7-azaindol-1-yl(organo)silanes and their PdCl2 complexes: Pd-capped tetrahedral silicon coordination spheres and paddlewheels with a Pd-Si axis

Article abstract of DOI:10.1021/om401220m

Supported by excess triethylamine, 7-azaindole (HL) and dichlorodimethylsilane (Me₂SiCl₂), methyltrichlorosilane (MeSiCl₃), and tetrachlorosilane (SiCl₄) react, respectively, with formation of the 7-azaindol-1-yl-substituted silanes Me ₂SiL₂, MeSiL₃, and SiL₄. In these compounds the silicon atom adopts [4+2], [4+3], and [4+4] coordination, respectively, with the pyridine N atoms of the 7-azaindol-1-yl groups capping the tetrahedral Si coordination sphere from distances of >3 A. Two pyridine nitrogen atoms of these silanes replace the acetonitrile ligands of [PdCl₂(NCMe)₂], thus forming the complexes Me ₂Si(μ-L)₂PdCl₂, MeSiL(μ-L) ₂PdCl₂, and SiL₂(μ-L)₂PdCl ₂. In addition to capping of the silicon coordination sphere by the pyridine N atoms of the dangling 7-azaindol-1-yl groups (in MeSiL(μ-L) ₂PdCl₂ and SiL₂(μ-L)₂PdCl ₂), these three palladium complexes exhibit capping of one tetrahedral face of the Si coordination sphere by the palladium atom (with Si···Pd separations of 3.34, 3.43, and 3.31 A, respectively). According to computational analyses, the paddlewheel complex ClSi(μ-L)₄PdCl should be energetically favored over its isomer SiL₂(μ-L)₂PdCl₂; however, isomerization into this paddlewheel compound requires higher temperatures (150 °C) or the addition of a Lewis acid (such as GaCl₃).

Full text of DOI:10.1021/om401220m

Article
pubs.acs.org/Organometallics
7
‑Azaindol-1-yl(organo)silanes and Their PdCl Complexes: Pd-
2
Capped Tetrahedral Silicon Coordination Spheres and Paddlewheels
with a Pd−Si Axis
Sven Wahlicht, Erica Brendler, Thomas Heine, Lyuben Zhechkov, and Jo
̈
rg Wagler*,†
†
‡
§
§
†
‡
§
Institut fu
̈
r Anorganische Chemie, TU Bergakademie Freiberg, D-09596 Freiberg, Germany
r Analytische Chemie, TU Bergakademie Freiberg, D-09596 Freiberg, Germany
Institut fu
̈
School of Engineering and Science, Theoretical Physics - Theoretical Materials Science, Jacobs University Bremen gGmbH, D-28759
Bremen, Germany
*
S Supporting Information
ABSTRACT: Supported by excess triethylamine, 7-azaindole (HL) and dichlorodimethylsilane (Me SiCl ), methyltrichlor-
2
2
osilane (MeSiCl ), and tetrachlorosilane (SiCl ) react, respectively, with formation of the 7-azaindol-1-yl-substituted silanes
3
4
Me SiL , MeSiL , and SiL . In these compounds the silicon atom adopts [4+2], [4+3], and [4+4] coordination, respectively,
2
2
3
4
with the pyridine N atoms of the 7-azaindol-1-yl groups capping the tetrahedral Si coordination sphere from distances of >3 Å.
Two pyridine nitrogen atoms of these silanes replace the acetonitrile ligands of [PdCl (NCMe) ], thus forming the complexes
2
2
Me Si(μ-L) PdCl , MeSiL(μ-L) PdCl , and SiL (μ-L) PdCl . In addition to capping of the silicon coordination sphere by the
2
2
2
2
2
2
2
2
pyridine N atoms of the dangling 7-azaindol-1-yl groups (in MeSiL(μ-L) PdCl and SiL (μ-L) PdCl ), these three palladium
2
2
2
2
2
complexes exhibit capping of one tetrahedral face of the Si coordination sphere by the palladium atom (with Si···Pd separations
of 3.34, 3.43, and 3.31 Å, respectively). According to computational analyses, the paddlewheel complex ClSi(μ-L) PdCl should
4
be energetically favored over its isomer SiL (μ-L) PdCl ; however, isomerization into this paddlewheel compound requires
2
2
2
higher temperatures (150 °C) or the addition of a Lewis acid (such as GaCl3).
INTRODUCTION
inherent coordinative preference for a soft and a hard central
■
atom clearly supports the architecture of those heterodinuclear
complexes. A set of such ambidentate buttresses can be
The chemistry of heterodinuclear complexes of transition metal
TM) and main group metal or metalloid elements (E), which
exhibit formal σ-lone-pair donation from d or d metal
complexes or other late transition metal compounds (TM →
E), has been explored for a variety of TM/E combinations
during the past decade. Investigations of the so-called
(
2b
1
0
8
combined within a tripodal ligand (e.g., in V ), as shown by Lu
2q
et al. Ambidentate ligands devoid of a net charge (e.g., in VI )
can also serve the same purpose. Examples of related TM−E
complexes with symmetric buttresses are rare, for instance the
2o
1
carboxylate-bridged Rh−Bi system VII and the naphthalene-
metallaboratranes (e.g., I), which accommodate a TM→B
2m
1
,8-diyl-bridged Hg−Sb compound VIII. The 7-azaindol-1-yl
bond within a cage structure of bridging bidentate ligands with
TM and B atoms in bridgehead positions, pioneered these
endeavors, thus initiating research on TM/E combinations
across the periodic table. The selection of compounds shown
in Chart 1 clearly demonstrates the fundamental characteristics
of the buttressing ligand, which is a monoanionic hetero-
moiety thus fills an intermediate gap between the highly
symmetric bidentate ligands and those with two different donor
atoms, as it bears two nitrogen donor atoms but in chemically
different environments. In reactions with hydroborates 7-
2
2
v
2d
bidentate 1,3-donor ligand in most cases (e.g., in II, III, and
IV ). The heterobidentate nature of the buttresses with the
Received: December 20, 2013
Published: May 12, 2014
2
i
©
2014 American Chemical Society
2479
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Article
Chart 1
Scheme 2. Generic Scheme for the Syntheses of 7-Azaindol-
1
-ylsilanes Me4−nSiL and Their Reaction with
n
[
PdCl (NCMe) ] with Formation of Complexes
2 2
Me4−nSiLn−2(μ-L) PdCl (n = 2, 3, 4)
2
2
azaindole has been shown to be capable of forming 7-azaindol-
1
-yl- and 7-azaindol-7-yl-substituted products, where the
coordination can be retained in transition metal complexes
obtained from these borates (IX and X, Scheme 1). In the
3
the form of ClSiL ·SiL . The compounds MeSiL and Me SiL
2
3
4
3
2
crystallized from acetonitrile without solvent of crystallization.
The above-mentioned 7-azaindolylsilanes were characterized by
single-crystal X-ray diffraction (Figure 1) and allow for insights
Scheme 1
context of the diagonal relationship of boron and silicon and in
2
v−x
the context of our own investigations
of TM→E
coordination compounds with E = Si we noticed a lack of
structurally characterized 7-azaindol-(1-or-7)-yl-substituted si-
lanes in the literature and became interested in exploring the 7-
azaindolylsilanes as starting materials for heterodinuclear
complexes with TM→Si coordination.
