Dipalladium complexes with bridging monoalkyl or monophenyl silyl ligands in the solid state and in solution

Article abstract of DOI:10.1021/om3012486

HexSiH₃, PhSiH₃, and PhSiClH₂ reacted with [Pd(PCy₃)₂] to yield dipalladium complexes with bridging silyl ligands: [{Pd(PCy₃)}₂(μ-HSiXR)₂] (1, R = Hex, X = H; 2, R = Ph, X = H; 3, R = Ph, X = Cl). The X-ray crystallographic results displayed a typical bis(silyl)-bridged dinuclear structure with an anti conformation of the substituents on the Si atom in the solid state. Temperature-dependent NMR spectroscopic analyses of 1 and 2 revealed a dynamic syn-anti isomerization of the complex via exchange of the bridging and nonbridging Si-H hydrogens in solution. Complex 3 with bridging chloro(phenyl)silyl ligands did not show such a dynamic behavior.

Full text of DOI:10.1021/om3012486

Article
pubs.acs.org/Organometallics
Dipalladium Complexes with Bridging Monoalkyl or Monophenyl
Silyl Ligands in the Solid State and in Solution
Makoto Tanabe, Atsushi Takahashi, Tetsuyuki Yamada, and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
S
* Supporting Information
ABSTRACT: HexSiH3, PhSiH3, and PhSiClH2 reacted with
[Pd(PCy3)2] to yield dipalladium complexes with bridging silyl
ligands: [{Pd(PCy3)}2(μ-HSiXR)2] (1, R = Hex, X = H; 2, R =
Ph, X = H; 3, R = Ph, X = Cl). The X-ray crystallographic
results displayed a typical bis(silyl)-bridged dinuclear structure
with an anti conformation of the substituents on the Si atom in
the solid state. Temperature-dependent NMR spectroscopic
analyses of 1 and 2 revealed a dynamic syn−anti isomerization
of the complex via exchange of the bridging and nonbridging Si−H hydrogens in solution. Complex 3 with bridging
chloro(phenyl)silyl ligands did not show such a dynamic behavior.
a silyl-bridged diplatinum structure and two {PtH(PR3)2}
fragments connected by bridging Si atoms.13 Braddock-Wilking
prepared a series of diplatinum complexes with arylsilyl ligands,
[{Pt(PPh3)}2(μ-SiH2Ar)2] (Ar = 2,4,6-trimethylphenyl, 2,4,6-
trimethoxyphenyl, etc.).14 Thus, bridging monoalkyl (or
monoaryl) silyl ligands bonded to Pd and Pt are less common
than bridging disubstituted silyl ligands of the multinuclear
complexes, and there have been only a few reports of
multinuclear palladium complexes with chelating primary silyl
or silylene ligands.15 In this paper, we report the isolation of
dipalladium complexes with bridging primary silyl ligands and
their structures in the solid state and in solution.
INTRODUCTION
■
Transition-metal multinuclear complexes with bridging primary
(μ-SiH2R) and secondary (μ-SiHR2) silyl ligands have been
investigated by many research groups because of their unique
bonding structures and chemical properties.1 Stone reported
such complexes containing group 10 metals, [{Pt(PCy3)}2(μ-
SiHR2)2] (R = Me, Ph), in 1980.2 The studies on related
diplatinum,3 dipalladium,4 dinickel,5 and Pt−Pd heterobimetal-
lic6 complexes revealed the detailed structures of the four-
membered M2Si2 ring composed of M−Si σ bonds and M−
Si(H) three-center−two-electron (3c-2e) bonds. Late-transi-
tion-metal complexes with primary and secondary silyl ligands
undergo 1,2-migration of the hydrido ligand from the silyl
groups to form monometallic silylene-coordinated complexes.7
The secondary silylene ligands are much more stable than the
primary silylene ligands in these complexes because of low
electrophilicity and significant steric hindrance of the Si atom.
