Kinetic investigation of the polymerization of 1-hexene by the {[t-BuNON]ZrMe}[B(C6F5)4] initiator

We have investigated the rates of polymerization of 1-hexene by cationic monoalkyl zirconium catalysts that contain the [t-BuNON](2-) ligand ([t-BuNON](2-) = {[(CH3)(CD3)(CN)-C-2-o-C6H4](2)O}(2-)). Catalysts obtained by activation of [t-BuNON] ZrMe2 with [Ph3C] [B(C6F5)(4)] at 0 degreesC in mixtures Of C6D6 and bromobenzene polymerize 1-hexene at a rate that is first order in Zr and first order in 1-hexene with k(p) = 9.2 +/- 0.7 M-1 min(-1) and activation parameters DeltaH double dagger = 7.9 +/- 0.4 kcal mol(-1) and DeltaS double dagger = -33.1 +/- 1.1 cal mol(-1) K-1. The rate of polymerization decreases upon addition of dimethylaniline to the initiator and increases upon addition of [t-BuNON]ZrMe2 to the initiator. In both circumstances, especially the latter, catalyst decomposition via beta hydride elimination compromised the strictly living character of the polymerization.