Thermal and photochemical reactions of phenylethynyltris-(trimethylsilyl) germane

Article abstract of DOI:10.1016/j.jorganchem.2012.12.018

The thermal and photochemical behavior of phenylethynyltris(trimethylsilyl) germane (1) has been reported. The thermolysis of 1 in the absence of a trapping agent in a sealed glass tube at 240 °C for 6 h gave 1,3-bis(trimethylsilyl) -1-tris(trimethylsilyl)germyl-1-germaindene (2) in 18% yield, together with phenyl(trimethylsilyl)acetylene in 60% yield. Similar thermolysis of 1 in the presence of 2,3-dimethylbutadiene afforded 3,4-dimethyl-1,1-bis(trimethylsilyl)- 1-germacyclopent-3-ene (3) in 62% yield, along with phenyl(trimethylsilyl) acetylene. When 1 was irradiated with a low-pressure mercury lamp in the presence of a large excess of 2,3-dimethylbutadiene at room temperature for 10 min, compound 3 was obtained in 11% yield, in addition to 17% of phenyl(trimethylsilyl)acetylene and 31% of the starting compound 1. The photolysis of 1 in the absence of a trapping agent under the same conditions afforded phenyl(trimethylsilyl)acetylene as the sole volatile product. The DFT calculations were carried out to investigate the reaction mechanisms for the thermal reaction of 1 leading to the germaindene 2.

Full text of DOI:10.1016/j.jorganchem.2012.12.018

Journal of Organometallic Chemistry 727 (2013) 50e59
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Thermal and photochemical reactions of phenylethynyltris-
(trimethylsilyl)germane
,
a
b
b
,
a,
*
Akinobu Naka a , Tomohito Kajihara , Toshiko Miura , Hisayoshi Kobayashi , Mitsuo Ishikawa
*
*
a Department of Life Science, Kurashiki University of Science and the Arts, 2640 Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505, Japan
b Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Kyoto 606-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The thermal and photochemical behavior of phenylethynyltris(trimethylsilyl)germane (1) has been
reported. The thermolysis of 1 in the absence of a trapping agent in a sealed glass tube at 240 ꢀC for 6 h
gave 1,3-bis(trimethylsilyl)-1-tris(trimethylsilyl)germyl-1-germaindene (2) in 18% yield, together with
Received 18 September 2012
Received in revised form
17 December 2012
phenyl(trimethylsilyl)acetylene in 60% yield. Similar thermolysis of
1 in the presence of 2,3-
Accepted 18 December 2012
dimethylbutadiene afforded 3,4-dimethyl-1,1-bis(trimethylsilyl)-1-germacyclopent-3-ene (3) in 62%
yield, along with phenyl(trimethylsilyl)acetylene. When 1 was irradiated with a low-pressure mercury
lamp in the presence of a large excess of 2,3-dimethylbutadiene at room temperature for 10 min, com-
pound 3 was obtained in 11% yield, in addition to 17% of phenyl(trimethylsilyl)acetylene and 31% of the
starting compound 1. The photolysis of 1 in the absence of a trapping agent under the same conditions
afforded phenyl(trimethylsilyl)acetylene as the sole volatile product. The DFT calculations were carried out
to investigate the reaction mechanisms for the thermal reaction of 1 leading to the germaindene 2.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Phenylethynyltris(trimethylsilyl)germane
Thermolysis
Photolysis
Germaindene
Germacyclopentene
1. Introduction
We have found that the thermolysis of pivaloyl- and ada-
mantoyltris(trimethylsilyl)germane, like many types of the acylpoly-
The chemistry of germenes constitutes one of the most active
areas of current research [1], and many papers dealing with the
synthesis and reactions of the germenes, including stable ones have
been published to date [2]. The synthetic methods reported for the
germenes so far mainly involve the following routes: reaction of
germylene with carbenes [2b,h], Peterson-type reaction [3], cyclo-
reversion of four-membered reactions [2i,4], and defluorosilylation
[2g] or defluorolithiation [2a,2cef]. The synthetic methods for the
germenes are rather limited, compared with those of the silenes. In
fact, the photolysis of acylpoly(silyl)silanes offers a convenient
route to the silenes, but similar photolysis of acylpoly(silyl)ger-
manes affords no germenes [5].
silanes, readily produces the respective germenes, and the germenes
thus formed react with butadienes [6], methyl vinyl ketone, and
acrolein [7] to give formal [2 þ 4] cycloadducts in good yields.
In order to learn more about the similarity and dissimilarity of
germyl compounds to silyl compounds, we have investigated the
thermolysis and photolysis of phenylethynyltris(trimethylsilyl)-
germane. Previously, we have reported that irradiation of phenyl-
ethynylpolysilanes with a low-pressure mercury lamp produces
two types of the reactive species, silacyclopropenes and silapro-
padienes, via a 1,2- and 1,3-silyl shift of the trimethylsilyl group on
a central silicon atom, respectively [8]. The silacyclopropenes thus
formed undergo a wide variety of the reactions, depending on the
substituents on the silacyclopropene ring [9].
* Corresponding authors.
E-mail addresses: anaka@chem.kusa.ac.jp (A. Naka), kobayashi@chem.kit.ac.jp
(H. Kobayashi), ishikawa-m@zeus.eonet.ne.jp (M. Ishikawa).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.12.018

