: +34-983-423-013
E-mail: fervilla@qi.uva.es
[b] Technische Universität Dortmund, Anorganische Chemie,
Otto-Hahn-Straße 6, 44227 Dortmund, Germany
Fax: +49-231-755-7062
E-mail: mail@carsten-strohmann.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200247.
Scheme 1. General synthesis of pseudohalide complexes by starting
from 1.
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Bridging Pseudohalides in Palladacycles
The reaction of 1 with potassium thiocyanate in THF those found in palladacycles with metallated chiral ferro-
led to a new dimer, [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ- cenylimines[8] and benzylideneaniline.[9]
SCN-κ1S,κ1N)]2 (2) in which the pseudohalide acts as
Each palladium atom is also coordinated by the nitrogen
bridging ligand. In general, thiocyanate may coordinate in and carbon donor atoms of the [CH2SiPh2(CH2NC5H10)]
one of the three following modes: Side-on or end-on, and moiety, thereby forming the palladacycle. The Pd–C dis-
in the later case, with S or N as donor (cf. Figure 1). In this tance of 2.045(2) Å is in the range typically found for Pd–
case, the IR spectrum of 2 immediately suggests a side-on C(sp3) single bonds.[10]
coordination mode as its CN stretching absorption appears
The conformation of the five-membered silapalladacycle
at 2137 cm–1, higher than would be expected for the two may be described as an envelope in which the average dihe-
end-on coordination modes.[4]
dral angle of the palladium center with respect to the other
four atoms is 36.2(2)°. The presence of palladium and sili-
con in the five-membered palladacycle results in a short
Pd···Si distance of 2.985(1) Å, and the Si–C1–Pd angle is
100.0(1)°. These distances and angles in the silapalladacycle
are in the range of those previously found.[2]
The nitrogen atoms of the bridging thiocyanate and the
cyclometallated ligand are coordinated in cis geometry. This
is to be expected taking into account the higher trans influ-
ence of the carbon donor ligand and of the sulfur donor
atom in the bridging thiocyanate compared with the lower
trans influence of the two nitrogen donors. This is a result
of the antisymbiotic effect of the palladium(II) soft metal
center.[11]
Figure 1. Coordination modes for a bridging thiocyanato ligand.
The molecular structure of 2 obtained unambiguously
supports this assignment (Figure 2). The compound crys-
tallizes from hexane/dichloromethane with a tetragonal
crystal system in the space group I41/a. The asymmetric
unit contains one half of the centrosymmetric dimeric struc-
ture.
In solution, only one isomer of 2 was detected (see the
Exp. Sect.). This suggests that the above geometry is main-
tained in solution, because any of the end-on modes would
give rise to cis and trans geometries. A singlet signal is ob-
served for each methylene group of the palladacycle
(PdCH2Si and SiCH2N), which results from the fast dy-
namic process usually observed in five-membered metalla-
cycles with an envelope conformation in which the Si and
C atoms move from one side of the plane to the other, mak-
ing both sides equivalent.
A mixture of isomers was obtained in solution after reac-
tion of the parent chlorido-bridging dimer 1 with sodium
azide, which gave [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-
N3-κ1κ1N)]2 (3). Like the thiocyanate, the azido ligand may
also coordinate side-on (Figure 3, a) or end-on (Figure 3,
b). In contrast to thiocyanate, in this case IR spectroscopy
does not allow differentiation between coordination modes
as the N=N stretching absorptions are very similar. An end-
on coordination is proposed for 3, as occurs in the few re-
ported examples of structures with bridging azides coordi-
nated to palladium(II).[13] Single crystals obtained from 3
Figure 2. Molecular structure and numbering scheme of compound
2 in the crystal form (SCHAKAL plot).[12] Selected distances [Å]
and angles [°]: C(1)–Pd 2.045(2), C(1)–Si 1.849(2), C(14)–Si
1.892(2), C(14)–N(1) 1.497(3), N(1)–Pd 2.1601(17), N(2)–Pd
2.1079(17), Pd–S 2.3071(6), S–C(20)#1 1.669(2), C(20)–N(2)
1.145(3); Si–C(1)–Pd 99.96(10), C(1)–Si–C(14) 104.05(10), N(1)–
C(14)–Si 109.59(14), C(14)–N(1)–Pd 103.12(12), C(1)–Pd–N(2)
174.78(9), C(1)–Pd–N(1) 86.19(8), N(2)–Pd–N(1) 96.70(6), C(1)–
Pd–S 83.49(7), N(2)–Pd–S 93.62(5), N(1)–Pd–S 169.67(5), N(2)–
C(20)–S#1 179.7(2), C(20)–N(2)–Pd 160.31(16), C(20)#1–S–Pd
104.34(7). Symmetry operator: #1: Ϫx + 1/2, Ϫy + 3/2, Ϫz + 1/2.
