ABSTRACT:Catalysis of catecholatotungsten(VI) complexes for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and dicyclopentadiene (DCPD) was studied. Bis(catecholato) complex, WCl 2 (cat) 2 (2, cat = catecholato), was found to be particularly active for the ROMP of norbornene in the presence of AlEt 3 as a cocatalyst to give polymers with relatively narrow molecular weight distributions. A bulky catecholato complex, WCl 2 ( t Bucat) 2 (3, t Bucat = 3,5-di-tert-butylcatecholato), afforded poly(NBE) with high cis-content. The use of modified methylaluminoxane (MMAO, Type 3A in toluene) as a cocatalyst improved activities at low temperature (−78• C). A mono(catecholato) complex, WCl 4 (cat) 1, showed high activity for the ROMP of a bulkier monomer, DCPD, to give poly(DCPD) with high cis-content. KEY WORDS Ring-opening Metathesis Polymerization / Norbornene / Dicyclopentadiene / Tungsten / Catecholato / 2,6-Dimethylphenoxo / Polynorbornene is an interesting polymer for its special properties such as shape memory resin and oil-absorbing rubber. Hydrogenated polynorbornene derivatives have high transparency and low glass transition point suitable for optical applications. Classical catalysts such as WCl 6 /AlEt 3 have been used for ring-opening metathesis polymerization (ROMP) of norbornene (NBE). 1 These classical catalyst systems are easily available and highly active, however, they have some disadvantages: high sensitivity to air and moisture, poor controllability of the molecular weight distribution and microstructure of the resulting polymers. Recent development of organometallic chemistry achieved controlled ROMP catalyzed by well-defined alkylidene complexes such as W(= NAr)(OR) 2 (= CHR ), 2 but those catalyst systems are also highly sensitive to air and moisture, and are expensive. For practical use, isolation of alkylidene complexes is not necessary and introduction of appropriate supporting ligands is important. For example, WOCl 4−n (OAr) n /R 3 SnH is a good catalyst precursor for bulk ROMP of dicyclopentadiene (DCPD). 3 We have been interested in the effect of chelating aryloxo ligands on the catalysis of tungsten compounds for ROMP. 4-8 However, these complexes also contained other ancillary ligands such as oxo and substituted alkyne, which could effect on their ROMP catalyses rather than the chelating aryloxo ligands. In order to clarify the effect of the chelating ligands on ROMP catalysis, we systematically studied a series of tungsten(VI) chloride complexes having chelating aryloxo † To whom correspondence should be addressed.ligands without any other ligands. Here we chose a commercially available and inexpensive ligand, catechol, as a practical ancillary ligand for tungsten catalysts. The ROMP catalyses of the catecholatotungsten complexes were compared with those of the monodentate aryloxo complexes and WCl 6 .
EXPERIMENTAL
GeneralAll the operations were performed under argon with standard Schlenk techniques. 1 H NMR spectra were recorded on a JEOL JNM-LA-400 spectrometer, a...
