Formation of silazirconacyclopentenes from zirconium-silene complex and alkynes and their reactivities

Article abstract of DOI:10.1021/ja003334x

During the course of our study on the formation of a complex having a zirconium-silicon bond, we found that zirconium-silene complex 7 was formed from CP₂ZrCl₂ and Me₂PhSiLi. In the presence of alkyne, diarylalkyne reacted with silene coordinated with zirconium to give silazirconacyclopentene 8. On the other hand, dialkylalkyne inserted into a zirconium-silene complex gave silazirconacyclopentene 9. Hydrolysis of 8 or 9 afforded vinylsilane 13 or allylsilane 16. Transmetalation of zirconacycle 8 into copper in the presence of allyl halide gave a bis-allylated compound in high yield, indicating that alkylation occurred on the alkyne carbon and the methyl group of silicon. From bis-allylated compounds, eight-membered ring compounds having silicon were obtained in high yield using olefin metathesis.

Full text of DOI:10.1021/ja003334x

J. Am. Chem. Soc. 2001, 123, 4139-4146
4139
Formation of Silazirconacyclopentenes from Zirconium-Silene
Complex and Alkynes and Their Reactivities
Shinji Kuroda, Fumiko Dekura, Yoshihiro Sato, and Miwako Mori*
Contribution from the Graduate School of Pharmaceutical Sciences, Hokkaido UniVersity,
Sapporo 060-0812, Japan
ReceiVed September 11, 2000
Abstract: During the course of our study on the formation of a complex having a zirconium-silicon bond,
we found that zirconium-silene complex 7 was formed from Cp2ZrCl2 and Me2PhSiLi. In the presence of
alkyne, diarylalkyne reacted with silene coordinated with zirconium to give silazirconacyclopentene 8. On the
other hand, dialkylalkyne inserted into a zirconium-silene complex gave silazirconacyclopentene 9. Hydrolysis
of 8 or 9 afforded vinylsilane 13 or allylsilane 16. Transmetalation of zirconacycle 8 into copper in the presence
of allyl halide gave a bis-allylated compound in high yield, indicating that alkylation occurred on the alkyne
carbon and the methyl group of silicon. From bis-allylated compounds, eight-membered ring compounds having
silicon were obtained in high yield using olefin metathesis.
Introduction
Reactivity between metal-metal bonds is very interesting
because it is expected that the insertion of unsaturated com-
pounds into these metal-metal bonds would form the new
carbon-metal bonds, which would be converted into the various
carbon-carbon bonds. Thus, a new methodology in synthetic
organic chemistry would be obtained.
We have been interested in the zirconium-silicon bonds
(Scheme 1).
Figure 1. Complexes having a Zr-Si bond.
There have not been many reports on the synthesis of complex
having a zirconium-silicon bond and the reactivity of such a
complex. Lappert reported the synthesis of complex 1a from
Cp2ZrCl2 and Ph3SiLi.1a Later Tilley reported the synthesis of
complex 1b from Cp2ZrCl2 and Al(SiMe3)3‚OEt2.2a Takahashi3
and Buchwald4 independently reported the formation of zirco-
nium-silicon complexes 1c and 1d by hydrosilylation of alkene
coordinated to zirconium metal. Berry5 and Xue6 reported the
synthesis of complex 1e and 1f (Figure 1).
Scheme 1. Silylzirconation of Alkynes and Alkenes
Little is known the reactivity of complexes having a
zirconium-silicon bond. Reaction of 1a with hydrogen chloride
afforded triphenylsilane.1a The insertion of carbon monoxide
or isocyanide into a zirconium-silicon bond gave acylzirconium
complex 2 or iminosilylzirconium complex 3.2b,c As for carbon-
carbon multiple bonds, it is known that ethylene can be inserted
into a zirconium-silicon bond of 1h,2g but other multiple bonds
such as alkene and alkyne could not be inserted into a zir-
conium-silicon bond2b,c (Scheme 2).
We have been very interested in complexes having a zir-
conium-silicon bond, and we have studied the reactivities of
such complexes.7 Complex 1i prepared from Cp2ZrCl2 and
tBuPh2SiLi was treated with phenylisocyanide to give air-stable
iminosilaacylzirconium complex 3c, which was treated with
LiEt3BH in the presence of alkyne to afford azazirconacyclopen-
tene 5 via azazirconacyclopropane 4. From this complex 5, vari-
ous organic compounds could be synthesized7c,d (Scheme 3).
In the present study, we tried to insert alkene or alkyne into
a zirconium-silicon bond and to produce complexes having
carbon-zirconium and silicon-carbon bonds (Scheme 1).
(1) (a) Cardin, D. J.; Keppie, S. A.; Kingston, B. M.; Lappert, M. F.
Chem. Commun. 1967, 1035. (b) Muir, K. W. J. Chem. Soc. (A) 1971,
2663. (c) Kingston, B. M.; Lappert, M. F. J. Chem. Soc., Dalton Trans.
1972, 69.
(2) (a) Tilley, T. D. Organometallics 1985, 4, 1452. (b) Tilley, T. D. J.
Am. Chem. Soc. 1985, 107, 4084. (c) Campion, B. K.; Falk, J.; Tilley, T.
D. J. Am. Chem. Soc. 1987, 109, 2049. (d) Elsner, F. H.; Woo, H.-G.; Tilley,
T. D. J. Am. Chem. Soc. 1988, 110, 313. (e) Elsner, F. H.; Tilley, T. D.;
Rheingold, A. L.; Geib, S. J. J. Organomet. Chem. 1988, 358, 169. (f)
Roddick, D. M.; Heyn, R. H.; Tilley, T. D. Organometallics 1989, 8, 324.
(g) Arnold, J.; Engeler, M. P.; Elsner, F. H.; Heyn, R. H.; Tilley, T. D.
Organometallics 1989, 8, 2284. (h) Heyn, R. H.; Tilley, T. D. Inorg. Chem.
1989, 28, 1768.
(3) Takahashi, T.; Hasegawa, M.; Suzuki, N.; Saburi, M.; Rousset, C.
J.; Fanwick, P. E.; Negishi, E. J. Am. Chem. Soc. 1991, 113, 8564.