As the structure of 2 is a centrosymmetric dimer, the confirmed this connectivity; however, the overall quality of
trans isomer is observed in which both carbon or both ni- the data was insufficient to merit publication.[14]
trogen donor atoms are at opposite sides of the molecule.
The thiocyanate groups have a linear geometry [S–C–N
179.7(2)°] and the S–C and C–N distances are typical of
double bonds.[5] The thiocyanato bridging ligands form an
eight-membered, nearly planar ring with both palladium
centers. The slight distortion from planarity is reflected in
the dihedral angle N–Pd–S–C20 of 8.0(4)° between the
metal atoms and the bridging ligands. This value is similar
Figure 3. Possible coordination modes for a bridging azido ligand.
1
Two signal sets are detected in the H and 13C NMR
to those found in other palladium complexes with bridging spectra of 3, which suggests the presence of two isomers
thiocyanato ligands, such as 11.9(3)° for [P(CH2Ph)Ph3]2- in solution. The most informative signals are those of the
[(C6F3H2)2Pd(μ-SCN)(μ-NCS)Pd(C6F3H2)2][6] or 5.2(4)° methylene groups PdCH2Si and SiCH2N, which resonate at
1
for [Pd(C2,N-dmba)(μ-SCN)]2,[7] but slightly larger than δ ≈ 1 and 3 ppm, respectively, in the H NMR spectra and
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C. Strohmann, F. Villafañe et al.
FULL PAPER
at δ ≈ 5 and 50 ppm, respectively, in the 13C NMR spectra.
For 3, the two isomers coexist in a ratio of 55:45 in CDCl3.
When the spectrum was recorded in (CD3)2CO, the ratio
changed to 60:40 (see the Exp. Sect.). This led to the assign-
ment of the major isomer observed to cis and the minor
isomer to trans on the basis of the higher polarity of the cis
isomer and acetone relative to the trans form and chloro-
form. Thus, the two isomers clearly undergo a slow equili-
brating process in solution (Scheme 2). However, the trans
structure is exclusively observed in the crystal. This obser-
vation has also been made for the parent chlorido-bridged
complex 1.[2b]
Scheme 2. Isomers of 3 detected in solution.
The third pseudohalide studied was cyanide. Whereas az-
ide and thiocyanate coordinate as bridging ligands in dimet-
allic species with bent geometries, cyanide, given its ten-
dency to form linear bridges, should promote a different
mode of assembly. Thus, parent chlorido-bridged dimer 1
was treated with equimolar amounts of silver cyanide lead-
Figure 4. Molecular structure and numbering scheme of compound
4 in the crystal (only one of the two independent molecules in the
asymmetric unit is shown, SCHAKAL plot).[12] Peripheral hydro-
gen atoms outside the palladacycles have been omitted for clarity.
Selected distances [Å] and angles [°]: Pd1–Si1 3.088(2), Pd1–N1
2.178(5), Pd1–N2 2.089(6), Pd1–C1 2.064(8), Pd1–C80 1.928(6),
Pd2–Si2 3.051(2), Pd2–N3 2.185(7), Pd2–N4 2.096(5), Pd2–C20
ing to the precipitation of AgCl and the formation of 1.9154(7), Pd2–C21 2.0608(6), Pd3–N5 2.1977(5) Pd3–N6
2.0992(6), Pd3–C40 1.936(6), Pd3–C41 2.055(7), Pd4–Si4 3.030(2),
the tetrametallic complex [Pd{CH2SiPh2(CH2NC5H10)-
Pd4–N7 2.180(6), Pd4–N8 2.093(5), Pd4–C60 1.943(7), Pd4–C61
κ2C,N}(μ-CN-κ1C,κ1N)]4 (4). The crystals obtained were
2.058(6), N2–C20 1.188(10), N4–C40 1.168(8), N6–C60 1.160(9),
N8–C80 1.174(8); Pd1–N2–C20 178.2(6), Pd2–N4–C40 170.2(5),
Pd3–N6–C60 175.8(6), Pd4–N8–C80 171.1(6), Pd1–C1–Si1
subjected to crystal structure determination, which gave the
structure shown in Figure 4.[13]
103.6(4), Pd2–C21–Si2 102.4(3), Pd3–C41–Si3 105.4(4), Pd4–C61–
Si4 101.2(3), Pd1–N2–C20 178.2(6), Pd2–N4–C40 170.2(5), Pd3–
N6–C60 175.8(6), Pd4–N8–C80 171.1(6), Pd2–C20–N2 178.4(6),
Pd3–C40–N4 179.4(6), Pd4–C60–N6 178.0(6), Pd1–C80–N8
178.3(6).