A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
51
In this paper, we report the thermolysis and photolysis of phenyl-
ethynyltris(trimethylsilyl)germane (1) in the presence or absence
of 2,3-dimethylbutadiene. To our knowledge, only paper concern-
ing the reactivity of 1 has been reported by Baumgartner and his
coworkers [10]. They have found that the reaction of 1 with zir-
conocene dichloride/magnesium in THF produces the zirconacy-
clopropene derivative.
experiments at 500 MHz are also consistent with the structure
proposed for 2. Thus, irradiation of a signal at 7.37 ppm, due to the
olefinic proton on the C2 carbon in the germaindene ring reveals
a strong enhancement of the signal at 0.17 ppm, attributed to the
trimethylsilyl protons on the germanium atom, and the signal at
0.29 ppm, due to the trimethylsilyl protons on the C3 carbon. These
results are wholly consistent with the structure proposed for 2.
2. Results and discussion
To learn more about the mechanism for the formation of 2,
we investigated the reaction of
1 in the presence of 2,3-
2.1. Synthesis of compound 1
dimethylbutadiene as a trapping agent under the same reaction
conditions. The reaction of 1 with 4.5 equiv of 2,3-dimethylbutadiene
gave 3,4-dimethyl-1,1-bis(trimethylsilyl)-1-germacyclopent-3-ene
(3), arising from [1 þ 4] cycloaddition of bis(trimethylsilyl)germy-
lene (C) to the butadiene in 62% yield, along with 69% of phenyl
(trimethylsilyl)acetylene.
Phenylethynyltris(trimethylsilyl)germane (1) was prepared us-
ing the method reported by Brook et al. [5] and Marschner et al.
[11], as shown in Scheme 1. Thus, the hydrolysis of (Me3Si)3GeK,
obtained by the reaction of (Me3Si)4Ge with tert-BuOK, with dilute
hydrochloric acid, followed by treatment of the resulting
(Me3Si)3GeH with CCl4 gave (Me3Si)3GeCl [5]. The reaction of the
chlorogermane with phenylethynyllithium afforded compound 1,
whose spectral data were identical with those reported by Baum-
gartner et al., as colorless viscous liquid [10].
The formation of compound 2 may be best understood in terms of
a series of the reactions shown in Schemes 2 and 3. Addition of
bis(trimethylsilyl)germylene C, which produced by the thermolysis
of 1,1,2-tris(trimethylsilyl)-3-phenyl-1-germacyclopropene (B) once
formed from the starting compound 1, to 3-phenyl-1,1,3-
tris(trimethylsilyl)-1-germapropadiene (A) generated simulta-
neously from 1 affords 3-phenyl(trimethylsilyl)methylene-1,1,2,2-
tetrakis(trimethylsilyl)-1,2-digermacyclopropane (D). The opening
of thedigermacyclopropaneringinD produces 1-tris(trimethylsilyl)-
germyl-1-germapropadiene (E). The hydrogen shift from the ortho
position of the phenyl ring to the internal carbon in E, to give a dir-
adical intermediate (F), and then intramolecular coupling of the
resulting phenyl radical with the germyl radical produces compound
2. Unfortunately, at present, evidence for the presence of D, and also
intermediates, B, E, and F, has not yet been obtained.
2.2. Thermolysis of 1
We first carried out the thermolysis of 1 in the absence of
a trapping agent. Thus the thermolysis of 1 in a sealed glass
tube at 240 ꢀC for
6 h produced 1,3-bis(trimethylsilyl)-1-
tris(trimethylsilyl)germyl-1-germaindene (2) in 18% yield, along
with phenyl(trimethylsilyl)acetylene in 60% yield. No other volatile
products were detected in the reaction mixture, after treatment of
the resulting mixture with column chromatography. Compound 2 is
stable toward atmospheric oxygen and can be handled in air without
decomposition. The structure of 2 was confirmed by mass and, 1H,
13C, and 29Si NMR spectrometric analysis. In fact, mass spectrometric
analysis for 2 indicates the presence of a molecular ion at m/z 614,
corresponding to the calculated molecular weight for C23H50Si5Ge2.
The 13C NMR spectrum for 2 shows three signals at ꢁ0.50, 0.17, and
3.08 ppm, due to Me3Si carbons, and eight signals attributed to the
sp2 carbons. The 29Si NMR spectrum reveals three signals at ꢁ8.5, e
6.0, e3.3 ppm, due to three different kinds of the silicon atoms.
Furthermore, the results obtained from NOE-DIF difference
In the silicon chemistry, it has been reported that the reaction of
a
silapropadiene derivative with silylene gives the di-
silacyclopropane derivative, arising from addition of silylene to
a siliconecarbon double bond in the silapropadiene [8c], and also
reported that addition of silylene to a silene produces the di-
silacyclopropane derivative [12].
Germylene C may be considered to be produced from two dif-
ferent routes, that is, the direct formation from 1 and the thermal
decomposition of germacyclopropane B once formed from 1, as
shown in Scheme 2. To clarify whether or not the direct formation
Scheme 1. Synthesis of the starting compound 1.

