Syntheses, dynamic behaviour and theoretical studies of [(Piperidinomethyl)silyl]methyl-cyclopalladated dimetallic complexes

Article abstract of DOI:10.1002/ejic.201200257

The cationic complex [Pd{CH₂SiPh₂(CH ₂NC₅H₁₀)-κ²C,N}(NCMe) ₂]BF₄ (CH₂NC₅H₁₀ = piperidinomethyl) is obtained from the reaction of [Pd{CH₂SiPh ₂(CH₂NC₅H₁₀)-κ²C,N} (μ-Cl)]₂ with TlBF₄ in the presence of NCMe. It reacts with KO₂CCH₃ leading to the dimetallic complex [Pd{CH ₂SiPh₂(CH₂NC₅H₁₀)- κ²C,N}(μ-O₂CCH₃-κO:κ'O)] ₂, which exists only as the transoid isomer in solution. A dynamic process due to inversion of the acetato bridges is detected by variable-temperature ¹H NMR spectroscopy. The reaction of the same parent complex with Kdmpz (dmpz = dimethylpyrazolate) leads to the dinuclear complex [Pd{CH₂SiPh₂(CH₂NC₅H ₁₀)-κ²C,N}(μ-dmpz-κN:κ'N)] ₂, which in solution exists as a mixture of cisoid and transoid isomers, but no inversion of the bridging pyrazolato groups has been observed. The reaction between equimolar amounts of these two complexes in CH ₂Cl₂ affords low yields of the expected mixed acetato/pyrazolato-bridged complex [Pd₂{CH₂SiPh ₂(CH₂NC₅H₁₀)-κ²C,N} ₂(μ-O₂CCH₃-κO:κ'O)(μ-dmpz- κN:κ'N)]. The mixed chlorido-pyrazolato-bridged complex [Pd ₂{CH₂SiPh₂(CH₂NC₅H ₁₀)-κ²C,N}₂(μ-Cl)(μ-dmpz-κN: κ'N)] is obtained by mixing equimolar amounts of the parent dichlorido- and bis(dimethylpyrazolato)-bridged dinuclear complexes, and exhibits a dynamic process in solution corresponding to the inversion of the bridges. Only the cisoid isomers are detected for both dimetallic complexes with mixed bridging ligands. The experimental findings of the preferred transoid or cisoid structure in these dinuclear Pd complexes were supported by quantum chemical calculations. The nature of the bridging ligands determines both the presence of transoid or cisoid isomers and the rigidity in solution of dimetallic complexes containing palladacycles with the [(piperidinomethyl)silyl]methyl ligand. Copyright

Full text of DOI:10.1002/ejic.201200257

FULL PAPER
DOI: 10.1002/ejic.201200257
Syntheses, Dynamic Behaviour and Theoretical Studies of [(Piperidinomethyl)-
silyl]methyl-Cyclopalladated Dimetallic Complexes
Victoria P. Colquhoun,[a] Daniel Schildbach,[a] Raquel Martín-Romo,[b]
Carsten Strohmann,*[a] and Fernando Villafañe*[b]
Keywords: Palladacycles / Carboxylate ligands / N ligands / Bridging ligands / Organosilanes
The cationic complex [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}-
(NCMe)2]BF4 (CH2NC5H10 = piperidinomethyl) is obtained
from the reaction of [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-
Cl)]2 with TlBF4 in the presence of NCMe. It reacts with
KO2CCH3 leading to the dimetallic complex [Pd{CH2SiPh2-
(CH2NC5H10)-κ2C,N}(μ-O2CCH3-κO:κЈO)]2, which exists
only as the transoid isomer in solution. A dynamic process
The reaction between equimolar amounts of these two com-
plexes in CH2Cl2 affords low yields of the expected mixed
acetato/pyrazolato-bridged
complex
[Pd2{CH2SiPh2-
(CH2NC5H10)-κ2C,N}2(μ-O2CCH3-κO:κЈO)(μ-dmpz-κN:κЈN)].
The mixed chlorido-pyrazolato-bridged complex [Pd2{CH2-
SiPh2(CH2NC5H10)-κ2C,N}2(μ-Cl)(μ-dmpz-κN:κЈN)] is ob-
tained by mixing equimolar amounts of the parent
due to inversion of the acetato bridges is detected by vari- dichlorido- and bis(dimethylpyrazolato)-bridged dinuclear
1
able-temperature H NMR spectroscopy. The reaction of the
same parent complex with Kdmpz (dmpz = dimethylpyrazol-
ate) leads to the dinuclear complex [Pd{CH2SiPh2-
(CH2NC5H10)-κ2C,N}(μ-dmpz-κN:κЈN)]2, which in solution
exists as a mixture of cisoid and transoid isomers, but no in-
version of the bridging pyrazolato groups has been observed.
complexes, and exhibits a dynamic process in solution corre-
sponding to the inversion of the bridges. Only the cisoid iso-
mers are detected for both dimetallic complexes with mixed
bridging ligands. The experimental findings of the preferred
transoid or cisoid structure in these dinuclear Pd complexes
were supported by quantum chemical calculations.
{[(aminomethyl)silyl]methyl}metal compounds,[8] and we
reported the first {[diphenyl(piperidinomethyl)silyl]methyl}-
palladium(II) complexes.[9] The incorporation of a silicon
atom into the palladacycle serves a double function: stabi-
lizing the metalated carbon atom by polarisation effects,
and preventing β-elimination. Moreover, the substituents at
the nitrogen centre play a second, important role, as they
allow the introduction of stereochemical information. This
is achieved by using chiral amines in the ligand synthesis.
