Living Ziegler-Natta polymerization by early transition metals: synthesis and evaluation of cationic zirconium alkyl complexes bearing beta-hydrogens as models for propagating centers.
The synthesis and characterization of a series of cationic zirconium and hafnium complexes with alkyl substituents bearing beta-hydrogens of general formula {(eta(5)-C5Me5)MR[N(Et)C(Me)N(t-Bu)]}[B(C6F5)4] [M = Zr; R = Et, n-Pr, i-Pr, n-Bu, i-Bu, and 2-ethylbutyl (5a-f) and M = Hf; R = i-Bu and t-Bu (6 and 7, respectively)] is described, including several isotopically labeled derivatives. The ability of these complexes to serve as model complexes for the living Ziegler-Natta polymerization of olefins that can be effected using the initiator 2a (R = Me in 5) has been addressed. The results obtained shed additional light on the steric and electronic factors that can contribute to the living character of a Ziegler-Natta polymerization based on an early transition metal initiator.
Harney
Matthew B
MB
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
Keaton
Richard J
RJ
Fettinger
James C
JC
Sita
Lawrence R
LR