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A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
Scheme 2. Route from compound 1 to germapropadiene A and germylene C.
of the germylene C is involved in the present reaction, we have
carried out the theoretical investigation for the thermal reaction of
1, as described below.
trimethylsilyl protons of 1 decreased gradually with the elapse of
time, and was replaced by the resonance due to the trimethylsilyl
protons of phenyl(trimethylsilyl)acetylene. Furthermore, the broad
resonances were also observed in the methylsilyl region. However,
when a hexane solution of 1 in the presence of a large excess of
2,3-dimethylbutadiene was photolyzed under the same conditions
for 10 min, compound 3 derived from addition of bis(silyl)germy-
lene C to 2,3-dimethylbutadiene was obtained in 11% yield, along
with 17% of phenyl(trimethylsilyl)acetylene and 31% of the starting
compound 1. No other volatile products were detected in the reac-
tion mixture. Compound 3 was identified by comparison of the
spectral data with those reported by Apeloig et al. [13], and also with
those of the sample obtained from the thermal reaction. In both
photolyses, no germacyclopropene derivatives such as B, D, and D0
were detected by spectrometric analysis (Scheme 4).
2.3. Photolysis of 1
Next, we investigated the photolysis of 1 in the absence of
a trapping agent. In contrast to the reaction of the corresponding
silyl derivative, phenylethynyltris(trimethylsilyl)silane, in which
3-phenyl-1,1,2-tris(trimethylsilyl)-1-silacyclopropene was readily
isolated [8b], germyl compound 1 afforded no isolable germacy-
clopropene B. Thus, compound 1 was irradiated with a low-pressure
mercury lamp bearing a Vycor filter in C6D6 at room temperature,
and the reaction was followed by 1H NMR spectrometry. The result
showed that the resonance at 0.28 ppm attributable to the
Scheme 3. Formation of compound 2.