Figure 1. Molecular structures of SiL (in the solvent-free crystal
4
structure), ClSiL (in the crystal structure of ClSiL ·SiL ), MeSiL
3
3
4
3
RESULTS AND DISCUSSION
(
one of the two crystallographically independent molecules), and
■
Me SiL (one of the two crystallographically independent molecules).
Supported by triethylamine as a sacrificial base, 7-azaindole and
methylchlorosilanes Me4−nSiCln (n = 2, 3, 4) react with
formation of the corresponding 7-azaindol-1-yl-substituted
2
2
into their intramolecular coordination patterns. The solution
1
13
29
silanes Me4−nSi(L) (n = 2, 3, 4, L = 7-azaindol-1-yl) (Scheme
NMR spectra ( H, C, Si) always exhibit only one set of
signals characteristic of the proposed compound with chemi-
cally equivalent 7-azaindolyl moieties. Thus, we can exclude
significant 7-azaindol-1-yl to 7-azaindol-7-yl isomerization in
solution. (For related aluminum compounds such an isomer-
n
2
). Following our previously published procedure for the
4
syntheses of methimazolylsilanes, we used small amounts of N-
methylimidazole (NMI) as a catalyst to promote complete
substitution in the case of the synthesis of SiL . Depending on
crystallization conditions, we found the two compositions of
4
5
ization has been proposed. ) The silicon coordination spheres
SiL and SiL ·(MeCN) to crystallize from acetonitrile. Also
are [4+n]-capped tetrahedral, n being the number of 7-
azaindolyl groups. The capping Si···N separations, which range
between 3.09 and 3.22 Å, are slightly shorter than the
4
4
aiming at the synthesis of the partially substituted azaindolylsi-
lane ClSiL , our investigations indicated the facile formation of
3
SiL even in the absence of NMI and even upon using the
desired stoichiometric amounts of the starting materials. Thus,
corresponding Al···N separations in related aluminum com-
4
5
pounds (e.g., 3.26 Å in AlL (LH)), and they are similar to
3
we have not been able to isolate ClSiL as a pure compound;
however we were able to characterize it crystallographically in
those observed for a 4-fold-capped SiO -coordination sphere
with diazobenzene N atoms as the capping lone-pair donors
3
4
2
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6
(
3.07−3.12 Å). Interestingly, crystal packing effects seem to
obtained from the reaction mixtures, agreement of the gross
product compositions with the compounds found in the single
dominate the molecular conformation of the 7-azaindolylsi-
lanes, because cappings of tetrahedral faces opposite Si−N (in
MeSiL ) and Si−C bonds (in Me SiL ) are observed.
29
crystals was established with Si solid-state NMR spectroscopy
and elemental analysis. In general, the silicon atoms in
Me Si(μ-L) PdCl , MeSiL(μ-L) PdCl , and SiL (μ-L) PdCl
2
3
2
2
Furthermore, the similarity of Si−N−C angles of each 7-
azaindolyl group (e.g., Si1−N1−C1 127.5(1)°, Si1−N1−C7
2
2
2
2
2
2
2
29
can be regarded as tetracoordinate, because the Si NMR shifts
1
26.5(1)° in Me SiL ) hints at only marginal interactions
of these compounds do not reveal an upfield shift characteristic
2
2
29
29
between silicon and the vacant N atoms. Accordingly, the Si
of a significantly enhanced silicon coordination number (δ Si
NMR shifts of SiL (−50.5 CDCl , −49.9 solid state), ClSiL
for the couples of silanes SiL
PdCl complexes are −49.9/−51.0; −16.1/−18.8; −1.9, −2.8/
+6.1). Especially in the case of the transition from Me SiL to
Me Si(μ-L) PdCl the downfield shift of the Si resonance by
2 2 2
about 8 ppm indicates formation of a silicon compound with
lower coordination number. In the context of the previously
4 3 2 2
, MeSiL , and Me SiL and their
4
3
3
(
−42.9 CDCl ), MeSiL (−17.9 CDCl , −16.1 solid state), and
2
3
3
3
Me SiL (+2.9 CDCl , −1.9 and −2.8 solid state) clearly reflect
2
2
2
2
3
29
tetracoordination of the silicon atoms. Furthermore, compar-
2
9
ison of the Si NMR shifts of SiL (−50.5) and tetrakis(indol-
4
7
1
-yl)silane (−51.3), which lacks the potential additional donor
function, underlines the apparent absence of noticeable N−Si
mentioned [4+2] coordination of the Si atom in Me SiL we
2 2
2
9
coordination in the Si NMR features of these 7-
azaindolylsilanes.
can rationalize this lowering of the coordination number as a
transition toward [4+1] coordination, i.e., removal of two
capping N atoms and addition of a Pd atom, which now caps
one of the tetrahedral faces. (Similar coordination patterns
(Lewis acidic site at the apex of a square pyramidal transition
metal coordination sphere) have been previously published for
The silanes Me SiL , MeSiL , and SiL are capable of
2
2
3
4
replacing acetonitrile ligands in [PdCl (NCMe) ] (whereas in
2
2
related batches [PdCl (PPh ) ] did not react with those
2
3 2
silanes) and forming (respectively) the palladium complexes
2
l
2aa
combinations such as Pd−Te and Pd−B. ) Even though this
Me Si(μ-L) PdCl , MeSiL(μ-L) PdCl , and SiL (μ-L) PdCl .
2
2
2
2
2
2
2
2
kind of lowering of the Si coordination number proceeds in the
These compounds are practically insoluble in organic solvents
such as acetonitrile, chloroform, or THF and were thus
characterized by solid-state methods. Whereas crystals suitable
for single-crystal X-ray diffraction analyses (Figure 2) were
related transformations of SiL4 and MeSiL3 into SiL (μ-
2
L) PdCl and MeSiL(μ-L) PdCl as well (from [4+3] and
2
2
2
2
[
4+4] to [4+2] and [4+3], respectively), replacement of the
2
9
remote donor moieties has less net impact on the Si shift in
these latter cases. From the combination of these results and
the observation that the Si NMR shift of SiL is similar to that
29
4
of tetrakis(indol-1-yl)silane, we can conclude that in these
compounds steric effects (bond angles near the Si coordination
sphere, orientation of aromatic moieties, etc.) exert far more
29
influence on the Si NMR shifts than the action of the remote
lone-pair donor moieties.
