Preparation and reactivity of an O,O-chelating silsesquioxane-palladium complex

Article abstract of DOI:10.1016/j.jorganchem.2010.09.029

An incompletely condensed silsesquioxane containing trisilanol (c-C ₅H₉)₇Si₇O₉(OH) ₃ reacts with [PdI₂(bpy)] (bpy = 2,2′-bipyridine) in the presence of Ag₂O to produce a palladium complex with an O,O-chelating silsesquioxanate ligand, [Pd{O₁₁Si₇(c-C ₅H₉)₇(OH)}(bpy)] (1). The reaction of Ph ₂SiClH with 1 in 2:1 ratio causes disilylations of the silsesquioxanate ligand, forming [PdCl₂(bpy)]. Addition of p-cresol to a solution of 1 yields the trisilanol and [Pd(OC₆H ₄CH₃-p)₂(bpy)].

Full text of DOI:10.1016/j.jorganchem.2010.09.029

Journal of Organometallic Chemistry 696 (2011) 1211e1215
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Preparation and reactivity of an O,O-chelating silsesquioxaneepalladium complex
*
Makoto Tanabe, Kohji Mutou, Neli Mintcheva, Kohtaro Osakada
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
An incompletely condensed silsesquioxane containing trisilanol (c-C5H9)7Si7O9(OH)3 reacts with
[PdI2(bpy)] (bpy ¼ 2,20-bipyridine) in the presence of Ag2O to produce a palladium complex with an
O,O-chelating silsesquioxanate ligand, [Pd{O11Si7(c-C5H9)7(OH)}(bpy)] (1). The reaction of Ph2SiClH with
1 in 2:1 ratio causes disilylations of the silsesquioxanate ligand, forming [PdCl2(bpy)]. Addition of
p-cresol to a solution of 1 yields the trisilanol and [Pd(OC6H4CH3-p)2(bpy)].
Received 10 August 2010
Received in revised form
8 September 2010
Accepted 8 September 2010
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Silsesquioxane
Chlorosilane
Palladium
Hydrogen bond
Silylation
1. Introduction
revealed dynamic behavior of the platina- and pallada-silses-
quioxane complexes in solution; the OeH and OeM oxygens
Polyhedral oligomeric silsesquioxanes (POSS) which contain
transition and main-group metals have been regarded as molecular
models for the heterogeneous catalysts using silica as the support
[1]. Most of the compounds have the metaleoxygen bonds between
the metal center and the silsesquioxanate ligands. The ligands form
stable coordination bonds with oxophilic early transition metals,
while metallasilsesquioxane complexes containing late transition
metals are less stable due to electron repulsion between the lone
pairs of coordinating oxygen atom and the filled d-orbitals of the
metal center [2]. Abbenhuis reported that a platinum complex with
the O,O-chelating silsesquioxanate ligand, [Pt{O11Si7(c-C5H9)7
(OSiMe3)}(dppe)] (dppe ¼ 1,2-bis(diphenylphosphino)ethane), in
solution was decomposed spontaneously into the metal species and
silsesquioxane disilanol with PteO bond cleavage [3]. This situation
is similar to alkoxide and aryloxide complexes of late transition
metals. Another characteristic of late transition metal alkoxides is
their associations with alcohols through intermolecular OeH/O
hydrogen bonds (Chart 1a) [4e7]. Recently, we reported the prep-
aration of palladium [8], platinum [9] and diplatinum [10]
complexes with monodentate silsesquioxanate ligands, and intra-
molecular OeH/O hydrogen bonds between the coordinating
oxygen and OH group in the POSS ligand in the solid state and in
solution (Chart 1b). Variable-temperature NMR spectroscopy
undergo exchange on the NMR time scale. In this paper we report
preparation of Pd complex with an O,O-chelating silsesquioxane
ligand by using 2,20-bipyridine ligand and its reactivity toward
electrophilic reagents.
R
a
b
R
O
O
R
Si
Si
H
H
R
O
O
O
Si
Si
PR'3
Ph
H
R
O
O
O
R
M
O
O
M
Si
Si
O
O
PR'3
R
O
R
O
Si
R
M = Pt, PR'3 = PEt3, PMe2Ph
M = Pd, PR'3 = PMe3
R = c-C5H9, i-C4H9
Chart 1.