(4) Kreutzer, K. A.; Fisher, R. A.; Davis, W. M.; Spaltenstein, E.;
Buchwald, S. L. Organometallics 1991, 10, 4031.
(5) (a) Procopio, L. J.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc.
1991, 113, 1870. (b) Procopio, L. J.; Carroll, P. J.; Berry, D. H.
Organometallics 1993, 12, 3087.
(6) (a) Xue, Z.; Li, L.; Hoyt, L. K.; Diminnie, J. B.; Pollitte, J. L. J. Am.
Chem. Soc. 1994, 116, 2169. (b) Wu, Z.; Diminnie, J. B.; Xue, Z.
Organometallics 1998, 17, 2917. (c) Wu, Z.; McAlexander, L. H.; Diminnie,
J. B.; Xue, Z. Organometallics 1998, 17, 4853. (d) Wu, Z.; Diminnie, J.
B.; Xue, Z. Organometallics 1999, 18, 1002.
(7) (a) Honda, T.; Satoh, S.; Mori, M. Organometallics 1995, 14, 1548.
(b) Honda, T.; Mori, M. Organometallics 1996, 15, 5464. (c) Honda, T.;
Mori, M. J. Org. Chem. 1996, 61, 1196. (d) Dekura, F.; Honda, T.; Mori,
M. Chem. Lett. 1997, 825.
10.1021/ja003334x CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/13/2001

4140 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Scheme 2. Reactivity of Cp2Zr(SiR3)Cl
Kuroda et al.
Figure 2.
Scheme 3. Reaction of a Complex Having Zr-Si Bond with
Isocyanide
Figure 3. Transition metal-silene complexes.
plexes 10g13 have subsequently been synthesized. Although
Berry reported the reaction of tungsten-silene complex with
MeOH, H2, and Me3SiH, little is known about the reactivity of
a complex coordinated by silene13 (Figure 3).
We tried to confirm the structure of zirconium-silene
complex 7 by 1H NMR spectra, and we investigated the
reactivity of zirconium-silene complex 7. It was found that
silazirconacyclopentene 8 was formed from zirconium-silene
complex 7 and diaryl alkyne 11 and that silazirconacyclopentene
9 was synthesized from zirconium-silene complex 7 and dialkyl
alkyne 16. The reactivity of silazirconacyclopentene 8 was also
investigated.
During the course of our study on the formation of complex 6
having a zirconium-silicon bond, we found that zirconium-
silene complex 7 or 7′ was formed from Cp2ZrCl2 and
Me2PhSiLi. In the presence of alkyne, the insertion of alkyne
into the zirconium-silicon bond or the zirconium-carbon bond
of silazirconacyclopropane 7′ gave silazirconacyclopentene 8
or 914a (Figure 2).
Silenes are usually reactive organosilicon species whose
formation has been confirmed by trapping reactions.8-10 Re-
cently, Tilley reported the first stable ruthenium-silene com-
plexes 10c-e,11 and iridium- 10f 12 and tungsten-silene com-
Results and Discussion
Formation of Zirconium-Silene Complex. It was thought
that the reaction of Cp2ZrCl2 with R3SiLi or (Me3Si)3Al‚Et2O
gave a complex having a zirconium-silicon bond. When a THF
solution of Me2PhSiLi 12 (1 equiv) was added to a THF solution
of Cp2ZrCl2 (1 equiv) and diphenylacetylene 11a (1 equiv) at
-78 °C and the solution was stirred at room temperature for 3
h, a reddish brown solution was obtained. After hydrolysis of
the reaction mixture with H2O, vinylsilane 13a was obtained
in 36% yield along with 11a in 40% yield. In this reaction,
when the reaction mixture was treated with D2O, compound
13a-D2 having two deuteriums was obtained. One deuterium
was introduced as the vinylic proton, and the other deuterium
was incorporated into the methyl proton on the silicon (39%
yield, each D-content; quant.). Although vinylsilane 13a was
an expected product from the insertion of alkyne 11a into the
zirconium-silicon bond of 6, we cannot at this stage explain
the formation of compound 13a-D2 having two deuteriums
(Scheme 4).
(8) For reviews see: (a) Zybill, C. E.; Liu, C. Synlett 1995, 687. (b)
Raabe, G.; Michl, J. Chem. ReV. 1985, 85, 419. (c) Gusel’nikov, L. E.;
Nametkin, N. S. Chem. ReV. 1979, 79, 529.
(9) (a) Gusel’nikov, L. E.; Flowers, M. C. Chem. Commun. 1967, 864.
(b) Gusel’nikov, L. E.; Nametkin, N. S.; Vdovin, V. M. Acc. Chem. Res.
1975, 8, 12. (c) Nametkin, N. S.; Gusel’nikov, L. E.; Ushakova, R. L.;
Vdovin, V. M. Dokl. Akad. Nauk SSSR. 1971, 201, 1365. (d) Brook, A. G.;
Abdesaken, F.; Gutekunst, B.; Gutekunst, G.; Kallury, R. K. J. Chem. Soc.,
Chem. Commun. 1981, 191. (e) Brook, A. G.; Nyburg, S. C.; Abdesaken,
F.; Gutekunst, B.; Gutekunst, G.; Kallury, R. K. M. R.; Poon, Y. C.; Chang,
Y.-M.; Wong-Ng, W. J. Am. Chem. Soc. 1982, 104, 5667. (f) Wiberg, N.;
Wagner, G. Angew. Chem., Int. Ed. Engl. 1983, 22, 1005. (g) Wiberg, N.;
Wagner, G.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl. 1985, 24, 229.
(10) (a) Pannell, K. H. J. Organomet. Chem. 1970, 21, P17. (b) Lewis,
C.; Wrighton, M. S. J. Am. Chem. Soc. 1983, 105, 7768. (c) Randolph, C.
L.; Wrighton, M. S. Organometallics 1987, 6, 365. (d) Cundy, C. S.;
Lappert, M. F.; Pearce, R. J. Organomet. Chem. 1973, 59, 161. (e) Windus,
C.; Sujishi, S.; Giering, W. P. J. Am. Chem. Soc. 1974, 96, 1951. (f) Pannell,
K. H.; Rice, J. R. J. Organomet. Chem. 1974, 78, C35. (g) Sharma. S.;
Kapoor, R. N.; Cervantes-Lee, F.; Pannell, K. H. Polyhedron 1991, 10,
1177. (h) Bulkowski, J. E.; Miro, N. D.; Sepelak, D.; Van Dyke, C. H. J.