Complex 4·hexane crystallizes from dichloromethane/
hexane in the monoclinic crystal system. The asymmetric
unit contains two independent molecules of the tetrametalla-
cycle 4 and two disordered hexane molecules. Each mole-
cule of 4 contains four palladium centers bridged by cyan-
ido ligands. However, the structural determination does not
allow differentiation of the carbon and nitrogen atoms of
The Pd–C distances [2.028(7)–2.061(6) Å] are in the
the bridging cyanide. Therefore, the structure was refined range found for Pd–C(sp3) single bonds.[10] The conforma-
by taking into account the antisymbiotic effect of the soft tion of the five-membered palladacycles may be described
palladium(II) center,[11] which led to the proposal of mutual as envelopes: The dihedral angles of the palladium atoms
cis coordination of both carbon donor ligands (i.e., methyl- with respect to the other four atoms range from 31.6° for
ene and cyanide-C, with higher trans influence) and both Pd(3) to 36.2° for Pd(1), as is usually found in these metalla-
nitrogen donor ligands (i.e., piperidyl and cyanide-N, with cycles. As with compounds 1 and 2, the distance between
lower trans influence). A cyclometalated (piperidinometh- the palladium and the silicon atom in the five-membered
yl)silylmethyl moiety is also coordinated to each palladium palladacycles in 4 is short; however, the Pd···Si distances in
center. The bridging cyanides are essentially linear: The Pd– the tetrametallacycle are slightly longer than those observed
C–N angles range from 175.5(7) to 179.5(8)°, and the C– in the thiocyanato-bridged dimer 2 and range from 3.015(2)
N–Pd angles are in the range 167.3(6)–178.0(5)°. These to 3.117(2) Å. These distances and angles in the silapallada-
angles and the C–N distances are similar to those found in cycles are similar to those previously found.[2]
other tetranuclear complexes with bridging cyanides.[15] The
The structure found in the solid is not maintained in
four palladium atoms are not coplanar, but form a dihedral solution, as evidenced by the NMR spectra displaying sig-
angle of 27°. With dihedral angles found in similar tetra- nals from two different species. The signals of the methylene
metallic structures ranging from 0 to 35°, this deviation groups NCH2Si and SiCH2Pd allowed a quantitative analy-
from planarity is relatively distinct.
sis of the concentration of each isomer. The two species
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Bridging Pseudohalides in Palladacycles
are present in a ratio that depends on the concentration, Table 1. Thermodynamic data for the equilibrium detected in solu-
tions of 4 as a function of concentration.
temperature, and solvent, but one of the isomers is always
Concentration [meqmL–1]
Trimetallic [%]
Tetrametallic [%]
dominant. To assign unequivocally the signals to each iso-
mer, an NMR sample of 4 in frozen CDCl3 was prepared
in a liquid-nitrogen bath and then allowed to melt and
simultaneously dissolve at –40 °C in the NMR probe. The
1H NMR spectrum immediately recorded under these con-
ditions showed only signals from the major isomer, which
led to the conclusion that the major isomer in solution is
always the tetranuclear complex detected in the crystal
structure. The concentration of the minor isomer is higher
in diluted solutions and at higher temperatures, and in po-
lar CDCl3 compared with nonpolar C6D6. On the other
hand, the IR spectra only show one CN stretching absorp-
tion in the solid state (2162 cm–1) as well as in CH2Cl2
(2159 cm–1) and toluene (2164 cm–1) solutions. As IR spec-
troscopy is a fast technique on the spectroscopic timescale,
that is, it differentiates between species present in solution
even when they are involved in slow processes in solution,
the conclusion is that the CN stretching absorption is the
same for both isomers.
All these data are in accord with the equilibrium pro-
posed in Scheme 3 between the tetrametallic complex de-
tected in the crystal structure and a trimetallic species. This
type of equilibria has been found for other tetrametallic
complexes, and the factors controlling the tetrametallic/tri-
metallic equilibria have recently been the target of extensive
studies.[16]
In our case, the ratio of tetrametallic/trimetallic species
in CDCl3 increases with concentration, with values of 80:20
at 0.08 mequiv.mL–1 and 69:31 at 0.003 mequiv.mL–1 (see
Table 1), which leads to an equilibrium constant, Keq, of
(1.93Ϯ0.07)ϫ10–4 molL–1 and a free energy, ΔGeq, of
20.83Ϯ0.11 kJmol–1 (see the Supporting Information) for
the equilibrium depicted in Scheme 3.