Thereby, diastereomerically highly enriched {[(amino-
methyl)silyl]methyl}lithium compounds with a stereogenic
metalated carbon atom with a specific configuration can be
synthesised.[8d,10]
Introduction
The chemistry of palladacycles has been one of the most
active fields of research on transition-metal organometallic
chemistry during the last decades.[1] There are different
reasons for this development, such as the potential applica-
tions of palladacycles, which range from their use as precur-
sors for novel organic compounds[2] to the design of new
materials[3] or drugs.[4] Some chiral complexes have been
used as chiral resolving agents,[5] and more recently, some
palladacycles have been investigated as catalysts in C–C
coupling reactions.[6] The latter aspect, which has been de-
veloped in the last few years, is undoubtedly one of the
main reasons for the renewed interest in these complexes.
However, it is now evident that the role of the palladacycle
consists in feeding Pd0 nanoparticles to the reaction mix-
ture, which seem to be the real catalysts of these processes.[7]
As part of our systematic studies on metalated organosil-
anes, we are studying the structure and reactivity of
The palladacycle complexes obtained so far with the
[diphenyl(piperidinomethyl)silyl]methyl
synthesised from the parent
ligand
chlorido-bridged
were
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-Cl)]2 (1), which was
obtained by the reaction of the appropriate organolithium
reagent and trans-[PdCl2(SMe2)2].[9b] As is common for
chlorido-bridged palladacycles, the structure of this dimet-
allic complex is planar, and in solution a slow exchange
equilibrium between the cisoid and the transoid isomer was
detected on the NMR timescale. Both isomers differ in the
relative orientation of the palladacycles.[9b]
[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
Following these studies, we were interested in the synthe-
sis of new dimetallic complexes with the [diphenyl(piper-
idinomethyl)silyl]methyl ligand containing other anionic
E-mail: mail@carsten-strohmann.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200257.
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C. Strohmann, F. Villafañe et al.
FULL PAPER
bridging ligands, such as acetato or pyrazolato groups. The support the proposed geometry, but no analytical data of
geometry and electronic features of this type of dimetallic the solid product or a 13C NMR spectrum could be ob-
palladacycles are well known,[1] therefore we decided to tained, because of the high instability of this complex both
complete this study by also obtaining complexes with two as a solid and in solution, even at low temperatures. This
mixed bridging ligands. To support the experimental obser- instability precluded the isolation of the pure complex.
vations, we decided to complete this study with quantum However, compound 2 could be used as an in situ starting
chemical calculations. Surprisingly, theoretical studies on material directly obtained from the reaction mixture.
this type of complexes are scarce.[11]
Thereby, the complex is stabilized by a large amount of
MeCN.
The reaction of 2 with a slight excess of KO2CCH3
leads to [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-O2CCH3-
κO:κЈO)]2 (3), which is isolated as a pale yellow solid. The
expected coordination of the acetato group as a bridging
ligand is immediately confirmed by the IR spectrum, since
the difference between both CO stretching absorptions
(177 cm–1) is typical for this coordination pattern.[12] Only
the transoid isomer is detected in solution, which is revealed
by the observation of only one singlet for the methyl group
Results and Discussion
Synthesis, Structure and Dynamic Behaviour of Dimetallic
Palladium Complexes
There are many examples of palladacycles with bridging
acetato groups. Therefore, the synthesis of an acetato-
bridged complex incorporating the [diphenyl(piperidino-
methyl)silyl]methyl moiety was our first target. However, we
were unable to obtain a pure acetato-bridged complex by
treating 1 with different acetate salts, as the final product
could not be obtained completely free of the starting mate-
rial. Finally, the acetato-bridged complex 3 could be ob-
tained in pure form by treating the cationic precursor
1
of the bridging acetato group in the H NMR spectrum.
Most of the signals in the 1H NMR spectrum are very
broad at room temperature, but are sharpened at 333 K,
indicating the presence of a dynamic process in solution.
The observation of only one singlet for the SiCH2N protons
at this temperature indicates an averaged structure. How-
ever, these protons are diastereotopic at 253 K. At this tem-
perature no dynamic process is observed and the signals of
only one species are found, corresponding to two (indistin-
guishable) enantiomers (Scheme 2). This dynamic process
had been previously studied in detail for other acetato-
bridged complexes.[13] It is assumed to proceed by the cleav-
age of one of the coordinating bonds of an acetato bridge,
followed by rotation of the Pd–O bond in the remaining
bridge and the renewed formation of the double bridge.[13]
The activation energy of this process seems to be lower for
3 than for most of the cyclopalladated complexes with
bridging acetato groups reported so far, which are usually
described as “rigid”.[14] Usually only the transoid isomer is
detected in solution,[13d,15] although mixtures containing
mainly the transoid isomer with a minor amount of the
cisoid isomer have also been reported.[13c,14b,16]
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(NCMe)2]BF4
with KO2CCH3 (Scheme 1).
(2),
Scheme 2. Dynamic process detected in solution between the two
enantiomers of 3 showing diastereotopic SiCH2N protons (piper-
idine groups are omitted for clarity).
Scheme 1. Syntheses of acetato- and dmpz-bridged cyclopalladated
dimetallic complexes.