Organomet. Chem. 1975, 101, 267. (i) Tamao, K.; Yoshida, J.; Okazaki,
S.; Kumada, M. Isr. J. Chem. 1976/77, 15, 265. (j) Ishikawa, M.; Ohshita,
J.; Ito, Y. Organometallics 1986, 5, 1518. (k) Thomson, S. K.; Young, G.
B. Organometallics 1989, 8, 2068. (l) Berry, D. H.; Procopio, L. J. J. Am.
Chem. Soc. 1989, 111, 4099. (m) Berry, D. H.; Chey, J. H.; Zipin, H. S.;
Carroll, P. J. J. Am. Chem. Soc. 1990, 112, 452. (n) Procopio, L. J.; Berry,
D. H. J. Am. Chem. Soc. 1991, 113, 4039. (o) Djurovich, P. I.; Carroll, P.
J.; Berry, D. H. Organometallics, 1994, 13, 2551. (p) Zlota, A. A.; Frolow,
F.; Milstein, D. J. Chem. Soc., Chem. Commun. 1989, 1826. (q) Dioumaev,
V. K.; Plo¨ssl, K.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 1999, 121,
8391.
(11) (a) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc.
1988, 110, 7558. (b) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J. Chem.
Soc., Chem. Commun. 1992, 1201. (c) Campion, B. K.; Heyn R. H.; Tilley,
T. D.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 5527.
(12) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1990,
112, 4079.
(13) Koloski, T. S.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 1990,
112, 6405.
(14) (a) Mori, M.; Kuroda, S.; Dekura, F. J. Am. Chem. Soc. 1999, 121,
5591. (b) Kuroda, S.; Sato, Y.; Mori, M. J. Organomet. Chem. 2000, 611,
304.

Formation of Silazirconacyclopentenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4141
Table 2. Synthesis of Allylsilanea
Scheme 4. Reaction of Cp2ZrCl2 and Me2PhSiLi in the
Presence of 11a
run
R
temp. (°C)
yield (%)
1
2
3
4
5
Et 15a
Et 15a
Et 15b
Pr 15b
Pr 15b
rt
16a 15
16a 41
16b 29b
16b 25
16b 35
40
40
40
70
a To a THF solution of Cp2ZrCl2 and 15 was added 12 in THF at
-78 °C, and the solution was stirred at -78 °C for 1 h, and then the
solution was stirred for 3 h. b PPh3 (1.0 eq.) was added.
Scheme 6. Reaction with Alkyne Having Alkyl Group
Table 1. Reaction of Cp2ZrCl2, Me2PhSiLi 12 and 11aa
run Cp2ZrCo2 (equiv) Me2PhSiLi (equiv °C yield of 13a (%)
1
2
3
4
5
6
7
8
9
1
1
2
1.5
1.5
1.5
2
1.5
1.5
1.5
1
2
2
3
3
3
4
3
3
3
rt
rt
rt
rt
rt
40
rt
0
36b
68
59
76
Scheme 7. Reaction of Zirconium-Silene Complex and
Enyne
78c
74
82
66
0
rt
74d
79e
10
a To a THF solution of Cp2ZrCl2 and 11a was added in 12 in THF
at -78 °C, and the solution was stirred at -78 °C for 1 h, and then the
solution was stirred at the ambient temperature for 3 h. b 11a was
recovered in 40% yield. c D2O was added to the reaction mixture and
13a-D2 was obtained. d Reaction time; 6 h. e Toluene was used as the
solvent and a THF solution of 12 was added.
the vinylic proton and one at the proton on the silicon of
16a-D2. (D-contents: 68% and 85%, respectively). The higher
reaction temperature increased the yield of the desired compound
16a (Table 2, run 2), but the addition of PPh3 as a ligand did
not give a good result (run 3). Allylsilane 16b was also obtained
when 4-octyne was used for this reaction (run 4), and in this
case, the yield of 16b increased when the reaction was carried
out at 70 °C (run 5) (Scheme 6).
Scheme 5. Synthesis of Various Vinyl Silanes 13
Furthermore, as the alkyne, enyne 17 was used in this reaction
to afford two inseparable regioisomers of vinylsilanes 18 in 54%
yield in a ratio of 3 to 1 (Scheme 7).
Possible Reaction Course
The reaction was carried out under various conditions to
estimate the reaction mechanism (Table 1). When 2 equiv of
Me2PhSiLi to Cp2ZrCl2 was used for this reaction, the yield of
13a increased to 68% along with dimeric compound 14a in
6% yield (run 2), but a 1 to 1 molar ratio of Cp2ZrCl2 and
Me2PhSiLi did not affect the yield of 13a (run 3). The yield
improved to 76% when 1.5 equiv of Cp2ZrCl2 and 3 equiv of
Me2PhSiLi were used (run 4). After deuteriolysis, the same
product 13a-D2 was also obtained in the reaction of a 1 to 2
molar ratio of Cp2ZrCl2 and Me2PhSiLi (run 5). The yield of
13a increased to 82% when excess amounts of Cp2ZrCl2 and
Me2PhSiLi 12 were used (run 7). The reaction proceeded even
at 0 °C (run 8), although the yield was slightly lower, but a
longer reaction time improved the yield of 13a (run 9). Toluene
can be used for this reaction (run 10). In all cases, a small
amount (less than 8%) of dimeric compound 14a was produced.
Various alkynes 11 were used for this reaction. In each case,
the desired vinylsilane 13 was obtained in high yield (Scheme
5). The electron-donating group on the aromatic ring caused a
slight increase in the yield of desired vinylsilane 13.