Less bulky primary silylene ligands are converted easily to form
dinuclear structures with bridging Si ligands.8 Diplatinum
complexes with bridging arylsilylene (μ-SiHAr) ligands are
proposed as potential intermediates for the Si−Si bond-forming
coupling reactions of arylsilanes.9
RESULTS AND DISCUSSION
■
Reactions of [Pd(PCy3)2] with HexSiH3, PhSiH3, and
PhSiClH2 at ambient temperature produced dipalladium
complexes with bridging silyl ligands, [{Pd(PCy3)}2(μ-
HSiXR)2] (1, R = Hex, X = H; 2, R = Ph, X = H; 3, R =
Ph, X = Cl), in 88−96% yields, as shown in eq 1. Secondary
Reactions of primary silanes having bulky 9-triptycyl and 2,6-
dimesitylphenyl substituents with low-valent complexes of Pd
and Pt did not cause Si−Si coupling reactions but led to the
formation of mononuclear silyl(hydrido)palladium10 and
-platinum11 complexes. Si ligands with a less bulky substituent
bridge two to four metal centers in multinuclear complexes of
group 10 metals. Mochida synthesized tri- and tetraplatinum
complexes with triply or quadruply bridging silylyne or
germylyne ligands.12 Tessier reported that the nonbridging
Si−H bonds of the silylene-bridged diplatinum complex
[{Pt(PR3)2}2{μ-SiHHex}2] (R = Et, iPr) reacted with
[PtH2(PR3)2] to form tetraplatinum complexes, [{Pt-
(PR3)}2{μ-SiHHex{PtH(PR3)2}}2], which were composed of
silanes were reported to react with the zerovalent complexes
[M(PCy3)2] (M = Pt,3f,g Pd,6a Ni5b,c) to produce the
Received: December 22, 2012
Published: March 11, 2013
© 2013 American Chemical Society
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corresponding dinuclear complexes, but the dipalladium
complexes with bridging monoalkyl (or monoaryl) silyl ligands
have not yet been reported.
Figure 1 shows the molecular structures of 1-anti, 2-anti, and
3-anti, which were determined by X-ray crystallography.
vector. The crystal structures of 1 and 2 contain short SiH···HC
distances (2.418 and 2.450 Å) between an nonbridging Si−H
bond of the Pd2Si2 ring and a HC group of the PCy3 ligand,
which are attributed to a weak dihydrogen bonding interaction
(ca. 2.4 Å) assisted by the electropositive Si atom.16 The
SiCl···HC hydrogen bonds of 3 (2.805 and 2.833 Å) are also
found within the sum of van der Waals radius of Si and Cl (2.95
Å). The Pd−Pd distances of 1-anti and 2-anti (2.7036(8) and
2.7110(6) Å) are slightly longer than those of dipalladium
complexes with diphenylsilyl ligands, [{Pd(PR3)}2(μ-SiHPh2)2]
(R = Cy, 2.691(1) Å; R = Me, 2.691(1) Å). Introduction of an
electron-withdrawing chloro substituent to the bridging silyl
ligand strengthens and shortens the Pd−Pd bond of 3-anti
(2.6952(9) Å) in comparison to the dipalladium complexes
with primary silyl ligands (1-anti, 2.7036(8) Å; 2-anti,
2.7110(6) Å). These bond distances are shorter than the sum
of the atomic radii of Pd (1.38 Å) and Pt (1.38 Å), indicating
the formation of a strong bond between the two metals.17
The Pd−Si σ bonds lengthen in the order 3-anti (2.300(2),
2.305(2) Å) < 1-anti (2.309(1) Å) < 2-anti (2.318(1), 2.324(1)
Å) < [{Pd(PR3)}2(μ-SiHPh2)2] (R = Cy, 2.326(2) Å; R = Me,
2.328(2) Å), whereas the Pd−Si(H) bonds are shortened in the
order 1-anti (2.410(2) Å) > 2-anti (2.381(1), 2.391(1) Å) ≈
[{Pd(PR3)}2(μ-SiHPh2)2] (R = Cy, 2.384(2) Å; R = Me,
2.386(2) Å) > 3-anti (2.371(2), 2.380(2) Å). The electron-
withdrawing chloro substituent of 3-anti shortens both Pd−Si σ
bonds and Pd−Si(H) bonds and stabilizes the σ bond
significantly. 1-anti has a Pd−Si(H) bond which is much
longer than those in other complexes with Si−Ph groups in
