Formation of silarzirconacyclopentene via zirconium - Silene complex and alkyne

Full text of DOI:10.1021/ja984137p

J. Am. Chem. Soc. 1999, 121, 5591-5592
Formation of Silazirconacyclopentene via
5591
Zirconium-Silene Complex and Alkyne
Miwako Mori,* Shinji Kuroda, and Fumiko Dekura
Figure 1. Silyl-zirconium complex.
Graduate School of Pharmaceutical Sciences
Hokkaido UniVersity, Sapporo 060-0812, Japan
Table 1. Reaction of Cp2ZrCl2, Me2PhSiLi 4 and 5aa
Cp2ZrCl2
(equiv)
Me2PhSiLi
(equiv)
temp
(°C)
yield of
6a (%)
ReceiVed December 2, 1998
run
Silenes are usually reactive organosilicone species whose
formation has been confirmed by trapping reactions.1,2 Recently,
Tilley reported the first stable ruthenium-silene complexes,3a,b
and iridium-3c and tungsten-silene complexes have subsequently
been synthesized.4,5 Although Berry reported the reaction of
tungsten-silene complex with MeOH, H2, and Me3SiH,4 little is
known about the reactivity of the complex coordinated by silene.
During the course of our study on the preparation and reactivity
of zirconium-silyl complex 2,6 we found that zirconium-silene
complex 1 would be formed from disilylzirconocene 3 (Figure
1). Here, we report the formation of silazirconacyclopentene from
zirconium-silene complex 1, generated from Cp2ZrCl2 and Me2-
PhSiLi 4, and alkyne.
When a THF solution of Me2PhSiLi 4 (1 equiv) was added to
a THF solution of Cp2ZrCl2 (1 equiv) and diphenylacetylene 5a
(1 equiv) at -78 °C and the solution was stirred at room
temperature for 3 h, a reddish brown solution was obtained. After
hydrolysis with H2O, vinylsilane 6a was obtained in 36% yield
along with 5a in 40% yield (Table 1, run 1). In this reaction,
when the reaction mixture was treated with D2O, the vinylic
proton and the methyl proton on the silyl group were deuterated
to give vinylsilane 6a-D2 (39% yield, each D-content; quant)
(Scheme 1). Although vinylsilane 6a was an expected product
by the insertion of alkyne 5a into the zirconium-silyl bond of
2a, we cannot explain the formation of 6a-D2 at this stage.
The reaction was carried out under various conditions (Table
1). When 2 equiv of Me2PhSiLi 4 to Cp2ZrCl2 were used for this
reaction, the yield of 6a increased to 68% along with dimeric
compound 7a in 6% yield (run 2). The same product 6a-D2 was
also obtained in the reaction of a 1 to 2 molar ratio of Cp2ZrCl2
and Me2PhSiLi 4 (run 5). The yield of 6a increased to 82% when
excess amounts of Cp2ZrCl2 and Me2PhSiLi 4 were used (run 7).
The reaction proceeded even at 0 °C (run 8). When a THF solution
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
78c
74
82
74d
35e
79f
rt
rt
10
a To a THF solution of Cp2ZrCl2 and 5a was added 4 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 5a was
recovered in 40% yield. c D2O was added to the reaction mixture, and
6a-D2 was obtained. d Reaction time; 6 h. e The solution of Cp2ZrCl2
and 4 was stirred at -78 °C for 1 h, 5a was added at -78 °C, and the
solution was stirred at rt for 3 h. f Toluene was used as the solvent,
and a THF solution of 4 was added.
Scheme 1
Scheme 2
(1) 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.
(2) Recent reports: (a) Toltl, N. P.; Leigh, W. J. Organometallics 1996,
15, 2554. (b) Brook, A. G.; Ionkin, A,; Lough, A. J. Organometallics 1996,
15, 1275. (c) Naka, A.; Ishikawa, M.; Matsui, S.; Ohshita, J.; Kunai, A.
Organometallics 1996, 15, 5759 and references therein.
(3) (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.; Rheingold, A. L.
J. Am. Chem. Soc. 1993, 115, 5527. (c) Campion, B. K.; Heyn, R. H.; Tilley,
T. D. J. Am. Chem. Soc. 1990, 112, 4079.
of Cp2ZrCl2 and Me2PhSiLi 4 was stirred at -78 °C for 1 h and
then alkyne 5a was added and the solution was stirred at room
temperature for 3 h, the desired product 6a was obtained, although
the yield decreased to 35% (run 9). In all cases, a small amount
(less than 8%) of dimeric compound 7a was produced. Various
alkynes 5 were used for this reaction. In each case, the desired
vinylsilane 6 was obtained in high yield (Scheme 2).
On the other hand, when 3-hexyne 9 was used for this reaction
as alkyne, we surprisingly obtained allylsilane 10 in 41% yield.