In the solid-state structures of MeSiL(μ-L) PdCl , Me Si(μ-
2
2
2
L) PdCl , and SiL (μ-L) PdCl (in this order) we observe
2
2
2
2
2
widening of the bond angles associated with the Pd-capped
tetrahedral face (sum of angles is 330.1°, 337.1°, and 339.8°),
which correspond to 5%, 27%, and 36% progress along the
coordinate of the transition from a tetrahedral coordination
sphere (sum of angles 328.5°) toward trigonal bipyramidal
(
sum of angles 360°). This progress of widening of angles is
systematically related to the shortening of the Pd−Si separation
in the same order (3.43, 3.34, and 3.31 Å). Steric repulsion
between the Pd-bound chlorine atoms and one of the Si-bound
substituents might contribute substantially to this angle
widening, because repulsion of the PdCl moiety away from
2
the Si atom is reflected in the smaller Pd1−N2−C6 and Pd1−
N4−C13 angles (which range between 114.7° and 118.3°)
versus wider Pd1−N2−C7 and Pd1−N4−C14 angles (122.8−
1
28.3°). Interestingly, the Pd−Si separations are only 0.8 Å
longer than the sum of the covalent radii (r ) with d(SiPd)/
cov
∑
rcov of 1.37, 1.34, and 1.32 for MeSiL(μ-L) PdCl , Me Si(μ-
2 2 2
L) PdCl , and SiL (μ-L) PdCl , respectively (according to the
2
2
2
2
2
8
covalent radii data published by Alvarez et al.). Noteworthily,
the weak Si←N coordination in some silatranes and oxinato
complexes (with Si−N separations of 2.75 Å, which exceed the
sum of the covalent radii even more, by about 0.9 Å) causes
more pronounced angle widening (sum of angles 344.5° and
9
3
48°, respectively). This allows for the conclusion that the
Pd−Si separations of about 3.3−3.4 Å found in our complexes
should in principle be sufficient for weak Pd−Si coordination,
but in the herein reported complexes the Pd atoms exert less
Figure 2. Molecular structures of (from top) SiL (μ-L) PdCl ,
2
2
2
MeSiL(μ-L) PdCl , and Me Si(μ-L) PdCl in their crystal structures.
2
2
2
2
2
2
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Figure 3. Gas phase optimized molecular structures of SiL (μ-L) PdCl , SiL (μ-L) PdClF, and their paddlewheel isomers ClSi(μ-L) PdCl and
2
2
2
2
2
4
FSi(μ-L) PdCl, respectively.
4
lone-pair donor action than nitrogen donors in silatranes and
oxinato silicon complexes with weak Si←N coordination. An
additional interaction between the Pd atom and the 7-
azaindolylsilane is found in the solid-state structures of
SiL (μ-L) PdCl and MeSiL(μ-L) PdCl . That is, the nitrogen
Table 1. Relative Energies [kcal/mol] and Pd−Si
Separations [Å] of the Gas Phase Optimized Molecular
Structures of SiL (μ-L) PdCl , SiL (μ-L) PdClF, and Their
2
2
2
2
2
Paddlewheel Isomers ClSi(μ-L) PdCl and FSi(μ-L) PdCl,
4
4
a
Respectively
2
2
2
2
2
atom N5 (see Figure 2) is slightly pyramidalized toward the Pd
E(PBE0/
E(B3LYP/
E(PBE/
E(BP/
atom (sum of angles about N5 is 356° in SiL (μ-L) PdCl and
2
2
2
Pd−Si
TZ2P)
TZ2P)
TZ2P)
TZ2P)
3
55° in MeSiL(μ-L) PdCl ) and thus indicates a weak N→Pd
2 2
SiL (μ-
3.31
21.3
11.2
29.3
27.1
2
donor−acceptor interaction (N−Pd separations are 3.19 and
L) PdCl2
2
3.04 Å, respectively). This feature, however, disappears upon
ClSi(μ-
2.62
0
0
0
0
L) PdCl
optimization of the gas-phase molecular structure (as shown for
4
E(PBE0/
TZ2P)
E(B3LYP/
TZ2P)
E(PBE/
TZ2P)
E(BP/
TZ2P)
SiL (μ-L) PdCl , vide infra) and thus appears to be inferior
2
2
2
Pd−Si
with respect to the also weak Pd→Si interaction.
SiL (μ-
3.39
3.16
2.62
58.3
58.0
0
49.2
49.3
0
63.0
61.4
0
61.4
59.9
0
2
For the SiL (μ-L) PdCl compound we had expected
2
2
2
L) PdClF (a)
2
isomerization into the paddlewheel-shaped (4,0)-ClSi(μ-
SiL (μ-
2
L) PdCl. In some first experiments, neither spontaneous
L) PdClF (b)
4
2
isomerization was observed (upon heating in chloroform) nor
did the addition of a soluble chloride salt (as chloride transfer
FSi(μ-L) PdCl
a
4
Optimized with PBE, TZ2P for Si and Pd, DZP for other atoms,
single-point energy analyses with different methods.
catalyst from Pd to Si) result in the isomerization of SiL (μ-
2
L) PdCl (i.e., no rearrangement observed in the presence of
2
2
Et NHCl in a chloroform suspension of SiL (μ-L) PdCl ). As
3
2
2
2
treated in chloroform with Bu NBF , which proved to be an
4
4
29
confirmed by Si solid-state NMR spectroscopy, we always
recovered the starting material. As this observation was in
contradiction to our expectations, which are based on the facile
effective fluoride source for the generation of Si−F-function-
2x
alized metallasilatranes. Once again, we could not observe
formation of any new Pd−Si compound; only the starting
material was recovered. Apparently, the formation of the
formation of (4,0)-ClSi(μ-mt) PdCl-type paddlewheel com-
4
plexes with mt = methimazolide, the energetic difference
paddlewheel-type compound ClSi(μ-L) PdCl (and its F−Si
4
between the isomers SiL (μ-L) PdCl and (4,0)-ClSi(μ-
2
2
2
analogue) is hindered by a kinetic barrier, which cannot be
overcome easily by the above-mentioned methods. Alternative
strategies include treatment of SiL (μ-L) PdCl at higher
L) PdCl was analyzed by computational methods. For
4
comparison, the molecular structures of the fluoro-analogous
2
2
2
compounds SiL (μ-L) PdClF (two isomers) and (4,0)-FSi(μ-
2
2
temperatures and the use of a Lewis acid for chloride
abstraction from Pd to initialize cage closure and paddlewheel
formation. These two strategies eventually were successful.
Whereas SiL (μ-L) PdCl did not isomerize at 120 °C (o-
L) PdCl were optimized as well and analyzed for their
4
energetics. Figure 3 shows the molecular structures of the gas
phase optimized complexes, and Table 1 lists their relative
energies and Pd−Si separations. We find that the isomerization
of compound SiL (μ-L) PdCl into its (4,0)-paddlewheel
2
2
2
dichlorobenzene, 5 days), slow isomerization was observed in o-
dichlorobenzene at 150 °C (as shown in Scheme 3 for X = Cl).
2
2
2
29
isomer should be energetically favorable. As expected,
formation of a Si−F bond should furthermore support the
formation of such kind of complex. Thus, SiL (μ-L) PdCl was
As indicated by Si solid-state NMR spectroscopy (see
Supporting Information), after 3 h the solid was composed of
the starting material (δ −51, predominant component) and a
2
2
2
2
482
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Scheme 3
disorder by symmetry (space group I /m, the 4-fold axis Cl−
4
Si−Pd−Cl of the molecule is perpendicular to a bisecting plane,
which generates the alternative orientation of the molecule with
opposite direction of the Cl−Si−Pd−Cl axis and the 7-
azaindolyl ligands). Thus, various restraints had to be used for
the refinement, and the structural parameters are therefore of
limited quality for the discussion of molecular features.
