Vinyl-addition copolymerization of norbornene and 1-octene catalyzed by a non-bridged half-titanocene with a tetrazole-phenoxy ligand

A catalyst system comprising Cp*TiCl2(OPhTz) (Cp* = C5Me(5), OPhTz = tetrazole-mono-ortho-substituted phenoxy anion), iBu(3)Al, and [Ph3C][B(C(6)F5)(4)] is employed in the vinyl-addition copolymerization of norbornene (NB) and 1-octene (OT) to understand the catalytic effects of the N-donor tetrazole substituent. Copolymerization is accompanied by significant beta-hydride elimination, producing poly(norbornene-co-1-octene) (P(NB-co-OT)) with low yield and molecular weight. Although the incorporation of OT into the copolymer is less than expected, competitive incorporation of the two monomers is observed. Increasing the mole fraction of OT in the feed reduces both the yield and molecular weight of the copolymer. Spectroscopic analysis reveals that the catalyst system yields P(NB-co-OT)s that are terminated prior to complete monomer conversion, along with non-isolated cooligomers and OT-derived isomers. The cationic titanium(IV) center stabilized by the N-donor tetrazole substituent facilitates the highly regioselective 2,1-insertion of OT. This slows subsequent monomer insertion, thereby promoting beta-hydride elimination.