Aryloxide derivatives of tungsten oxytetrachloride as ring-opening metathesis polymerization catalysts

Article abstract of DOI:10.1016/0304-5102(92)80155-A

Pure WOCl_4-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., WOCl_4-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.