With the aid of GaCl as a chloride scavenger SiL (μ-
3
2
L) PdCl could be transformed into a paddlewheel complex at
2
2
room temperature in chloroform (Scheme 4). In a first reaction
a 1:1 stoichiometric mixture of SiL (μ-L) PdCl and GaCl was
2
2
2
3
layered with chloroform (aiming at slow crystallization of the
product). As we found a fine powdery solid in the Schlenk tube
even after 3 weeks, the solvent was removed in a vacuum (trap
condensation) and the solid residue was recrystallized from
acetonitrile. Within a few days a crystalline solid formed, which
contained tetragonal plates suitable for X-ray analysis, and Si
solid-state NMR spectroscopy confirmed the presence of only
one Si species in the solid product with a chemical shift (δ
new compound, which produced a significantly upfield-shifted
resonance (δ −143). The latter is at the expected chemical shift
2
9
for compound ClSi(μ-L) PdCl, because the Si NMR shifts
4
calculated for the solid-state structure of SiL (μ-L) PdCl (as a
2
2
2
benchmark) and for the optimized molecular structure of
2
9
ClSi(μ-L) PdCl are −55.3 and −142.2, respectively. Thus,
4
another sample of SiL (μ-L) PdCl in o-dichlorobenzene was
2
2
2
kept at 150 °C for 15 h to afford a solid, which contained only
the rearrangement product. The solid product contained thin
tetragonal crystalline plates, which were suitable for X-ray
diffraction analysis (Figure 4, left). The crystal structure
−
143) similar to that observed with ClSi(μ-L) PdCl. As
4
proven by single-crystal X-ray analysis, the gallium chloride had
captured a chloride, and the cation of the product is a
paddlewheel complex with a Cl−Si−Pd axis and four 7-
azaindolyl bridges (Figure 5, top). In this cation, the axial
coordination site at palladium is occupied by an acetonitrile
molecule to furnish the compound (ClSi(μ-L) PdNCMe)-
4
(
GaCl ). In order to probe whether GaCl would isomerize
4
3
SiL (μ-L) PdCl into ClSi(μ-L) PdCl if added in substoichio-
2
2
2
4
metric amounts, a mixture of SiL (μ-L) PdCl (0.36 mmol)
2
2
2
and GaCl (0.11 mmol) was stirred in chloroform at room
3
temperature for 1 day. Thereafter, upon filtration, some solid
2
9
SiL (μ-L) PdCl (0.14 mmol) was recovered, and Si solid-
2
2
2
state NMR spectroscopy proved this solid to consist of SiL (μ-
2
L) PdCl only. Hence, 0.22 mmol of the starting material had
2
2
Figure 4. Molecular structures of ClSi(μ-L) PdCl in (from left) the
solvent-free crystal structure and in the crystal structure of the
4
reacted with the 0.11 mmol of GaCl3 added. Gas phase
diffusion of n-pentane into the filtrate led to the formation of a
multicrystalline solid, and by crystal picking two different
compounds could be identified by single-crystal X-ray
diffraction analysis. One of them is the ionic compound
(ClSi(μ-L) Pd) (Cl)(GaCl )(CHCl ) (Figure 5, bottom),
chloroform solvate (ClSi(μ-L) PdCl) (CHCl ) .
4
2
3 3
analysis confirms the identity of the product as the paddlewheel
complex ClSi(μ-L) PdCl. Unfortunately, the structure suffers
4
4
2
4
3 2
Scheme 4
2
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∑
rcov = 1.05, calculated for ClSi(μ-L) PdCl, 2.64(1) and
4
2
.642(3) Å, d(SiPd)/∑r
= 1.06, found in the crystal
cov
structures), whereas in the methimazolyl-bridged complex
ClSi(μ-mt) PdI the S···N separation (2.74 Å) is wider than
4
the Pd−Si bond (2.56 Å). Thus, propeller tilt of methimazolyl
moieties versus straight alignment of 7-azaindolyl moieties can
be interpreted as structural features that contribute to the
accommodation of the Pd−Si bond and parallel SiN and PdN
4
4
(
5
or PdS ) planes in a paddlewheel fashion. As shown in Scheme
, Si−Cl versus Si−F substitution can be expected to have only
4
Scheme 5. Selected Interatomic Separations [Å] in the Gas
Phase Optimized Paddlewheel Complexes ClSi(μ-L) PdCl
4
and FSi(μ-L) PdCl
4
Figure 5. Molecular structures of (from top) the cations [ClSi(μ-
+
+
L) PdNCMe] and [(ClSi(μ-L) Pd) (Cl)] in the crystal structures
4
4
2
of their tetrachlorogallate salts (ClSi(μ-L) PdNCMe)(GaCl ) and
4
4
(
ClSi(μ-L) Pd) (Cl)(GaCl )(CHCl ) , respectively. In the latter, Cl3
4 2 4 3 2
bridges Pd1 and Pd2 in a rather symmetric linear manner (Pd1−Cl3
little influence on the Pd−Si bond length. In a more
pronounced manner, intramolecular H-contacts with the halide
atoms correspond to this substitution with shortening of the
Si−N bonds upon transition to the Si−F derivative. Similar Si−
N bond length shortening has been observed with related
2.95 Å, Pd2−Cl3 2.91 Å, Pd1−Cl3−Pd2 174°).
and the other compound is the chloroform solvate of (ClSi(μ-
2
9
L) PdCl) (CHCl ) (Figure 4, right). Si solid-state NMR
4
2
3 3
2x
spectroscopy of the solid product revealed the presence of two
different hexacoordinate silicon compounds (δ −135, −143).
The more upfield signal was assigned to (ClSi(μ-
L) PdCl) (CHCl ) and the other signal to (ClSi(μ-
methimazolyl-bridged complexes.
The cationic paddlewheel complexes [(ClSi(μ-
+
+
L) PdNCMe)] and [(ClSi(μ-L) Pd) (Cl)] exhibit slightly
4
4
2
longer Pd−Si bonds (2.662(2), d(SiPd)/∑r = 1.06, and
4
2
3
3
cov
L) Pd) (Cl)(GaCl )(CHCl ) . Thus, from the 2:1 stoichiom-
2.683(1)/2.684(1) Å, d(SiPd)/∑r = 1.07, respectively). The
4
2
4
3 2
cov
etry of the reaction observed (i.e., from the amount of
recovered starting material) we conclude that in chloroform
SiL (μ-L) PdCl and GaCl (substoichiometric) react with
slightly weaker Pd−Si coordination most likely arises from the
different trans-disposed donor moieties (acetonitrile and
bridging chloride, respectively, versus chloride in ClSi(μ-
2
2
2
3
+
−
formation of [(ClSi(μ-L) Pd) (Cl)] and [GaCl ] , and upon
L) PdCl). The Si−N bond lengths (1.883(3) and 1.863(3)−
4
2
4
4
addition of pentane this compound crystallizes and/or
1.893(3) Å, respectively) are slightly shorter than those
undergoes dissociation into ClSi(μ-L) PdCl (which also
crystallizes as a chloroform solvate) and other compounds.