On the other hand, when 3-hexyne 15a was used as the alkyne
for this reaction, surprisingly, allylsilane 16a was obtained in
15% yield. In this reaction, the reaction mixture was treated
with D2O, and two deuteriums were also incorporated, one at
On the basis of these results, we considered the possible
reaction course (Scheme 8). At first, complex 6 would be formed
from Cp2ZrCl2 and Me2PhSiLi, and then it would be converted
into disilylzirconocene 19. It is known that dibutylzirconocene,
prepared from Cp2ZrCl2 and 2 equiv of BuLi, gives zirconocene
coordinated by a butene ligand (Negishi’s reagent, eq 1).15
Therefore, 19 would be converted into zirconium-silene
complex 7 or silazirconacyclopropane 7′. The insertion of alkyne
11a into the zirconium-silicon bond of 7′ gives silazircona-
cyclopentene 8a. On the other hand, the insertion of dialkyl
alkyne 15a into the carbon-zirconium bond of 7′ gives
silazirconacyclopentene 9a.
Deuteriolysis of silazirconacyclopentene 8a or 9a gives
13a-D2 or 16a-D2, respectively. In the case of enyne 17, the
olefin part would have the same role as that of the aromatic
ring on alkyne 11, and the insertion of the alkyne part of 17
into the zirconium-silicon bond occurs to give silazirconacy-
(15) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett. 1986,
27, 2829.

4142 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Scheme 8. Possible Reaction Course
Kuroda et al.
Figure 4. 1H NMR spectra of the reaction of Cp2ZrCl2 and 12 in the
presence of 11b.
clopentene and hydrolysis of it gives 18. The reasons why the
alkyne having the aryl group or the vinyl group inserts into the
zirconium-silicon bond of 7′ and the alkyne having the alkyl
group inserts into the carbon-zirconium bond of 7′ are still
not clear. Presumably, the electronic factor of alkyne is im-
portant for the insertion reaction.
Figure 5. 1H NMR spectra of the reaction of Cp2ZrCl2 and 12.
It is known that silene is a very unstable and reactive organo-
silicon species. In this case, it is very interesting that silene is
generated from disilylzirconocene 19 and coordinates to zirco-
nium to give zirconium-silene complex 7.
Confirmation of the Reaction Mechanism. To confirm this
reaction mechanism, the reaction of Cp2ZrCl2 and Me2PhSiLi
(12) with bis-4-methoxyphenylacetylene 11b was monitored by
1
the H NMR spectra. As the first experiment, we monitored
the formation of silazirconacyclopentene 8b under the standard
reaction conditions for the formation of vinyl silane 13b by the
1H NMR spectra. At first, the NMR spectrum of a THF-d8
solution of Cp2ZrCl2 (Cp; δ 6.48) and 11b was measured. Then
a THF solution of Me2PhSiLi was added to this solution at -78
Figure 6. 1H NMR spectra of the reaction of Cp2ZrCl2 and 12 and
then the addition of 11b.
Next, after a THF solution of 12 was added to Cp2ZrCl2 in
1
1
°C, and then the H NMR spectrum was measured at room
THF-d8, H NMR spectrum was measured (Figure 6, Chart 7,
temperature. The Cp-protons appeared at δ 5.07, and a Si-H
proton of Me2PhSiH was clearly shown at δ 4.42, whose δ value
was confirmed by authentic Me2PhSiH in THF-d8 (0 min). Then
the solution was allowed to stand at room temperature and was
the same conditions as that of Chart 4). Then alkyne 11b was
at once added in the NMR tube. New peaks appeared at δ 6.30
and 6.17 (Figure 6, Chart 8). After 2 h, the peaks of δ 5.06,
6.01, and 6.11 disappeared (Figure 6, Chart 9), whose chart
was almost the same as Chart 3. From this reaction mixture,
we obtained 13b in 33% yield.
The δ-values of the typical Cp-signals of zirconacycles and
zirconocenes in the literature are shown in Figure 7.2a,c,15-17
From these data (Figure 7), the results of our 1H NMR
experiments suggested the following. Although the chemical
shift of the Cp peak of zirconium-silene complex [Zr(II)] or
silazirconacyclopropane is not known, it is already reported that
the Cp protons of zirconacyclopropane 21 (δ 5.25)16 or
zirconocene 22 [Zr(II), δ 5.50]17 coordinated by the ethylene
ligand show the values of the higher chemical shift compared
with those of Cps of Zr(IV) complexes. Thus, the peak of δ
5.06 appearing at a higher chemical shift should be that of the
Cp peak of Zr(II), and it would be the Cp signal of the
zirconium(II)-silene complex 7. This is supported by the fact
1
monitored by the H NMR spectrum each time. After 7 min,
new peaks appeared at δ 6.30 and 6.17 (Figure 4, Chart 1).
With the passage of time, the peak at δ 5.07 decreased, and the
peaks at δ 6.30 and 6.17 increased (Figure 4, Chart 2), and
after 4.3 h, the peak at δ 5.07 disappeared (Figure 4,Chart 3).
When HCl-Et2O was added to the reaction mixture, a single
peak of Cp2ZrCl2 appeared at δ 6.50. From the reaction mixture
in the NMR tube, 13b was obtained in 69% yield. It means
that the Cp-protons of δ 6.30 and 6.17 in Chart 3 are those of
silazirconacyclopentene 8b.
Subsequently, the reaction of Cp2ZrCl2 and Me2PhSiLi in the
absence of alkyne 13b was monitored by 1H NMR spectra. The
results are shown in Figure 5, Charts 4-6. After addition of
Me2PhSiLi to the solution of Cp2ZrCl2 in THF-d8, the 1H NMR-
spectrum was immediately measured. The Cp-protons appeared
at δ 6.11, 6.01 and 5.06 (Figure 5, Chart 4). After 3.5 min,
there was no change in the spectrum (Figure 5, Chart 5). How-
ever, after 1.5 h, many peaks appeared on the NMR spectrum
(Figure 5, Chart 6).
(16) Takahashi, T.; Swanson, D. R.; Negishi, E.; Chem. Lett. 1987,
623.
(17) Takahashi, T.; Suzuki, N.; Kageyama, M.; Nitto, Y.; Saburi, M.;
Negishi, E. Chem. Lett. 1991, 1579.

