Syntheses of mono- and dinuclear silylplatinum complexes bearing a diphosphino ligand via stepwise bond activation of unsymmetric disilanes

Article abstract of DOI:10.1039/c000545b

Zero-valence platinum complex [Pt(dppe)(η²-C ₂H₄)] (1, dppe = 1,2-bis(diphenylphosphino)ethane) treated with disilanes HR¹R²SiSiMe₃ (a, R¹ = R² = Me; b, R¹ = R² = Ph; c, R¹ = H, R² = Ph) afforded the corresponding disilanylplatinum hydrides [Pt(dppe)(H)(SiR¹R²SiMe₃)] (2a-c) by oxidative addition of the Si-H bond to the platinum center. The 1,2-silyl migration in 2a,b led to the formation of bis(silyl)platinum complexes [Pt(dppe)(SiHR ¹R²)(SiMe₃)] (3a,b) with a first-order rate constant of 7.2(2) × 10^-4 s^-1 at 25°C for 2a and 3.86(4) × 10^-4 s^-1 at 40°C for 2b, whereas 2c with R¹ = H followed by the transient generation of 3c dimerized rapidly to give the bis(μ-silylene)diplatinum complex [Pt(dppe)(μ-SiHPh)] ₂ (4c) in a mixture of cis/trans isomers. Heating of the toluene solution of 3b at 100°C resulted in a similar dimerization to 4b. In addition, a trinuclear platinum complex [Pt₃(dppe) ₃(μ₃-SiPh)₂] (5) with a trigonal bipyramidal Pt₃Si₂ core arose from the reaction of 4c with 1 at 60°C in toluene. Unsymmetric disilanes therefore accomplished the syntheses of various monomeric and dimeric platinum complexes via 1,2-hydrogen and silyl migration to the platinum center. The Royal Society of Chemistry.

Full text of DOI:10.1039/c000545b

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www.rsc.org/dalton | Dalton Transactions
Syntheses of mono- and dinuclear silylplatinum complexes bearing a
diphosphino ligand via stepwise bond activation of unsymmetric disilanes†
Hidekazu Arii,a Makiko Takahashi,a Masato Nanjoa,b and Kunio Mochida*a
Received 11th January 2010, Accepted 7th May 2010
First published as an Advance Article on the web 7th June 2010
DOI: 10.1039/c000545b
2
Zero-valence platinum complex [Pt(dppe)(h -C2H4)] (1, dppe = 1,2-bis(diphenylphosphino)ethane)
treated with disilanes HR1R2SiSiMe3 (a, R1 = R2 = Me; b, R1 = R2 = Ph; c, R1 = H, R2 = Ph) afforded
the corresponding disilanylplatinum hydrides [Pt(dppe)(H)(SiR1R2SiMe3)] (2a–c) by oxidative addition
of the Si–H bond to the platinum center. The 1,2-silyl migration in 2a,b led to the formation of
bis(silyl)platinum complexes [Pt(dppe)(SiHR1R2)(SiMe3)] (3a,b) with a first-order rate constant of
7.2(2) ¥ 10-4 s-1 at 25 ◦C for 2a and 3.86(4) ¥ 10-4 s-1 at 40 ◦C for 2b, whereas 2c with R1 = H followed
by the transient generation of 3c dimerized rapidly to give the bis(m-silylene)diplatinum complex
[Pt(dppe)(m-SiHPh)]2 (4c) in a mixture of cis/trans isomers. Heating of the toluene solution of 3b at
100 ◦C resulted in a similar dimerization to 4b. In addition, a trinuclear platinum complex
[Pt3(dppe)3(m3-SiPh)2] (5) with a trigonal bipyramidal Pt3Si2 core arose from the reaction of 4c with 1 at
60 ◦C in toluene. Unsymmetric disilanes therefore accomplished the syntheses of various monomeric
and dimeric platinum complexes via 1,2-hydrogen and silyl migration to the platinum center.
benzene ring.10 Moreover, using a group 10 transition metal Pd,
the same group as Pt, generates a trinuclear complex containing
Introduction
a high-valence Pd(VI) center through dehydrocoupling.11 These
findings suggest that a silane compound with multi Si–H bonds
induces the oligomerization of complexes and the formation of a
multiple M–Si bond, such as silylene or silylyne ligands.
