- Aryloxide derivatives of tungsten oxytetrachloride as ring-opening metathesis polymerization catalysts
-
Pure WOCl4-x(OAr)x complexes (x = 1, 2, 3 or 4; OAr = aryloxide, e.g., -OC6H3-2,6-Me2) were prepared in essentially quantitative yields by reacting tungsten oxytetrachloride (WOCl4) with the stoichiometric amount of the parent substituted phenol or lithium aryloxide. A structural study of WOCl2(OC6H3-2,6-Pr2i)2 and WO(OC6H3-2,6-Me2)4 procatalysts showed them to have pseudo-square-pyramidal geometry about the tungsten center (cf. WOCl4). A trans arrangement of 2,6-diisopropylphenoxide ligands was found for the WOCl2(OC6H3-2,6-Pr2i)2 procatalyst. The ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) by WOCl3(OAr), WOCl2(OAr)2, and WOCl(OAr)3, in combination with trialkyltin hydrides (R3SnH) or triaryltin hydrides (Ar3SnH), was assessed. Pure tungsten-oxytetrachloride-based procatalysts, i.e., WOCl4-x(OAr)x, activated by a tin hydride, are capable of bulk-polymerizing dicyclopentadiene (DCPD) with very high polymer yields (≥99.5%). The polymerization ability of a particular procatalyst was correlated with the reduction potential (W(VI)→W(V)) of the complex and the charge on the oxygen of the 2,6-disubstituted or 2,4,6-trisubstituted phenoxide ion. The effects of changing DCPD:W, Sn:W and rate moderator:W ratios on residual monomer levels were studied.
- Bell
-
p. 165 - 180
(2008/10/08)
-
- Synthesis and reactivity of two monomeric tungsten(IV) phenoxide complexes
-
W(DIPP)4 (DIPP = O-2,6-C6H3-i-Pr2) has been prepared by adding LiDIPP to WCl4(Et2S)2. W(DMP)4 (DMP = O-2,6-C6H3Me2) can be prepared by an analogous procedure or by reducing trans-W(DMP)4Cl2 with sodium in ether. W(DIPP)4 belongs to the space group C2/c with a = 30.557 (5) ?, b = 13.434 (2) ?, c = 23.312 (3) ?, β = 91.99 (1)°, V = 9153.6 ?3, and Z = 8. Final R1 = 0.042 and R2 = 0.046. W(DIPP)4 contains a ruffled distorted square planar WO4 core with trans O-W-O angles of 168° cis O-W-O angles of 90-91°, and W-O-C angles of 154-159°. W(DMP)4 belongs to the space group P4/n with a = b = 14 475 (2) ?, c = 7.097 (3) ?, V = 1487.0 ?3, and Z = 2. Final R1 = 0.055 and R2 = 0.057. W(DMP)4 contains an essentially planar WO4 core in which trans O-W-O angles are 173.7 (3)°, cis O-W-O angles are 89.8 (2)°, and W-O-C angles are 160.7 (4)°. W(DIPP)4 is too crowded to react with a simple substrate such as an internal acetylene while W(DMP)4 reacts with 3-hexyne to yield W(3-hexyne)(DMP)4, with trimethylsilyl azide to yield W(NSiMe3)(DMP)4, with (SiMe3)CHN2 to yield W[N2CH-(SiMe3)](DMP)4, and with O2, cyclohexene oxide, or iodosylbenzene to yield W(O)(DMP)4. An attempt to replace the DMP ligands by S-2,4,6-R3C6H2 (R = Me or i-Pr) ligands yielded W(S)(DMP)4.
- Listemann, Mark L.,Schrock, Richard R.,Dewan, John C.,Kolodziej, Richard M.
-
p. 264 - 271
(2008/10/08)
-