Table 1. Less effective coordination of the Si−H group without
Ph groups to Pd may cause elongation of the Pd−Si(H) bond
and consequent shortening of the Pd−Si σ bond. These bond
parameters of complexes 1-anti and 3-anti obtained in this
study differ from those of analogous complexes. The
dipalladium complexes with two bridging silyl ligands prepared
so far, [{Pd(PR3)}2(μ-SiHPh2)2] (R = Me, Et, Cy), and their
optimized structures by theoretical calculations have ratios of
the Pd−Si(H) bond length to the Pd−Si σ bond length (d(Pd−
Si(H))/d(Pd−Si)) close to 1.025−1.027.4,6a The ratios of the
bond lengths of 1-anti and 3-anti are larger (1.044 and 1.032),
and the unique structural parameters of the new complexes are
attributed to electronic effects of hexyl and chloro groups on
the Si atom. Diplatinum complexes with bridging dialkylsilyl
groups, [{Pt(PR′3)}2(μ-SiHR2)2] (R′ = Cy, R = Me, Et, Hex;
R′ = Ph, R = Me),2,3e,g have bond length ratios (1.041−1.043)
that are larger than those with diphenylsilyl ligands ([{Pt-
(PCy3)}2(μ-SiHPh2)2], 1.025).3g
NMR spectra of the complexes provided detailed informa-
tion of the structures in solution. Complexes 1−3 display a
single 31P NMR signal at δ 44.8−46.7 at room temperature. As
shown in Figure 2, the 31P{1H} NMR signal of 1 at 25 °C (δ
46.2 in toluene-d8) is broadened on cooling to −20 °C and is
split into two signals at δ 46.0 and 46.7 in an approximate 2:1
intensity ratio at −50 °C. The signals are assigned to the two
isomers 1-anti and 1-syn, and the former is assigned to the more
stable anti structure. Two 31P NMR signals of 2-anti and 2-syn
(δ 45.2 and 44.9) at −60 °C also coalesce into a single signal (δ
Figure 1. Thermal ellipsoids (50% probability) of (a) 1-anti, (b) 2-
anti, and (c) 3-anti. Hydrogen atoms, except for Si−H hydrogens, are
omitted for simplicity. The molecule of 1-anti has a crystallographic
symmetry at the midpoint of the two Pd atoms. The n-hexyl group of
1-anti was disordered and refined anisotropically.
Selected bond parameters for these compounds and dipalla-
dium analogues with bridging diphenylsilyl ligands, [{Pd-
(PR3)}2(μ-SiHPh2)2] (R = Cy,6a Me4a), are summarized in
Table 1. The molecule of 1-anti has a crystallographic C2
symmetry around the midpoint of the Pd(I)−Pd(I) bond. The
molecules of 1−3 contain a typical bis(silyl)-bridged dinuclear
structure with a Pd−Si(H) 3c-2e bond and adopt an anti
conformation of the organic substituents relative to the Si−Si
1
45.4) at −30 °C. The H NMR spectrum of 1 at −50 °C
showed a signal for the nonbridging Si−H hydrogen signal at δ
7.18, while the corresponding signal of 2 (−60 °C) was
observed as two signals at δ 6.59 and 6.69 in an 81:19 ratio, and
they are assigned to 2-anti and 2-syn, respectively (Figure 3). As
the temperature of the solution of 2 is increased, the two Si−H
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Table 1. Selected Bond Distances (Å) and Angles (deg) of 1-anti, 2-anti, 3-anti, and [{Pd(PR3)}2(μ-HSiPh2)2] (R = Cy, Me)
a
b
1-anti
2-anti
2.7110(6)
3-anti
2.6952(9)
[{Pd(PCy3)}2(μ-HSiPh2)2]
[{Pd(PMe3)}2(μ-HSiPh2)2]
Pd−Pd
Pd−Si
Pd−Si(H)
Pd−P
Si−H(Pd)
Si−H
Pd−H
2.7036(8)
2.309(1)
2.410(2)
2.306(2)
1.659(2)
1.401
2.691(1)
2.326(2)
2.384(2)
2.316(2)
1.63
2.691(1)
2.328(2)
2.386(2)
2.294(2)
1.75
2.318(1), 2.324(1)
2.381(1), 2.391(1)
2.319(1), 2.319(1)
1.38(8), 1.63(6)
1.39(6), 1.41(6)
1.90(7), 1.82(5)
70.27(3), 70.36(3)
2.305(2), 2.300(2)
2.371(2), 2.380(2)
2.326(2), 2.325(2)
1.52(8), 1.48(7)
1.9045(5)
69.87(4)
1.55(8), 1.74(7)
1.61
1.91
Pd−Si−Pd
70.46(5), 70.22(5)
69.68(7)
69.61(5)
a
b
Reference 6a. Reference 4a.