In order to gain more information on the factors that
The cationic complex 2 is easily obtained in thf upon determine the stereochemistry of these cyclopalladated di-
treatment of complex 1 with equimolar amounts of TlBF4 metallic species, we decided to synthesise a new dimetallic
in the presence of acetonitrile. This reaction leads to the complex with a different bridging ligand. Therefore, com-
precipitation of TlCl, and compound 2 is obtained from the plex 2 was treated with an equimolar amount of Kdmpz,
solution. Its spectroscopic data (see Experimental Section) leading to [Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-dmpz-
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[(Piperidinomethyl)silyl]methyl-Cyclopalladated Dimetallic Complexes
κN:κЈN)]2 (4), which was isolated as colourless crystals. The ligands is 82.6(2)° (the rms deviation of fitted atoms is
structure of this complex could be confirmed by an X-ray 0.04 Å and 0.05 Å). Both Pd centres display the usual
diffraction analysis, which is shown in Figure 1. Table 1 lists square-planar coordination environment, and the angle be-
selected bond lengths and angles.
tween the normals of these planes is 78.0(1)° (the rms devia-
tion of fitted atoms is 0.04 Å and 0.02 Å).
The distances between the palladium atoms and the ni-
trogen atoms of the bridging pyrazolato groups reflect the
different trans influences of the donor atoms of the pallada-
cycle: As expected, bonds trans to the carbon donor atoms
are longer [2.113(5) Å and 2.131(5) Å] than bonds trans to
the piperidine moiety [2.014(5) Å and 2.002(5) Å]. This dif-
ference in bond length is quite large in comparison to other
pyrazolato-bridged complexes with different donor atoms
coordinated in trans position.[17a,17b]
The five-membered [diphenyl(piperidinomethyl)silyl]-
methyl metallacycles adopt the typical envelope conforma-
tion.[9b] The palladium atoms are bent by 46.9(2)° and
48.4(2)° out of the pseudoplanes defined by the other four
atoms in the metallacycle (the rms deviation of fitted atoms
is 0.09 Å and 0.06 Å). This conformation allows for mini-
mised repulsion between the substituents in the cyclometall-
ated ligand. The distance between Pd and C, as well as the
other bond lengths and angles found in the palladacycles
are similar to those reported previously.[9b]
Figure 1. Molecular structure and numbering scheme of compound
4 in the crystal (SCHAKAL[18] plot, additional hexane molecule
has been omitted for clarity).
Table 1. Selected bond lengths [Å] and angles [°] of compound 4.
The 1H NMR spectrum of the first batch of crystals,
which were also subjected to the X-ray diffraction analysis,
reveals the presence of only the transoid isomer in solution.
However, a small amount of a second minor isomer, which
has been assigned to the cisoid structure, is always detected
in the solid obtained in a second batch after concentration
of the mother liquor. The solutions of either the pure
transoid isomer or the mixture of isomers show no isomeri-
sation even after prolonged heating. Therefore, it can be
assumed that the isomers detected in solution are formed
during the reaction, but no exchange equilibrium is estab-
lished between them once they are formed. Conversely, the
consistency of the spectra even upon heating indicates that
both isomers are rigid in solution. This is what is usually
observed for dimethylpyrazolato-bridged dimetallic com-
plexes, in opposition to the less-hindered pyrazolato-
bridged dinuclear species, where inversion of the central
M(N–N)2M ring is often detected on the NMR time
scale.[17e,17f]
C1–Si1
1.845(6)
2.067(6)
1.503(7)
1.897(7)
1.845(6)
2.065(6)
1.501(7)
1.916(6)
1.344(7)
1.382(8)
1.378(8)
1.361(7)
1.357(7)
1.381(8)
1.374(8)
1.347(7)
2.155(5)
2.164(5)
1.383(6)
2.113(5)
2.014(5)
1.378(6)
2.002(5)
2.131(5)
Si1–C1–Pd1
N1–C14–Si1
Si2–C20–Pd2
N2–C33–Si2
C14–N1–Pd1
C33–N2–Pd2
N4–N3–Pd2
N3–N4–Pd1
N6–N5–Pd2
N5–N6–Pd1
N4–Pd1–C1
N4–Pd1–N6
C1–Pd1–N6
N4–Pd1–N1
C1–Pd1–N1
N6–Pd1–N1
N5–Pd2–C20
N5–Pd2–N3
C20–Pd2–N3
N5–Pd2–N2
C20–Pd2–N2
N3–Pd2–N2
C1–Si1–C14
104.5(3)
110.3(4)
103.5(3)
110.3(4)
104.0(3)
104.4(3)
118.7(3)
115.6(3)
117.0(3)
117.6(3)
89.9(2)
C1–Pd1
C14–N1
C14–Si1
C20–Si2
C20–Pd2
C33–N2
C33–Si2
C39–N3
C39–C40
C40–C41
C41–N4
C44–N5
C44–C45
C45–C46
C46–N6
N1–Pd1
N2–Pd2
N3–N4
86.5(2)
175.4(2)
176.4(2)
87.1(2)
96.6(2)
90.5(2)
84.5(2)
174.7(2)
177.7(2)
87.2(2)
97.7(2)
103.5(3)
N3–Pd2
N4–Pd1
N5–N6
N5–Pd2
N6–Pd1
In summary, the three complexes 1, 3 and 4 with different
bridging ligands described above show different structures
Complex 4, which crystallises with 0.5 equiv. of hexane, and different behaviour in solution. The parent chlorido-
displays pseudo-C2 symmetry and consists of two Pd atoms bridged complex 1 is planar and shows a slow equilibrium
bridged by two dmpz ligands with the usual boat-like con- between the transoid and cisoid isomers,[9b] whereas com-
formation of the Pd2N4 six-membered metallacycle.[17] The plexes 3 and 4 are bent: the acetato-bridged complex ap-
distance between the two palladium atoms is 3.275(1) Å, pears only as the transoid isomer but undergoes a dynamic
indicating no metal–metal bond interaction, and similar to process forming two enantiomers. The dimethylpyrazolato-
those found in other diazolato-bridged Pd complexes.[17] bridged complex 4 is rigid, and no equilibrium is detected
The two remaining coordination sites surrounding each Pd between the transoid and cisoid isomers.[19]
atom are occupied by the cyclopalladated ligands mutually
To complete this study, we used the complexes 1, 3 and
coordinated in a transoid position, thus minimising the in- 4 to synthesise new mixed dimetallic complexes containing
teractions between the piperidine groups, which tend to fill two different bridging ligands. The interest of these dinu-
the space between both coordination planes. The angle be- clear complexes lies in the isolation of only cisoid geome-
tween the normals of both planes containing the pyrazolato tries, in accordance with the anti-symbiotic effect of the soft
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palladium(II) centre,[20] also redefined as transphobia.[21] No pected product, [Pd2{CH2SiPh2(CH2NC5H10)-κ2C,N}2(μ-
mixed chlorido/acetato-bridged complex could be obtained, O2CCH3-κO:κЈO)(μ-dmpz-κN:κЈN)] (6), (Scheme 5), al-
as heating equimolar amounts of 1 and 3 in CDCl3 or thf though only in low yields. Other solvents, such as toluene,
led to the deposition of metallic Pd. This is not surprising acetone, or thf, led to rapid decomposition of the reaction
as we have no knowledge of any report on this type of com- mixture.[22,23]
plex, although many reports describe dichlorido- or diacet-
ato-bridged complexes. However, the reaction between 1
and 4 yields the new, pure chlorido/dimethylpyrazolato-
bridged complex [Pd2{CH2SiPh2(CH2NC5H10)-κ2C,N}2(μ-
Cl)(μ-dmpz-κN:κЈN)] (5) (Scheme 3).
