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