1
Figure 3. H NMR spectra of 2 in CD2Cl2 at −90, −60, −30, 0, and
25 °C.
reported to involve the silylene character with sp2 hybridization,
as supported by theoretical calculations.18 The chemical shifts
of Si−H hydrogens of 1 and 2 may be influenced by the above
bonding situation.
Figure 2. 31P{1H} NMR spectra of 1 in toluene-d8 at −50, −20, and
25 °C.
Scheme 1 displays a plausible pathway for the fluxional
behavior of the bridging silyl ligands of 1 and 2. Activation of
the Pd−Si(HA) 3c-2e bond of A-anti generates the intermediate
signals coalesce into one broad signal (δ 6.62) at −30 °C and
then the combined signal does not appear in any region at 0 °C.
The chemical shifts of nonbridging Si−H hydrogens are at low
magnetic field positions, similarly to the reported diplatinum
complexes [{Pt(PPh3)}2(μ-H2SiAr)2] (Ar = 2,4,6-trimethyl-
phenyl, δ 8.95; Ar = pentaphenylphenyl, δ 7.48).14 The
bridging Si−H hydrogen signals of 1 and 2 are overlapped with
PCy3 hydrogen signals. The 2H{1H} NMR spectrum of
[{Pd(PCy3)}2(μ-D2SiHex)2] (1-d4), obtained from an analo-
gous reaction of [Pd(PCy3)2] with HexSiD3, shows two
deuterated resonances at δ 7.08 and 1.00 at −50 °C, while
the spectrum of [{Pd(PCy3)}2(μ-D2SiPh)2] (2-d4) at −60 °C
shows broadened nonbridging and bridging Si−D signals at δ
6.72 and 1.03. Warming the latter solution to 30 °C causes
coalescence of the deuterium signals to a broadened peak
around δ 4.0. Mononuclear Ru complexes with silylene and
hydride ligands, [Cp*(iPr2MeP)(H)RuSiHAr] (Cp* =
pentamethylcyclopentadienyl; Ar = 2,4,6-triisopropylphenyl, δ
9.41; Ar = 2,6-dimesitylphenyl, δ 8.00), also exhibited the Si−H
hydrogen peak at low magnetic field.7e The bridging organosilyl
ligands of the group 10 metal dinuclear structures were
Scheme 1
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36.3 (br, PCH), 33.8 (Si(CH2)4CH2), 32.6 (Si(CH2)2CH2 or
Si(CH2)3CH2), 31.1 (PCHCH2), 30.9 (SiCH2CH2), 28.0
(PCHCH2CH2), 26.7 (PCHCH2CH2CH2), 23.2 (Si(CH2)2CH2 or
Si(CH2)3CH2), 21.1 (SiCH2), 14.5 (Si(CH2)5CH3). 29Si{1H} NMR
(79 MHz, C6D6, room temperature): δ 132 (m, JP−Si = 46 Hz).
B, in which the Si−HA bond interacts with Pd to form a σ
complex. Further activation of the interaction and rotation of
the Pd−Si bond leads to formation of a new Pd−Si(HB) bond
to give A-syn, with the two organic substituents on the same
side of the Pd2Si2 plane. This dynamic motion of the bridging
silyl group at −30 °C is slow enough to allow the HA and HB
31P{1H} NMR (162 MHz, C6D6, room temperature): δ 46.1 (JSi−P
=
46 Hz). 31P{1H} NMR (162 MHz, toluene-d8, −50 °C): δ 46.7 (1-
syn), 46.0 (1-anti), The ratio of 1-anti and 1-syn was estimated to be
67:33. IR (KBr): 2034 (s, νSi−H), 1114 (w, νSi−H−Pd) cm−1.
1
signals to be distinguished in the H NMR spectrum. The anti
conformation of the dinuclear structures is more stable than the
syn form and exists as the major structure in solution and as the
exclusive structure in the solid state.19 Braddock-Wilking
reported on the fluxional NMR behavior of diplatinum
analogues and estimated the ΔG⧧ values (15−17 kcal mol−1)
with coalescence of the two 31P NMR signals at 69−83 °C.14
The activation free energy of 1 was estimated as 6.4 kcal mol−1
(Tc = −20 °C) from the line-shape analysis of the 31P NMR
signals.20 A smaller ΔG⧧ value and lower coalescence
temperature of 1 in comparison to those of the diplatinum
complexes suggest that the rotation of the Pd−Si σ bond occurs
more easily than rotation of the Pt−Si σ bond. In contrast, the
1H and 31P{1H} NMR spectra of 3 do not change with
temperature.
