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

Abstract

Protonation of the trimethylenemethane derivatives, Cp*Zr(σ 2,π-C 4H 6)[N(R 1)C(Me)N(R 2)] ( 1a: R 1=R 2= i-Pr and 1b: R 1=Et, R 2= t-Bu) (Cp*=η 5-C 5Me 5), by [PhNMe 2H][B(C 6F 5) 4] in chlorobenzene at −10 °C provides the cationic methallyl complexes, Cp*Zr(η 3-C 4H 7)[N(R 1)C(Me)N(R 2)] ( 2a: R 1=R 2= i-Pr and 2b: R 1=Et, R 2= t-Bu), which are thermally robust in solution at elevated temperatures as determined by 1H NMR spectroscopy. Addition of B(C 6F 5) 3 to 1a and 1b provides the zwitterionic allyl complexes, Cp*Zr{η 3-CH 2C[CH 2B(C 6F 5) 3]CH 2}[N(R 1)C(Me)N(R 2)] ( 3a: R 1=R 2= i-Pr and 3b: R 1=Et, R 2= 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.