Synthesis and characterization of cationic and zwitterionic allyl zirconium complexes derived from trimethylenemethane (TMM) cyclopentadienylzirconium acetamidinates

Protonation of the trimethylenemethane derivatives, Cp*Zr(σ2,π-C4H6)[N(R1)C(Me)N(R2)] (1a: R1=R2=i-Pr and 1b: R1=Et, R2=t-Bu) (Cp*=η5-C5Me5), by [PhNMe2H][B(C6F5)4] in chlorobenzene at −10 °C provides the cationic methallyl complexes, Cp*Zr(η3-C4H7)[N(R1)C(Me)N(R2)] (2a: R1=R2=i-Pr and 2b: R1=Et, R2=t-Bu), which are thermally robust in solution at elevated temperatures as determined by 1H NMR spectroscopy. Addition of B(C6F5)3 to 1a and 1b provides the zwitterionic allyl complexes, Cp*Zr{η3-CH2C[CH2B(C6F5)3]CH2}[N(R1)C(Me)N(R2)] (3a: R1=R2=i-Pr and 3b: R1=Et, R2=t-Bu). The crystal structures of 2b and 3a have been determined. Neither the cationic complexes 2 or the zwitterionic complexes 3 are active initiators for the Ziegler-Natta polymerization of ethylene and α-olefins.