Dipalladium complex with bridging silylene ligands, {Pd(dmpe)} 2(μ-SiPh2)2L formed via dimerization of a bis(silyl)paliadium complex

Article abstract of DOI:10.1021/om070075c

Heating a toluene solution of the bis(silyl)palladium complex [Pd(SiHPh₂)₂(dmpe)] (1) (dmpe = 1,2-bis(dimethylphosphino) ethane) at 60°C afforded a dipalladium complex with bridging silylene ligands, [{Pd(dmpe)}₂(μ-SiPh₂)₂] (2), accompanied by H₂SiPh₂ elimination. An X-ray crystallographic study of 2 suggested the presence of a Si...Si interaction in the four-membered Pd₂Si₂ ring.

Full text of DOI:10.1021/om070075c

Organometallics 2007, 26, 2937-2940
2937
Notes
Dipalladium Complex with Bridging Silylene Ligands,
[{Pd(dmpe)}2(µ-SiPh2)2], Formed via Dimerization of a
Bis(silyl)palladium Complex
Makoto Tanabe, Akane Mawatari, and Kohtaro Osakada*
Chemical Resources Laboratory (R1-3), Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
ReceiVed January 25, 2007
Summary: Heating a toluene solution of the bis(silyl)palladium
complex [Pd(SiHPh2)2(dmpe)] (1) (dmpe ) 1,2-bis(dimeth-
ylphosphino)ethane) at 60 °C afforded a dipalladium complex
with bridging silylene ligands, [{Pd(dmpe)}2(µ-SiPh2)2] (2),
accompanied by H2SiPh2 elimination. An X-ray crystallographic
study of 2 suggested the presence of a Si‚‚‚Si interaction in the
four-membered Pd2Si2 ring.
induce another type of Si-Si bond formation, affording a
diplatinum complex with a bridging disilene ligand.6 Diplatinum
complexes with two bridging silylene ligands contain a four-
membered Pt2Si2 ring with short distances between two Si atoms
(2.58(2)-2.718(2) Å).7 They may have a partial contribution
of a dinuclear structure with a π,π-bridging disilene ligand,
although this is not universally accepted. The diplatinum model
complexes, [{Pt(PH3)2}2(µ-SiR2)2], also have a weak Si‚‚‚Si
interaction on the basis of the results of theoretical calculations.8
Dipalladium complexes with the Pd2Si2 rhombi have not been
prepared as yet, but a more significant Si‚‚‚Si interaction than
that in the diplatinum model complexes has been suggested to
occur by theoretical study.9 Dipalladium complexes with two
bridging N-heterocyclic silylene ligands, namely, [{Pd(PPh3)}2-
{µ-Si(tBuNCHdCHNtBu)}2]10 and [{Pd(PtBu3)}2{µ-Si(tBuNCH2-
CH2NtBu)}2],11 were reported to have short Pd-Pd distances
(2.6501(2)-2.7070(2) Å) and the separation of two Si atoms
in the Pd2Si2 ring. In this paper, we report on the preparation
of a dinuclear Pd complex with bridging SiPh2 ligands with
the structure having a close contact between two Si atoms.
Introduction
Silicon-silicon bond formation promoted by late-transition-
metal complexes has been of significant interest in organosilicon
chemistry, relevant to the dehydrocoupling dimerization or the
polymerization of organosilanes catalyzed by Rh,1 Ni,2 or Pt3
complexes. Although early-transition-metal complexes promote
metathesis-type dehydrocoupling of organosilanes, this type of
reaction is not common for late-transition-metal complexes. Both
reductive elimination via a coupling of two silyl ligands4a,b and
insertion of a silylene (SiR2) ligand into the M-silyl bond4c
were proposed as a crucial step in the formation of a new Si-
Si bond. A dinuclear rhodium hydride complex catalyzes
dehydrogenative coupling of primary and secondary silanes,
reactions that have been proposed to involve the oxidative
addition of Si-H bonds and the reductive elimination of
disilanes at the dinuclear Rh centers.5 The dimerization of a
mononuclear Pt(IV) tris(phenylsilyl)complex was reported to
Results and Discussion
Heating a mixture of [PdMe2(dmpe)] (665 mM) and H2SiPh2
(1:3 molar ratio) in toluene at 60 °C produced a bis(silyl)-
palladium complex, [Pd(SiHPh2)2(dmpe)] (1), in 91% yield (eq
1). Use of 3 equiv of H2SiPh2 led to formation of 1 in high
yield and with 1 as the sole product.