Unfortunately, despite the different packing in the chloro-
calculated for ClSi(μ-L) PdCl (1.91 Å) and found in the
4
4
crystal structures of this compound (1.902(1) and 1.898(5)−
1.939(11) Å for the solvent-free and the chloroform-solvated
form, respectively). Also, the Si−Cl bonds (2.139(3) and
2.105(1)/2.090(1) Å, respectively) are shorter than those
form solvate, the molecule of ClSi(μ-L) PdCl again suffers
4
severe disorder problems. Thus, for closer inspection of the
structural features of ClSi(μ-L) PdCl the results of the
calculated for ClSi(μ-L) PdCl (2.16 Å). These observations are
in accord with the slightly weaker donor strength of the Pd
atom in these cationic complexes.
4
4
computationally predicted molecular structure could be more
reliable. In the case of the ionic compounds (ClSi(μ-
L) PdNCMe)(GaCl ) and (ClSi(μ-L) Pd) (Cl)(GaCl )-
For a more quantitative discussion of the different donor
strengths of the Pd atom, natural localized molecular orbital
(NLMO) analyses were carried out for SiL (μ-L) PdCl
2
4
4
4
2
4
(
CHCl ) the crystal structures allow for reasonable discussion
3 2
of molecular features.
2
2
The optimized molecular structures of ClSi(μ-L) PdCl and
(coordinates from optimized structure), ClSi(μ-L) PdCl
4
4
FSi(μ-L) PdCl show the straight alignment of the 7-azaindolyl
(coordinates from optimized structure), and [ClSi(μ-
4
+
bridges parallel to the X−Si−Pd−Cl (X = Cl, F) axis, which
clearly distinguishes these complexes from related methimazolyl
bridged (4,0)-type paddlewheel complexes such as ClSi(μ-
L) PdNCMe] (coordinates from partially optimized struc-
4
ture) as representatives of the herein presented classes of
compounds with capping (weak) Pd donor action and strong
Pd donor function in neutral and cationic paddlewheel
complexes with a Pd−Si bond, respectively (Table 2). In
addition to the NLMO representative of the Pd−Si interaction
the electron localization function (ELF) is shown in Figure 6.
In SiL (μ-L) PdCl we find marginal contributions of the Si
2
x
mt) PdI, which exhibit noticeable propeller tilt of the bridging
4
ligands. This feature is in general reflected by the crystal
structures of ClSi(μ-L) PdCl and (ClSi(μ-L) PdCl) -
4
4
2
(
CHCl ) . The apparent reason for this different positioning
3 3
of the bridging moieties is the different separation of the lone-
pair donor atoms. The 7-azaindolyl N···N separation (2.40 Å)
is noticeably shorter than the Pd−Si bond (2.62 Å, d(SiPd)/
2
2
2
atom to this NLMO (1%), which thus has Pd lone-pair
character. Visualization of the NLMO shows a polarization of
2
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Article
Table 2. Selected Data of the NLMO Analyses of the Pd−Si Interaction in SiL (μ-L) PdCl , ClSi(μ-L) PdCl, and [ClSi(μ-
2
2
2
4
+
L) PdNCMe]
4
Pd hybrid
% p
Si hybrid
% p
%
Pd orbital contribution
% Si orbital contribution
% s
% d
% s
% d
SiL (μ-L) PdCl
2
97.5
82.6
89.1
1.0
15.2
7.6
1.8
3.2
2.7
0.1
0.1
0.1
98.1
96.6
97.2
7.5
44.7
28.4
88.9
53.8
68.9
3.0
1.4
2.6
2
2
ClSi(μ-L) PdCl
4
[
ClSi(μ-L) PdNCMe]+
4
Figure 6. Color representations of the NLMO of the Pd−Si interaction (top) and of the ELF along the PdSi axis (bottom) of SiL (μ-L) PdCl ,
2
2
2
+
ClSi(μ-L) PdCl, and [ClSi(μ-L) PdNCMe] (color scale for ELF diagrams: red 0.0, green 0.5, dark blue 0.9).
4
4
this lone pair toward the Si atom, thus hinting at a weak
donor−acceptor interaction. Furthermore, the ELF map also
indicates a weak electron density shift toward Si (green area on
the Pd−Si axis). For the paddlewheel complexes ClSi(μ-
CONCLUSION
■
In the herein presented 2-, 3-, and 4-fold substituted 7-
azaindolylsilanes the 7-azaindol-1-yl substitution pattern was
encountered and the nitrogen atoms in 7-position establish
only weak cappings of tetrahedral faces of the Si coordination
sphere. These silanes can serve as chelating ligands, as shown
by formation of their PdCl complexes. Even though they
replace the N-donor ligand acetonitrile from [PdCl (NCMe) ],
they did not replace the phosphine ligands in [PdCl (PPh ) ],
which is in sharp contrast to the reactivity of methimazolylsi-
lanes such as Si(mt)4. In the compounds Me Si(μ-L) PdCl ,
+
L) PdCl and [ClSi(μ-L) PdNCMe] we find noticeably higher
4
4
contributions of the Si atom to this NLMO (15.2% and 7.6%,
respectively), and the graphical representations of both the
NLMO and the ELF map show reasonable electron density
localization on the Pd−Si bond axis. The Pd−Si bond in
2
2
2
2
3 2
2v
ClSi(μ-L) PdCl is similar to that in the methimazolyl-bridged
4
2 2 2
analogue ClSi(μ-mt) PdCl, which has contributions of 84% Pd
and 12% Si to the corresponding NLMO. Comparison of the
MeSiL(μ-L) PdCl , and SiL (μ-L) PdCl the Pd atom is
2 2 2 2 2
always capping a tetrahedral face of the silicon coordination
sphere. Even though computational analyses predict the isomer
4
2w
NLMO and ELF of the two paddlewheel complexes ClSi(μ-
+
ClSi(μ-L) PdCl to be energetically more favorable than
4
L) PdCl and [ClSi(μ-L) PdNCMe] confirms that in the latter
4
4
SiL (μ-L) PdCl , the formation of paddlewheel-shaped com-
2
2
2
Pd is indeed a weaker donor. Both the noticeably smaller Si
contribution to the NLMO and the less pronounced electron
density shift toward Si (blue area on the Pd−Si axis in ClSi(μ-
pounds of the type ClPd(μ-ligand) SiX (X = Cl, F) with Pd→
4
Si donor−acceptor interaction is hampered in the case of ligand
=
7-azaindolyl; once again this is in contrast to compounds with
L) PdCl versus green area for the corresponding part in
ligand = methimazolyl. Transformation into the paddlewheel-
shaped isomer ClSi(μ-L) PdCl required elevated temperatures
(150 °C) or the use of a chloride scavenger (GaCl ), whereas
4
+
[
ClSi(μ-L) PdNCMe] ) allow for this interpretation.