A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
53
Scheme 4. Thermolysis and photolysis of compound 1 in the presence of 2,3-dimethyl-1,3-butadiene.
2.4. Theoretical calculations
both directions, i.e., reactant and product. The IRC analysis was
limited rather in the neighborhood of TS, and full optimization was
followed at the end points of IRC analysis. Finally we confirmed that
the reaction path was connected from the reactant to the product
via the TS. The standard Becke-three-parameter-LeeeYangeParr
hybrid method [15] implemented in the Gaussian 03 program
[16] was used with the 6-31(d) basis set.
The reaction mechanisms shown in Schemes 2 and 3 were
investigated by the Density Functional Theory calculations. Whole
reaction was divided into several elementary steps, in which the
transition state (TS) was characterized, and the Intrinsic Reaction
Coordinate (IRC) analysis [14] was carried out at each TS for the
Fig. 1. Structures of LMs and TSs locating between 1 and A along a 1,3-shift of the trimethylsilyl group (Route a). The number in parentheses for TS structures indicates the weight of
the internal parameter (such as bond length) in direction of the reaction coordinate.

54
A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
Fig. 2. Structures of LMs and TSs locating between 1 and the product (C þ PhCCSiMe3) in the stepwise manner, a 1,2-shift of the trimethylsilyl group, followed by degradation of
germacyclopropane B (Route b). See caption of Fig. 1 for numbers in parentheses.

A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
55
Fig. 1 shows the local minima (LMs) and transition states (TSs)
locating between the starting compound 1 and germapropadiene A
(Route a). The formation of A involves a 1,3-shift of a trimethylsilyl
group from a germanium atom onto a phenyl-substituted ethynyl
carbon atom in 1. In detail, the potential energy surface shown in
Fig. 7 indicates that a trimethylsilyl group on the germanium atom
migrates to the germyl-substituted ethynyl carbon, and then
phenyl-substituted ethynyl carbon through a twice-consecutive
1,2-silyl shift. LMa-1 is the product arising from the initial
1,2-shift of the trimethylsilyl group. However, the energy change
from TSa-1, LMa-1 to TSa-2 is very small, and the reaction essen-
tially proceeds with a 1,3-silyl shift.
Two routes are considered for the formation of germylene C
from the starting compound 1. One involves the degradation of the
germacyclopropane B formed from 1 (Route b), and the other is the
formation of germylene C and phenyl(trimethylsilyl)acetylene from
1 in the concerted manner (Route c). Figs. 2 and 3 show the LMs and
TSs locating along the reaction from 1 to the products, germylene C
and phenyl(trimethylsilyl)acetylene. The germacyclopropane B is
a rather stable, and the energy is higher than that of 1 only by
66 kJ molꢁ1. However, as shown in Fig. 2, the energies for TSs
(TSb-2, TSb-3) and LMs (LMb-2, LMb-3) in the subsequent reaction
of germacyclopropane B to the final product, germylene C and
phenyl(trimethylsilyl)acetylene are higher than that of B by more
Fig. 3. Structures of LMs and TSs locating between 1 and the product (C þ PhCCSiMe3) in the concerted manner (Route c). See caption of Fig. 1 for numbers in parentheses.

56
A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
than 200 kJ molꢁ1. Fig. 3 shows the structures and energy changes
along the route involving no germacyclopropene structure (Route
c). The potential energy surface is still higher than that of the route
with the germacyclopropene ring (Route b). In both cases, the po-
tential energy surface is up-hill, and the product is more unstable
D to 2 are shown in Fig. 8 (Route d), where the sum of energies of A
and C is adopted as the reference. The formation of digermacyclo-
propane D is strongly exothermic more than 300 kJ molꢁ1. 1,3-
Bis(silyl)-1-germyl-1-germapropadiene E is more stable than D by
40 kJ molꢁ1, but F is more unstable by 168 kJ molꢁ1. DeE(TS1) and
DeE(TS2) correspond to migration of the trimethylsilyl group and
scission of the CeGe bond, respectively. The highest energy point
on the reaction path is the TS between F and 2, Fe2(TS), whereas it
is below zero, and still more stable than those of the isolated A and
C. As expected from Scheme 3, F has a biradical character, and the
electronic structures for EeF(TS), F, and Fe2(TS) are evaluated by
the broken symmetry solution, i.e., the spin polarized singlet state.
than the reactant by 251 kJ molꢁ1
.
Next, we carried out theoretical treatment for addition of ger-
mylene C to a CeGe double bond in germapropadiene A, leading to
the final product 2, as shown in Scheme 3. The structures of LMs
and TSs between digermacyclopropane D and 1,3-bis(silyl)-1-
germyl-1-germapropadiene E, and between E and the product 2
are shown in Figs. 4 and 5, respectively. The relative energies from
Fig. 4. Structures of LMs and TSs locating between D and E in the reaction of A with C (Route d). See caption of Fig. 1 for numbers in parentheses.