* To whom correspondence should be addressed. E-mail: kosakada@
res.titech.ac.jp.
Figure 1a shows the molecular structure of 1 (obtained from
recrystallization at room temperature): a square-planar Pd(II)
(1) (a) Ojima, I.; Inaba, S. I.; Kogure, T.; Nagai, Y. J. Organomet. Chem.
1973, 55, C7-C8. (b) Brown-Wensley, K. A. Organometallics 1987, 6,
1590-1591. (c) Corey, J. Y.; Chang, L. S.; Corey, E. R. Organometallics
1987, 6, 1595-1596. (d) Chang, L. S.; Corey, J. Y. Organometallics 1989,
8, 1885-1893. (e) Rosenberg, L.; Davis, C. W.; Yao, J. J. Am. Chem. Soc.
2001, 123, 5120-5121. (f) Jackson, S. M.; Hughes, C. E.; Monfette, S.;
Rosenberg, L. Inorg. Chim. Acta 2006, 359, 2966-2972.
(2) (a) Fontaine, F.-G.; Kadkhodazadeh, T.; Zargarian, D. Chem.
Commun. 1998, 1253-1254. (b) Fontaine, F. -G.; Zargarian, D. Organo-
metallics 2002, 21, 401-408. (c) Fontaine, F.-G.; Zargarian, D. J. Am.
Chem. Soc. 2004, 126, 8786-8794.
(3) (a) Yamamoto, K.; Okinoshima, H.; Kumada, M. J. Organomet.
Chem. 1970, 23, C7-C8. (b) Chauhan, B. P. S.; Shimizu, T.; Tanaka, M.
Chem. Lett. 1997, 785-786.
(4) (a) Kobayashi, T.; Hayashi, T.; Yamashita, H.; Tanaka, M. Chem.
Lett. 1988, 1411-1414. (b) Shimada, S.; Rao, M. L. N.; Hayashi, T.;
Tanaka, M. Angew. Chem., Int. Ed. 2001, 40, 213-216. (c) Goikhman, R.;
Milstein, D. Chem.-Eur. J. 2005, 11, 2983-2988.
(5) (a) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Organometallics 1991,
10, 2537-2539. (b) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Inorg. Chim.
Acta 1994, 222, 345-364. (c) Rosenberg, L.; Fryzuk, M. D.; Rettig, S. J.
Organometallics 1999, 18, 958-969.
(6) Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114, 1917-
1919.
(7) (a) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J. J. Am. Chem.
Soc. 1988, 110, 4068-4070. (b) Zarate, E. A.; Tessier-Youngs, C. A.;
Youngs, W. J. J. Chem. Soc., Chem. Commun. 1989, 577-578. (c) Sanow,
L. M.; Chai, M.; McConnville, D. B.; Galat, K. J.; Simons, R. S.; Rinaldi,
P. L.; Youngs, W. J.; Tessier, C. A. Organometallics 2000, 19, 192-205.
(d) Braddock-Wilking, J.; Levchinsky, Y.; Rath, N. P. Organometallics
2001, 20, 474-480.
(8) (a) Anderson, A. B.; Shiller, P.; Zarate, E. A.; Tessier-Youngs, C.
A.; Youngs, W. J. Organometallics 1989, 8, 2320-2322. (b) Aullo´n, G.;
Alemany, P.; Alvarez, S. J. Organomet. Chem. 1994, 478, 75-82.
(9) (a) Sakaki, S.; Yamaguchi, S.; Musashi, Y.; Sugimoto, M. J.
Organomet. Chem. 2001, 635, 173-186. (b) Nakajima, S.; Yokogawa, D.;
Nakao, Y.; Sato, H.; Sakaki, S. Organometallics 2004, 23, 4672-4681.
(10) Fu¨rstner, A.; Krause, H.; Lehmann, C. W. Chem. Commun. 2001,
2372-2373.
(11) Herrmann, W. A.; Ha¨rter, P.; Gsto¨ttmayr, C. W. K.; Bielert, F.;
Seeboth, N.; Sirsch, P. J. Organomet. Chem. 2002, 649, 141-146.