Activation of Si–H and Si–Si bonds is one of the important
steps in the development of novel organosilicon compounds. Low-
valence transition metal complexes can activate these bonds, and
among them platinum reagents are well known to be effective
catalysts in hydrosilylation or double-silylation with unsaturated
hydrocarbons.1,2 The structure and reactivity of complexes with
Pt–Si bonds are interesting because of an active intermediate
in the catalytic cycle.3 Zero-valence platinum complexes bearing
phosphine ligands are often utilized in a variety of reactions.
Many researchers have synthesized and characterized various
types of Pt–Si complexes such as silylplatinum hydrides,4 and
bis(silyl)platinum5 and multinuclear platinum complexes bridged
by silyl or silylene ligands.6,7 And, N-donor ligands allow a
formation of a silylplatinum(IV) hydride by oxidative addition of
the Si–H bond to the Pt(II) center.8
We investigated the reaction of a zero-valence platinum com-
2
plex [Pt(PPh3)2(h -C2H4)] with symmetric disilanes HR2SiSiR2H
(R = Ph, Me) to identify several thermally unstable plat-
2
inum complexes.12 Recently, [Pt(dppe)(h -C2H4)] (1, dppe = 1,2-
bis(diphenylphosphino)ethane) treated with H2MeSiSiMe3 af-
forded the unique bis(silylyne)triplatinum complex [Pt3(dppe)3(m3-
SiMe)2], indicating the activation of all Si–H and Si–Si bonds in
H2MeSiSiMe3.13 In the present paper, we focused on the reactive
behavior of unsymmetric disilanes HR1R2SiSiMe3 (a, R1 = R2 =
Me; b, R1 = R2 = Ph; c, R1 = H, R2 = Ph) by varying the
alkyl groups on one of the two silane centers, and studied the
spectroscopic and structural characterization for the platinum
complexes formed by Si–H and Si–Si activation.
A silane trihydride requires the formation of a structurally
attractive platinum complex via a multistep Si–H bond activation.
Heyn and Tilley reported that heating [Pt(dmpe)(SiH2Ar)2]2(m-
dmpe) (dmpe = 1,2-bis(dimethylphosphino)ethane; Ar = Ph, p-
Tol) at 60 ◦C converts it a diplatinum complex [Pt(dmpe)(H)]2(m-
Experimental
1
1
SiHAr)2(m-h ,h -HArSiSiArH), indicating that four Si–H bonds
are activated and a Si–Si bond is formed.9 Shimada et al.
synthesized a mixed valence Pt(II)Pt(IV) complex derived from 1,2-
bis(silyl)benzene which has two trihydrosilyl groups attached to a
General considerations
All experiments were carried out using a standard vacuum line
and Schlenk techniques or in an M. Braun inert atmosphere
dry box. All the reagents were of the highest grade available
and were used without further purification. All solvents used for
the syntheses were distilled according to the general procedure.
Benzene-d6 and toluene-d8 were distilled from potassium metal
under Ar atmosphere. Complex 114 and disilanes a–c15 were
aDepartment of Chemistry, Gakushuin University, 1-5-1 Mejiro, Toshima-ku,
Tokyo, 171-8588, Japan. E-mail: kunio.mochida@gakushuin.ac.jp;
Fax: +81-3-5992-1029; Tel: +81-3-3986-0221
bDepartment of Chemistry and Biotechnology, Graduate School of Engineer-
ing, Tottori University, Koyama-cho-Minami, Tottori, 680-8552, Japan
1
synthesized according to previously reported methods. The H
1
† Electronic supplementary information (ESI) available: Selected H and
NMR spectral measurements were performed on a JEOL AL-
1
31P{ H} NMR data and kinetics data. CCDC reference numbers 761290–
1
300 NMR spectrometer at 300 MHz for H, 122 MHz for 31P
761295. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c000545b
and 60 MHz for 29Si. The chemical shifts of the protons are
6434 | Dalton Trans., 2010, 39, 6434–6440
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reported relative to the residual protonated solvents benzene-d6
(7.15 ppm) and toluene-d8 (2.09 ppm). The chemical shifts of
phosphorous and silicon are corrected relative to external H3PO4
(0 ppm) and SiMe4 (0 ppm). Elemental analysis was performed on
a CE Instruments EA1110 corrected by acetoanilide.