Scheme 5. Synthesis of the mixed acetato/dimethylpyrazolato-
bridged dimetallic complex 6.
The bridging coordination of the acetato group is con-
firmed by the IR spectrum, given the large difference be-
tween both CO stretching absorptions (142 cm–1).[12] The
Scheme 3. Synthesis of the mixed chlorido/dimethylpyrazolato-
bridged dimetallic complex 5.
equivalence of the methyl groups of the bridging dimethyl-
1
pyrazolato ligand in the H NMR spectrum also supports
The cisoid geometry is confirmed by the NMR spectra,
which show the equivalence of the two methyl groups of the
bridging dimethylpyrazolato ligand. This cisoid geometry is
expected considering the anti-symbiotic or transphobia ef-
the cisoid geometry proposed by the anti-symbiotic or
transphobia effect.[20,21] The protons of the methylene group
in the PdCH2Si and SiCH2N moieties are diastereotopic,
which indicates that complex 6 is not planar in solution. In
fact a boat-type conformation is expected for this complex,
since both the acetato- and pyrazolato-bridged complexes
present non-planar structures. This conformation of com-
plex 6 is rigid, since the H NMR spectrum remains un-
changed upon heating. A similar rigid structure was also
observed for complex 4.
In summary, the replacement of a dimethylpyrazolato
group by an acetato ligand in 4 gives rise to another rigid
dimetallic complex, whereas the replacement of a dimethyl-
pyrazolato group by a chlorido ligand lowers the barrier of
this inversion process (Scheme 3).
1
fect.[20,21] As observed for 3, some signals in the H NMR
spectrum at room temperature are broad, and sharpen in
the 1H NMR spectrum at 333 K. This spectrum is expected
for an averaged planar structure. This data points to a dy-
namic process in solution similar to that observed for 3. In
solution, the five-membered ring formed by the metal
atoms and the bridging ligands of complex 5 invert as
shown in Scheme 4. Upon lowering the temperature, most
of the signals start to duplicate, although they still remain
broad at –80 °C, making their assignment impossible.
1
Computational Studies
To support our experimental findings of the preferred
transoid or cisoid structure in the Pd dinuclear complexes
3–6 quantum chemical calculations were applied. Possible
Scheme 4. Dynamic behaviour of compound 5, [(piperidinometh-
yl)silyl]methyl groups have been omitted for clarity.
Equimolar amounts of the two dimetallic complexes de- cisoid and transoid geometries were optimised for the afore-
scribed in this work, 3 and 4, were mixed and heated to mentioned compounds by using the B3LYP hybrid func-
40 °C in order to obtain a mixed acetato/pyrazolato- tional and the 6-31+G(d) basis set for all atoms except pal-
bridged dinuclear complex. Only chlorinated solvents, ladium, for which the Stuttgart basis set and pseudopoten-
such as CH2Cl2 or CHCl3 allowed the isolation of the ex- tial ECP28MWB[24] was applied. In the chlorido-bridged
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[(Piperidinomethyl)silyl]methyl-Cyclopalladated Dimetallic Complexes
complex, which was used as a starting material, both the
cisoid and transoid geometries coexist in solution,[9b] and
therefore no energy difference between the possible calcu-
lated isomers was found (see Supporting Information).
However, in solution, both the pure acetato- and dimethyl-
pyrazolato-bridged complexes 3 and 4 form a transoid
structure. This was supported by an energy difference of
11 kJmol–1 (3, Figure 2) and 10 kJmol–1 (4) between the
preferred transoid and the energetically less stable cisoid
structure. Both bridging ligands, the acetato as well as the
dimethylpyrazolato group, give rise to bent structures;
therefore, the preference of the transoid forms may be due
to steric reasons.
Conclusions
Several dimetallic complexes containing palladacycles
with the [(piperidinomethyl)silyl]methyl ligand have been
synthesised and characterised. The nature of the bridging
ligands determines both the presence of transoid or cisoid
isomers and the rigidity of the complex in solution. The
latter is especially demonstrated by the examples of mixed
bridged dimetallic compounds. As previously reported,
small and non-directional bridging chlorido groups give rise
to a planar arrangement and to a slow equilibrium in solu-
tion due to the presence of transoid and cisoid isomers.[9b]
If the bridging ligand is larger and more directional, the
transoid isomer is preferred, and the complex is more rigid.
