Ring-Opening Metathesis Polymerization of Norbornene with Catecholato Complexes of Tungsten(VI) as Effective Catalyst Precursors

Catalysis of catecholatotungsten(VI) complexes for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and dicyclopentadiene (DCPD) was studied. Bis(catecholato) complex, WCl2(cat)2 (2, cat = catecholato), was found to be particularly active for the ROMP of norbornene in the presence of AlEt3 as a cocatalyst to give polymers with relatively narrow molecular weight distributions. A bulky catecholato complex, WCl2(tBucat)2 (3, tBucat = 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, WCl4(cat) 1, showed high activity for the ROMP of a bulkier monomer, DCPD, to give poly(DCPD) with high cis-content.