Ruthenium-catalyzed ring-closing reaction of α,ω-bis(vinylsilyl) compounds via a silyl transfer mechanism

Article abstract of DOI:10.1039/a800293b

Compounds having a vinyldimethylsilyl group at both terminals have been successfully cyclized by ruthenium hydride catalysts to give selectively disilacycles of various ring sizes via a metathetical reaction, i.e. ethene elimination from the two terminal vinyl groups, not involving metallocarbene-metallacyclobutane type intermediates.

Full text of DOI:10.1039/a800293b

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Ruthenium-catalyzed ring-closing reaction of a,w-bis(vinylsilyl) compounds via
a silyl transfer mechanism
Takaya Mise,*a† Yutaka Takaguchi,a Takeshi Umemiya,b Shoichi Shimizub and Yasuo Wakatsukia
a The Institute of Physical and Chemical Research (RIKEN), Wako-shi, Saitama 351-0198, Japan
b Department of Industrial Chemistry, College of Industrial Technology, Nihon University, Narashino, Chiba 275, Japan
Compounds having a vinyldimethylsilyl group at both
terminals have been successfully cyclized by ruthenium
hydride catalysts to give selectively disilacycles of various
ring sizes via a metathetical reaction, i.e. ethene elimination
from the two terminal vinyl groups, not involving metallo-
carbene–metallacyclobutane type intermediates.
and co-workers, who pointed out the possibility of involvement
of metallocarbene and metallacyclobutane intermediates.2–5
A
remaining problem is that the regioselectivity of this reaction is
poor in some cases, particularly for self-disproportionation-type
reactions, where almost equal amounts of (E)-R3SiCHNCHSiR3
and CH2NC(SiR3)2 are formed.1 Apparently, the regioselection
is controlled simply by the direction of insertion of the second
olefin molecule into the Ru–Si bond.
Our efforts to improve the regioselectivity of the self-
disproportionation of vinyltrimethylsilane, by modifying the
electronic character and bulkiness of the ligands or by using
coordinating additives, met with only partial success, yielding
the (E)-1,2- and 1,1-isomers in an 88:12 ratio in one case and
a 15:85 ratio at the other extreme (Scheme 2). The catalyst
precursor used in the former was [RuCl(CNC6H4-
NO2)(PPh3)3(H)] while in the latter case, a small amount of
MeCN was added to the initial reaction mixture containing
[RuCl(CO)(PPh3)3(H)]: without MeCN, the isomer ratio was
44:56.
In 1991 we reported ruthenium hydride catalyzed homo- and
cross-disproportionation reactions between CH2NCH-SiR3 and
CH2NCHRA (RA = SiR3, Me, Ph, CO2Me, OBun) to yield
CH2NCH2 and RACHNCHSiR3.1 When R = Me and RA = SiMe3
(homo-disproportionation), one of the disubstituted products
originally assigned as the (Z)-isomer was subsequently identi-
fied by Marciniec and Pietrasuk as 1,1-bis(silyl)ethene.2 We
have also confirmed by NMR studies that in the case of cross
disproportionations, e.g. R = RA = Me, a minor product
originally referred to as the (Z)-isomer is actually the 1,1-iso-
mer. As a result, the catalytic sequence is now written as
outlined in Scheme 1.
CH2=CHSiR3
insertion
CH2=CH2
Table 1 Disproportionation of a,w-bis(vinylsilyl) compounds
β-(SiR3) elimination
Entry,
Catalysta
Substrate
Product
Yield (%)
Me2
Si
Me2
Si
[Ru]–H
[Ru]–SiR3
87c
1b,
A
A
Si
Si
Me2
Me2
β-(H) elimination
insertion
1
2
Me2
Si
Me2
Si
Me2
Si
O
O
(E)-R′CH=CHSiR3
R′CH=CH2
O
O
+
75e
2d
Si
Me2
Si
,
O
Me2
O
CH2=C(R′)(SiR3)
Si
Me2
Si
Me2
O
Si
Me2
O
Scheme 1
3
4
Me2
Si
The reaction mechanism involving b-silyl elimination and
insertion of a CNC double bond into the resulting Ru–Si bond
was established in the original report based on isolation of the
ruthenium–silyl intermediate [RuCl(CO)(PPh3)2(SiMe3)] and
its reaction with ethene.1 This mechanism has been re-
confirmed by a series of elaborate experiments by Marciniec
Me2
Si
83c
3f,
B
A
Si
Me2
Si
Me2
5
6
Me2
Si
Me2
Si
97c
4g,
Me3Si
H
H
H
SiMe3
SiMe3
Si
i
Si
+
Me2
Me2
–C2H4
H
SiMe3
7
8
Me2
Si
(42%)
(6%)
2 CH2 CHSiMe3
Me2
Si
Me3Si
H
H
H
SiMe3
SiMe3
(CH2)10
(CH2)10
76e
5h,
B
ii
+
–C2H4
Si
Si
Me2
H
SiMe3
Me2
(6%)
(35%)
9
10
Scheme 2 Reagents and conditions: i, [RuCl(PPh3)3(CNC6H4-4-NO2)(H)]
(20 mg), vinylsilane (0.2 ml), toluene (2 ml), 100 °C, 20 h; ii,
[RuCl(PPh3)3(CO)(H)] (20 mg), MeCN (0.1 ml), vinylsilane (0.2 ml),
toluene (2 ml), 100 °C, 20 h. GLC yields in parentheses.
a
b
A: [RuCl(CO)(PPh3)3(H)], B: [RuCl(CO)(PPri3)2(H)]. 80 °C, 24 h,
toluene. GLC yield. 100 °C, 15 h, THF. e Isolated yield. 60 °C, 24 h,
THF. g 80 °C, 25 h, toluene. h 110 °C, 42 h, toluene.
c
d
f
Chem. Commun., 1998
699