4
4
In the order of decreasing lone-pair donor strength of the Pd
3
related methimazolyl-bridged paddlewheel complexes formed
at room temperature and without addition of a chloride
scavenger.
atom (i.e., in the order ClSi(μ-L) PdCl, [ClSi(μ-
4
+
L) PdNCMe] , SiL (μ-L) PdCl ) we find systematic variation
4
2
2
2
of the hybrid orbital contributions to this NLMO. That is, the
already high d character of the Pd hybrid increases (at the
expense of s character), and the Si contribution shifts from a
EXPERIMENTAL SECTION
General Considerations. Chemicals commercially available were
used as received without further purification. [PdCl (NCMe) ] was
■
close to ideal sp hybrid in ClSi(μ-L) PdCl to a predominant p
4
2
2
contribution in SiL (μ-L) PdCl .
prepared by stirring commercially available PdCl (3.00 g, 16.9 mmol)
2
2
2
2
2
485
dx.doi.org/10.1021/om401220m | Organometallics 2014, 33, 2479−2488

Organometallics
Article
2
9
1
in acetonitrile (15 mL) at room temperature for 2 weeks, filtration,
washing with acetonitrile (5 mL), and drying in a vacuum (yield: 4.30
g, 16.6 mmol, 98%). THF, hexane, and toluene were distilled from
sodium benzophenone and were stored over sodium wire (hexane,
toluene) or activated 3 Å molecular sieves under an argon atmosphere
122.9 (3), 128.3 (1), 130.1 (4), 142.9 (6), 153.5 (7). Si{ H} NMR
29
1
(CDCl , 79.5 MHz): δ 2.9. Si{ H} NMR (CP/MAS, 79.5 MHz): δ
−1.9, −2.8. Anal. Found (%): C 65.1, H 5.8, N 19.1. Calcd for
3
C H N Si (M = 292.42): C 65.72, H 5.52, N 19.16.
16
16
4
Synthesis of (7-Azaindol-1-yl) SiMe (MeSiL ). A solution of 7-
3
3
(
THF). Chloroform, acetonitrile, and o-dichlorobenzene were stored
over 3 Å molecular sieves. All reactions involving chlorosilanes and/or
-azaindolylsilanes were carried out under an atmosphere of dry argon
utilizing standard Schlenk techniques.
azaindole (2.01 g, 17.0 mmol) and triethylamine (2.43 g, 24.0 mmol)
in THF (50 mL) was stirred at room temperature, and
methyltrichlorosilane (0.85 g, 5.7 mmol) was added dropwise via
syringe. The white suspension thus obtained was heated to and stirred
at 50 °C (for 2 h) and then cooled to room temperature. Thereafter,
the triethylamine hydrochloride precipitate was filtered off and washed
with THF (3 mL), and from the combined filtrate and washings the
solvent was removed under reduced pressure (condensation into a
cold trap). The residue was recrystallized from acetonitrile (4 mL),
and the crystalline product was separated by decantation, washed with
acetonitrile (2 × 1 mL), and dried under vacuum. Yield: 1.50 g (3.80
mmol, 67%). Mp: 153−155 °C.
7
1
13
29
Solution NMR spectra ( H, C, Si) were recorded on a Bruker
29
DPX 400 MHz spectrometer (Me Si as internal standard). Si solid-
state (CP/MAS) NMR spectra were recorded on a Bruker Avance 400
4
1
WB spectrometer with 7 mm ZrO rotors and KelF inserts. H and
2
1
3
C NMR signal assignments adhere to the labels shown in Scheme 6.
Scheme 6
1
H NMR (CDCl , 400.1 MHz): δ 1.91 (s, 3 H, SiCH ), 6.50 (d, 3.6
3
3
Hz, 3 H, b), 6.65 (d, 3.6 Hz, 3 H, a), 7.09 (dd, 8.0 Hz, 4.8 Hz, 3 H, d),
7
.90 (dd, 8.0 Hz, 1.6 Hz, 3 H, c), 8.24 (dd, 4.8 Hz, 1.6 Hz, 3 H, e).
13
1
C{ H} NMR (CDCl , 100.6 MHz): δ −0.9 (SiCH ), 105.1 (2),
3
3
1
17.1 (5), 123.1 (3), 128.6 (1), 130.1 (4), 143.4 (6), 153.4 (7).
2
9
1
29
1
Si{ H} NMR (CDCl , 79.5 MHz): δ −17.9. Si{ H} NMR (CP/
3
MAS, 79.5 MHz): δ −16.1. Anal. Found (%): C 67.0, H 4.6, N 21.2.
Calcd for C H N Si (M = 394.50): C 66.98, H 4.60, N 21.30.
22
18
6
Synthesis of (7-Azaindol-1-yl) Si (SiL ). A solution of 7-azaindole
4
4
Elemental analyses were performed using an Elementar Vario
MICRO cube.
(2.04 g, 17.3 mmol) and triethylamine (2.14 g, 21.2 mmol) in THF
(60 mL) was stirred at room temperature, and N-methylimidazole (10
drops) and tetrachlorosilane (0.73 g, 4.3 mmol) were added dropwise
via syringe. The white suspension thus obtained was heated to and
stirred at 50 °C (for 2.5 h) and then stored at 6 °C for 12 h.
Thereafter, the triethylamine hydrochloride precipitate was filtered off
and washed with THF (3 × 3 mL), and from the combined filtrate and
washings the solvent was removed under reduced pressure
(condensation into a cold trap). The residue was recrystallized from
acetonitrile (10 mL) by heating in an oil bath and slow cooling of the
Schlenk flask (which was stored in the oil bath), and after 12 h the
crystalline product was separated by decantation, washed with
acetonitrile (2 × 1 mL), and dried under vacuum. Yield: 1.27 g
Single-crystal X-ray diffraction data were collected on a STOE
IPDS-2T diffractometer using Mo Kα-radiation. The structures were
solved by direct methods using SHELXS-97 and refined with the full-
2
matrix least-squares method of F against all reflections with SHELXL-
10
9
7. All non-hydrogen atoms were anisotropically refined. Hydrogen
atoms were isotropically refined in idealized positions (riding model).
Graphics of molecular structures (Figures 1−5) were generated with
11
12
ORTEP-3 and POV-Ray 3.62.
Computational analyses were performed with the ADF2012.01
13
package. The molecular structures of SiL (μ-L) PdCl , SiL (μ-
2
2
2
2
L) PdClF (two isomers), ClSi(μ-L) PdCl, and FSi(μ-L) PdCl were
2
4
4
14
optimized using the PBE functional in combination with a mixed
basis set (TZ2P for Si and Pd, DZP for all the other elements)
including scalar relativistic corrections. The single-point energies have
been calculated with TZ2P for all the atoms, using the following levels
(2.56 mmol, 59%). Mp: decomposition without melting.
1
H NMR (CDCl , 400.1 MHz): δ 6.59 (d, 3.6 Hz, 4 H, b), 6.93 (dd,
3
8.0 Hz, 4.8 Hz, 4 H, d), 7.49 (d, 3.6 Hz, 4 H, a), 7.80 (d, 8.0 Hz, 4 H,
c), 7.94 (d, 4.8 Hz, 4 H, e). 13C{ H} NMR (CDCl
1
, 100.6 MHz): δ
3
1
4
15
16
14
of theory: PBE,1 BP, B3LYP, PBE0.