A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
57
Fig. 5. Structures of LMs and TSs locating between E and 2 (common with Routes d and e). See caption of Fig. 1 for numbers in parentheses.
For the formation of E, there is another possible route (Route e)
from 1 and germylene C, via tris(trimethylsilyl)germyl-substituted
germacyclopropene D0 as illustrated in Scheme 3. The structure
and energy changes along this route are shown in Figs. 6 and 8.
There are two TSs, i.e., D0eE(TS1) and D0eE(TS2), and this situation
is similar to Route d. The energy of D0 is only by 8 kJ molꢁ1 lower
than D. Although the energy of reactant (1 þ C) is lower than that of
(A þ C), the potential energy surface lies higher than that of Route d.
Especially, D0eE(TS2) is unstable probably due to the migration of
the bulky tris(trimethylsilyl)germyl group.
1. Addition of germylene C to germapropadiene A would produce the
reactive digermacyclopropane intermediate D, and the digermacy-
clopropane derivative thus formed isomerizes, to give the final
product, germaindene 2. On the other hand, irradiation of 1 in the
presence of 2,3-dimethylbutadiene with a low-pressure mercury
lamp gave 3,4-dimethyl-1,1-bis(trimethylsilyl)-1-germacyclopent-3-
ene 3, arising from [1 þ 4] cycloaddition of germylene C to the
butadiene, as the volatile product. All the LMs and TSs locating on the
reaction paths were characterized by the DFT calculations. The for-
mation of C was the most endothermic process. However, if C is once
formed, the latter half reactions proceed on the down-hill potentials.
In whole reactions, the formation of germylene C is the most
endothermic reaction. Once germylene C is produced, the reaction
of C with A to give the product 2 proceeds within the attractive
potential energy region.
3. Experimental
In conclusion, the thermolysis of 1 at 240 ꢀC for 6 h in a sealed
glass tube gave 1,3-bis(trimethylsilyl)-1-tris(trimethylsilyl)germyl-1-
germaindene 2. Compound 2 would be produced by the reaction of
the germapropadiene A with germylene C, generated thermally from
3.1. General procedures
Thermal reactions were carried out in a degassed sealed tube
(1.0 cm
f
ꢂ 15 cm). Yields of the products were calculated on the

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A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
Fig. 6. Structures of LMs and TSs locating between D’ and E in the reaction of 1 with C (Route e). See caption of Fig. 1 for numbers in parentheses.
basis of the isolated products. NMR spectra were recorded on
a JNM-LA300 spectrometer and JNM-LA500 spectrometer. Low-
resolution mass spectra were measured on a JEOL Model JMS-700
instrument. Column chromatography was performed by using
Wakogel C-300 (WAKO).
3.3. Thermolysis of 1 at 240 ꢀC
0.1347 g (0.343 mmol) of 1 in a sealed glass tube was heated at
240 ꢀC for 6 h. The reaction mixture was chromatographed on
a silica gel column, eluting with hexane to give 0.0191 g (18% yield)
of 2 and 0.0356 g (60% yield) of phenyl(trimethylsilyl)acetylene.
Data for 2: Calcd for C23H50Si5Ge2: C, 45.12; H, 8.23. Found: C,
3.2. Materials
45.00; H, 8.01. MS m/z 614 (Mþ); 1H NMR
d (CDCl3) 0.10 (s, 9H,
Me3Si), 0.17 (s, 27H, Me3Si), 0.29 (s, 9H, Me3Si), 7.12 (t, 1H, ring
Compound 1 was prepared by the method reported by Baum-
proton, J ¼ 7.5 Hz), 7.26 (t, 1H, ring proton, J ¼ 7.5 Hz), 7.37 (s, 1H,
gartner et al. [10].
Fig. 7. Relative energies for LMs and TSs locating between 1 and the product (C þ PhCCSiMe3).