RT): d 7.71 (m, 4H, PPh), 7.59 (m, 4H, PPh), 7.15–7.0 (m, 12H,
PPh), 4.85 (dsept, 1H, 2JPtH = 96 Hz, 3JHH = 42 Hz, 3JPH = 18 Hz,
SiH), 1.9–1.6 (m, 4H, CH2P), 0.56 (d, 9H, 3JPtH = 27 Hz, 4JPH
=
2.7 Hz (trans), SiMe3), 0.49 (dd, 6H, 3JPtH = 30 Hz, 3JHH = 3.9 Hz,
1
4JPH = 3.3 Hz (trans), SiHMe2) ppm; 31P{ H} NMR (toluene-d8,
1
2
1
RT): d 58.5 (d, JPtP = 1217 Hz, JPP = 7 Hz), 58.2 (d, JPtP
=
1405 Hz, 2JPP = 8 Hz) ppm. Found C, 51.08; H, 5.54%. Calcd for
3a (C31H40P2PtSi2), C, 51.30; H, 5.55%.
Syntheses of platinum complexes
Synthesis of [Pt(dppe)(H)(SiMe2SiMe3)] (2a)
Synthesis of [Pt(dppe)(SiHPh2)(SiMe3)] (3b)
To a toluene solution (0.5 mL) of HMe2SiSiMe3 (10.6 mg,
0.080 mmol) was added solid 1 (49.8 mg, 0.080 mmol) at -30 ◦C,
Complex 3b was synthesized by the same method as that used for
3a, except that HPh2SiSiMe3 was used to obtain colorless crystals.
Yield: 115.5 mg (84%); 1H NMR (toluene-d8, RT): d 7.8–7.6 (m,
8H, ArH), 7.33 (m, 4H, PPh), 7.15–7.05 (m, 12H, PPh), 6.95–6.85
(m, 6H, SiPh), 5.81 (dd, 1H, 2JPtH = 80 Hz, 3JPH = 19 Hz (trans),
3JPH = 9.3 Hz (cis), SiH), 1.85–1.60 (m, 4H, CH2P), 0.44 (d, 9H,
◦
and the resulting solution was stored in a chilled box at -30 C
overnight. Pentane (4 mL) was added to the resulting solution.
The solution was allowed to stand for 1 day in the chilled box to
afford colorless crystals. Yield: 38.2 mg (66%); 1H NMR (toluene-
d8, -30 ◦C): d 7.74 (m, 4H, PPh), 7.65 (m, 4H, PPh), 7.05–7.00 (m,
12H, PPh), 2.0–1.8 (br, 2H, CH2P), 1.8–1.6 (br, 2H, CH2P), 0.76
(d, 6H, 3JPtH = 37.1 Hz,4JPH = 3.9 Hz (trans), SiMe2SiMe3), 0.66
(dd, 1H, 1JPtH = 1144 Hz, 2JPH = 169 Hz (trans), 2JPH = 14 Hz (cis),
2JPtH = 25 Hz, 4JPH = 2.7 Hz (trans), SiMe3) ppm; 31P{ H} NMR
1
1
2
(toluene-d8, RT): d 58.0 (d, JPtP = 1588 Hz, JPP = 8 Hz), 57.3
(d, 1JPtP = 1187 Hz, 2JPP = 8 Hz) ppm. Found C, 60.96; H, 5.39%.
Calcd for 3b·toluene (C48H52P2PtSi2), C, 61.19; H, 5.56%.
1
PtH), 0.53 (s, 9H, SiMe2SiMe3) ppm; 31P{ H} NMR (toluene-d8,
-30 ◦C): d 61.6 (s, 1JPtP = 1375 Hz), 57.2 (s, 1JPtP = 2086 Hz) ppm.
Found C, 51.29; H, 5.76%. Calcd for 2a (C31H40P2PtSi2), C, 51.30;
H, 5.55%.
Synthesis of [Pt(dppe)(l-SiPh2)]2 (4b)
Heating a toluene solution of 3b at 100 ◦C for 11 days gave a yellow
Synthesis of [Pt(dppe)(H)(SiPh2SiMe3)] (2b)
1
1
powder of 4b. Identification was carried out by H and 31P{ H}
NMR spectroscopy according to the previous report.6d
Complex 2b was synthesized by the same method as that used
for 2a, except HPh2SiSiMe3 was used to obtain colorless crystals.