Formation of Silazirconacyclopentenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4143
Scheme 10. Reaction of Silazirconacyclopentene with
Carbon Monoxide
Figure 7. The δ values of Cp signal.
that the peak of δ 5.06 decreased when alkyne 11b was added
to the d8-THF solution, and the new peaks appeared at δ 6.30
and 6.17 (Charts 8 and 9). It indicates that zirconium-silene
complex 7 or 7′ converted into silazirconacyclopentene 8b in
the presence of alkyne, and we could obtain vinyl silane13b
from the reaction mixture in the NMR tube (Experiments I and
III). Therefore, the Cp peaks at δ 6.30 and 6.17 in Charts 3 and
9 are those of zirconacyclopentene 8b because the chemical
schift of Cp peaks of zirconacyclopentene 20 was known to be
δ 5.96.15 Silene is thought to be very unstable, and it
decomposed after 1.5 h in the absence of alkyne (Chart 6). The
Cp peaks of δ 6.11 and 6.01 (Chart 4) are thought to be those
Scheme 11. Possible Reaction Mechanism
of disilylzirconocene or chlorosilylzirconocene by comparison
2a
with that of disilylzirconocene 23 (δ 6.13),
and those of
chlorosilylzirconocenes, 1b or 1g (δ 5.752c or 5.972c). These
results strongly suggested that silene is formed from Cp2ZrCl2
and 2 equiv of Me2PhSiLi, and it reacted with 11b to give
silazirconacyclopentene 8b, which afforded vinyl silane 13b
after hydrolysis.
Scheme 12. Difference in Reaction Course
The Reactivity of Silazirconacyclopentene. Insertion of
Carbon Monoxide. The results of the insertion of isocyanide
into silazirconacyclopentene 8 has been already reported.14b In
this reaction, the formation of iminosilazirconacyclohexene 24b
1
(Ar ) 4-MeOC6H4) was monitored by H NMR spectra, and
the structure of the product 25d (Ar ) 4-CF3C6H4) was
confirmed by X-ray crystallography (Scheme 9).
Scheme 9. Reaction of Silazirconacyclopentene with
Isocyanide
Insertion of carbon monoxide into the carbon-zirconium
bond in silazirconacyclopentene 8 gave silazirconacyclohex-
enone 29, whose carbonyl oxygen would coordinate to zirco-
nium metal. Then the zirconium carbon bond migrates to silicon
to afford oxazirconacyclohexene 31 via 30.18 Hydrolysis of 31
with D2O would afford 26-D2.
It was quite interesting that hydrolysis of iminosilacylcyclo-
hexene 24 gave iminozirconium complex 25, while silazircona-
cyclohexenone 29 converted into oxazirconacycle 31, which was
treated with H2O and gave methyl silyl ketone 26. The
differences in the reactivity between iminosilazirconacyclohex-
ene 24 and silazirconacyclohexenone 27 would be due to the
strong coordination of the carbonyl oxygen in 27 to zirconium
metal compared with that of the imino nitrogen in 24 to
zirconium metal (Scheme 12).
Thus, we next attempt to insert of carbon monoxide into
silazirconacyclopentene 8b. A THF solution of silazirconacy-
clopentene 8b, which was prepared from alkyne 11b, Cp2ZrCl2,
and Me2PhSiLi in THF, was stirred under carbon monoxide at
room temperature overnight. After hydrolysis of the reaction
mixture, the carbonylation product was obtained. However, from
the 1H NMR, mass, and IR spectra, it was clear that the desired
carbonylation product 27b was not formed. To estimate the
structure of the product, when the reaction mixture was
quenched with D2O, two deuteriums were incorporated at the
vinyl carbon and at the acetyl methyl carbon of the product.
Hydrogenation of 26b afforded bibenzyl 28b. On the basis of
these results, the structure of the product was determined to be
methyl silyl ketone 26b. Treatment of alkynes 11a and 11c in
a similar manner gave the corresponding methyl silyl ketones
26a and 26c in moderate yields (Scheme 10).
These substituents were introduced on the methyl group on
the silicon moiety via silazirconacyclopentene 8.
(18) (a)Lappert, M. F.; Raston, C. L.; Engelhardt, L. M.; White, A. H.
J. Chem. Soc., Chem. Commun. 1985, 521. (b) Petersen, J. L.; Egan, J. W.,
Jr. Organometallics 1987, 6, 2007.
The possible reaction mechanism for the formation of 26 was
shown in Scheme 11.

4144 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Kuroda et al.
Table 3. Transmetalation of 8 to Copper
Transmetalation of Zirconium to Copper of Silazircona-
cyclopentene. It is already known that transmetalation from
zirconium to copper is a useful tool for the formation of a new
carbon-carbon bond. Schwarts reported the first transmetalation
from zirconium to copper.19 Then Lipschuts20 and Takahashi21
independently reported the transmetalation of zirconium to
copper. If this transmetalation were used for our zirconacycle
8, new carbon-carbon bonds would be formed on the vinyl
carbon and on the methyl carbon of the silicon center. To a
THF solution of CuCl (2 equiv to Cp2ZrCl2) and allyl chloride
was added a THF solution of silazirconacyclopentene 8a,
generated from Cp2ZrCl2, alkyne 11a, and Me2PhSiLi 12, and
the solution was stirred at room temperature for 18 h. After the
usual work up, bis-allylated compound 33a was obtained in 76%
yield (Scheme 13).
run
Ar
R
product
yield (%)
1
2
3
4
Ph
H (32a)
H (32a)
H (32a)
Me (32b)
33a
33b
33c
33d
76
72
76
66
4-CH3OC6H4
4-CH3OC6H4
Ph
Scheme 14. Transmetalation of Zr on
Silazirconacyclopentene with Cu
Scheme 13. Transmetalation of Zr on
Silazirconacyclopentene with CuCl
and the results are shown in Table 3. In each case, bisallylated
compound 33 was obtained in high yield (Scheme 14).
Synthesis of Eight-Membered Ring Componds Containing
Silicon. Little has been reported about the synthesis of eight-
membered ring compounds containing silicon.22 It was ex-
pected that eight-membered ring compounds containing sili-
con could be synthesized from compounds 33 using ruthen-
ium-catalyzed olefin metathesis.23 When a CH2Cl2 solution of
diene 33a was stirred at room temperature in the presence of
10 mol % of ruthenium carbene complex 34 overnight, the
desired eight-membered ring compound 35a was obtained in
The results indicated that two allyl groups were introduced
on the alkyne carbon and on the methyl group on the silicon
moiety. As the results, two different substituents were introduced
on the alkyne carbons, respectively, by a one-pot reaction. One
is the allyl group, and the other is the butenylmethylphenyl silyl
group (Figure 8). Transmetalations of various zirconacycles 8
to copper were carried out in the presence of allyl halide 32,
1
quantitative yield. The structure of 35a was confirmed by H
NMR, 13C NMR, COSY, and mass spectra. Various dienes 33
were treated in a similar manner, and eight-membered ring
compounds 35 were obtained in high yields (Scheme 15 and
Table 4).