0.080
0.050
0.025
0.012
0.006
0.003
20
22
25
28
30
31
80
78
75
72
70
69
Table 2. Thermodynamic data for the equilibrium detected in the
solutions of 4 as a function of temperature.
T [K]
Trimetallic [%]
Tetrametallic [%]
Keq
253
273
293
313
6
94
87
80
70
9.86ϫ10–7
2.74ϫ610–5
1.98ϫ10–4
1.49ϫ10–3
13
20
30
As expected, the enthalpy of the process depicted in
Scheme 3 is positive (ΔH = 75Ϯ5 kJmol–1), which reflects
the lower strain of the tetrametallic structure, and the en-
tropy is quite large and also positive (186Ϯ15 Jmol–1 K–1),
which reflects the higher disorder that results from the
greater number of particles when trimetallic isomers are
formed from tetrametallic isomers.
These thermodynamic values are similar to those ob-
tained for similar equilibria previously reported between
tetra- and trimetallic palladium complexes.[16d–16f] An im-
portant difference between complex 4 and those previously
described is that 4 is neutral, whereas those reported in the
literature are cationic. This might be the cause of their dif-
ferent behavior when the polarity of the solvent changes:
for the cationic complexes, the equilibrium is shifted
towards the trimetallic isomer as the solvent polarity
increases,[16d,16f] whereas for 4, the equilibrium constant
A study of the concentrations of the isomers as a func-
tion of temperature allowed us to determine the values of
ΔHeq and ΔSeq for the equilibrium process (Table 2) from
the van’t Hoff equation (1).
detected in nonpolar C6D6 is smaller [Keq
=
(4.5 Ϯ0.2)ϫ10–5 molL–1], and thus the free energy is
higher (ΔGeq = 24.40Ϯ0.14 kJmol–1; see the Supporting
Information) than in CDCl3 (see above). This feature might
be interpreted on the basis that the equilibrium proposed
(1) in Scheme 2 should occur through a dissociative mechanism
lnKeq = –(ΔGeq/RT) = –(ΔHeq/RT) + (ΔSeq/R)
Scheme 3. Isomers detected in solutions of 4.
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C. Strohmann, F. Villafañe et al.
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[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-N3-κ1κ1N)]2 (3): A mixture
of 1 (0.087 g, 0.1 mmol) and NaN3 (0.014 g, 0.22 mmol) in THF
(10 mL) was stirred at 40 °C for 15 h. The volatiles were removed
in vacuo, and the residue was extracted with toluene (ca. 20 mL).
The yellow solution was filtered and concentrated in vacuo, and
hexane (ca. 10 mL) was added. Cooling to –20 °C afforded yellow
crystals, which were decanted, washed with hexane (3ϫ 3 mL), and
due to metal–ligand bond cleavage, and therefore polar sol-
vents should favor this step.
Conclusions
The coordination of the pseudohalides cyanide, thio-
cyanate, or azide to a “soft” PdII center with two potential
coordinating positions in cis geometry led to different types
of assemblies. The bridging azide and thiocyanate give rise
to dimetallic species in which the azide is coordinated end-
on and the thiocyanate is coordinated side-on. In contrast,
the linear bridging cyanide gives rise to a square-shaped
tetrametallic complex. The latter is in equilibrium with a
trimetallic isomer in solution, whereas the bridging azide
dimer persists as a mixture of cis and trans isomers in solu-
tion. The trimetallic species is always the minor isomer, but
its ratio increases with dilution, increasing temperature, and
increasing polarity of the solvent used.