2. Results and discussion
2.1. Preparation of palladasilsesquioxane complex
Treatment of trisilanol (c-C5H9)7Si7O9(OH)3 with equimolar
diiodopalladium complex [PdI2(bpy)] (bpy ¼ 2,20-bipyridine) in
* Corresponding author. Tel./fax: þ81 45 924 5224.
E-mail address: kosakada@res.titech.ac.jp (K. Osakada).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.09.029

1212
M. Tanabe et al. / Journal of Organometallic Chemistry 696 (2011) 1211e1215
Table 1
the presence of excess Ag2O gave a palladium complex with the
O,O-chelating silsesquioxanate ligand, [Pd{O11Si7(c-C5H9)7(OH)}
(bpy)] (1), in 90% yield at room temperature, as shown in Eq. (1).
Selected bond distances (Å) and angles (deg) of 1.
PdeO1
PdeN1
O1/O5
O1eSi1
1.982(6), 1.966(6)
2.022(7), 2.010(7)
4.652(9), 4.655(9)
1.582(7), 1.577(6)
PdeO2
PdeN2
O2/O5
O2eSi2
2.012(6), 2.020(5)
1.986(7), 2.004(9)
2.597(9), 2.607(9)
1.600(7), 1.603(6)
R
R
R
O
O
Si
R
R
Si
O1ePdeO2
PdeO1eSi1
96.0(2), 95.5(2)
140.0(4), 139.5(4)
N1ePdeN2
PdeO2eSi2
80.8(3), 81.8(3)
125.6(3), 130.0(4)
O
OH
O
Si
Si
O
I
I
N
N
O
R7Si7O9(OH)3
Ag2O, r.t., THF
(1)
Pd
O
O
Si
O
N
N
R
Si
Si
Pd
O
(R = c-C5H9)
O
slightly longer than the PdeO1 bond (1.982(6) and 1.966(6) Å)
probably due to the above hydrogen bond. An iron(II) complex with
the O,O-chelating silsesquioxanate ligand [Fe{O11Si7(c-C5H9)7(OH)}
(dcpe)] (dcpe ¼ 1,2-bis(dicyclohexylphosphino)ethane) wasreported
to possess a similar hydrogen bond between free OH group and the
Fe-coordinated oxygen (O/O distances: 2.743 Å). The FeeO bond
with the OeH/O hydrogen bond (1.907(3) Å) is longer than that
without hydrogen bond (1.869(3) Å) [11]. The IR spectrum of 1 in the
solid state shows two bands at 710 and 725 cmꢀ1, which are assigned
to the stretching vibrations of the SieO groups bonded to palladium.
Thecorrespondingpeaksof thePteAgheterobimetalliccomplex with
O,O-coordinated silsesquioxanate ligand, [Pt{O11Si7R7(OH)(AgPPh3)}
(Ph)(PPh3)], were observed at 695 and 745 cmꢀ1 (R ¼ c-C5H9), and
694 and 739 cmꢀ1 (R ¼ i-C4H9) [9].
R
1
Fig. 1 shows the molecular structure of 1 determined by X-ray
crystallography. Selected bond distances and angles of 1 are listed in
Table 1. A crystal lattice involves two crystallographically indepen-
dent molecules. Their bpy ligands are stacked (the shortest
distance ¼ 3.42(1) Å), as shown in Fig. 1b. Complex 1 possesses
a square-planar coordination around the Pd(II) center, bonded with
a bpy ligand and an O,O-coordinated silsesquioxanate ligand.