Scheme 15. Synthesis of Eight-Membered Ring Compounds
Using Olefin Metathesis
Figure 8.
(19) Yoshifuji, M.; Loots, M. J.; Schwartz, J. Tetrahedron Lett. 1977,
1303.
(20) (a) Lipshutz, B. H.; Ellsworth, E. L. J. Am. Chem. Soc. 1990, 112,
7440. (b) Lipshutz, B. H.; Kato, K. Tetrahedron Lett. 1991, 32, 5647. (c)
Lipshutz, B. H.; Fatheree, P.; Hagen, W.; Stevens, K. L. Tetrahedron Lett.
1992, 33, 1041. (d) Venanzi, L. M.; Lehmann, R.; Keil, R.; Lipshutz, B.
H. Tetrahedron Lett. 1992, 33, 5857. (e) Lipshutz, B. H.; Keil, R. J. Am.
Chem. Soc. 1992, 114, 7919. (f) Lipshutz, B. H.; Wood, M. R. J. Am. Chem.
Soc. 1993, 115, 12625. (g) Lipshutz, B. H.; Segi, M. Tetrahedron 1995,
51, 4407. (h) Lipshutz, B. H. Acc. Chem. Res. 1997, 30, 277.
(21) (a) Takahashi, T.; Kotora, M.; Kasai, K.; Suzuki, N. Tetrahedron
Lett. 1994, 35, 5685. (b) Kasai, K.; Kotora, M.; Suzuki, N.; Takahashi, T.
J. Chem. Soc., Chem. Commun. 1995, 109. (c) Takahashi, T.; Kotora, M.;
Kasai, K.; Suzuki, N.; Nakajima, K. Organometallics 1994, 13, 4183. (d)
Takahashi, T.; Kotora, M.; Xi, Z. J. Chem. Soc., Chem. Commun. 1995,
1503. (e) Takahashi, T.; Xi, Z.; Kotora, M.; Xi, C.; Nakajima, K.
Tetrahedron Lett. 1996, 37, 7521. (f) Takahashi, T.; Kotora, M.; Xi, Z. J.
Chem. Soc., Chem. Commun. 1995, 361. (g) Takahashi, T.; Hara, R.;
Nishihara, Y.; Kotora, M. J. Am. Chem. Soc. 1996, 118, 5154. (h) Xi, C.;
Huo, S.; Afifi, T. H.; Hara, R.; Takahashi, T. Tetrahedron Lett. 1997, 38,
4099. (i) Hara, R.; Liu, Y.; Sun, W.-H.; Takahashi, T. Tetrahedron Lett.
1997, 38, 4103. (j) Takahashi, T.; Nishihara, Y.; Hara, R.; Huo, S.; Kotora,
M. Chem. Commun, 1997, 1599. (k) Kotora, M.; Xi, Z.; Takahashi, T. J.
Synth. Org. Chem., Jpn. 1997, 55, 958. (l) Kotora, M.; Umeda, C.; Ishida,
T.; Takahashi, T. Tetrahedron Lett. 1997, 38, 8355. (m) Ubayama, H.; Sun,
W.-H.; Xi, Z.; Takahashi, T. Chem. Commun. 1998, 1931. (n) Takahashi,
T.; Sun, W.-H.; Liu, Y.; Nakajima, K.; Kotora, M. Organometallics 1998,
17, 3841. (o) Takahashi, T.; Xi, Z.; Yamazaki, A.; Liu, Y.; Nakajima, K.;
Kotora, M. J. Am. Chem. Soc. 1998, 120, 1672. (p) Liu, Y.; Shen, B.; Kotora,
M.; Takahashi, T. Angew. Chem., Int. Ed. 1999, 38, 949.
Table 4. Synthesis of Eight-Membered Ring Compounds
run
R
product
yield (%)
1
2
3
H
OCH3
CH3
35a
35b
35c
quant.
97
99
The synthesis of eight-membered ring compounds having
silicon was quite interesting, and in this case, they could be
obtained from alkyne by a two-step synthesis.
In conclusion, zirconium-silene complex 7 or 7′ can be
formed from disilylzirconocene 19 generated from Cp2ZrCl2 and
(22) Kagoshima, H.; Hayashi, M.; Hashimoto, Y.; Saigo, K. Organo-
metallics 1996, 15, 5439.
(23) (a) Fu, G.; Grubbs, R. H. J. Am. Chem. Soc., 1992, 114, 5426. (b)
Furstner, A. Topics in Organometallic Chemistry; Springer-Verlag: Berlin
Heidelberg, 1998; Vol 1. (c) Miller, S. J.; Kim, S.-H.; Chen, Z.-R.; Grubbs,
R. H. J. Am. Chem. Soc. 1995, 117, 2108.

Formation of Silazirconacyclopentenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4145
Hz, 2H); 13C NMR (125 MHz, CDCl3) δ -5.45, 37.16, 55.11, 113.35,
144.38, 128.10, 129.02, 129.54, 129.98, 131.16, 132.81, 133.33, 135.02,
136.02, 142.17, 158.07, 159.01, 243.86; MS m/z 402 (M+), 387, 359,
281, 266, 121; HRMS calcd for C25H26O3Si: 402.1651, found:
402.1632.
2 equiv of Me2PhSiLi 12. The insertion of alkyne 11, 17, or 15
into the zirconium-silicon bond or zirconium-carbon bond of
zirconium-silene complex 7′ gives silazirconacyclopentenes 8
or 9. As a result, novel carbon-silicon or carbon-carbon bond
formation occurs on the alkyne carbons. It is quite interesting
that the methyl group on the silicon can react with various
electrophiles such as protons, deuteriums, isocyanide, carbon
monoxide, and allyl halides.
