Catalysts For Ring-opening Metathesis Polymerization Research Articles

From ring-opening metathesis polymerization to Ziegler—Natta polymerization: A method for obtaining polynorbornene—polyethylene block copolymers

We have transformed titanacyclobutanes, catalysts for living ring-opening metathesis polymerization (ROMP), into σ-alkyltitanocene complexes, components of catalysts for Ziegler—Natta polymerizations, with the aim of obtaining poly-α-olefin-polynorbornene block copolymers. 3,3-Dimethylcyclopropene-titanacyclobutane, the most effective Ti-based initiator of ROMP polymerizations, and the chain propagating titanacycle, have been converted into alkoxy derivatives. 13C 2H 4 (1- 13C, 90% enriched) polymerizations, catalyzed by these alkyltitanocene alkoxides in the presence of the AlEtCl 2 cocatalyst, have been monitored by 13C NMR spectroscopy. We have shown that polyethylene can grow on the Tialkyl bond derived from the ROMP catalysts.

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

Pure WOCl 4- x (OAr) x complexes ( x = 1, 2, 3 or 4; OAr = aryloxide, e.g., −OC 6H 3-2,6-Me 2 were prepared in essentially quantitative yields by reacting tungsten oxytetrachloride (WOCl 4) with the stoichiometric amount of the parent substituted phenol or lithium aryloxide. A structural study of WOCl 2(OC 6H 3-2,6-Pr i 2) 2 and WO(OC 6H 3-2,6-Me 2) 4 procatalysts showed them to have pseudo-square-pyramidal geometry about the tungsten center ( cf. WOCl 4). A trans arrangement of 2,6-diisopropylphenoxide ligands was found for the WOCl 2(OC 6H 3-2,6-Pr i 2) 2 procatalyst. The ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) by WOCl 3(OAr), WOCl 2(OAr) 2, and WOCl(OAr) 3, in combination with trialkyltin hydrides (R 3SnH) or triaryltin hydrides (Ar 3SnH), 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(V1) → 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.

Progress toward new catalysts for acyclic diene metathesis (ADMET) polymerization reactions

The compounds Tp′W(CHR)(E)X (Tp′= hydridotris(3,5-dimethylpyrazolyl)borate; RCMe 3, Ph; EO, NPh; XCl, Br), 4a–c, have been synthesized by reaction of Tp′W(CR)X 2, (R CMe 3, XCl; RPh, XBr), 3a, b, with neutral alumina or aniline. Compounds 3a, b and 4a–c are air stable and thermally stable to ⪢ 100 °C in the solid state. When combined with 1 equivalent of AlCl 3, Tp′W(CHPh)(NPh)Br, 4c, catalyzes the acyclic diene metathesis (ADMET) oligomerization of 1,9-decadiene, giving a mixture of 1,9,17-octadecatriene, 1,9,17,25-hexadodecatetraene and ethylene (≈30% conversion). The new alkylidene complex, 4a, is an efficient ring-opening metathesis polymerization (ROMP) catalyst in the presence of AlCl 3, as a co-catalyst.

The mechanism of stereoselective ring-opening metathesis polymerization of norbornene and several derivatives

The properties of several noble metal halide catalysts for ring-opening metathesis polymerization of norbornene, endo-dicyclopentadiene and norbomadiene have been investigated as a function of prior or in situ treatment by the latter pair of diolefins, which may also be monomers as stated. Microstructures of the various polymers and sometimes copolymers were examined in detail using 13C NMR, 1H NMR and IR spectroscopic techniques. In the case of Ru and Os chlorides, there is a dramatic swing from high- trans to high- cis polymer in all cases where chelating diolefin is present, whereas IrCl 3 is unaffected in this respect. High- cis polymers of norbornene, made using RhCl 3 and endo-dicyclopentadiene-modified RuCl 3, show a strong tendency for the small number of trans units that are present to occur in triplets and larger blocks, an unusual blockiness feature previously noted only when the OsCl 3 catalyst was used. The usual tendency for high- cis-poly(norbornene) made using numerous Mo, W and Re based catalysts is to have the trans units in pairs. In all cases, therefore, there is a virtual absence of ctc triads, in contradiction to expectation for random high- cis polymers. This general feature is discussed in terms of a new mechanism based on two or more kinetically distinct metallacarbenes and various conformational forms of metallacyclobutanes undergoing disrotatory [2 + 2] cycloreversion reactions.