Although position of the OH hydrogen of 1 was not determined by
difference Fourier synthesis, much shorter O2/O5 distances (2.597
(9) and 2.607(9) Å) than O1/O5 (4.652(9) and 4.655(9) Å) indicate
intramolecularO2/HeO5hydrogenbondinthesolidstate, similarto
the palladium and platinum complexes with monodentate O-coor-
dinated silsesquioxanate ligands (O/O distance: 2.547(4)e2.612
(2) Å) [8,9]. The PdeO2 bond distances (2.012(6) and 2.020(5) Å) are
The 1H NMR spectrum of 1 exhibits that CH and CH2 hydrogen
signals of the seven cyclopentyl groups appear in the ranges
between
The aromatic hydrogens of the bpy ligands show four signals at
6.26, 7.64, 8.26 and 8.74 with equal intensities. A low-field sharp
d 1.20 and 1.36 and between d 1.56 and 2.12, respectively.
d
signal at
d
9.34 for OH hydrogen (25 ꢁC) is shifted downfield to
d
9.68 at ꢀ60 ꢁC, indicating the presence of the hydrogen bonds in
solution [8,9]. The molecule in the solid state adopts the unsym-
metrical structure due to the O/HeO hydrogen bond between
one OH group and the coordinating oxygen atom. The NMR
spectroscopic data, however, show that two pyridyl groups in bpy
are magnetically equivalent in solution. The NMR spectroscopic
results suggest that 1 undergoes rapid exchange of the OH group
with two O atoms bonded to the Pd, as shown in Scheme 1, on the
NMR time scale even at ꢀ80 ꢁC. The 29Si{1H} NMR spectrum of 1
shows the five distinct signals are observed at
d
ꢀ66.8, ꢀ64.4,
ꢀ63.7, ꢀ58.0 and ꢀ54.4 in a 2:1:1:2:1 ratio in accord with Cs
symmetry of the silsesquioxane moiety. Two downfield signals in
2:1 ratio (
d
ꢀ58.0 and ꢀ54.4) are attributed to the silicon nuclei of
SieOePd and SieOeH groups, because the peak positions are
similar to those of trans-[Pd{O10Si7(c-C5H9)7(OH)2}(Ar)(PMe3)2]
(Ar ¼ Ph: ꢀ58.3 and ꢀ57.3, Ar ¼ C6F5: ꢀ58.0 and ꢀ56.9) in 1:2
ratio [9]. The 13C{1H} NMR spectrum is consistent with the
structure mentioned above. Five signals (
and 26.2 in ratio 1:1:1:2:2) are observed for CH carbon atoms of
seven cyclopentyl substituents. The signal at 26.2, the lowest
d 23.4, 23.6, 23.6, 24.2
d
magnetic field position, is assigned to two carbons attached to Si
atoms bonded to coordinating oxygens. Previously reported
R
Si
R
Si
O
O
H
H
O
O
O
O
N
N
N
N
Si
Si
Pd
Pd
R
R
Si
Si
R
R
Fig. 1. a) ORTEP drawing of 1 and with thermal ellipsoids shown at 50% probability
level. Hydrogen atoms and the CH2 units of the cyclopentyl groups are omitted for
simplicity. b) Two crystallographically independent molecules in the unit cell.
Scheme 1.

M. Tanabe et al. / Journal of Organometallic Chemistry 696 (2011) 1211e1215
1213
O-coordinated silsesquioxane complexes also exhibited the signals
of the carbon in the PdeOeSi linkage at low magnetic field
positions [8e10].
(3)). Methanol did not react with 1 under the same conditions. 1H
and 13C{1H} NMR spectroscopic data of 4 are similar to the reported
bis(phenoxo)palladium complex [Pd(OC6H5)2(bpy)] [16]. Similar
exchange reactions of alkoxo complexes of Pt with phenol deriva-
tives were reported to lead to the aryloxoplatinum complexes [17].
The chelating silyloxo ligands undergo facile exchange upon addi-
tion of cresol and high stability of the PdeOAr bond.
2.2. Reactions of 1 with Ph2SiClH and with p-cresol
Complex 1 reacted with twice molar amount of Ph2SiClH in
toluene at room temperature to form a disilylated silsesquioxane
(c-C5H9)7Si7O11(OH)(SiPh2H)2 (2) in 98% yield (Eq. (2)). [PdCl2(bpy)]
(3) was separated as a yellow solid from the reaction mixture.