Thus, bridging acetato ligands result in the transoid isomer
only, and a dynamic process is detected in solution due to
the formation of two enantiomers. However, the complex
with bridging pyrazolato groups is rigid, and only a small
amount of cisoid isomer is detected. No exchange process
with the major transoid isomer is observed. The behaviour
of the mixed bridged dimetallic compounds in solution also
depends on the size and directionality of the bridging li-
gands, since the presence of small and non-directional
chlorido groups in the chlorido/pyrazolato-bridged com-
plex results in a ring inversion process. In contrast, the com-
bination of both an acetato and pyrazolato ligand, direc-
tional and larger, results in a rigid structure. As expected
from the anti-symbiotic effect, only the cisoid isomer is de-
tected for these mixed bridged dimetallic complexes.
Figure 2. Calculated energy difference between the transoid and ci-
soid acetato-bridged complex 3 [B3LYP; Pd: ECP28MWB,[25]
others: 6-31+G(d)].
For the complexes with mixed bridging ligands, a
chlorido/dimethylpyrazolato (5) and acetato/dimethyl-
pyrazolato (6) bridge, the preferred structure in solution is
cisoid. This behaviour was also simulated in the calculations
of these compounds, resulting in an energy difference of
22 kJmol–1 between the preferred one of two possible cisoid
geometries and the transoid structure for complex 5. A sim-
ilar difference in energy of 18 kJmol–1 was found for the
Experimental Section
General Remarks: IR (KBr pellets, 4000–450 cm–1): Perkin–Elmer
Spectrum RX I FT-IR. 1H NMR [solvent CDCl3; internal standard
CHCl3 (δ = 7.20 ppm); recorded at room temperature unless other-
wise indicated]: Bruker AC-300 or ARX-300 (300.13 MHz). 13C
NMR [solvent and internal standard CDCl3 (δ = 77.00 ppm); re-
corded at room temperature]: Bruker ARX-300 (75.78 MHz). As-
signment of the 13C NMR spectroscopic data was supported by
DEPT experiments and relative intensities of the resonance signals.
Microanalyses: Perkin–Elmer 2400B microanalyzer, Departamento
de Química Inorgánica, Facultad de Ciencias, Valladolid (Spain).
All reactions were carried out under oxygen-free and dried N2 by
conventional Schlenk techniques. Filtrations were carried out on
dry Celite under N2. The solvents were dried according to common
procedures. Complex 1 was obtained as described previously.[7b]
acetato/dimethylpyrazolato-bridged complex
6
(Fig-
ure 3).[25] In the case of these complexes, the preference of
the cisoid form may be due to the transphobia effect.
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(NCMe)2]BF4 (2): MeCN
(1 mL) and TlBF4 (0.058 g) (Caution: TlI derivatives are toxic and
should be handled with care) were added to a solution of 1 (0.087 g,
0.1 mmol) in thf (10 mL). The mixture was stirred at room tem-
perature for 3 h, during which time TlCl precipitated as a white
solid. This mixture was used without further purification to obtain
3 or 4. In order to obtain 2, the mixture was filtered, and the filtrate
was concentrated to dryness. The greenish-yellow solid obtained
was washed with hexane (4ϫ3 mL) and dried in vacuo, yielding
1
0.087 g (76%) of spectroscopically pure 2. H NMR: δ = 1.19 (m,
1 H, NCH2CH2CH2), 1.53 (s, 2 H, PdCH2Si), 1.54 (m, 1 H,
NCH2CH2CH2), 1.67 (m, 4 H, NCH2CH2), 2.24 (s, 3 H, NCCH3),
2.29 (m, 2 H, NCH2CH2), 2.35 (s, 3 H, NCCH3), 2.97 (s, 2 H,
SiCH2N), 3.15 (m, 2 H, NCH2CH2), 7.36 (m, 6 H, C6H5), 7.58 (m,
Figure 3. Calculated energy difference between the transoid and the
most stable cisoid mixed acetato/dimethylpyrazolato-bridged com-
plex 6 [B3LYP; Pd: ECP28MWB,[25] others: 6-31+G(d)].
Eur. J. Inorg. Chem. 2012, 3427–3434
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3431

C. Strohmann, F. Villafañe et al.
FULL PAPER
4 H, C H ) ppm. IR: ν = 3067 (w), 3047 (w), 2941 (m), 2863 (w),
different samples studied was 85:15. 13C{1H} NMR: δ = –7.4 (s,
˜
6
5
1826 (w), 1485 (w), 1452 (w), 1428 (m), 1378 (w), 1284 (w), 1262 PdCH2Si, transoid), –6.7 (s, PdCH2Si, cisoid), 14.1 (s, CH3 dmpz,
(w), 1231 (w), 1084 (br. vs), 910 (w), 864 (w), 806 (w), 768 (m), 735 transoid), 14.2 (s, CH3 dmpz, transoid), 14.3 (s, CH3 dmpz, cisoid),
(s), 700 (s), 620 (w), 519 (w), 492 (m), 472 (m) cm–1.