vacuum-dried to yield 0.040 g (46%) of 3. IR (KBr): ν = 3064 (w),
˜
2943 (w), 2860 (w), 2050 (vs), 1448 (w), 142 7 (m), 1357 (w), 1285
(m), 1261 (w), 1234 (w), 1110 (s), 1029 (m), 998 (m), 947 (w), 867
(m), 804 (s), 733 (s), 699 (s), 622 (w), 550 (m), 504 (w), 489 (m),
1
466 (w) cm–1. H NMR: δ = 7.73 (m, 4 H, C6H5, 2 isomers), 7.40
(m, 6 H, C6H5, 2 isomers), 3.17 (m, 2 H, CH2 pip, 2 isomers), 3.08
(s, 2 H, NCH2Si, 2 isomers), 2.50 (m, 2 H, CH2 pip, 2 isomers),
1.77 (m, 5 H, CH2 pip, 2 isomers), 1.44 (m, 1 H, CH2 pip, 2 iso-
mers), 1.25 (s, 2 H, SiCH2Pd, cis isomer), 1.12 (s, 2 H, SiCH2Pd
pip, trans isomer) ppm; ratio cis/trans = 55:45. 13C{1H} NMR: δ =
136.3 (s, SiC6H5 ipso, cis isomer), 136.2 (s, SiC6H5 ipso, trans iso-
mer), 134.6 (s, SiC6H5 ortho, cis isomer), 134.5 (s, SiC6H5 ortho,
trans isomer), 129.4 (SiC6H5 para, 2 isomers), 128.0 (SiC6H5 meta,
trans isomer), 127.9 (SiC6H5 meta, cis isomer), 61.6 (s,
NCH2CH2CH2, cis isomer), 61.4 (s, NCH2CH2CH2, trans isomer),
55.5 (s, NCH2Si, cis isomer), 55.1 (s, NCH2Si, trans isomer), 22.9
(s, NCH2CH2CH2, 2 isomers), 21.8 (s, NCH2CH2CH2, cis isomer),
21.4 (s, NCH2CH2CH2, trans isomer), 6.7 (s, PdCH2Si, cis isomer),
5.6 (s, PdCH2Si, trans isomer) ppm. C38H48N8Pd2Si2 (885.82):
calcd. C 51.62, H 5.46, N 12.55; found C 51.90, H 5.37, N 12.20.
Experimental Section
General: IR (KBr pellets, 4000–450 cm–1): Perkin–Elmer Spectrum
RX I FT-IR spectrometer. 1H NMR [solvent CDCl3; internal stan-
dard: CHCl3 (δ = 7.24 ppm); recorded at room temperature]:
Bruker AC-300 or ARX-300 spectrometer (300.13 MHz). 13C
NMR [solvent and internal standard: CDCl3 (δ = 77.00 ppm); re-
corded at room temperature; integrations are indicated per
“CH2SiPh2(CH2NC5H10)” unit]: Bruker ARX-300 spectrometer
(75.78 MHz). Assignment of the 13C NMR spectroscopic data is
supported by DEPT experiments and the relative intensities of the
resonance signals. Microanalyses: Perkin–Elmer 2400B microana-
lyzer, Área de Química Inorgánica, Facultad de Ciencias, Vallado-
lid (Spain). All reactions were carried out under oxygen-free and
dried dinitrogen according to conventional Schlenk techniques. The
solvents were dried according to common procedures. Complex 1
was obtained as described previously.[2b] The other reactants were
obtained from the usual commercial suppliers.
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-CN-κ1C,κ1N)]4 (4): A mix-
ture of 1 (0.044 g, 0.05 mmol) and freshly prepared AgCN (from
0.019 g, 0.11 mmol of AgNO3 and 0.007 g, 0.012 mmol of NaCN)
in THF (5 mL) was stirred at room temp. for 3 h. Workup as for 3
gave 0.030 g (70%) of 4 as colorless crystals. IR (KBr): ν = 3065
˜
(w), 3046 (m), 2938 (s), 2856 (m), 2813 (w), 2162 (s), 1451 (m),
1427 (s), 1381 (w), 1261 (w), 1109 (s), 1037 (m), 999 (w), 865 (w),
802 (m), 768 (s), 735 (s), 700 (vs), 557 (w), 503 (m), 488 (m), 473
1
(w), 437 (w) cm–1. H NMR: δ = 7.66 (m, 4 H, C6H5, 2 isomers),
7.34 (m, 6 H, C6H5, 2 isomers), 3.25 (m, 2 H, CH2 pip, 2 isomers),
2.75 (s, 2 H, NCH2Si, minor isomer), 2.73 (s, 2 H, NCH2Si, major
isomer), 2.05 (m, 2 H, CH2 pip, 2 isomers), 1.65 (m, 2 H, CH2 pip,
2 isomers), 1.34 (m, 3 H, CH2 pip, 2 isomers), 1.05 (m, 1 H, CH2
pip, 2 isomers), 0.76 (s, 2 H, SiCH2Pd, minor isomer), 0.65 (s, 2 H,
SiCH2Pd, major isomer) ppm; ratio major/minor isomers = 80:20.