R
R
R
O
O
Si
R
R
Si
O
OH
O
Si
Si
O
2
Me
OH
O
R
R
R
O
O
Si
r.t., toluene
O
Si
R
R
O
Si
O
N
N
R
Si
O
OH
Si
Pd
O
Si
(R = c-C5H9)
Si
O
O
O
O
2 Ph2SiClH
R
O
O
Si
1
N
N
r.t., toluene
(R = c-C5H9)
O
R
Si
R
Si
Pd
R
O
R
O
O
O
O
Si
R
R
Si
R
O
OH
Si
Si
O
1
O
Me
Me
O
O
N
N
R
O
+
(3)
Pd
R
O
Si
R
OH
OH
O
O
R
O
Si
R
R
Si
Si
Si
O
O
OH
Cl
N
N
Si
Si
O
R
4
(2)
+
Pd
O
O
O
Cl
Si
SiPh2H
SiPh2H
O
R
Si
Si
O
O
In summary, we prepared palladium complex 1 with the O,O-
R
2
chelating silsesquioxanate ligand starting from silsesquioxane and
diiodopalladium complex. Crystallographic results in the solid state
and NMR data in solution suggest that the OH group is bonded to
one of the coordinating oxygen atoms and that the three oxygen
atom close to the Pd center undergo rapid exchange, similarly to the
complexes with monodentate silsesquioxane ligand containing two
OH groups. Selective disilylation of the O,O-coordinated metal-
lasilsesquioxane complex is achieved, although silylation of the
incompletely condensed silsesquioxanes promoted by amine lacks
the selectivity.
3
IR spectrum of 2 displays two characteristic peaks at 2137 and
3650 cmꢀ1. The former peakis assigned as stretching vibrationof the
SieH bonds of the diphenylsiloxo groups. The latter signal is shifted
to higher wavenumber than that of incompletely condensed sil-
sesquioxane (c-C6H11)7Si7O9(OH)3 (3158 cmꢀ1 in Nujol) [12] due to
the absence of intra- and/or inter-molecular hydrogen bonds caused
bythe sterichindrance of SiPh2H groups. The 29Si{1H}NMR signals of
the silsesquioxane framework of 2 display a different signal pattern
3. Experimental
from 1 and appear at
1:2:2:1:1), where the SiOePd signal of 1 (
after the incorporation of SiOeSiPh2H groups. The 29Si signal for
OSiPh2H groups appears at
ꢀ21.2, similar to that of disiloxane,
HPh2SiOSiPh2H (
ꢀ22.9 in CDCl3) [13].
d
ꢀ66.6, ꢀ65.8, ꢀ65.5, ꢀ64.6 and ꢀ57.3 (ratio
d
ꢀ58.0) is shifted upfield
3.1. General procedures
d
All manipulations of the complexes were carried out using
standard Schlenk techniques under an argon or nitrogen atmo-
sphere. Hexane and toluene were purified by using a solvent
purification system (Glass Contour). THF was distilled from sodium
benzophenone ketyl and stored under nitrogen. 1H, 13C{1H} and 29Si
{1H} NMR spectra were recorded on a JEOL EX-400 spectrometer.
Chemical shifts in 1H and 13C{1H} NMR spectra were referenced to
the residual peaks of the solvents used. The peak position of the 29Si
d
Feher et al. reported mono- and trisilylation of trisilanols with
Me3SiCl in the presence of Et3N [14]. Molar ratio between the tri-
silanol and Me3SiCl influences ratio of the products. Selective dis-
ilylation in Eq. (2) suggests that the coordinating oxygens react
more readily than the OH group toward the O-silylation. The
reaction probably involves direct bond exchange or
s-bond
metathesis between the PdeO bond and SieCl bond, as shown in
Scheme 2. Alternative pathway involving oxidative addition of the
SieCl bond to Pd and subsequent coupling of the silyloxo ligand and
SiPh2H ligands is less plausible because oxidative addition of
chlorosilanes having SieH bonds causes SieH bond cleavage more
easily than SieCl bond cleavage [15].
{1H} NMR spectrum was referenced to external SiMe4 (
d 0) in C6D6
or toluene-d8. IR absorption spectra were recorded on a Shimadzu
FT/IR-8100 spectrometer. Elemental analysis was carried out using
a LECO CHNS-932 or Yanaco MT-5 CHN autorecorder at the Center
for Advanced Materials Analysis, Technical Department, Tokyo
Institute of Technology. [PdI2(bpy)] [18] and (c-C5H9)7Si7O9(OH)3
[19] were prepared according to the reported procedure. Ag2O,
Ph2SiClH and p-cresol (Wako Pure Chemical) are commercially
available products and are used without any purification.
p-Cresol also reacted with 1 to afford [Pd(OC6H4CH3-p)2(bpy)]
(4) in 87% yield, accompanied with formation of a trisilanol (Eq.