Typical Procedure for Transmetalation. 6-Methyl-4,5,6-tri-
phenyl-6-sila-1,4,9-decatriene (33a). To a solution of Cp2ZrCl2 (203.8
mg, 0.697 mmol) and 11a (62.2 mg, 0.349 mmol) in THF (7.0 mL)
was added Me2PhSiLi (0.77 M THF solution, 1.8 mL, 1.39 mmol),
and the solution was stirred overnight to afford a solution of 8a. To
the solution of CuCl (138.2 mg, 1.40 mmol) and allyl chloride (0.11
mL, 1.35 mmol) in THF (1.0 mL) was added a solution of 8a, and
then the solution was stirred at room-temperature overnight. Water was
added and the aqueous layer was extracted with Et2O and the organic
layer was washed with water, dried over Na2SO4 and concentrated.
The residue was purified by column chromatography on silica gel
(hexane) to give a colorless oil of 33a (105 mg, 0.266 mmol, 76%).
IR (neat) ν 3068, 1638, 1596, 1586, 1486, 1440, 1428, 1252, 1108,
Experimental Section
General. All manipulations were performed under an argon atmo-
sphere unless otherwise mentioned. All solvents and reagents were
purified when necessary using standard procedures. Column chroma-
tography was performed on silica gel 60 (Merck, 70-230 mesh), and
flash chromatography was performed silica gel 60 (Merck, 230-400
mesh) using the indicated solvent. 1H and 13C NMR spectra were
recorded at 270 or 500 MHz and at 67.5, 100, 125 MHz, respectively.
Infrared spectra were recorded on a Perkin-Elmer FTIR 1605 spec-
trometer. Mass spectra were measured on JEOL DX-303 and JEOL
JMS-700TZ, JEOL JMS-PABmate, and Perkin-Elmer Q-mass910 mass
spectrometers.
1
1026, 994, 910 cm-1; H NMR (500 MHz, CDCl3) δ 0.31 (s, 3H),
0.94 (t, J ) 8.5 Hz, 2H), 1.92-2.06 (m, 2H), 3.25 (d, J ) 6.5 Hz,
2H), 4.69 (d, J ) 17.4 Hz, 1H), 4.79 (d, J ) 10.0 Hz, 1H), 4.85 (d, J
) 10.0 Hz, 1H), 4.91 (d, J ) 17.3 Hz, 1H), 5.46 (m, 1H), 5.81 (m,
1H), 6.86 (m, 2H), 6.93 (m, 2H), 6.95-7.00 (m, 2H), 7.04-7.08 (m,
4H), 7.41-7.43 (m, 3H), 7.68-7.71 (m, 2H); 13C NMR (125 MHz,
CDCl3) d 2.1 (CH3), 15.1 (CH2), 27.9 (CH2), 42.8 (CH2), 112.8 (CH2),
116.3 (CH2), 124.7 (CH), 125.8 (CH), 127.2 (CH), 127.4 (CH), 128.0
(CH), 128.9 (CH), 129.0 (CH), 129.2 (CH), 134.0 (CH), 135.1 (CH),
138.7 (C), 141.4 (CH), 142.3 (C), 144.0 (C), 153.5 (C); MS (EI) m/z
(%) 394 (M+, 2.95), 339 (74.92), 316 (3.10), 261 (31.07), 197 (43.53),
121 (100.00), 97 (31.60).; HRMS (EI) calcd for C28H30Si: 394.2118,
found: 394.2117.
Typical Procedure for the Synthesis of (E)-R-Phenylsilyl-
Stilbene 13a. To a solution of Cp2ZrCl2 (204.6 mg, 0.700 mmol) and
diphenyl acetylene 11a (62.5 mg, 0.351 mmol) in THF (3.8 mL) was
added Me2PhSiLi (0.70 M THF solution, 2.0 mL, 1.40 mmol) at -78
°C and the solution was stirred at -78 Å °C for 1 h and then at room
temperature for 3 h. Water was added at 0 °C, and the color of the
solution was changed from reddish brown to colorless. The aqueous
layer was extracted with Et2O. The organic layer was washed with brine,
dried over Na2SO4, and evaporated. The residue was purified by column
chromatography on silica gel (hexane) to give a colorless oil of 13a
(90.9 mg, 0.289 mmol, 82%). IR (neat) ν 3066, 2956, 1598, 1570,
Typical Procedure for Synthesis of Eight-Membered Ring
Compound. (2E,5Z)-1-Methyl-1,2,3-triphenyl-1-silacycloocta-2,5-
diene (35a). A solution of ruthenium carbene complex 31 (14.9 mg,
18.1 µmol) and 33a (65.3 mg, 0.165 mmol) in CH2Cl2 (6 mL) was
stirred at room temperature overnight. The solvent was evaporated, and
the residue was purified by column chromatography on silica gel
(hexane/Et2O, 100/1) to give a colorless oil of 35a (60.4 mg, 0.165
mmol, quant).
1
1494, 1446, 1428, 1112, 954 cm-1; H NMR (500 MHz, CDCl3) δ
0.43 (s, 6H), 6.87 (s, 1H), 6.93 (m, 2H), 6.98 (m, 2H), 7.07-7.12 (m,
3H), 7.20 (m, 1H), 7.26 (m, 2H), 7.35-7.42 (m, 3H), 7.58 (m, 2H);
13C NMR (125 MHz, CDCl3) δ -3.1 (CH3), 125.7 (CH), 127.2 (CH),
127.6 (CH), 127.7 (CH), 127.9 (CH), 128.5 (CH), 129.1 (CH), 129.5
(CH), 134.2 (CH), 137.2 (C), 137.6 (C), 139.2 (CH), 142.3 (C), 145.0
(C); MS (EI) m/z (%) 314 (M+, 47.99), 299 (27.64), 236 (10.02), 221
(38.47), 178 (10.87), 136 (17.00); HRMS (EI) calcd for C22H22Si:
314.1492, found: 314.1508.