105.6 (2), 117.1 (5), 123.1 (3), 128.3 (1), 132.0 (4), 143.0 (6), 153.5
7
18
29
1
For NLMO and ELF analyses, the optimized molecular
(7). Si{ H} NMR (CDCl , 79.5 MHz): δ −50.5. Anal. Found (%):
3
structures of SiL (μ-L) PdCl and ClSi(μ-L) PdCl (see above) and
C 67.5, H 4.8, N 22.5. Calcd for C28
4.06, N 22.56.
H N Si (M = 496.60): C 67.72, H
20 8
2
2
2
4
the partially optimized (H atoms only) structure of the cation [ClSi(μ-
+
L) PdNCMe] were used.
[Note: In a similar preparation, i.e., recrystallization of 5.3 mmol of
crude product from 14 mL of acetonitrile, but with different cooling
rate, because the hot Schlenk flask was removed from the oil bath,
4
For 29Si NMR calculations the reference molecule SiMe has been
19
4
optimized using scalar-relativistic approximation (same level of theory
29
as for the previously mentioned optimizations). Si NMR shifts were
SiL
(MeCN) crystallized. Yield: 2.01 g (3.74 mmol, 71%).] Anal.
4
20
calculated with DFT PBE (ZORA QZ4P(Si, Pd), TZ2P(other
atoms)) including spin−orbit approximation.
Found (%): C 67.0, H 4.3, N 23.5. Calcd for C H N Si (M =
3
0
23
9
1
13
29
537.65): C 67.02, H 4.44, N 22.83. H, C, and Si NMR data
Synthesis of (7-Azaindol-1-yl) SiMe (Me SiL ). A solution of 7-
(CDCl solution) are consistent with SiL (see above) and contain the
2
2
2
2
3
4
29
1
azaindole (1.01 g, 8.6 mmol) and triethylamine (1.25 g, 12.4 mmol) in
THF (30 mL) was stirred at room temperature, and dimethyldi-
chlorosilane (0.55 g, 4.2 mmol) was added dropwise via syringe. The
white suspension thus obtained was heated to and stirred at 50 °C (for
signals of MeCN in the expected intensity. Si{ H} NMR (CP/MAS,
79.5 MHz): δ −49.9.
Synthesis of (ClSiL )·(SiL ). A solution of 7-azaindole (1.00 g, 5.0
3
4
mmol) and triethylamine (1.12 g, 11.1 mmol) in THF (30 mL) was
stirred at room temperature, and tetrachlorosilane (0.49 g, 2.9 mmol)
was added dropwise via syringe. The white suspension thus obtained
was heated to and stirred at 45 °C (for 2 h) and then cooled to room
temperature. Thereafter, the triethylamine hydrochloride precipitate
was filtered off and washed with THF (2 × 3 mL), and from the
combined filtrate and washings two-thirds of the solvent was removed
under reduced pressure (condensation into a cold trap). The
remaining solution was layered with diethyl ether (20 mL) and stored
at 6 °C. After 3 days the crystalline product was separated from the
supernatant by decantation. Yield: 0.64 g. As confirmed by X-ray
crystallography, this product contains crystals of (ClSiL )·(SiL ).
3
h) and then cooled to room temperature. Thereafter, the
triethylamine hydrochloride precipitate was filtered off and washed
with THF (2 × 2 mL), and from the combined filtrate and washings
the solvent was removed under reduced pressure (condensation into a
cold trap). The residue was recrystallized from acetonitrile (4 mL),
and the crystalline product was separated by decantation, washed with
acetonitrile (2 × 1 mL), and dried in a vacuum. Yield: 0.85 g (2.91
mmol, 69%). Mp: 86−87 °C.
1
H NMR (CDCl , 400.1 MHz): δ 1.19 (s, 6 H, Si(CH ) ), 6.52 (d,
3
3 2
3
.5 Hz, 2 H, b), 7.06 (dd, 7.9 Hz, 4.7 Hz, 2 H, d), 7.10 (d, 3.5 Hz, 2 H,
13
1
a), 7.88 (dd, 7.9 Hz, 1.5 Hz, 2 H, c), 8.27 (d, 4.7 Hz, 2 H, e). C{ H}
NMR (CDCl , 100.6 MHz): δ −0.8 (Si(CH ) ), 103.9 (2), 116.5 (5),
3
4
Furthermore, the 29Si NMR spectrum exhibited two peaks of similar
3
3 2
2
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Organometallics
Article
intensity at δ −42.9 (ClSiL ) and −50.5 (SiL ), which hints at the
temperature for 3 weeks. Thereafter, the solvent was removed in vacuo
(trap condensation) and the residue was recrystallized from
acetonitrile (9 mL). After storage at room temperature for 5 d the
resultant solid was filtered off, washed with acetonitrile (1 mL), and
dried in vacuo. Yield: 128 mg (0.144 mmol, 48%).
3
4
1
gross product composition (ClSiL )·(SiL ). The H NMR spectrum
3
4
revealed the presence of large amounts of triethylamine hydrochloride
in the product, and therefore melting point and elemental analysis
have not been performed. As this product did not serve the purpose of
our further investigations, we have not pursued its further purification
yet.
29
1
Si{ H} NMR (CP/MAS, 79.5 MHz): δ −143.0. Anal. Found (%):
C 41.6, H 2.8, N 13.7. Calcd for C H N SiCl PdGa (M = 891.06): C
30
23
9
5
Synthesis of Me Si(μ-L) PdCl . In a Schlenk flask Me SiL (0.23 g,
40.44, H 2.60, N 14.15.
2
2
2
2
2
0
.80 mmol) and [PdCl (NCMe) ] (0.21 g, 0.80 mmol) were stirred in
Crystals for X-ray diffraction analysis were found in the Schlenk
tube and were isolated for analysis before filtration of the product
suspension.
2
2
acetonitrile (6 mL) for 12 h at room temperature. Thereafter, the light
yellow solid was filtered, washed with acetonitrile (2 × 1 mL), and
dried under vacuum. Yield: 0.34 g (0.72 mmol, 90%). Decomposition
without melting occurred above 250 °C. Solution NMR spectroscopy
was hampered by the very poor solubility of this compound in solvents
such as chloroform, DMSO, acetonitrile, and THF.
Reaction of SiL
Schlenk tube SiL (μ-L)
chloroform (3 mL), and a solution of GaCl
(μ-L)
PdCl
with GaCl
(246 mg, 0.36 mmol) was stirred in
(20 mg, 0.11 mmol) in
in Chloroform. In a
2
2
2
3
PdCl
2
2
2
3
chloroform (1 mL) was added. The resultant suspension was stirred at
room temperature for 26 h. Thereafter, the remaining yellow solid was
filtered off and dried in vacuo. Yield: 98 mg (0.14 mmol) of the starting
29
1
Si{ H} NMR (CP/MAS, 79.5 MHz): δ 6.1. Anal. Found (%): C
4
4
0.7, H 3.3, N 12.0. Calcd for C H N SiCl Pd (M = 469.37): C
18
16
4
2
0.91, H 3.43, N 11.93.