Cl
Si'
Si' Cl
Pd
Si'
Cl
+
+
O
3.2. Preparation of [Pd{O11Si7(c-C5H9)7(OH)}(bpy)] (1)
O
Pd
O
Pd
Si
Si
Si
To a THF solution (5 mL) of (c-C5H9)7Si7O9(OH)3 (202 mg,
Scheme 2.
0.23 mmol) were added Ag2O (129 mg, 0.56 mmol) and [PdI2(bpy)]

1214
M. Tanabe et al. / Journal of Organometallic Chemistry 696 (2011) 1211e1215
(120 mg, 0.23 mmol). The gray suspension was allowed to stir at
room temperature for 2 days. The formed solid was filtrated off by
using Celite, and the solvent was pumped off. The remained yellow
solid was recrystallized from THF/acetonitrile (1:1) to give 1 as
yellow crystals (236 mg, 90%). Anal. Calcd for C45H72O12N2PdSi7: C,
47.57; H, 6.39; N, 2.47. Found: C, 47.26; H, 6.36; N, 2.51. 1H NMR
on a Rigaku Saturn CCD diffractometer equipped with mono-
chromated Mo K radiation (
¼ 0.71073 Å). Calculations were
a
l
carried out using the program package Crystal Structure, version
3.8, for Windows. A full-matrix least-squares refinement was used
for the non-hydrogen atoms with anisotropic thermal parameters.
Hydrogen atoms, except for the OH hydrogens of 1, were located by
assuming the ideal geometry and were included in the structure
calculations without further refinement of the parameters. Crys-
tallographic data for 1∙C7H8: C97H152N4O24Pd2Si14; MW ¼ 2364.28;
crystal size 0.12 ꢂ 0.14 ꢂ 0.18 mm3; monoclinic; P21 (No. 4);
(400 MHz, toluene-d8, rt): d 1.20e1.36 (m, 7H, CH pentyl), 1.56e2.12
(m, 56H, CH2 pentyl), 6.26 (apparent triplet, 2H, H5 bpy, J ¼ 6.6 Hz),
7.64 (apparent triplet, 2H, H4 bpy, J ¼ 7.6 Hz), 8.26 (d, 2H, H3 bpy,
J ¼ 5.2 Hz), 8.74 (d, 2H, H6 bpy, J ¼ 8.0 Hz), 9.34 (s, 1H, OH). 13C{1H}
NMR (100 MHz, toluene-d8, rt):
d
23.4, 23.6, 23.6, 24.2, 26.2 (CH
a ¼ 12.411(1); b ¼ 34.706(2); c ¼ 13.031(1) Å;
b
¼ 96.455(5)ꢁ;
pentyl, ratio 1:1:1:2:2), 27.8, 27.9, 27.9, 28.2, 28.2, 28.3, 28.5, 28.6,
28.6, 29.6, 29.7 (CH2 pentyl), 128.5 (C3 bpy), 129.3 (C5 bpy), 140.5 (C4
bpy), 147.9 (C6 bpy), 155.4 (C2 bpy). 29Si{1H} NMR (79 MHz, toluene-
V ¼ 5577.2(8) Å3; Z ¼ 2; Dcalcd ¼ 1.408 g cmꢀ3; F(000) ¼ 2484;
m
¼ 0.5425 mmꢀ1; variables ¼ 1272; 153,54 reflections measured
11062 independent reflections (Rint ¼ 0.019); R(I > 2 (I)) ¼ 0.0531,
s
d8, 0.02 M Cr(acac)3, rt):
(ratio 2:1:1:2:1). IR data (KBr): 3400 (w, nOeH), 2949 (s, nCeH), 2864
(s, nCeH), 1113 (s, nSieO), 725 (w, nSieOePd), 710 (w, nSieOePd) cmꢀ1
d
ꢀ66.8, ꢀ64.4, ꢀ63.7, ꢀ58.0 and ꢀ54.4
Rw(I > 2
s
(I)) ¼ 0.1143; GOF ¼ 1.068.