13C{1H} NMR: δ = 137.6 (s, SiC6H5 ipso, minor isomer), 137.4 (s,
SiC6H5 ipso, major isomer), 134.9 (s, SiC6H5 ortho, major isomer),
134.7 (s, SiC6H5 ortho, minor isomer), 130.5 (s, CN, 2 isomers),
128.9 (SiC6H5 para, 2 isomers), 127.6 (SiC6H5 meta, 2 isomers),
61.5 (s, NCH2CH2CH2, minor isomer), 60.7 (s, NCH2CH2CH2,
major isomer), 54.7 (s, NCH2Si, minor isomer), 53.2 (s, NCH2Si,
major isomer), 23.1 (s, NCH2CH2CH2, 2 isomers), 22.6 (s,
NCH2CH2CH2, 2 isomers), –7.6 (s, PdCH2Si, 2 isomers) ppm.
C80H96N8Pd4Si4 (1707.64): calcd. C 51.62, H 5.46, N 12.55; found
C 51.90, H 5.37, N 12.20.
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-SCN-κ1S,κ1N)]2 (2): A mix-
ture of 1 (0.087 g, 0.1 mmol) and KSCN (0.097 g, 1.0 mmol) in
THF (10 mL) was stirred at 40 °C for 15 h. The volatiles were re-
moved in vacuo, and the residue was extracted with CH2Cl2 (ca.
20 mL). The yellow solution was filtered, and hexane (ca. 10 mL)
was added. Concentration in vacuo and cooling to –20 °C afforded
yellow crystals, which were decanted, washed with hexane (3ϫ
3 mL), and vacuum-dried to yield 0.052 g (57%) of 2. IR (KBr): ν
˜
= 3066 (m), 2945 (s), 2856 (s), 2808 (m), 2137 (vs), 1587 (w), 1567
(w), 1486 (w), 1468 (m), 1442 (s), 1426 (m), 1374 (w), 1298 (w),
1282 (w), 1261 (w), 1225 (w), 1175 (w), 1111 (s), 1039 (m), 998 (m),
910 (w), 882 (w), 862 (m), 797 (m), 765 (s), 720 (s), 698 (s), 575
X-ray Diffraction Study of 2 and 4: Crystals were grown by slow
diffusion of hexane into concentrated solutions of the complexes
1
(w), 551 (m), 508 (s), 491 (s), 461 (m), 419 (w) cm–1. H NMR: δ
= 7.65 (m, 4 H, C6H5), 7.38 (m, 6 H, C6H5), 3.34 (m, 2 H, CH2 in CH2Cl2 at –20 °C. The crystallographic data were collected with
pip), 2.98 (s, 2 H, NCH2Si), 2.36 (m, 2 H, CH2 pip), 1.86 (m, 2 H, a Stoe IPDS diffractometer and are presented in Table 3. The struc-
CH2 pip), 1.66 (m, 3 H, CH2 pip), 1.37 (m, 1 H, CH2 pip), 0.64 (s,
2 H, SiCH2Pd) ppm. 13C{1H} NMR: δ = 136.5 (s, SiC6H5 ipso), by full-matrix least-squares methods (based on Fo2), anisotropic
134.7 (s, SiC6H5 ortho), 129.3 (SiC6H5 para), 127.9 (SiC6H5 meta), thermal parameters for all non-H atoms in the final cycles, H atoms
tures were solved by using direct and Fourier methods: Refinement
126.7 (s, SCN), 62.7 (s, NCH2CH2CH2), 55.0 (s, NCH2Si), 23.1 (s, were refined by using a riding model in their ideal geometric posi-
NCH2CH2CH2), 22.9 (s, NCH2CH2CH2), 1.3 (s, PdCH2Si) ppm. tions. SHELXS-86 and SHELXL-97 were used in the structural
C40H48N4Pd2S2Si2 (917.94): calcd. C 52.34, H 5.27, N 6.10; found
C 52.11, H 5.14, N 5.96.
solutions and refinements.[17] CCDC-870641 (for 2) and -870642
(for 4) contain the detailed crystallographic data for this paper.
3306
www.eurjic.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 3302–3307

Bridging Pseudohalides in Palladacycles
[5] F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G.
Orpen, R. Taylor, J. Chem. Soc. Perkin Trans. 2 1987, S1–S19.
[6] G. López, G. García, M. D. Santana, G. Sánchez, J. Ruiz, J. A.
Hermoso, A. Vegas, M. Martinez-Ripoll, J. Chem. Soc., Dalton
Trans. 1990, 1621–1626.