In summary, we prepared dipalladium complexes 1−3 with
bridging monoalkyl and monophenyl silyl ligands and
characterized the molecular structures by X-ray crystallography.
Although the organic substituents on the Si atom of 1−3 are
located on opposite sides of the Pd2Si2 rings in the solid state,
the dynamic syn−anti exchange behavior of 1 and 2 in solution
suggests dissociation/coordination of the Si−H bonds to the
Pd center or formation of a σ complex coordinated by the Si−
H bond to Pd.
Preparation of [{Pd(PCy3)}2(μ-D2SiHex)2] (1-d4). The procedure
to synthesize 1-d4 was similar to the preparation of 1. The reaction of
[Pd(PCy3)2] (300 mg, 0.45 mmol) with D3SiHex (53.6 mg, 0.45
mmol) gave the deuterated dipalladium complex 1-d4 (128 mg, 56%)
2
as a white solid. H{1H} NMR (77 MHz, toluene, −50 °C): δ 7.08
(br, 1D, SiD), 1.00 (br, 1D, SiDPd). 31P{1H} NMR (162 MHz, C6D6,
room temperature): δ 46.2.
Preparation of [{Pd(PCy3)}2(μ-H2SiPh)2] (2). To a toluene
solution (10 mL) of [Pd(PCy3)2] (1.60 g, 2.40 mmol) was added
H3SiPh (355 μL, 2.88 mmol), and the solution was stirred for 1 h at
room temperature. The solvent was removed under reduced pressure
to give a residue, which was washed with hexane (5 mL × 2) and dried
in vacuo to afford 2 as a white solid (1.14 g, 96%). Single colorless
crystals suitable for X-ray crystallography were obtained by diffusion of
hexane into the toluene solution at room temperature. Anal. Calcd for
C48H80P2Pd2Si2: C, 58.35; H, 8.16. Found: C, 58.68; H, 7.97. 1H NMR
(500 MHz, C6D6, room temperature): δ 8.02 (dd, 4H, C6H5 ortho,
JH−H = 7.5 Hz), 7.29 (t, 4H, C6H5 meta, JH−H = 7.5 Hz), 1.84 (br, 18H,
PC6H11), 1.59−1.52 (m, 18H, PC6H11), 1.38 (m, 12H, PC6H11),
1.10−0.88 (m, 18H, PC6H11), The C6H5 para proton signal was
1
overlapped. H NMR (400 MHz, CD2Cl2, −60 °C): δ 7.50 (C6H5
ortho; 2-anti), 7.46 (C6H5 ortho; 2-syn), 7.26−7.19 (C6H5 meta and
para), 6.69 (nonbridging SiH; 2-syn), 6.59 (nonbridging SiH; 2-anti),
1.80−0.86 (PC6H11, PdHSi). The ratio of 2-anti and 2-syn was
estimated to be 81:19. 13C{1H} NMR (126 MHz, CD2Cl2, room
temperature): δ 144.0 (C6H5 ipso), 136.3 (C6H5 ortho), 128.0 (C6H5
para), 127.6 (C6H5 meta), 35.9 (apparent triplet, PCH, JP−C = 8.3 Hz),
31.0 (s, PCHCH2), 27.8 (apparent triplet, PCHCH2CH2, JP−C = 6.2
Hz), 26.7 (s, PCHCH2CH2CH2). 29Si{1H} NMR (79 MHz, CD2Cl2,
room temperature): δ 126 (JP−Si was not determined). 31P{1H} NMR
(202 MHz, C6D6, room temperature): δ 46.7 (JSi−P = 67 Hz). 31P{1H}
NMR (162 MHz, CD2Cl2, −60 °C): δ 45.2 (2-anti, JSi−P = 70 Hz),
44.9 (2-syn). IR (KBr): 2051 (s, νSi−H), 1093 (w, νSi−H−Pd) cm−1.