Crystals for X-ray diffraction analysis were grown by layering
stoichiometric amounts of Me SiL and [PdCl (NCMe) ] with
material SiL (μ-L) PdCl . The Schlenk flask with the filtrate was then
2 2 2
equipped with a bridge and a flask with n-pentane for gas phase
diffusion of pentane into the filtrate. Within 2 d a mixture of crystalline
2
2
2
2
acetonitrile and keeping the Schlenk flask undisturbed for 1 day.
Synthesis of MeSiL(μ-L) PdCl . In a Schlenk flask MeSiL (0.26 g,
solids formed, which were identified as (ClSi(μ-L)
Pd) (Cl)(GaCl )-
4 2 4
(CHCl and (ClSi(μ-L) PdCl) (CHCl by single-crystal X-ray
)
3
)
3 3
2
2
3
2
4
2
0
.65 mmol) and [PdCl (NCMe) ] (0.17 g, 0.66 mmol) were stirred in
analyses. The crystals were separated from the supernatant by
decantation, washed with pentane (0.5 mL), and briefly dried in
vacuo. Yield: 84 mg of product mixture.
2
2
acetonitrile (6 mL) for 12 h at room temperature. Thereafter, the light
yellow solid was filtered, washed with acetonitrile (2 × 1 mL), and
dried under vacuum. Yield: 0.34 g (0.59 mmol, 91%). Decomposition
without melting occurred above 200 °C. Solution NMR spectroscopy
was hampered by the very poor solubility of this compound in solvents
such as chloroform, DMSO, acetonitrile, and THF.
29
1
Si{ H} NMR (CP/MAS, 79.5 MHz): δ −135.3; −143.4.
ASSOCIATED CONTENT
Supporting Information
■
29
1
Si{ H} NMR (CP/MAS, 79.5 MHz): δ −18.8. Anal. Found (%):
*
S
C 45.9, H 3.6, N 14.7. Calcd for C H N SiCl Pd (M = 571.83): C
22
18
6
2
An ORTEP diagram of the decomposition product L′PdCl ,
2
4
6.21, H 3.17, N 14.70.
Crystals for X-ray diffraction analysis were grown by layering
stoichiometric amounts of MeSiL3 and [PdCl (NCMe) ] with
CIF files with crystallographic details of the crystal structures
reported in this paper, tables with atomic coordinates of the
optimized molecular structures of SiL (μ-L) PdCl , SiL (μ-
2
2
2
2
2
2
acetonitrile and keeping the Schlenk flask undisturbed for 1 day.
From the filtrate, upon storage for 2 weeks, an orange crystal of a
decomposition product (L′PdCl ) was obtained, which is a PdCl
L) PdClF (two isomers), ClSi(μ-L) PdCl, and FSi(μ-
2
4
29
L) PdCl, and Si CP/MAS NMR spectra of the products
4
2
2
complex of a bidentate ligand formed by addition of the NH group of
obtained from SiL (μ-L) PdCl upon heating in o-dichlor-
2 2 2
7
-azaindole across the CN bond of acetonitrile. Details of this crystal
structure can be found in the Supporting Information.
Synthesis of SiL (μ-L) PdCl . In a Schlenk flask SiL ·(MeCN)
obenzene and upon reaction with GaCl in chloroform. This
material is available free of charge via the Internet at http://
3
2
2
2
4
pubs.acs.org. The crystallographic data for Me SiL (CCDC
2
2
(
0.19 g, 0.39 mmol) and [PdCl (NCMe) ] (0.094 g, 0.39 mmol) were
2 2
9
77928), MeSiL (CCDC 977921), SiL (CCDC 977924),
3
4
stirred in acetonitrile (10 mL) for 1 d at room temperature.
Thereafter, the light yellow solid was filtered, washed with acetonitrile
SiL ·(MeCN) (CCDC 977922), ClSiL ·SiL (CCDC 977923),
4
3
4
[
(
(L′)PdCl ] ·MeCN (CCDC 977927), Me Si(μ-L) PdCl
2
2
2
2
2
(
2 × 1 mL), and dried under vacuum. Yield: 0.23 g (0.34 mmol, 94%).
CCDC 977929), MeSiL(μ-L) PdCl (CCDC 977926),
Decomposition without melting occurred above 290 °C. Solution
NMR spectroscopy was hampered by the very poor solubility of this
compound in solvents such as chloroform, DMSO, acetonitrile, and
THF.
2 2
SiL (μ-L) PdCl (CCDC 977925), ClSi(μ-L) PdCl (CCDC
2
2
2
4
995082), (ClSi(μ-L)
PdCl)
(CHCl
)
(CCDC 995083),
4
2
3
3
(ClSi(μ-L) PdNCMe)(GaCl ) (CCDC 995084), and (ClSi-
4
4
29
1
Si{ H} NMR (CP/MAS, 79.5 MHz): δ −51.0. Anal. Found (%):
(μ-L) Pd) (Cl)(GaCl )(CHCl ) (CCDC 995081) may also
4 2 4 3 2
C 49.6, H 3.3, N 16.8. Calcd for C H N SiCl Pd (M = 673.92): C
28
20
8
2
be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request.cif.
4
9.90, H 2.99, N 16.63.
Crystals for X-ray diffraction analysis were grown by layering
stoichiometric amounts of SiL ·(MeCN) and [PdCl (NCMe) ] with
4
2
2
AUTHOR INFORMATION
acetonitrile and keeping the Schlenk flask undisturbed for 1 day.
Synthesis of ClSi(μ-L) PdCl. In a sealed ampule SiL (μ-L) PdCl
2
■
4
2
2
Corresponding Author
(0.19 g, 0.28 mmol) and o-dichlorobenzene (0.7 mL) were stored at
*
Fax: +49 3731 39 4058. E-mail: joerg.wagler@chemie.tu-
freiberg.de.
1
50 °C for 15 h and then stored at room temperature for 1 d. The
resultant suspension was filtered, and the solid was washed with o-
dichlorobenzene (1 mL), diethyl ether/o-dichlorobenzene, 3:1 (2
mL), and diethyl ether (2 mL) and dried in vacuo. Yield: 0.105 g
Notes
The authors declare no competing financial interest.
(
0.156 mmol, 56%).
29
1
Si{ H} NMR (CP/MAS, 79.5 MHz): δ −143.1. Anal. Found (%):
C 50.2, H 3.1, N 16.5. Calcd for C H N SiCl Pd (M = 673.92): C
ACKNOWLEDGMENTS
28
20
8
2
■
49.90, H 2.99, N 16.63.
Dedicated to the memory of Professor Daniel Kost, a precious
colleague and friend and a marvelous researcher in silicon
coordination chemistry. We thank the reviewers for their
helpful suggestions, which added significant value to the
content of this paper.
Crystals for X-ray diffraction analysis were found in the ampule and
were isolated for analysis before filtration of the product suspension.
Synthesis of [ClSi(μ-L) PdNCMe][GaCl ]. In a Schlenk tube
SiL (μ-L) PdCl (0.20 g, 0.30 mmol) and GaCl3 (53 mg, 0.30
4
4
2
2
2
mmol) were layered with chloroform (1 mL) and stored at room
2
487
dx.doi.org/10.1021/om401220m | Organometallics 2014, 33, 2479−2488

Organometallics
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