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Application of this catalytic system for intramolecular
disproportionation of a,w-bis(vinylsilyl) compounds was found
to be more successful, giving disilacycles of various ring sizes:
in particular, the regioselectivity was almost perfect (Table 1).‡
Only very small amounts of intermolecular reaction products
was formed at normal concentrations of the reaction mixture, as
detected by GC–MS, and they could be easily separated. By
using either [RuCl(CO)(PPh3)3(H)] or Werner’s hydride [RuCl-
(CO)(PPri3)2(H)] as the catalyst precursor,6 the cyclic com-
pounds with an exo-methylene unit were obtained as the sole
cyclization products (Table 1, entries 1–4); the existence of the
methylene unit in the products was confirmed by NMR DEPT
studies. In contrast, a product which corresponds to the
(E)-isomer, i.e. a 14-membered disilacycloolefin, was obtained
selectively when the substrate had a longer aliphatic chain
spacer (entry 5).§ In all of the cases examined, no isomeric
material could be detected. Werner’s hydride is in general more
active as catalyst than the PPh3 analog, but separation of the
product from the catalyst and its residues is easier for the latter
due to its low solubility.
Notes and References
† E-mail: tmise@postman.riken.go.jp
‡ All new compounds gave satisfactory microanalytical data and mass
spectra. Selected data for 2: dH (270 MHz, CDCl3) 6.53 (NCH2); dC 154.2
(CN), 140.9 (NCH2). For 4: dH 6.33 (NCH2); dC 154.2 (CN), 142.8 (NCH2).
For 6: dH 6.37 (NCH2); dC 156.5 (CN), 138.4 (NCH2). For 8: dH 6.28 (NCH2);
dH 155.4 (CN), 139.4 (NCH2). For 10: dH 6.53 (HCNCH); dC 150.4
(HCNCH).
§ The (E)-confuguration of 10 was confirmed by preparing the product by
another route, i.e. the reaction of (E)-Me2ClSiCHNCHSiClMe2 with
BrMg(CH2)10MgBr under diluted conditions. This route, however, also
gives by-products.
1 Y. Wakatsuki, H. Yamazaki, M. Nakano and Y. Yamamoto, J. Chem.
Soc., Chem. Commun., 1991, 703.
2 B. Marciniec and C. Pietraszuk, J. Chem. Soc., Chem. Commun., 1995,
2003.
3 B. Marciniec, Z. Foltynowicz, C. Pietraszuk, J. Gul´ınski and H.
Maciejewski, J. Mol. Catal., 1994, 90, 213.
4 B. Marciniec, C. Pietraszuk and Z. Foltynowicz, J. Organomet. Chem.,
1994, 474, 83.
The products in entries 1–4 correspond to the 1,1-isomer
depicted in Scheme 2 and should not be formed in principle by
the Grubbs type ring-closing metathesis using ruthenium–
carbene initiators.7 Obviously, the insertion–b-elimination
mechanism shown in Scheme 1, is operating in an intramole-
cular fashion.
Further application of this novel ring-closing reaction to the
synthesis of mono- and di-silamacrocycles, as well as to
silicone-containing polymers, is now under investigation.
5 B. Marciniec and C. Pietraszuk, Organometallics, 1997, 16, 4320.
6 M. A. Esteruelas and H. Werner, J. Organomet. Chem., 1986, 303,
221.
7 For example, see P. Schwab, M. B. France, J. W. Ziller and R. H. Grubbs,
Angew. Chem., Int. Ed. Engl., 1995, 34, 2039. For a recent review on
olefin metathesis, see M. Schuster and S. Blechert, Angew. Chem., Int.
Ed. Engl., 1997, 36, 2037.
Received in Cambridge, UK, 12th January 1998; 8/00293B
700
Chem. Commun., 1998