Yield: 54.7 mg (88%); 1H NMR (toluene-d8, -30 ◦C): d 7.80 (brs,
8H, PPh), 7.2–6.8 (22H, ArH), 1.9–1.5 (m, 4H, CH2P), 0.52 (s,
9H, SiMe3), 0.25 (dd, 1H, 1JPtH = 1073 Hz, 2JPH = 166 Hz (trans),
Synthesis of [Pt(dppe)(l-SiHPh)]2 (4c)
To a toluene solution (2 mL) of H2PhSiSiMe3 (29.6 mg,
0.164 mmol) was added a toluene solution (2 mL) of 1 (100 mg,
0.161 mmol) at room temperature, and the resulting solution was
stored overnight. Pentane (2 mL) was added to the solution. The
solution was allowed to stand for 1 day to afford light yellow
crystals. Yield: 61.0 mg (54%); 1H NMR (toluene-d8, RT): d 7.8–
7.6 (m, 8H, PPh), 7.50 (m, 4H, SiPh), 7.30 (m, 8H, PPh), 7.1–6.6
◦
1
2JPH = 12 Hz (cis), PtH) ppm; 31P{ H} NMR (toluene-d8, -30 C):
d 61.2 (s, 1JPtP = 1524 Hz), 55.7 (s, 1JPtP = 2111 Hz) ppm. Found C,
60.83; H, 5.51%. Calcd for 2b·toluene (C48H52P2PtSi2): C, 61.19;
H, 5.56%.
Synthesis of [Pt(dppe)(H)(SiHPhSiMe3)] (2c)
2
3
(30H, ArH), 6.59 (apparent septet, 2H, JPtH = 32 Hz, JPH
=
8.0 Hz, SiH for trans-4c), 6.21 (apparent septet, 2H, 2JPtH = 43 Hz,
Complex 2c was synthesized by the same method as that used for
2a, except that H2PhSiSiMe3 was used to obtain colorless crystals.
3JPH = 11 Hz, SiH for cis-4c), 2.0–1.6 (br, 8H, CH2P) ppm; 31P{ H}
1
NMR (toluene-d8, RT): d 59.3 (s, 1JPtP = 1458 Hz, 3JPtP = 260 Hz,
4JPP = 29 Hz for cis-4c), 58.9 (s, 1JPtP = 1463 Hz, 3JPtP = 214 Hz,
4JPP = 25 Hz for trans-4c) ppm; 1H–29Si HMQC NMR (toluene-d8,
RT): d -100, -107 ppm. Found C, 55.34; H, 4.62%. Calcd for 4c
(C64H60P4Pt2Si2), C, 54.93; H, 4.32%.
◦
1
Yield: 53.1 mg (80%); H NMR (toluene-d8, -30 C): d 8.32 (d,
2H, 3JHH = 6.9 Hz, SiPh), 7.85–7.6 (m, 4H, PPh), 7.44 (apparent
3
triplet, 2H, PPh), 7.31 (t, 2H, JHH = 7.2 Hz, SiPh), 7.18 (t, 1H,
3JHH = 7.2 Hz, SiPh), 7.1–6.8 (m, 12H, PPh), 4.71 (dd, 1H, 3JPH
=
3
20 Hz (trans), JPH = 7.5 Hz (cis), SiH), 2.0–1.7 (br, 4H, CH2P),
0.87 (dd, 1H, 1JPtH = 1097 Hz, 2JPH = 168 Hz (trans), 2JPH = 14 Hz
1
(cis), PtH), 0.39 (s, 9H, SiMe3) ppm; 31P{ H} NMR (toluene-d8,
Kinetics
◦
1
1
-30 C): d 62.0 (s, JPtP = 1629 Hz), 55.8 (d, JPtP = 1976 Hz,
2JPP = 10 Hz) ppm. Found C, 54.66; H, 5.24%. Calcd for 2c
(C35H40P2PtSi2), C, 54.32; H, 5.21%.
