141613-73-2Relevant articles and documents
Synthesis, properties, and ring-ring transformation reactions of cyclic siloxanes incorporating skeletal boron atoms: X-ray crystal structures of the strained boracyclotrisiloxane (PhBO)(Ph2SiO)2 and the boracyclotetrasiloxane (PhBO)(Ph2SiO)3
Foucher, Daniel A.,Lough, Alan J.,Manners, Ian
, p. 3034 - 3043 (2008/10/08)
The cyclic boratrisiloxanes (PhBO)(RR′SiO)2 (1, R = R′ = Me; 2, R = Me, R′ = Ph; 3, R = R′ = Ph) have been prepared via the reaction of the dichlorodisiloxanes 1,3-ClRR′SiOSiRR′Cl with phenylboric acid in the presence of NEt3 as an HCl acceptor. Similar procedures using the appropriate α,ω-dichlorosiloxanes ClMe2Si(OSiMe2)nOSiMe2Cl (n = 1 or 2) afforded the boracyclotetrasiloxane (PhBO)(Me2SiO)3 (4) and the boracyclopentasiloxane (PhBO)(Me2SiO)4 (5). The boracyclotetrasiloxane (PhBO)(Ph2SiO)3 (8) was isolated in low yield from the reaction of 2:1 excess of 1,3-ClPh2SiOSiPh2Cl with PhB(OH)2 in the presence of NEt3. The cyclic borasiloxanes 1 and 3 undergo extensive ring-ring transformation reactions when heated at elevated temperatures in the presence of small quantities of K[OSiMe3]. Similar reactions were detected in solution in the presence of acid or base catalysts. The products of these reactions mainly consist of larger rings containing a single boron atom, together with cyclic and polymeric siloxanes and the boroxin [PhBO]3. Similar, but slower, ring-ring redistribution reactions were detected for the boracyclotetrasiloxane 4. These results are consistent with the presence of additional strain in borasiloxanes containing a six-membered ring. This analysis was supported by a comparison of X-ray structural data obtained for 3 with that for 8. Thus, the boracyclotrisiloxane 3 was found to possess a highly strained six-membered ring with considerable bond angle distortion whereas the nonplanar eight-membered ring present in 8 is appreciably less strained. Crystals of 3 are monoclinic, space group C2/c, with a = 15.703 (6) A?, b = 10.864 (3) A?, c = 17.733 (4) A?, β = 119.14 (2)°, V = 2641 (14) A?3, and Z = 4. Crystals of 8 are monoclinic, space group P21/n, with a = 14.692 (2) A?, b = 13.707 (2) A?, c = 19.932 (3) A?, β = 111.38 (0)°, V = 3737.7 (9) A?3, and Z = 4.