Preparation of [{Pd(PCy3)}2(μ-D2SiPh)2] (2-d4). The procedure
to synthesize 2-d4 was similar to the preparation of 2. The reaction of
[Pd(PCy3)2] (300 mg, 0.45 mmol) with D3SiPh (105 mg, 0.94 mmol)
gave the deuterated dipalladium complex 2-d4 (97 mg, 44%) as a white
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out using
standard Schlenk techniques under an argon or nitrogen atmosphere
or in a nitrogen-filled glovebox (Miwa MFG). Hexane and toluene
were purified by using a Grubbs-type solvent purification system
(Glass Contour).21 The H, 13C{1H}, 29Si{1H}, and 31P{1H} NMR
1
spectra were recorded on JEOL EX-400 MHz, Bruker Biospin Avance
III 400 MHz, and JEOL JNM-500 MHz NMR spectrometers.
1
Chemical shifts in H and 13C{1H} NMR spectra were referenced to
the residual peaks of the solvents used.22 The 29Si and 31P chemical
shifts were referenced to external SiMe4 (δ 0) and 85% H3PO4 (δ 0) in
C6D6, toluene-d8, or CD2Cl2. IR spectra were recorded on a JASCO
FTIR-4100 spectrometer. Elemental analyses were performed using a
LECO CHNS-932 or Yanaco MT-5 CHN autorecorder. The
2
solid. H{1H} NMR (77 MHz, CH2Cl2, −60 °C): δ 6.72 (br, 1D,
SiD), 1.03 (br, 1D, SiDPd).
Preparation of [{Pd(PCy3)}2(μ-HSiClPh)2] (3). To a toluene
solution (3 mL) of [Pd(PCy3)2] (400 mg, 0.60 mmol) was added
PhClSiH2 (240 μL, 1.80 mmol), and then the reaction mixture was
stirred at room temperature for 60 h. The solvent was removed under
reduced pressure to give a residue, which was washed with hexane (1
mL × 10) and dried in vacuo to give 3 (303 mg, 96%) as a white
powder. Single colorless crystals suitable for X-ray crystallography
were obtained by slow diffusion of hexane into a THF solution at
room temperature. Anal. Calcd for C48H78Cl2P2Pd2Si2: C, 54.54; H,
7.44. Found: C, 54.82; H, 6.45. It was difficult to obtain satisfactory
24
compounds [Pd(PCy3)2]23 and HexSiH3 were prepared according
to the reported procedures. PhSiH3 and PhClSiH2 (Sigma-Aldrich)
were used as received.
Preparation of [{Pd(PCy3)}2(μ-H2SiHex)2] (1). To a hexane
solution (3 mL) of [Pd(PCy3)2] (500 mg, 0.75 mmol) was added
HexSiH3 (152 μL, 0.94 mmol), and the reaction mixture was stirred at
room temperature for 15 h to give a white precipitate. The white solid
was collected by filtration, washed with hexane (1 mL × 4), and dried
in vacuo to afford 1 (331 mg, 88%). Single crystals suitable for X-ray
crystallography were obtained by recrystallization from hexane at −20
°C. All signals of 1 in the 1H and 13C{1H} NMR spectra were assigned
by using 2D NMR experiments. Anal. Calcd for C48H96P2Pd2Si2: C,
57.41; H, 9.64. Found: C, 57.25; H, 9.76. 1H NMR (400 MHz, C6D6,
room temperature): δ 2.01−1.90 (18H, PCH, PCHCH2), 1.73 (12H,
PCHCH2CH2), 1.66−1.50 (30H, PCHCH2, PCHCH2CH2CH2,
SiCH2, SiCH2CH2, Si(CH2)4CH2), 1.44 (8H, Si(CH2)2CH2, Si-
(CH2)3CH2), 1.30−1.18 (m, 18H, PCHCH2CH2, PCHCH2CH2CH2),
0.96 (t, 6H, Si(CH2)5CH3, JH−H = 7.0 Hz). Si−H signals were not
observed, due to the fluxional behavior. 1H NMR (400 MHz, toluene-
d8, −50 °C): δ 7.18 (nonbridging SiH), 1.91−1.02 (PC6H11, SiC6H13,
bridging SiH). 13C{1H} NMR (101 MHz, C6D6, room temperature): δ
1
data for the elemental analysis due to severe air sensitivity. H NMR
(400 MHz, C6D6, room temperature): δ 8.09 (d, 4H, C6H5 ortho),
7.26 (d, 4H, C6H5 meta), 2.30 (apparent triplet, 2H, SiHPd, JH−P = 4.8
Hz), 1.90 (m, 12H, PCH, PCHCH2), 1.69 (m, 6H, PCHCH2), 1.59
(m, 6H, PCHCH2CH2), 1.49 (m, 12H, PCHCH2CH2,
PCHCH2CH2CH2), 1.37−1.29 (m, 12H, PCHCH2), 1.13 (m, 6H,
PCHCH2CH2), 0.98 (m, 12H, PCHCH2CH2, PCHCH2CH2CH2).