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-O2CCH3-κO:κЈO)]2
14.4 (s, CH3 dmpz, cisoid), 21.6 (s, NCH2CH2, cisoid), 22.6 (s,
NCH2CH2, transoid), 23.7 (s, NCH2CH2CH2, cisoid and transoid),
56.5 (br., SiCH2N, cisoid), 61.8 (s, NCH2CH2, cisoid), 62.5 (s,
NCH2CH2, transoid), 64.2 (s, SiCH2N, transoid), 102.6 (s, CH
dmpz, transoid), 102.7 (s, CH dmpz, cisoid), 102.8 (s, CH dmpz,
cisoid), 127.8 (s, Si-m-C6H5, cisoid and transoid), 128.7 (s, Si-p-
C6H5, cisoid), 128.7 (s, Si-p-C6H5, cisoid), 128.8 (s, Si-p-C6H5,
transoid), 134.4 (s, Si-o-C6H5, transoid), 134.6 (s, Si-o-C6H5, cisoid),
134.8 (s, Si-o-C6H5, transoid), 138.3 (s, Si-i-C6H5, cisoid), 138.7 (s,
Si-i-C6H5, cisoid), 138.9 (s, Si-i-C6H5, cisoid), 139.4 (s, Si-i-C6H5,
transoid), 145.4 (s, CCH3 dmpz, transoid), 146.7 (s, CCH3 dmpz,
cisoid), 146.9 (s, CCH3 dmpz, cisoid), 147.0 (s, CCH3 dmpz,
(3):
KO2CCH3 (0.022 g, 0.22 mmol) was added to the mixture obtained
after 1 (0.087 g, 0.1 mmol), thf (10 mL), MeCN (1 mL), and TlBF4
(0.058 g, 0.02 mmol) had been stirred at room temperature for 3 h.
The mixture was stirred at room temperature for an additional 1 h
and then evaporated to dryness, yielding a dark residue, which was
extracted with toluene (3ϫ5 mL). The yellow solution thus ob-
tained was concentrated to dryness, and the yellow solid obtained
was washed with hexane (3ϫ5 mL) and dried in vacuo, yielding
0.089 g (97%) of 3. 1H NMR (333 K): δ = 1.40 (br. m, 6 H, NC5H10
and 4 H, PdCH2Si), 1.64 (br. m, 4 H, NC5H10), 1.86 br (m, 2 H,
NC5H10), 1.88 (s, 6 H, CH3CO2), 2.46 (br. m, 4 H, NC5H10), 3.04
(s, 4 H, SiCH2N), 3.31 (br. m, 4 H, NC5H10), 7.30 (m, 12 H, C6H5),
transoid) ppm. IR: ν = 3065 (w), 3046 (w), 2925 (s), 2855 (s), 1526
˜
(w), 1485 (w), 1441 (w), 1426 (s), 1358 (w), 1304 (w), 1262 (w),
1230 (w), 1177 (w), 1143 (w), 1102 (s), 1067 (w), 1041 (m), 944 (w),
863 (m), 766 (s), 732 (vs), 698 (vs), 649 (w), 544 (m), 502 (w), 489
(m) cm–1. C48H62N6Pd2Si2 (992.03): calcd. C 58.12, H 6.31, N 8.47;
found C 58.32, H 6.57, N 8.13.
1
7.65 (m, 8 H, C6H5) ppm. H NMR (293 K): δ = 1.28 (br. m, 6 H,
NC5H10 and 4 H, PdCH2Si), 1.62 (br. m, 6 H, NC5H10), 1.87 (s, 6
H, CH3CO2), 2.27 (br. m, 2 H, NC5H10), 2.72 (br. m, 4 H, SiCH2N
and 2 H, NC5H10), 3.52 (br. m, 4 H, NC5H10), 7.31 (m, 12 H,
1
C6H5), 7.65 (br. m, 8 H, C6H5) ppm. H NMR (253 K): δ = 1.07 [Pd2{CH2SiPh2(CH2NC5H10)-κ2C,N}2(μ-Cl)(μ-dmpz-κN:κЈN)] (5):
(d, J = 11.6 Hz, 2 H, PdCH2Si), 1.18 (br. m, 4 H, NC5H10), 1.27
(d, J = 11.6 Hz, 2 H, PdCH2Si), 1.41 (br., 2 H, NC5H10), 1.60 (br.,
6 H, NC5H10), 1.87 (s, 6 H, CH3CO2), 2.67 (d, J = 12.2 Hz, 2 H,
SiCH2N), 2.84 (br., 2 H, NC5H10), 3.04 (br. m, 2 H, NC5H10), 3.26
(br. m, 2 H, NC5H10), 3.36 (overlapped with the following signal,
2 H, NC5H10), 3.36 (d, J = 12.2 Hz, 2 H, SiCH2N), 7.29 (m, 10 H,
C6H5), 7.44 (m, 4 H, C6H5), 7.62 (m, 2 H, C6H5), 7.82 (m, 4 H,
C6H5) ppm. 13C{1H} NMR: δ = –3.3 (br., PdCH2Si), 1.0 (s,
CH2Cl2 (10 mL) was added to a mixture of 4 (0.050 g, 0.05 mmol)
and 1 (0.044 g, 0.05 mmol), and the solution was heated in a closed
Schlenk flask at 40 °C for 24 h. The solution was filtered, and hex-
ane (ca. 20 mL) was added to the resulting yellow solution, which
was then concentrated in vacuo and cooled to –20 °C. The yellow
crystals thus obtained were washed with hexane (3ϫ3 mL) and
1
dried in vacuo, yielding 0.073 g (80%) of 5. H NMR (333 K): δ =
1.45 (br. m, 4 H, NC5H10 and 4 H, PdCH2Si), 1.69 (br. m, 8 H,
CH3CO2), 22.2 (s, NCH2CH2CH2), 23.4 (s, NCH2CH2CH2), 53.5 NC5H10), 2.50 (s, 6 H, CH3 dmpz), 2.53 (m, 4 H, NC5H10), 2.99
(br. s, SiCH2N), 61.3 (s, NCH2CH2), 127.9 (s, Si-m-C6H5), 129.2 (s, 4 H, SiCH2N), 3.65 (m, 4 H, NC5H10), 5.67 (s, 1 H, CH dmpz),
(s, Si-p-C6H5), 134.7 (s, Si-o-C6H5), 136.8 (s, Si-i-C6H5), 180.0 (br.