10.1021/om070075c CCC: $37.00 © 2007 American Chemical Society
Publication on Web 04/18/2007

2938 Organometallics, Vol. 26, No. 11, 2007
Notes
analogous diplatinum complexes (Si‚‚‚Si ) 2.58(2)-2.718(2)
Å)7 suggest a weak interaction, although they are longer than a
typical covalent Si-Si single bond (2.35 Å). Mononuclear
palladium complexes with η2-disilene ligands, [Pd{Si(SiMe2-
tBu)2}2L2] (L ) PMe3, L2 ) dmpe) (Si-Si bond: 2.303(1) and
2.318(6) Å), show an elongated SidSi bond distance of free
disilene (2.202(1) Å) due to π-bonding.13 The Si‚‚‚Si interaction
in the four-membered Pd2Si2 ring renders the Si-Pd-Si angle
of 2 (63.92(2)°) smaller than that in 1 (79.74(3)°). Chart 1
t
compares the bond parameters of 1, 2, and [Pd{Si(SiMe2 Bu)2}2-
(dmpe)].
Although the limited solubility of 2 in any organic solvent
prevented 29Si{1H} NMR measurement in solution, the solid-
state 29Si{1H} NMR spectrum of 2 exhibited a single resonance
at δ -51.0 (Figure 2). The diplatinum complexes, having a close
Si‚‚‚Si contact, also exhibit 29Si NMR chemical shifts in the
negative region, [{Pt(PPr3)2}2(µ-SiH(Hex))2] (δ -94)7c and [{Pt-
(dmpe)}2(µ-SiHAr)2] (Ar ) 2-isopropyl-6-methylphenyl) (δ
-134.2).7d The 29Si resonance of the dipalladium complex
bridged by N-heterocyclic silylene ligands, [{Pd(PPh3)}2{µ-Si-
(tBuNCHdCHNtBu)}2],10 was observed at highly positive
position (δ 109.5), which was partly due to the N-donors on
the Si atom.
cis-Bis(silyl)palladium complexes with monophosphine ligands
have a tendency to decompose in solution due to the rapid
reductive elimination of disilane,14 whereas 1, with the chelating
ligand, is stable in solution, as is the palladium bis(silyl)complex
reported by Fink, [Pd(SiHMe2)2(dcpe)] (dcpe ) 1,2-bis-
(dicyclohexylphosphino)ethane).12a The 1H NMR signal of the
Si-H hydrogens of 1 appears at δ 5.69, accompanied by the
coupling of two phosphorus nuclei (JP-H ) 9.9 Hz). The
chemical shift of 1 is similar to that of the Si-H hydrogens of
an analogous platinum complex, [Pt(SiHPh2)2(dmpe)] (δ 5.81
in C6D6).15 The 29Si{1H} NMR spectrum of 1 shows a doublet
of doublets at δ -4.5 (JP-Si ) 13.6 and 160 Hz), consistent
with the crystal structure of 1. Heating a solution of 1 in toluene-
d8 at 60 °C induced the partial conversion of 1 to palladium
dimer 2 and H2SiPh2, as shown in eq 2. Figure 3 plots the
amounts of 1, 2, and H2SiPh2 present during the course of the
thermal reaction, as obtained on the basis of intensity of C6H5
ortho signals. After 5 h, the concentration of 1 was reduced
from its original value (40 mM), whereas that of 2 and H2-
SiPh2 increased gradually to attain an equilibrium mixture of
[1] ) 24 mM, [2] ) 7.2 mM, and [H2SiPh2] ) 11 mM. The
quantitative conversion of the isolated 2 to 1 was confirmed by
the addition of an excess of H2SiPh2 at room temperature and
leaving the mixture standing for 24 h, indicating the reversible
reaction of eq 2. Almost exclusive formation of 1 in reaction 1
Figure 1. ORTEP drawings of (a) 1 and (b) 2 with ellipsoids drawn
at the 50% probability level. Hydrogen atoms are omitted for
simplicity. The molecule of 2 has a C2 symmetric center at the
midpoint of two Pd centers. Atoms with asterisks are crystallo-
graphically equivalent to those having the same number without
asterisks. Selected distances (Å) and angles (deg) for 1: Pd-Si1
2.3548(9), Pd-Si2 2.3550(7), Pd-P1 2.3395(9), Pd-P2 2.3356-
(7), Si1-H1 1.52(4), Si2-H2 1.50(4), P1-Pd-P2 85.17(2), P1-
Pd-Si2 96.84(2), P2-Pd-Si1 98.29(3), Si1-Pd-Si2 79.74(3).