When the reaction mixture was treated with D2O, two deuteriums
were also incorporated, at the vinylic proton and at the proton on
the silyl center of 10-D2. (D-contents: 68 and 85%, respectively)
(Scheme 3).
On the basis of these results, we considered the possible
reaction course as shown in Scheme 4. At first, silylzirconium
complex 2a is formed, and it is then converted into disilylzir-
conocene 3a. It is known that dibutylzirconocene gives zir-
conocene coordinated by butene ligand (Negishi’s reagent).7
Therefore, 3a would convert into zirconium-silene complex 1a
or 1a′. The insertion of alkyne 5a into the zirconium-silyl bond
(4) (a) Koloski, T. S.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 1990,
112, 6405. (b) Berry, D. H.; Procopio, L. J. J. Am. Chem. Soc. 1989, 111,
4099.
(5) Other metal-mediated silene formations: (a) Pannell, K. H. J. Orga-
nomet. Chem. 1970, 21, P17. (b) Windus, C.; Sujishi, S.; Giering, W. P. J.
Am. Chem. Soc. 1974, 96, 1951. (c) Cundy, C. S.; Lappert, M. F.; Pearce, R.
J. Organomet. Chem. 1973, 59, 161. (d) Bulkowski, J. E.; Miro, N. D.; Sepelak,
D.; Van Dyke, C. H. J. Organomet. Chem. 1975, 101, 267. (e) Tamao, K.;
Yoshida, J.; Okazaki, S.; Kumada, M. Isr. J. Chem. 1976/77, 15, 265. (f)
Lewis, C.; Wrighton, M. S. J. Am. Chem. Soc. 1983, 105, 7768. (g) Conlin,
R. T.; Bobbitt, K. L. Organometallics 1987, 6, 1406. (h) Randolph, C. L.;
Wrighton, M. S. Organometallics 1987, 6, 365. (i) Zlota, A. A.; Frolow, F.;
Milstein, D. J. Chem. Soc., Chem. Commun. 1989, 1826. (j) Thomson, S. K.;
Young, G. B. Organometallics 1989, 8, 2068. (k) Sharma. S.; Kapoor, R. N.;
Cervantes-Lee, F.; Pannell, K. H. Polyhedron 1991, 10, 1177.
(6) (a) Honda, T.; Satoh, S.; Mori, M. Organometallics 1995, 14, 1548.
(b) Honda, T.; Mori, M. Organometallics 1996, 15, 5494. (c) Honda, T.; Mori,
M. J. Org. Chem. 1997, 61, 11196. (d) Dekura, F.; Honda, T.; Mori, M. Chem.
Lett. 1997, 825.
10.1021/ja984137p CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/29/1999

5592 J. Am. Chem. Soc., Vol. 121, No. 23, 1999
Communications to the Editor
Scheme 3
Scheme 5
Cp2ZrCl2 appeared at δ 6.50. From the reaction mixture in the
NMR tube, 6b was obtained in 69% yield. These results indicate
that the former Cp-signal at δ 5.07 would be that of silene
complex 1a,9 and the latter peaks at δ 6.30 and 6.17 should be
those of silazirconacyclopentene 8b.10
Scheme 4
It is already known that transmetalation from zirconium to
copper is a useful tool for new carbon-carbon bond formations.11
If this transmetalation proceeds, new carbon-carbon bond would
be formed on the methyl carbon of the silyl center. When CuCl
(2 equiv to Cp2ZrCl2) and allyl chloride were added to a THF
solution of silazirconacyclopentene 8a, generated from Cp2ZrCl2,
alkyne 5a and Me2PhSiLi 4, and the solution was stirred at room
temperature for 18 h, diallylated compound 12 was obtained in
62% yield (Scheme 5).
In conclusion, zirconium-silene complex 1a or 1a′ would be
formed from disilylzirconocene 3a generated from Cp2ZrCl2 and
2 equiv of Me2PhSiLi 4. The insertion of alkyne 5 and 9 into the
silyl-zirconium bond or zirconium-carbon bond of silazircona-
cyclopropane 1a′ gave silazirconacyclopentenes 8 and 11. As a
result, the methyl group on the silyl center could react with
electrophiles such as proton, deuterium, and allyl halide.
Further studies are in progress.
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 Ministry of Education. Science, Sports
and Culture, Japan. We thank the Japan Society for the Promotion of
Science (JSPS) Research Fellowships for Young Scientists (to K.S.).
Supporting Information Available: Experimental details and 1H
spectra (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
Figure 2.