[7] A. E. Mauro, A. V. G. Netto, A. C. Moro, J. G. Ferreira, R. H.
de A. Santos, E. T. de Almeida, Anal. Sci.: X-ray Struct. Anal.
Online 2009, 25, 65–66.
This data may be obtained free of charge from the Cambridge
Crystallographic Data Center through www.ccdc.cam.ac.uk/data_
request/cif.
Table 3. Crystal and experimental data for compounds 2 and 4.
2
4·hexane
[8] G. Zhao, Q.-C. Yang, T. C. W. Mak, Organometallics 1999, 18,
3623–3636.
[9] A. M. Santana, A. V. de G. Netto, E. T. de Almeida, A. E.
Mauro, J. Souza, R. H. de A. Santos, Z. Kristallogr. New Cryst.
Struct. 2002, 217, 147.
Empirical formula
M [gmol–1]
Crystal system
Space group
Crystal size [mm]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C40H48N4Pd2S2Si2 C86H110N8Pd4Si4
917.92
tetragonal
I41/a
1793.78
monoclinic
¯
P1
0.20ϫ0.20ϫ0.20 0.20ϫ0.20ϫ0.10
[10] a) P. M. Maitlis, P. Espinet, M. J. H. Rusell in Comprehensive
Organometallic Chemistry, vol. 6 (Eds.: G. Wilkinson, F. G. A.
Stone, E. W. Abel), Pergamon Press, Oxford, 1982, pp. 333–
334; b) A. J. Canty in Comprehensive Organometallic Chemistry
II, vol. 9 (Eds.: G. Wilkinson, F. G. A. Stone, E. W. Abel), Per-
gamon Press, Oxford, 1995, pp. 271–272.
20.3965(9)
20.3965(9)
19.4889(13)
90
90
90
15.291(4)
23.438(5)
25.862(6)
73.91(3)
86.30(4)
73.32(3)
8530(3)
4
γ [°]
V [Å3]
8107.7(7)
8
[11] R. G. Pearson, Inorg. Chem. 1973, 12, 712.
[12] E. Keller, SCHAKAL99, University of Freiburg, 1999.
[13] a) W. P. Fehlhammer, L. F. Dahl, J. Am. Chem. Soc. 1972, 94,
3370–3377; b) W. Beck, W. P. Fehlhammer, K. Feldl, T. M.
Klapötke, G. Kramer, P. Mayer, H. Piotrowski, P. Pollmann,
W. Ponikwar, T. Schutt, E. Schuierer, M. Vogt, Z. Anorg. Allg.
Chem. 2001, 627, 1751; c) E. T. de Almeida, A. E. Mauro,
A. M. Santana, S. R. Ananias, A. V. G. Netto, J. G. Ferreira,
R. H. A. Santos, Inorg. Chem. Commun. 2007, 10, 1394–1398.
Z
ρcalcd. [gcm–3]
1.504
1.083
1.397
0.933
μ [mm–1]
Refl. measured
Scan range [°]
Unique refl.
Refl. observed [IϾ2σ(I)]
R1, wR2
44752
57780
1.45Ͻ2θϽ27.00 0.941Ͻ2θϽ25.00
4420
3777
28281
17531
0.0261, 0.0640
0.0576, 0.1499
[14] Colorless
blocks
from
hexane/dichloromethane:
C38H98N8Si2Pd2, M = 936.25 gmol–1, monoclinic, space group
P21 (no. 4), a = 9.7370(15), b = 14.5009(22), c = 29.0035(4) Å,
β = 99.677(2)°, V = 4036.89(18) Å3.
Supporting Information (see footnote on the first page of this arti-
cle): Thermodynamic data for the tetrametallic/trimetallic equilib-
rium of the CN-bridging complex in CDCl3, and ORTEP plot for
molecular structure of 4.
[15] a) For a review, see: G. N. Newton, M. Nihei, H. Oshio, Eur. J.
Inorg. Chem. 2011, 3031–3042; b) W. C. Kalb, Z. Demidowicz,
D. M. Speckman, C. Knobler, R. G. Teller, M. F. Hawthorne,
Inorg. Chem. 1982, 21, 4027–4036; c) P. Schinnerling, U.
Thewalt, J. Organomet. Chem. 1992, 431, 41–45; d) F. Olbrich,
J. Kopf, E. Weiss, J. Organomet. Chem. 1993, 456, 293–298; e)
S. M. Contakes, T. B. Rauchfuss, Angew. Chem. 2000, 112,
2060; Angew. Chem. Int. Ed. 2000, 39, 1984–1986; f) A. Gal-
styan, P. J. S. Miguel, J. Wolf, E. Freisinger, B. Lippert, Eur. J.