Selected distances (Å) and angles (deg) for 2: Pd-P1 2.3346(7),
Pd-P2 2.3423(3), Pd-Si 2.3822(4), Pd-Si* 2.3840(6), Si‚‚‚Si*
2.5227(7), Pd‚‚‚Pd* 4.0438(2), P1-Pd-P2 85.75(2), P1-Pd-Si
103.53(2), P2-Pd-Si* 108.15(2), Si-Pd-Si* 63.92(2), Pd-Si-
Pd* 116.08(2), C1-Si-C7 108.73(9).
center coordinated by two SiHPh2 ligands and a chelating dmpe
ligand. The Pd-Si bond distances of 1 (2.3548(9) and 2.3550-
(7) Å) are similar to those in the bis(silyl)palladium complexes
(2.3563(9)-2.3818(8) Å).12
Heating a dilute toluene solution of 1 (41 mM) at 60 °C
produced a dipalladium complex, [{Pd(dmpe)}2(µ-SiPh2)2] (2),
which was isolated in 24% yield from the reaction mixture
containing 1, 2, and H2SiPh2 (eq 2).
Complex 2 was characterized by X-ray crystallography. A
molecule of the dinuclear complex has a crystallographic C2
symmetry around the midpoint of the two Pd centers (Figure
1b). The palladium atoms of 2 are coordinated by a chelating
dmpe ligand and two bridging diphenylsilylene ligands. The
distances between the two Si atoms of 2 (2.5227(7) Å) and of
(13) (a) Hashimoto, H.; Sekiguchi, Y.; Sekiguchi, Y.; Iwamoto, T.;
Kabuto, C.; Kira, M. Can. J. Chem. 2003, 81, 1241-1245. (b) Kira, M.;
Sekiguchi, Y.; Iwamoto, T.; Kabuto, C. J. Am. Chem. Soc. 2004, 126,
12778-12779. (c) Iwamoto, T.; Sekiguchi, Y.; Yoshida, N.; Kabuto, C.;
Kira, M. Dalton Trans. 2006, 177-182. For Pt-disilene complexes, see:
(d) Pham, E. K.; West, R. J. Am. Chem. Soc. 1989, 111, 7667-7668. (e)
Pham, E. K.; West, R. Organometallics 1990, 9, 1517-1523. (f) Hashimoto,
H.; Sekiguchi, Y.; Iwamoto, T.; Kabuto, C.; Kira, M. Organometallics 2002,
21, 454-456.
(14) Schubert, U.; Mu¨ller, C. J. Organomet. Chem. 1989, 373, 165-
172.
(15) Tanabe, M.; Osakada, K. J. Am. Chem. Soc. 2002, 124, 4550-
4551.
(12) (a) Pan, Y.; Mague, J. T.; Fink, M. J. Organometallics 1992, 11,
3495-3497. (b) Murakami, M.; Yoshida, T.; Ito, Y. Organometallics 1994,
13, 2900-2902. (c) Suginome, M.; Oike, H.; Park, S.-S.; Ito, Y. Bull. Chem.
Soc. Jpn. 1996, 69, 289-299. (d) Chen, W.; Shimada, S.; Hayashi, T.;
Tanaka, M. Chem. Lett. 2001, 1096-1097. (e) Lee, Y. -J.; Lee, J. -D.;
Kim, S.-J.; Keum, S.; Ko, J.; Suh, I.-H.; Cheong M.; Kang, S. O.
Organometallics 2004, 23, 203-214.

Notes
Organometallics, Vol. 26, No. 11, 2007 2939
Table 1. Crystallographic Data and Details of Refinement
for 1 and 2
1
2
formula
fw
C30H38P2PdSi2
623.16
C36H52P4Pd2Si2
877.68
cryst color
cryst syst
cryst size/mm
space group
a/Å
colorless
yellow
triclinic
monoclinic
0.70 × 0.20 × 0.10
P21/n (No. 14)
11.862(2)
19.652(3)
13.331(2)
1.00 × 0.65 × 0.60
P1h (No. 2)
9.386(2)
10.946(2)
11.355(2)
102.354(1)
113.113(1)
104.349(2)
974.0(3)
1
b/Å
c/Å
R/deg
â/deg
104.291(2)
γ/deg
V/Å3
3011.3(8)
4
1.368
Z
D
calcd/g cm-3
1.496
Figure 2. CPMAS 29Si{1H} NMR spectrum of 2. Signals with
asterisks are attributed to the spinning sideband that resulted from
the spinning speed of 6.478 kHz.