JA984137P
of 1a′ gives silazirconacyclopentene 8a. On the other hand, the
insertion of dialkyl alkyne 9 into the zirconium-carbon bond of
1a′ gave silazirconacyclopentene 11. Deuteration of silazircona-
cyclopentene 8a or 11 gave 6a-D2 or 10-D2, respectively. The
reason the alkyne having a phenyl group inserts into the
zirconium-silyl bond and the alkyne having an alkyl group inserts
into the zirconium-carbon bond is still not clear. Presumably,
the electronic factor of alkyne is important for the insertion
reaction.
To confirm this reaction mechanism, the reaction of Cp2ZrCl2
and Me2PhSiLi 4 with di-p-methoxyphenylacetylene 5b was
monitored by the 1H NMR spectrum8 (see Figure 2). When a THF
solution of Me2PhSiLi 4 was added to a THF-d8 solution of Cp2-
ZrCl2 and 5b, the Cp-protons appeared at δ 5.07, and a Si-H
proton of Me2PhSiH was clearly shown at δ 4.42. After 7 min,
new peaks appeared at δ 6.30 and 6.17. With the passage of time,
the peak at δ 5.07 decreased and the peaks at δ 6.30 and 6.17
increased, and after 4.3 h, the peak at δ 5.07 disappeared. When
HCl-Et2O was added to the reaction mixture, a single peak of
(9) We carried out the other three 1H NMR experiments. When the reaction
of Cp2ZrCl2 (1.5 equiv) and Me2PhSiLi (3 equiv) in the presence of PMe3
(1.5 equiv) in THF-d8 was monitored by H NMR, the peaks of δ 5.27 (d, J
1
) 1.4 Hz), 5.02 (d, J ) 1.4 Hz), and 5.06 (s) were shown. Then the peaks of
δ 5.27 and 5.02 gradually increased and the peak of δ 5.06 decreased. After
4.5 h, alkyne 5b (1 equiv) was added. The new peaks of δ 6.30 and 6.17
appeared and the peaks of δ 5.27, 5.02, and 5.06 disappeared. After the usual
work up, the desired vinyl silane 6b was obtained in 28% yield along with
5b (54% yield). The second experiment is the reaction of Cp2ZrCl2 (1 equiv)
and Me2PhSiLi (2 equiv). The third one: after the same reaction as the second
one was carried out and the peak of δ 5.06 was confirmed, 5b was added at
once, and 6b was obtained in 33% yield. These reactions were monitored by
1H NMR, and the spectral data are shown in Supporting Information.
(10) (a) Takahashi, T.; Murakami, M.; Kunishige, M.; Saburi, M.; Uchida,
Y.; Kozawa, K.; Uchida, T.; Swanson, D. R.; Negishi, E. Chem. Lett. 1989,
761. (b) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett. 1986,
27, 2829. (c) Warner, B. P.; Davis, W. M.; Buchwald, S. L. J. Am. Chem.
Soc. 1994, 116, 5471.
(7) (a) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett. 1986,
27, 2829. (b) Xi, Z.; Hara, R.; Takahashi, T. J. Org. Chem. 1995, 60, 4444.
(8) The reaction was performed in an NMR tube under argon atmosphere.
To a solution of Cp2ZrCl2 (16.5 mg, 56.4 µmol) and di-4-methoxypheny-
lacetylene 5b (8.8 mg, 36.9 µmol) in THF-d8 (0.8 mL) was added Me2PhSiLi
4 (0.7 M in THF, 0.16 mL, 112 µmol), and the mixture was stirred at -78
°C. 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. 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 silicagel (hexane/AcOEt )
50/1) to give vinylsilane 6b (69% yield).
(11) (a) Takahashi, T.; Kotra, M.; Kasai, K.; Suzuki, N. Organometallics
1994, 13, 4183. (b) Kasai, K.; Kotra, M.; Suzuki, N.; Takahashi, T. J. Chem.
Soc., Chem. Commun. 1995, 109. (c) Takahashi, T.; Xi, Z.; Kotra, M.; Xi, C.
Tetrahedron Lett. 1996, 37, 7521. (d) Takahashi, T.; Hara, R.; Nishihara, Y.;
Kotra, M. J. Am. Chem. Soc. 1996, 118, 5154. (e) Takahashi, T.; Kotra, M.;
Xi, Z. J. Chem. Soc., Chem. Commun. 1995, 1503. (f) Takahashi, T.; Xi, Z.;
Kotra, M.; Xi, C. Tetrahedron Lett. 1996, 37, 7521. (g) Kotra, M.; Xi, Z.;
Takahashi, T. J. Synth. Org. Chem. Jpn. 1997, 55, 958. (h) Venanzi, L. M.;
Lehmann, R.; Keli, R.; Lipshutz, B. H. Tetrahedron Lett. 1992, 33, 5857. (i)
Takahashi, T.; Kotra, M.; Kasai, K.; Suzuki, N. Tetrahedron Lett. 1994, 35,
5685. (j) Lipshutz, B. H.; Segi, M. Tetrahedron 1995, 51, 4407.