s, CH CO ) ppm. IR: ν = 3066 (w), 3010 (w), 2944 (m), 2854 (m), δ = 1.20 (d, J = 9 Hz, 2 H, PdCH2Si), 1.36 (m, 2 H, NC5H10 and
7.26 (m, 12 H, C6H5), 7.72 (m, 8 H, C6H5) ppm. 1H NMR (293 K):
˜
3
2
1590 (vs), 1441 (m), 1413 (vs), 1260 (w), 1192 (w), 1106 (m), 1042
2 H, PdCH2Si), 1.56 (br., 6 H, NC5H10), 1.67 (br., 4 H, NC5H10),
(w), 959 (w), 866 (w), 765 (s), 735 (s), 703 (s), 556 (w), 504 (w), 488 2.18 (s, 6 H, CH3 dmpz), 2.37 (br., 4 H, NC5H10), 2.93 (s, 4 H,
(m) cm–1. C42H54N2O4Pd2Si2 (919.87): calcd. C 54.84, H 5.92, N
3.05; found C 54.54, H 5.93, N 3.07.
SiCH2N), 3.54 (br., 4 H, NC5H10), 5.66 (s, 1 H, CH dmpz), 7.30
(br. m, 12 H, C6H5), 7.69 (br. m, 8 H, C6H5) ppm. 13C{1H} NMR:
δ = –1.4 (s, PdCH2Si), 15.1 (s, CH3 dmpz), 21.8 (s, NCH2CH2),
23.4 (s, SiCH2N), 53.2 (br., NCH2CH2CH2), 61.4 (br., NCH2CH2),
62.7 (br., NCH2CH2), 105.2 (s, CH dmpz), 127.8 (s, Si-m-C6H5),
129.1 (s, Si-p-C6H5), 134.7 (s, Si-o-C6H5), 137.4 (s, Si-i-C6H5), 148.7
[Pd{CH2SiPh2(CH2NC5H10)-κ2C,N}(μ-dmpz-κN:κЈN)]2 (4):
A
solution of Kdmpz (0.20 mmol) in MeOH, previously prepared
from dmpzH (0.020 g) and KOH in MeOH (0.078 m, 2.6 mL), was
added to the mixture obtained after 1 (0.087 g, 0.1 mmol), thf
(10 mL), MeCN (1 mL), and TlBF4 (0.058 g, 0.02 mmol) had been
stirred at room temperature for 3 h. The mixture was stirred at
room temperature for an additional 1 h and then concentrated to
dryness, yielding a dark residue that was extracted with CH2Cl2
(3ϫ5 mL). Hexane (ca. 10 mL) was added to the colourless solu-
tion thus obtained, which was concentrated in vacuo and cooled
to –20 °C. The colourless microcrystalline solid thus obtained was
washed with hexane (3ϫ5 mL) and dried in vacuo, yielding 0.082 g
(83%) of 4. The first crystals obtained are usually only the transoid
isomer, whereas concentration of the mother liquor usually gives a
(s, CCH dmpz) ppm. IR: ν = 3064 (w), 3018 (w), 2956 (m), 2921
˜
3
(s), 2850 (s), 2807 (w), 2056 (w), 1992 (w), 1586 (w), 1528 (w), 1484
(w), 1427 (s), 1374 (w), 1354 (w), 1302 (w), 1258 (w), 1177 (w),
1156 (w), 1110 (s), 1034 (w), 998 (w), 966 (w), 910 (w), 883 (w),
862 (m), 796 (w), 768 (s), 760 (s), 732 (vs), 718 (s), 699 (vs), 650
(w), 618 (w), 576 (w), 549 (w), 503 (w), 490 (m), 478 (w), 460 (w)
cm–1. C43H55ClN4Pd2Si2 (932.36): calcd. C 55.39, H 5.95, N 6.01;
found C 55.05, H 5.96, N 5.83.