Inorg. Chem. 2011, 1649–1656.
[16] a) For a review, see: E. Zangrando, M. Casanova, E. Alessio,
Chem. Rev. 2008, 108, 4979–5013; b) A. Galstyan, W.-Z. Shen,
E. Freisinger, H. Alkam, W. Hiller, P. J. S. Miguel, M.
Schürmann, B. Lippert, Chem. Eur. J. 2011, 17, 10771–10780;
c) M. Ferrer, A. Pedrosa, L. Rodríguez, O. Rossell, M. Vilaseca,
Inorg. Chem. 2010, 49, 9438–9449; d) K. Uehara, K. Kasai, N.
Mizuno, Inorg. Chem. 2010, 49, 2008–2015; e) S. Ghosh, P. S.
Mukherjee, Inorg. Chem. 2009, 48, 2605–2613; f) T. Weilandt,
R. W. Troff, H. Saxell, K. Rissanen, C. A. Schalley, Inorg.
Chem. 2008, 47, 7588–7598; g) E. Holló-Sitkei, G. Tárkányi,
L. Párkányi, T. Megyes, G. Besenyei, Eur. J. Inorg. Chem. 2008,
1573–1583; h) K. Suzuki, M. Kawano, M. Fujita, Angew.
Chem. 2007, 119, 2877; Angew. Chem. Int. Ed. 2007, 46, 2819–
2822; i) S. Derossi, M. Casanova, E. Iengo, E. Zangrando, M.
Stener, E. Alessio, Inorg. Chem. 2007, 46, 11243–11253; j) M.
Ferrer, A. Gutiérrez, M. Mounir, O. Rossell, E. Ruiz, A. Rang,
M. Engeser, Inorg. Chem. 2007, 46, 3395–3406; k) K. Uehara,
K. Kasai, N. Mizuno, Inorg. Chem. 2007, 46, 2409–2416.
[17] a) G. M. Sheldrick, SHELXS-90, Structure Solving Program
for Crystal Structure Determination, University of Göttingen,
Göttingen, 1990; b) G. M. Sheldrick, SHELXL-97, A Com-
puter Program for Refinement of Crystal Structures, University
of Göttingen, Göttingen, 1997.
Acknowledgments
The authors in Valladolid thank the Spanish Ministerio de Educa-
ción y Ciencia (CTQ2009-12111) and the Junta de Castilla y León
(GR125 Programa de Grupos de Excelencia de la Junta de Castilla
y León) for financial support. M. A. and P. G.-I. thank the Minis-
terio de Educación y Ciencia (MEC) and the Universidad de Valla-
dolid (FPI Programs), respectively, for their grants. The authors in
Dortmund thank the Deutsche Forschungsgemeinschaft, the Fonds
der Chemischen Industrie, and Wacker Chemie AG for their sup-
port.
[1] A. N. Golub, H. Kohler, V. V. Skopenko, Chemistry of the Pseu-
dohalides, Elsevier, Amsterdam, 1986.
[2] a) C. Strohmann, B. C. Abele, K. Lehmen, F. Villafañe, L. Si-
erra, S. Martín-Barrios, J. Organomet. Chem. 2002, 661, 149–
158; b) D. Schildbach, M. Arroyo, K. Lehmen, S. Martín-Bar-
rios, L. Sierra, F. Villafañe, C. Strohmann, Organometallics
2004, 23, 3228–3238.
[3] a) C. Strohmann, K. Lehmen, K. Wild, D. Schildbach, Organo-
metallics 2002, 21, 3079–3081; b) T. H. Chan, P. Pellon, J. Am.
Chem. Soc. 1989, 111, 8737–8738; c) G. Fraenkel, J. H. Dun-
can, K. Martin, J. Wang, J. Am. Chem. Soc. 1999, 121, 10538–
10544; d) C. Strohmann, D. H. M. Buchold, T. Seibel, K. Wild,
D. Schildbach, Eur. J. Inorg. Chem. 2003, 3453–3463; e) C. Un-
kelbach, B. C. Abele, K. Lehmen, D. Schildbach, B. Waerder,
C. Strohmann, Chem. Commun. 2012, 48, 2492–2494.
[4] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 3rd ed., Wiley, 1978, p. 274.
Received: March 10, 2012
Published Online: June 1, 2012
Eur. J. Inorg. Chem. 2012, 3302–3307
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3307