The conversion of disilanylplatinum hydride into the correspond-
ing bis(silyl)platinum complex was confirmed by decreasing the
peak intensity at 0.66 of 2a and 7.25 ppm of 2b, respectively, in
1H NMR spectra. A residual protonated solvent at 2.09 ppm in
toluene-d8 was used as an internal standard, and the conversion
rate of 2a was estimated from the area ratio of the each peak to
that at 2.09 ppm. The data collection was performed at 5 or 10 min
intervals at verified temperature over three times that of the half-
life. The data were analyzed with Igor (WaveMatrics, Inc.) on a
Macintosh computer and fitted to an exponential function by a
non-linear least-squares method.
Synthesis of [Pt(dppe)(SiHMe2)(SiMe3)] (3a)
To a toluene solution (2 mL) of HMe2SiSiMe3 (11.5 mg,
0.087 mmol) was added a toluene solution (2 mL) of 1 (50.0 mg,
0.80 mmol) at room temperature, and the resulting solution was
stored overnight. Pentane (2 mL) was added to the resulting
solution. The solution was allowed to stand for 1 day to afford
1
colorless crystals. Yield: 35.3 mg (61%); H NMR (toluene-d8,
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Table 1 Crystallographic data for the platinum complexes
2a·THF
2b·C7H8
2c
3a
3b
4c·C7H8
Formula
Fw
Crystal system
C35H48O1P2PtSi2
797.94
C48H52P2PtSi2
942.11
C35H40P2PtSi2
773.88
C31H40P2PtSi2
725.84
C41H44P2PtSi2
849.97
C71H68P4Pt2Si2
1491.49
Orthorhombic
P212121 (#19)
12.6750(3)
16.3880(6)
29.958(1)
90
90
90
6222.8(3)
4
1.592
Monoclinic
P21/n (#14)
13.049(3)
10.517(2)
26.795(6)
90
103.762(3)
90
3571.8(14)
4
1.484
4.111
36 745
8162 (0.0665)
379
Monoclinic
P21/n (#14)
9.2600(4)
41.553(2)
11.4170(6)
90
101.692(3)
90
4301.9(4)
4
1.455
3.424
34 573
9176 (0.090)
481
Monoclinic
P21/n (#14)
9.133(4)
31.933(12)
11.720(4)
90
104.992(5)
90
3302(2)
4
1.557
4.442
16 071
6084 (0.1189)
371
Triclinic
Monoclinic
C2/c (#15)
40.488(1)
10.2430(6)
20.520(1)
90
115.089(3)
90
7707.1(7)
8
1.465
3.814
34 652
8848 (0.061)
418
¯
Space group
P1 (#2)
˚
a/A
9.4840(4)
11.5970(8)
16.377(1)
107.605(3)
98.424(4)
107.803(4)
1576.97(17)
2
1.529
4.645
15 156
6961 (0.042)
361
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
rc/g cm-3
m(Mo-Ka)/mm-1
Total no. of data
No. of unique data (Rint
No. of params
4.674
54 920
8147 (0.089)
719
0.0526
)
a
R1
0.0874
0.2112
0.0568
0.1496
0.0530
0.1082
0.0495
0.1235
0.0405
0.1028
wR2 (all data)b
0.1396
ꢀ
ꢀ
ꢀ
ꢀ
a I > 2.00s(I). R1 = ꢀFo| - |Fcꢀ/ |Fo|. b wR2 = { (w(|Fo| - |Fc|)2)/ wFo
}
.
2
1/2
X-Ray crystallography†
Single crystals of 2a, 2b, 2c, 3a, 3b, and 4c suitable for X-ray
diffraction analyses were obtained by allowing their corresponding
solutions to stand for a few days. Each crystal was mounted on a
loop or a glass fiber, and the data were collected on a Bruker-AXS
M06XCE Imaging Plate for 2b, 3a, 3b and 4c or APEX II CCD
detector for 2a and 2c using graphite monochromated Mo-Ka
radiation. The crystal data and experimental details are listed in
Scheme 1 Reaction of 1 with unsymmetric disilanes a–c.
1JPtP because of strong trans influence of Si, which is consistent
with the existence of two unequivalent phosphorus atoms.
Table 1.