[Pd2{CH2SiPh2(CH2NC5H10)-κ2C,N}2(μ-O2CCH3-κO:κЈO)(μ-
dmpz-κN:κЈN)] (6): CH2Cl2 (10 mL) was added to a mixture of 3
mixture with the minor cisoid isomer (ca. 90:10). 1H NMR: transoid (0.046 g, 0.05 mmol) and 4 (0.050 g, 0.05 mmol), and the solution
isomer: δ = 0.84 (AB system, J = 9.5 Hz, 4 H, PdCH2Si), 1.28 (m,
NC5H10, 4 H), 1.62 (m, NC5H10, 6 H), 1.81 (s, CH3 dmpz, 6 H), was filtered, and hexane (ca. 15 mL) was added to the resulting
2.28 (m, NC5H10, 4 H), 2.41 (s, CH3 dmpz, 6 H), 2.82 (d, J = yellow solution, which was then concentrated in vacuo and cooled
was heated in a closed Schlenk flask at 40 °C for 24 h. The solution
14.0 Hz, SiCH2N, 2 H), 2.84 (m, NC5H10, 2 H), 3.24 (m, NC5H10, to –20 °C. After some crops of crystals of the starting materials
2 H), 3.56 (m, NC5H10, 2 H), 3.65 (d, J = 14.0 Hz, SiCH2N, 2 H), had been collected, concentration of the mother liquor yielded
5.41 (s, CH dmpz, 2 H), 7.34 (m, C6H5, 12 H), 7.62 (m, C6H5, 4
H), 7.80 (m, C6H5, 4 H); cisoid isomer (detected signals): δ = 2.01
(s, 6 H, CH3 dmpz), 2.47 (s, 6 H, CH3 dmpz), 3.07 (m, 2 H,
SiCH2N), 5.57 (s, 2 H, CH dmpz), 7.34 (m, 12 H, C6H5), 7.73 (m,
8 H, C6H5) ppm; the lowest ratio transoid/cisoid detected for the
0.022 g of 6 (23%) as pale yellow crystals, which were washed with
hexane (3ϫ3 mL) and dried in vacuo. H NMR: δ = 0.91 (d, J =
13.4 Hz, 2 H, PdCH2Si), 1.16 (d, J = 13.4 Hz, 2 H, PdCH2Si), 1.45
(m, 6 H, NC5H10), 1.75 (s, 3 H, CH3CO2), 1.78 (m, 6 H, NC5H10),
2.26 (s, 3 H, CH3 dmpz), 2.67 (br. d, J = 12.0 Hz, 2 H, NC5H10),
1
3432
www.eurjic.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 3427–3434

[(Piperidinomethyl)silyl]methyl-Cyclopalladated Dimetallic Complexes
2.82 (d, J = 14.3 Hz, 2 H, SiCH2N), 2.95 (d, J = 13.5 Hz, 2 H,
NC5H10), 3.24 (d, J = 14.3 Hz, 2 H, SiCH2N), 3.33 (t, J = 11.3 Hz,
2 H, NC5H10), 3.58 (t, J = 11.3 Hz, 2 H, NC5H10), 5.70 (s, 1 H,
CH dmpz), 7.19 (m, 4 H, C6H5), 7.33 (m, 8 H, C6H5), 7.60 (m, 4
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. The authors in Dortmund thank
the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen
Industrie and Wacker Chemie AG for their support.
H, C H ) ppm. IR: ν = 3065 (w), 2932 (m), 2854 (m), 1560 (vs),
˜
6
5
1540 (m), 1522 (w), 1507 (w), 1456 (m), 1418 (s), 1374 (w), 1339
(w), 1260 (w), 1108 (m), 1032 (w), 998 (w), 967 (w), 866 (w), 804
(w), 777 (w), 728 (m), 700 (m), 668 (w), 617 (w), 556 (w), 504 (m),
492 (m), 472 (m) cm–1. C45H58N4O2Pd2Si2 (955.95): calcd. C 56.54,
H 6.12, N 5.86; found C 56.23, H 5.95, N 5.93.
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Crystal Structure Determination of Complex 4: Crystals were grown
by slow diffusion of hexane into a concentrated solution of the
complex in CH2Cl2 at –20 °C. Crystallographic details are given in
Table 2. Measurements were carried out with a Bruker Apex CCD
diffractometer; programs used for data collection, cell determi-
nation and refinement: Smart V. 5622 (Bruker AXS, 2001), integra-
tion: SaintPlus V. 6.02 (Bruker AXS, 1999), empirical absorption
correction: Sadabs V. 2.01 (Bruker AXS, 1999). The structure was
solved by using direct and Fourier methods. Refinement was per-
2
formed by full-matrix least-squares methods (based on Fo
,
SHELXL-97). Anisotropic thermal parameters for all non-hydro-
gen atoms were included in the final cycles. Hydrogen atoms were
refined by using a riding model in their ideal geometric positions.
The SHELXS-86 and SHELXL-97 computer programs were used
for solving the structure.[26] CCDC-865034 contains the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Table 2. Crystal data and refinement details for 4.
Empirical formula
M
C51H69N6Pd2Si2
1035.10
T
173(2) K
λ (Mo-Kα)
Crystal system
Space group
0.71073 Å
triclinic
¯
P1
a
b
13.268(5) Å
14.863(4) Å
c
α
15.112(4) Å
92.95(3)°
β
106.60(3)°
γ
V
Z
ρcalcd.
110.75(4)°
2631.5(13) Å3
2
1.306 gcm–3
μ
0.767 mm–1
F(000)
1074
Crystal size
Scan range
Index ranges
0.20ϫ0.10ϫ0.10 mm
2.48° Յ θ Յ 25.00°
–15 Յ h Յ 15
–17 Յ k Յ 17
–17 Յ l Յ 17
22886
Reflections collected
Independent reflections
Completeness to θ = 25.00°
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
8707 [R(int) = 0.0642]
94.0%
0.9273 and 0.8618
full-matrix least squares on F2
8707/0/553
0.993
R1 = 0.0535, wR2 = 0.1493
R1 = 0.0697, wR2 = 0.1621
1.686 and –1.244 eÅ–3
Largest diff. peak and hole
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Supporting Information (see footnote on the first page of this arti-
cle): Total energies and Cartesian coordinates for all computed
structures.
Eur. J. Inorg. Chem. 2012, 3427–3434
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3433

C. Strohmann, F. Villafañe et al.
FULL PAPER
A. V. MedvedЈko, N. V. Zyk, A. L. Maximov, S. A. Kurzeev,
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2011, 14, 83–86.
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[25] Additional information and graphics on these calculations are
included in the Supporting Information.
[26] G. M. Sheldrick, SHELXS-86, Structure Solving Program for
Crystal Structure Determination, University of Göttingen,
Göttingen, 1986; G. M. Sheldrick, SHELXL-97, A Computer
Program for Refinement of Crystal Structures, University of
Göttingen, Göttingen, 1997.
Received: March 13, 2012
Published Online: June 6, 2012
3434
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Eur. J. Inorg. Chem. 2012, 3427–3434