The C6H5 para proton signal was overlapped. 13C{1H} NMR (101
MHz, C6D6, room temperature): δ 144.7 (C6H5 ipso), 134.3 (C6H5
ortho), 129.2 (C6H5 para), 35.9 (apparent triplet, PCH, JP−C = 8.1 Hz),
31.0 (PCHCH2), 30.7 (PCHCH2), 27.7 (m, PCHCH2CH2), 26.4
(PCHCH2CH2CH2). The C6H5 meta carbon signal was overlapped.
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31P{1H} NMR (162 MHz, C6D6, room temperature): δ 44.8 (JSi−P
=
(4) (a) Kim, Y.-J.; Lee, S.-C.; Park, J.-I.; Osakada, K.; Choi, J.-C.;
Yamamoto, T. Organometallics 1998, 17, 4929−4931. (b) Kim, Y.-J.;
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71, 27 Hz). IR (KBr): 1508 (νSi−H−Pd) cm−1. The 29Si{1H} NMR
spectrum was not obtained due to decomposition of 3 during the
measurement overnight.
X-ray Crystal Structure Analysis. Single crystals of 1−3 suitable
for an X-ray diffraction study were mounted on MicroMounts
(MiTeGen). The crystallographic data of 1−3 were collected on a
Rigaku Saturn CCD area detector equipped with monochromated Mo
Kα radiation (λ = 0.71073 Å) at 113 K. Calculations were carried out
using the program package Crystal Structure, version 4.0, for
Windows. The positional and thermal parameters of non-hydrogen
atoms were refined anisotropically on F2 by full-matrix least-squares
methods using SHELXL-97.25 Hydrogen atoms, except for the Si−H
hydrogens, were placed at calculated positions and refined with a
riding mode on their corresponding carbon atoms. All SiH hydrogens
were located from difference Fourier maps. Disordered hexyl groups
were refined as two sets of positions, one with an occupancy of 0.64
and with anisotropic displacement parameters and the other with an
occupancy of 0.36. Crystallographic data of 1−3 are given in the
Supporting Information.
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ASSOCIATED CONTENT
■
S
* Supporting Information
A CIF file and a table giving crystallographic data for 1−3 and
figures giving NMR and IR spectroscopic data for 1−3 and an
Eyring plot of 1. This material is available free of charge via the
Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail for K.O.: kosakada@res.titech.ac.jp.
Notes
(10) Nakata, N.; Fukazawa, S.; Kato, N.; Ishii, A. Organometallics
2011, 30, 4490−4493.
(11) (a) Simons, R. S.; Sanow, L. M.; Galat, K. J.; Tessier, C. A.;
Youngs, W. J. Organometallics 2000, 19, 3994−3996. (b) Nakata, N.;
Fukazawa, S.; Ishii, A. Organometallics 2009, 28, 534−538.
(12) (a) Arii, H.; Takahashi, M.; Nanjo, M.; Mochida, K.
Organometallics 2009, 28, 4629−4631. (b) Arii, H.; Takahashi, M.;
Nanjo, M.; Mochida, K. Organometallics 2011, 30, 917−920. (c) Arii,
H.; Hashimoto, R.; Mochida, K.; Kawashima, T. Organometallics 2012,
31, 6635−6641.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by Grants-in-Aid for
Scientific Research (B) (No. 24350027) for Young Chemists
(No. 23750059) from the Ministry of Education, Culture,
Sport, Science, and Technology of Japan. We thank our
colleagues in the Center for Advanced Materials Analysis,
Technical Department, Tokyo Institute of Technology, for
elemental analysis.
(13) Sanow, L. M.; Chai, M.; McConnville, D. B.; Galat, K. J.;
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Organometallics 2000, 19, 192−205.
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Organometallics 1999, 18, 2583−2586. (b) Braddock-Wilking, J.;
Levchinsky, Y.; Rath, N. P. Organometallics 2000, 19, 5500−5510.
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