All the structures were solved by the combination of the direct
In the crystal structures of 2a–c (Fig. 1, Table 2), the platinum
atoms have a planar structure with a P2SiH donor set. A
strong trans influence of Si causes the Pt(1)–P(1) bond lengths
to elongate compared with the Pt(1)–P(2) ones. The Pt–Si bond
lengths were similar to those of silylplatinum complexes reported
previously,4,5,12 and the Pt–Si bond length of 2a was shorter by ca.
method and Fourier techniques, and all the non-hydrogen atoms
were anisotropically refined by full-matrix least-squares calcula-
tions. The atomic scattering factors and anomalous dispersion
terms were obtained from the International Tables for X-ray
Crystallography IV.16 The location of the hydrogen atoms of Si–
H and Pt–H were determined from difference Fourier maps and
refined. All the calculations were carried out on a Silicon Graphic
work station by the maXus program.
˚
0.02 A than that of 2b and 2c because the phenyl groups on the
Si atom avoid steric repulsion to the phenyl groups of dppe. The
˚
˚
Pt–H bond lengths were 1.51(8) A for 2a, 1.49(9) A for 2b, and
˚
1.56(8) A for 2c, within the range of the characteristic Pt–H bond
length. Coordination of the disilanes to the platinum center does
˚
not affect the Si–Si bond lengths of 2.34 to 2.36 A diagnostic
Results and discussion
of the Si–Si single bond in disilanes.18 The Si–Si alignment is
perpendicular to the P2Si plane because the phenyl groups of
dppe prevent accessibility to the sterically bulky SiMe3 group.
Reaction of complex 1 with disilanes a–c at -30 ◦C
◦
Treatment of 1 with a–c in toluene at -30 C produced a corre-
sponding disilanylplatinum hydride (2a–c) by oxidative addition
of the Si–H bond to the platinum center (Scheme 1). In the H
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 2a–c
1
NMR spectra, the Pt–H signals were observed as a doublet of a
doublet with 195Pt satellites centered at 0.66 ppm for 2a, 0.25 ppm
for 2b, and 0.87 ppm for 2c accompanied by the disappearance of
the Si–H signal of free a–c. The hydride resonances of 2a–c with a
bidentate ligand, dppe, shifted to a lower magnetic field than that
of a monodentate ligand system in the range of -5–0 ppm.4,17 The
Si–H signal in 2c appeared as a doublet of a doublet with 195Pt
2a
2b
2c
Pt(1)–P(1)
Pt(1)–P(2)
Pt(1)–Si(1)
Pt(1)–H
2.311(3)
2.279(3)
2.345(3)
1.51(8)
2.351(5)
85.13(11)
173.57(12)
99.60(12)
2.3000(17)
2.2877(16)
2.3694(18)
1.49(9)
2.362(2)
85.92(6)
2.286(3)
2.264(3)
2.352(3)
1.56(8)
2.337(4)
86.60(10)
174.87(10)
97.49(10)
Si(1)–Si(2)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–Si(1)
P(2)–Pt(1)–Si(1)
172.85(6)
101.19(6)
1
satellites at 4.71 ppm. The 31P{ H} NMR spectra of 2a–c had two
singlets with 195Pt satellites of which one is flanked with the small
6436 | Dalton Trans., 2010, 39, 6434–6440
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Fig. 1 Crystal structure of 2a (A), 2b (B) and 2c (C) showing 50% probability thermal ellipsoids. The hydrogen atoms except for one on Pt and Si are
omitted for clarity.
◦
1
Fig. 2 31P{ H} NMR spectra of 2a at -30 C in toluene-d8 (bottom) and
after standing for 2 days at RT (top).
Fig. 3 Eyring plots for the conversion of 2a (circle) and 2b (triangle).
Conversion of complexes 2a–c at room temperature
In the 1H NMR spectra of 2a and 2b in toluene-d8 at room
temperature, the Pt–H signal disappeared and a new peak
appeared as a doublet of a septet at 4.85 ppm and a doublet of a
doublet at 5.81 ppm, respectively, in the typical Si–H region. The
1
31P{ H} NMR spectra had two unequivalent phosphine signals
approaching each other, which indicates the similar chemical
environment of two phosphorus atoms (Fig. 2). The JPtP value
around 1200 Hz was attributed to a strong trans influence of
Scheme 2 Conversion of 2 into 3.