.
Acknowledgments
3.3. Reaction of Ph2SiClH with 1
This work was financially supported from the Ministry of
Education, Culture, Sports, Science, and Technology, Japan. N.M.
thanks to JSPS Postdoctoral Fellowship Program.
To a 5 mL of toluene solution of 1 (227 mg, 0.20 mmol) was
added twice the molar amount of Ph2SiClH (80 mL, 0.41 mmol) at
ꢀ50 ꢁC. The reaction mixture was stirred for 1 h at room temper-
ature to precipitate a yellow solid, which was collected through
filtration, washed twice with 2 mL of hexane and dried in vacuo to
give [PdCl2(bpy)] (3), whose NMR spectroscopic data were consis-
tent with the literature [20]. The toluene solution was evaporated
under reduced pressure to give a colorless oil, which was washed
twice with 3 mL of MeCN to produce (c-C5H9)7Si7O11(OH)(SiPh2H)2
(2) (242 mg, 98%) as a white solid. Anal. Calcd for C59H86O12Si9: C,
57.14; H, 6.99. Found: C, 57.10; H, 6.72. 1H NMR (400 MHz, C6D6, rt):
Appendix A. Supplementary material
CCDC-787795 contains the supplementary crystallographic data
for 1. This material is available free of charge from the Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_
request/cif. The 29Si{1H} NMR spectra of 1 and 2 are included in
supplementary datawhich are associated with this article and found
in the online version at doi:10.1016/j.jorganchem.2010.09.029.
d
1.24 (m, 7H, CH pentyl), 1.54e2.06 (m, 56H, CH2 pentyl), 6.00 (s,
References
2H, SiH), 7.25e7.34 (m, 12H, C6H5 meta and para), 7.89 (m, 8H, C6H5
ortho). The OH signal is not observed. 13C{1H} NMR (100 MHz, C6D6,
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3.4. Reaction of p-cresol with 1
A 2 mL of toluene solution of 1 (214 mg, 0.19 mmol) was treated
withp-cresol(41 mg,0.38 mmol).Thereactionmixturewasstirredfor
2 h at room temperature and the solvent was removed under reduced
pressure. The remained solid was extracted with 3 mL of MeCN. The
extracts were evaporated to afford [Pd(OC6H4CH3-p)2(bpy)] (4)
(79 mg, 87%). Anal. Calcd for C24H22N2O2Pd∙H2O: C, 58.25; H, 4.89, N,
5.66. Found: C, 58.29; H, 4.77, N, 5.63. 1H NMR (400 MHz, THF-d8, rt):
d
2.05 (s, 6H, CH3), 6.60 (d, 4H, C6H4 ortho, 3JHeH ¼ 8.0 Hz), 7.00 (d, 4H,
3
C6H4 meta, JHeH ¼ 8.0 Hz), 7.62 (apparent triplet, 2H, H5 bpy,
J ¼ 6.4 Hz), 8.13(apparenttriplet, 2H, H4 bpy, J ¼ 7.8 Hz), 8.25(d, 2H, H3
bpy, J ¼ 7.6 Hz), 8.74(d, 2H,H6 bpy, J ¼ 5.2 Hz).13C{1H} NMR (100 MHz,
THF-d8, rt): d 20.8 (CH3), 120.1 (OC6H4 ortho), 122.4 (C3 bpy), 123.1 (C5
bpy), 127.2 (OC6H4 para), 129.1 (OC6H4 meta), 140.5 (C4 bpy), 149.3
(OC6H4 ipso), 149.9 (C6 bpy), 166.8 (C2 bpy). The white solid insoluble
to MeCN was collected by filtration and confirmed as (c-C5H9)7
Si7O9(OH)3 by 1H and 29Si{1H} NMR spectra.
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3.5. Crystallographic data for 1
Crystals of 1 suitable for X-ray diffraction study were sealed in
glass capillaries and mounted. Data for 1 were collected at ꢀ160 ꢁC
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