F(000)
1276
0.8195
21 677
6663 (Rint ) 0.028)
5824
448
1.1737
6110
3775 (Rint ) 0.011)
3614
µ/mm-1
no. of rflns measd
no. of unique rflns
no. of obsd rflns
(I > 2.00σ(I))
no. of variables
R1 (I > 2.00σ(I))
wR2 (I > 2.00σ(I))
GOF
Chart 1
360
225
0.0383
0.1386
0.973
0.0252
0.0805
1.003
13C{1H}, 29Si{1H}, and 31P{1H} NMR spectra were recorded on a
Varian Mercury 300 or JEOL EX-400 spectrometer. The peak
positions of the 31P{1H} and 29Si{1H} NMR spectra were referenced
to external 85% H3PO4 and external SiMe4 in C6D6, respectively.
Solid-state CPMAS 29Si{1H} NMR measurements were carried out
at 79.3 MHz on a JEOL ECA-400 spectrometer using a spinning
speed of 6480 Hz. 29Si chemical shifts were referenced to poly-
(dimethylsilane)s (δ -34.0). [PdMe2(dmpe)] was prepared accord-
ing to a previous report.16 Ph2SiH2 is a commercially available
product from Aldrich. IR absorption spectra were recorded on a
Shimadzu FT/IR-8100 spectrometer. Elemental analysis was carried
out with a LECO CHNS-932 CHNS or Yanaco MT-5 CHN
autocorder.
Preparation of [Pd(SiHPh2)2(dmpe)] (1). To a toluene solution
(20 mL) of [PdMe2(dmpe)] (3.81 g, 13.3 mmol) in an evacuated
Schlenk flask was added a 3-fold molar amount of Ph2SiH2 (7.88
mL, 39.9 mmol). The reaction mixture was stirred at 60 °C for 46
h in an inert-gas atmosphere. The solution changed from colorless
to orange. The solvent was removed under reduced pressure. The
residue material was washed four times with 5 mL of hexane and
dried in Vacuo to give 1 as a pale yellow solid (7.51 g, 91%).
Crystals of 1 suitable for X-ray crystallography were obtained from
recrystallization from toluene/hexane (1:10) at room temperature.
Anal. Calcd for C30H38P2PdSi2: C, 57.82; H, 6.15. Found: C, 57.49;
H, 6.34. 1H NMR (300 MHz, C6D6, room temperature): δ 7.83 (d,
Figure 3. Change in amounts of 1, 2, and H2SiPh2 during the
thermal reaction of 1 at 60 °C. [1] ) 40 mM in toluene-d8. Dibenzyl
was used as an internal standard (48 mM).
is ascribed to a shift of the equilibrium to the left at much higher
Pd concentration (665 mM).
3
8H, C6H5 ortho, JH-H ) 7.5 Hz), 7.21 (m, 12H, C6H5 meta and
This study revealed that dipalladium complex 2, with two
bridging diphenylsilylene ligands, possesses a strong Si‚‚‚Si
interaction in its four-membered Pd2Si2 framework, as suggested
by the previous theoretical study reported by Sakaki and co-
workers.9 Transformation from 1 to 2 and H2SiPh2 occurs
reversibly in solution, but details of the reversible reaction are
not clear at present.
3
para), 5.69 (apparent triplet, 2H, SiH, JP-H ) 9.9 Hz), 0.75 (d,
2
2
4H, PCH2, JP-H ) 16 Hz), 0.54 (d, 12H, PCH3, JP-H ) 6.9 Hz).
13C{1H} NMR (100 MHz, C6D6, -50 °C): δ 144.4 (C6H5 ipso),
136.6 (C6H5 ortho), 127.4 (C6H5 meta), 28.2 (m, PCH2), 11.6 (m,
PCH3). The para-carbon signals of the C6H5 group were overlapped
with the solvent signals. 31P{1H} NMR (122 MHz, C6D6, room
2
temperature): δ 12.6 (2JSi-Pcis ) 13 Hz, JSi-Ptrans ) 160 Hz).
29Si{1H} NMR (79 MHz, toluene-d8, -50 °C): δ -4.5 (dd, 2JPcis-Si
2
) 13 Hz, JPtrans-Si ) 160 Hz). IR (KBr): 2040 (νSiH) cm-1
.
Experimental Section
Preparation of [{Pd(dmpe)}2(µ-SiPh2)2] (2). This experiment
should be performed in the strict absence of oxygen and moisture.