1
the peralkylated silicon found in cis-[Pt(PR3)2(H)(SiR¢2R¢¢)]4d and
cis-[Pt(PEt3)2(SiMe3)2].5e These new species could be assigned
to the bis(silyl)platinum complexes [Pt(dppe)(SiHMe2)(SiMe3)]
(3a) and [Pt(dppe)(SiHPh2)(SiMe3)] (3b) because the reaction of
the zero-valence platinum complex with symmetrical disilanes,
HnR3-nSiSiR3-nHn, generates a bis(silyl)platinum complex by 1,2-
silyl migration in a disilanylplatinum hydride (Scheme 2). The
conversion rate◦of 2a and 2b obeyed first-order kinetics in the
range of 25–55 C, and the activation parameters DH‡ and DS‡
estimated from Eyring plots were DH‡ = 62(4) kJ mol-1, DS‡ =
-97(12) J K-1 mol-1 for 2a and DH‡ = 83(3) kJ mol-1, DS‡ =
-44(9) J K-1 mol-1 for 2b, respectively (Fig. 3). We reported that
rate constant of a disilanylplatinum hydride to a bis(silyl)platinum
◦
complex was 5.5(2) ¥ 10-4 s-1 at -40 C.12 The rate constants
at -40 ◦C of 2a and 2b, calculated by an extrapolation from
the activation parameters, were 5.1 ¥ 10-7 s-1 and 4.7 ¥ 10-9 s-1,
respectively, and were approximately 103–5 times slower than
that of the PPh3 ligand. For 1,2-silyl migration, a coordinative
saturated platinum complex acquires a vacant site by liberating
one of two phosphine atoms to afford a bis(silyl)platinum complex
via an intermediate (silyl)(silylene)platinum hydride.19 The high
coordination ability of the bidentate ligand dppe to the platinum
center increases the thermal stability of 2a and 2b. Moreover,
1
the DH‡ is likely to correlate with the JPtP with respect to the
2
in the [Pt(PPh3)2(h -C2H4)]/HPh2SiSiPh2H system, the first-order
Pt–P bond cleavage, which implies that strong trans influence of a
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◦
˚
Dimerization of platinum-silylene species derived by the
Table 3 Selected bond lengths (A) and angles ( ) for 3a and 3b
elimination of SiHMe3
3aa
3b
The 1H NMR spectrum of 3b in toluene-d8 at 100 ◦C changed to a
bis(m-silylene)diplatinum complex [Pt(dppe)(m-SiPh2)]2 (4b) after
11 days accompanied by the exsertion of SiHMe3 gas (a doublet at
0.02 ppm and a dectet at 4.16 ppm) while 3a decomposed gradually
to complete a homoleptic zero-valence complex [Pt(dppe)2] under
Pt(1)–P(1)
Pt(1)–P(2)
Pt(1)–Si(1)
Pt(1)–Si(2)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–Si(1)
P(2)–Pt(1)–Si(2)
Si(1)–Pt(1)–Si(2)
2.3183(12)
2.3237(13)
2.3855(15)
2.398(3)
84.13(5)
94.83(5)
2.3375(11)
2.3170(12)
2.3602(12)
2.3973(12)
84.48(4)
97.44(4)
96.41(4)
1
the same conditions (Scheme 3).20 The 31P{ H} NMR spectrum
99.73(10)
81.36(10)
exhibited part of an AA¢A¢¢A¢¢¢XX¢ spin system pattern diagnostic
for dinuclear platinum complexes.21 Complex 4b was synthesized
by Osakada and coworkers by ligand exchange of the diplatinum
complex [Pt(PCy3)(m-SiHPh2)]2 with two equivalents of dppe.
83.33(4)
a The bond lengths and angles associated with Si(2A) are listed as one of
the disordered components.
silicon atom with an aliphatic alkyl group supports the liberation
of a phosphine ligand.
The platinum centers in 3a and 3b have a four-coordinate planar
geometry with a P2Si2 donor set (Fig. 4, Table 3). All Pt–P bond
˚
lengths elongate more than 2.31 A due to the trans influence of Si
atom, and the bite angle of dppe in 3b becomes slightly smaller
than that of 2b. The small bite angle results in the large Si–Pt–
Si angle of 3a and 3b compared with the cis-[Pt(PR3)2(SiR1R2 )2]
Scheme 3 Dimerization of 3 to 4.
2
complexes (79–81◦) with a monodentate phosphine ligand.5,12 The
location of Si–H in 3a could not be determined because the two
silyl groups are disordered.