A. Naka et al. / Journal of Organometallic Chemistry 727 (2013) 50e59
59
Fig. 8. Relative energies for LMs and TSs locating between A þ C or 1 þ C and 2.
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(b) H. Meyer, G. Baum, W. Massa, A. Berndt, Angew. Chem. Int. Ed. Engl. 26
(1987) 798;
ring proton), 7.56 (d, 1H, ring proton, J ¼ 7.5 Hz), 7.62 (d, 1H, ring
proton, J ¼ 7.5 Hz); 13C NMR
d
(CDCl3) ꢁ0.50, 0.17, 3.08 (Me3Si),
124.65, 125.88, 126.81, 133.26, 148.24, 151.41, 152.48, 159.14 (ring
(c) C. Anselme, J. Escudié, C. Couret, J. Satgé, J. Organomet. Chem. 403 (1991) 93;
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(1996) 893;
carbons); 29Si NMR
d
(CDCl3) ꢁ8.5, ꢁ6.0, ꢁ3.3.
3.4. Thermolysis of 1 at 240 ꢀC in the presence of 2,3-dimethyl-1,3-
butadiene
(h) H. Schumann, M. Glanz, F. Girgsdies, F.E. Hahn, M. Tamm, A. Grzegorzewski,
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(l) S.Ech-Cherif ElKettani, M.Lazraq, F.Ouhsaine, H.Gornitzka,H.Ranaivonjatovo,
J. Escudié, Org. Biomol. Chem. 6 (2008) 4064;
A mixture of 0.1081 g (0.275 mmol) of 1 and 0.1019 g
(1.24 mmol) of 2,3-dimethylbutadiene in a sealed glass tube was
heated at 240 ꢀC for 6 h. After evaporation of the reaction mixture,
the residue was chromatographed on a silica gel column, eluting
with hexane to give 0.0515 g (62% yield) of 3 and 0.0331 g (69%
yield) of phenyl(trimethylsilyl)acetylene. Data for 3: Calcd for
C12H28Si2Ge: C, 47.86; H, 9.37. Found: C, 47.80; H, 9.01. MS m/z 302
(Mþ); 1H NMR
4H, CH2); 13C NMR
131.63 (ring carbons); 29Si NMR
d
(CDCl3) 0.15 (s,18H, Me3Si),1.68 (s, 6H, CH3),1.73 (s,
(CDCl3) ꢁ0.24 (Me3Si),19.39 (CH2), 21.98 (CH3),
(C6D6) ꢁ9.0.
(m) D. Ghereg, S. Ech-Cherif El Kettani, M. Lazraq, H. Ranaivonjatovo,
W.W. Schoeller, J. Escudié, H. Gornitzka, Chem. Commun. (2009) 4821.
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d
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194 (1980) 147;
3.5. Photolysis of 1 in the presence of 2,3-dimethyl-1,3-butadiene
A mixture of 0.1250 g (0.318 mmol) of 1 and 0.2767 g
(3.37 mmol) of 2,3-dimethylbutadiene in 50 mL of hexane was
irradiated for 10 min internally with a 6 W low-pressure mercury
lamp bearing a Vycor filter. The solvent was evaporated, and
the residue was chromatographed on a silica gel column with
hexane as a eluent to give the product 3 (0.0110 g, 11% yield),
phenyl(trimethylsilyl)acetylene (0.0094 g, 17% yield), and the
starting compound 1 (0.0384 g). All spectral data for 3 were iden-
tical with those of the authentic sample.
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Acknowledgments
This work was supported by JSPS KAKENHI Grant Number
23550063. We thank Shin-Etsu Chemical Co., Ltd. for a gift of
chlorosilanes.
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