In a glovebox, a toluene solution (20 mL) of 1 (511 mg, 0.82 mmol)
was heated at 60 °C for 20 h. The reaction solution gradually
General Procedures. All manipulations of the complexes 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 passing through a solvent
purification system (Glass Contour). THF was distilled from sodium
benzophenone ketyl and stored in a nitrogen atmosphere. 1H,
(16) de Graaf, W.; Boersma, J.; Smeets, W. J. J.; Spek, A. L.; van Koten,
G. Organometallics 1989, 8, 2907-2917.

2940 Organometallics, Vol. 26, No. 11, 2007
Notes
changed from a yellow liquid to an orange suspension. The solvent
was removed under reduced pressure. To remove the starting
material and H2SiPh2, the resulting residue was washed three times
with 5 mL of hexane and five times with 5 mL of toluene and
dried in Vacuo to yield 2 as a yellow powder (85.7 mg, 24%).
Orange crystals suitable for X-ray crystallography were obtained
by recrystallization from THF/hexane (1:10). Anal. Calcd for
C36H52P4Pd2Si2: C, 49.26; H, 5.97. Found: C, 48.96; H, 6.11. 1H
NMR (300 MHz, C6D6, room temperature): δ 8.19 (d, 8H, C6H5
ortho, JH-H ) 7.5 Hz), 7.26 (t, 8H, C6H5 meta, JH-H ) 7.5 Hz),
0.88 (d, 8H, PCH2, JP-H ) 14 Hz), 0.76 (br, 24H, PCH3). The para-
hydrogen signals of the C6H5 group were overlapped with the
solvent signals. 13C{1H} NMR (100 MHz, C6D6, room tempera-
ture): δ 136.8 (C6H5 ortho), 126.8 (C6H5 meta), 125.5 (C6H5 para),
30.2 (m, PCH2), 14.4 (m, PCH3), The ipso-carbon signals of the
C6H5 group were not observed due to their small intensity. 31P-
{1H} NMR (122 MHz, C6D6, room temperature): δ 2.97. Solid-
state CPMAS 29Si{1H} NMR (79 MHz, room temperature): δ
-51.0.
Thermal Reaction of 1. 1 (14.9 mg, 0.024 mmol) and dibenzyl
(5.2 mg, 0.029 mmol) as an internal standard in toluene-d8 (0.6
mL) were heated at 60 °C in an NMR sample tube, and the reaction
mixture was monitored for 5 h. The concentrations of 1 (δ 7.69),
2 (δ 8.02), and H2SiPh2 (δ 7.46) were estimated from the intensity
of the C6H5 ortho signals in the 1H NMR spectra. An almost
equilibrium mixture of 1, 2, and H2SiPh2 (24 mM, 7.2 mM, and
11 mM) was obtained within 5 h of heating of the sample solution.
Reaction of 2 with an Excess of H2SiPh2. In a glovebox, an
excess of H2SiPh2 (50 µL, 0.253 mmol) was added to a C6D6
solution (1 mL) of 2 (20.5 mg, 0.023 mmol) in an NMR sample
tube. After 24 h at room temperature, the quantitative reversible
conversion into 1 was confirmed by 1H and 31P{1H} NMR
spectroscopy.
X-ray Crystallography. Crystals of 1 and 2 suitable for X-ray
diffraction study were mounted on a glass capillary. Data for 1
and 2 were collected at -160 °C on a Rigaku Saturn CCD
diffractometer equipped with monochromated Mo KR radiation (λ
) 0.71073 Å). Calculations were carried out using the program
package Crystal Structure, version 3.7, for Windows. A full-matrix
least-squares refinement was used for the non-hydrogen atoms with
anisotropic thermal parameters. Hydrogen atoms, except for the
SiH hydrogens of 1, were located by assuming the ideal geometry
and were included in the structure calculations without further
refinement of the parameters. Crystallographic data and details of
refinement are summarized in Table 1.
Acknowledgment. This work was financially supported by
a Grant-in-Aid for Scientific Research for Young Chemists (No.
17750049) and for Scientific Research on Priority Areas, from
the Ministry of Education, Culture, Sport, Science, and Technol-
ogy of Japan. We also thank Dr. Y. Nakamura for measuring
solid-state 29Si{1H} NMR spectra.
Supporting Information Available: Crystallographic data for
1 and 2 as a CIF file. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM070075C