On the other hand, thermolysis of 2c also involved the reductive
elimination of SiHMe3 and the generation of 4c in which two
phosphine resonances were observed at 58.9 and 59.3 ppm flanked
1
by two sets of satellites. Complex 3c observed transiently on H
and 31P NMR spectra may rapidly convert to 4c (Fig. 5(C)). The
1H NMR spectrum of 4c had two apparent septets of Si–H at 6.21
and 6.59 ppm that correlated with two silicon resonances at upfield
-107 and -100 ppm, respectively, characteristic of the bis(m-
silylene)diplatinum complexes in the 1H–29Si HMQC experiment.20
The two peaks were attributed to a mixture of cis/trans isomers
due to the orientation of the phenyl group on the Si atom, and the
ratio of cis to trans isomers independent of ambient temperature
was roughly 1 : 4, as estimated from the integral value of Si–H
signals. The structure of trans-4c was confirmed by XRD analysis
Fig. 4 Crystal structure of 3a (A) and 3b (B) showing 50% probability
thermal ellipsoids. One of the two disordered positions of the silyl groups
in 3a is shown. The hydrogen atoms except for one on Si in 3b are omitted
for clarity.
Although 2c converted into bis(silyl)platinum complex,
[Pt(dppe)(SiH2Ph)(SiMe3)] (3c), a small amount of 3c maintained
despite the reduction of 2c to proceed a subsequent reaction to a
dinuclear complex 4c, as described in the next section.
1
Fig. 5 31P{ H} NMR spectra of 2c in benzene-d6 (A), standing for 4 h (B)
and for 3 days at RT (C). The peaks marked with an asterisk are assigned
to the bis(silyl)platinum complex 3c.
6438 | Dalton Trans., 2010, 39, 6434–6440
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˚
(Fig. 6). The Pt–Si bond lengths of 2.404(3) and 2.422(4) A for
Pt(1) were at the upper limit of the Pt–Si single bond length. The
˚
shorter Pt–Pt distance of 3.8885(5) A relevant to the reported
diplatinum complexes21 was associated with a puckering of the
Pt2Si2 ring by 23.5(2)◦ to accommodate the acute Si–Pt–Si angles
of 67.95(11)◦ for Pt(1) and 68.76(11)◦ for Pt(2). The Si–Si bond
˚
distance of 2.697(5) A indicates a very weak interaction between
the two silylene ligands on the base of the theoretical calculation
of [Pt2(PH3)4(m-SiH2)2] reported hitherto.22 The analogues of 4c
were prepared using various methods, such as the dealkylation
coupling of monosilane with the alkylplatinum complex and
ligand exchange on the dinuclear platinum complex.
Scheme 4 Reaction of 4c with zero-valence complex 1.
valence platinum complex from approaching the Si–H bond of the
bridging silylene.
Conclusions
2
The reaction of a platinum complex [Pt(dppe)(h -C2H4)] (1) with
a bidentate phosphine ligand dppe was investigated by NMR
spectroscopy and XRD analysis. For unsymmetric disilane, the
bis(m-silylene)diplatinum complex forms via the disilanylplatinum
hydride and subsequent bis(silyl)platinum complex, except for
HMe2SiSiMe3. In particular, H2PhSiSiMe3 is activated the Si–
H bond to effect conversion into the bis(m3-silylyne)triplatinum
complex.
Acknowledgements
Fig. 6 Crystal structure of 4c showing 50% probability thermal el-
This work was financially supported by a grant from Iketani
Science and Technology Foundation (H. A.) and a Grant-in-Aid
for Scientific Research from the Ministry of Education, Science,
Sports, and Culture, Japan (K. M.).
lipsoids. The hydrogen atoms except for one on Si are omitted for
◦
˚
clarity. Selected bond lengths (A) and angles ( ): Pt(1)–P(1) 2.311(3),
Pt(1)–P(2) 2.331(3), Pt(1)–Si(1) 2.422(4), Pt(1)–Si(2) 2.404(3), Pt(2)–P(3)
2.330(3), Pt(2)–P(4) 2.302(3), Pt(2)–Si(1) 2.394(3), Pt(2)–Si(2) 2.382(3);
P(1)–Pt(1)–P(2) 84.97(10), Si(1)–Pt(1)–Si(2) 67.95(11), P(3)–Pt(2)–P(4)
84.56(10), Si(1)–Pt(2)–Si(2) 68.76(11).
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