1
IR (neat) ν 3018, 2862, 1596, 1486, 1426, 1252, 1106 cm-1; H
NMR (500 MHz, CDCl3) δ -0.07 (s, 3H), 1.13 (ddd, J ) 14.9, 12.4,
2.4 Hz, 1H), 1.47 (ddd, J ) 14.9, 8.8, 1.4 Hz, 1H), 2.35 (m, 1H), 2.51
(m, 1H), 2.88 (dd, J ) 12.7, 5.3 Hz, 1H), 3.60 (dd, J ) 12.7, 9.5 Hz,
1H), 5.75-5.83 (m, 2H), 6.81-6.83 (m, 2H), 6.92 (m, 1H), 7.00-
7.06 (m, 5H), 7.09-7.12 (m, 2H), 7.41-7.44 (m, 3H), 7.72-7.74 (m,
2H); 13C NMR (125 MHz, CDCl3) δ -0.2, 16.3, 21.8, 38.0, 124.6,
126.0, 127.3, 127.5, 128.1, 128.4, 129.0, 129.1, 130.1, 130.9, 134.2,
138.0, 138.2, 143.9, 144.11, 156.2; MS m/z 366 (M+), 351, 288, 275,
245, 121; HRMS calcd for C26H26Si: 366.1804, found: 366.1801.
1H NMR Experiment. The reaction was performed in an NMR tube
under argon atmosphere. To a solution of Cp2ZrCl2 (16.5 mg, 56.4
µmol) and bis-4-methoxyphenylacetylene 11b (8.8 mg, 36.9 µmol) in
THF-d8 (0.8 mL) was added Me2PhSiLi (0.7 M in THF, 0.16 mL, 112
µmol), and the mixture was stirred at -78 °C. Then the mixture was
monitored at room temperature by the 1H NMR spectrum. After 4.5 h,
anhydrous HCl (1.0 M in Et2O) was added. To the mixture was added
H2O, and the aqueous layer was extracted with Et2O, and the organic
layer was washed with brine, dried over Na2SO4, and concentrated.
The residue was purified by flash column chromatography on silica
gel (hexane/AcOEt ) 50/1) to give vinylsilane 13b (69% yield).
(E)-3-Methylphenylsilylmethyl-3-hexene (16). IR (neat) δ 3068,
2962, 2120, 1458, 1428, 1250, 1114, 880 cm-1 1H NMR (500
;
MHz, CDCl3) δ 0.34 (d, J ) 3.6 Hz, 3 H), 0.91 (t, J ) 7.5 Hz, 3 H),
0.96 (t, J ) 7.5 Hz, 3 H), 1.72 (dd, J ) 14.0, 4.3 Hz, 1 H), 1.80
(dd, J ) 14.0, 2.5 Hz, 1 H), 1.95-2.02 (m, 4H), 4.39 (m, 1 H), 4.99
(t, J ) 7.2 Hz, 1H), 7.33-7.40 (m, 3 H), 7.53-7.55 (m, 2 H); 13C
NMR (125 MHz, CDCl3) δ -5.7 (CH3), 13.1 (CH3), 14.9 (CH3), 21.1
(CH2), 23.2 (CH2), 24.8 (CH2), 125.7 (CH), 127.7 (CH), 129.2 (CH),
134.4 (CH), 136.6 (C), 136.8 (C); MS (EI) m/z (%) 218 (M+, 9.80),
189 (2.63), 162 (19.49), 148 (15.68), 135 (10.12), 121 (100.00), 105
(12.42), 43 (17.15); HRMS (EI) calcd for C14H22Si: 218.1492, found:
218.1492.
Typical Procedure for Carbonylation of Silazirconacyclopentene
8b. (4E)-4,5-Bis(4-methoxyphenyl)-3-methyl-3-phenyl-3-silapent-4-
en-2-one (26b). A THF solution of silazirconacyclopentene 2b, which
was prepared from Cp2ZrCl2 (154.9 mg, 0.530 mmol), 11b (84.0 mg,
0.353 mmol) in THF (3.5 mL), and Me2PhSiLi (0.70 M THF sol. 1.5
mL, 1.05 mmol), was stirred under carbon monoxide (1 atm) at room-
temperature overnight. Water was added at 0 °C, and the solution was
stirred until the color of the solution was changed from red-black to
colorless. The aqueous layer was extracted with ether. The organic layer
was washed with brine, dried over Na2SO4, and concentrated. The
residue was purified by column chromatography on silica gel (hexanes-
ethyl acetate, 5:1) to give a colorless oil of 26b (55.2 mg, 39%). IR ν
Reaction of Cp2ZrCl2 and Me2PhSiLi. When to the solution of
Cp2ZrCl2 (1.0 equiv) was added Me2PhSiLi (2 equiv) in THF-d8 and
the 1H NMR was monitored, the peak of δ 5.06 (s) was shown instantly.
However, this peak gradually disappeared. After 1.5 h, many peaks
were shown with a small peak of δ 5.06.
Reaction of Cp2ZrCl2 and Me2PhSiLi and Then the Addition of
1
(neat) 2958, 1642, 1604, 1508 cm-1; H NMR (500 MHz, CDCl3) δ
Alkyne 11b. When to the solution of Cp2ZrCl2 (1.5 equiv) was added
1
0.56 (s, 3H), 2.21 (s, 3H), 3.71 (s, 3H), 3.78 (s, 3H), 6.63 (d, J ) 8.6
Hz, 2H), 6.81 (d, J ) 8.4 Hz, 2H), 6.84 (s, 1H), 6.91 (d, J ) 8.4 Hz,
2H), 6.92 (d, J ) 8.6 Hz, 2H), 7.37-7.43 (m, 3H), 7.62 (bd, J ) 7.5
Me2PhSiLi (3 equiv) in the absence of ligand in THF-d8 and the H
1
NMR was monitored after the peak of δ 5.06 was recognized on H
NMR chart, 11b (1 equiv) was added at once. The new peaks was

4146 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Kuroda et al.
shown at δ 6.30 and 6.17 with the peak of δ 5.06. The peak at δ 5.06
disappeared after 6 h, and 13b was obtained in 33% yield along with
11b in 40% yield after the usual work up.
Japan Society for the Promotion of Science (JSPS) Research
Fellowships for Young Scientists (to K.S.).
Supporting Information Available: The spectral data of
13a-D2, 13b-d, 14b, 16a-D2, 18a, 18b, 26a, 26c, 33b-d,
and 35b-c (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas, “The Chemistry
of Inter-element Linkage” (No. 09239203), from the Ministry
of Education, Science, Sports and Culture, Japan. We thank the
JA003334X