Cationic zirconium complexes that contain mesityl-substituted diamido/donor ligands. Decomposition via CH activation and its influence on 1-hexene polymerization

The dialkyl complexes [MesNMe]ZrMeNp (2b) and [MesNMe]ZrNp2 ([MesNMe](2-) = [(MesNCH(2)CH(2))(2)NMe](2-); Np = CH2CMe3) were prepared and shown to hav e distorted trigonal bipyramidal structures in which the two amido groups o ccupy equatorial positions. The neopentyl. group in 2b was found in the axi al position. Compound 2b was found to convert to another species (2a) in a first-order manner with k = 1.68 x 10(-3) min(-1) at 20 degreesC and to rea ch an equilibrium with K-eq = [2a]/[2b] = 0.43 in C6D6. Activation of [MesN Me]ZrMeNp with [Ph3C] [B(C6F5)(4)] led to formation of unobservable {[MesNM e]ZrNp} [B(C6F5)(4)], which decomposed by CH activation of an ortho mesityl methyl group to give an inactive dimer of {[activ-MesNMe]Zr} [B(C6F5)(4)], or in the presence of dimethylaniline by beta methyl elimination to give { [MesNMe]ZrMe(PhNMe2)}[B(C6F5)(4)]. {[MesNMe]ZrMe}[B(C6F5)(4)] also decompos es to give the dimer of {[activ-MesNMe]Zr}[B(C6F5)(4)] with k(d) = 6.0 x 10 (-5) s(-1) at 20 degreesC. A dimethyl complex was prepared that contained a second "internal amine" donor, i.e., [(MesNCH(2)CH(2))(2)NCH(2)CH(2)NMesMe ]ZrMe2. Upon activation of the dimethyl species with [Ph3C][B(C6F5)(4)], on e of the (now six) ortho methyl groups was CH activated; the methyl cation was not observed. 1-Hexene was polymerized too rapidly by {[MesNMe]ZrMe}[B( C6F5)(4)] to follow readily by NMR methods, while polymerization by {[MesNM e]Zr( PhNMe2)Me}[B(C6F5)(4)] and {{[MesNMe]ZrMe}(2)(mu -Me)}[B(C6F5)(4)] wa s found to be retarded by dimethylaniline and [MesNMe]ZrMe2, respectively. The marked curvature of the log plot of the consumption of 1-hexene by {[Me sNMe]Zr(PhNMe2)Me}[B(C6F5)(4)] could be modeled by assuming that intermedia tes in the polymerization process decompose by CH activation of a mesityl m ethyl group and are thereby removed from the system as propagating species.