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Group 4 Dimethylsilylenebisamido Complexes Bearing the 6‐[2‐(Diethylboryl)phenyl]pyrid‐2‐yl Motif: Synthesis and Use in Tandem Ring‐Opening Metathesis/Vinyl‐Insertion Copolymerization of Cyclic Olefins with Ethylene
Author(s) -
Zou Yuanlin,
Wang Dongren,
Wurst Klaus,
Kühnel Christa,
Reinhardt Ingrid,
Decker Ulrich,
Gurram Venkatanavarana,
Camadanli Sebnem,
Buchmeiser Michael R.
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101829
Subject(s) - polymer chemistry , copolymer , romp , metathesis , polymerization , chemistry , ethylene , ring opening metathesis polymerisation , cyclopentene , monomer , migratory insertion , organic chemistry , catalysis , polymer
Two novel Zr IV ‐ and Hf IV ‐based bisamido complexes bearing the 6‐[2‐(diethylboryl)phenyl]pyrid‐2‐yl motif, that is, [ZrCl 2 {Me 2 Si(DbppN) 2 }(thf)] ( 9 ) and [HfCl 2 {Me 2 Si(DbppN) 2 }(thf) 2 ] ( 10 ) (DbppN=6‐[2‐(diethylboryl)phenyl]pyridine‐2‐amido) have been prepared. Their reactivities have been compared with that of a model precatalyst that does not bear the aminoborane motif. Upon activation with methylalumoxane, precatalysts 9 and 10 are active in the homopolymerization of ethylene (E) yielding high‐density polyethylene (HDPE). In the copolymerization of E with cyclopentene (CPE), for example by the action of 9 , the presence of CPE resulted in a dramatic increase in the polymerization activity of E, while CPE incorporation remained close to or at zero. In the vinyl‐insertion copolymerization of norborn‐2‐ene (NBE) with E by the action of 9 , statistical cyclic olefin copolymers of these two monomers were obtained. At higher NBE concentrations, however, 9 gave rise to reversible ring‐opening metathesis (ROMP)/vinyl‐insertion polymerization (VIP) of NBE with E, resulting in the formation of multi‐block copolymers of the general formula poly(NBE) ROMP ‐ co ‐poly(NBE) VIP ‐ co ‐poly(E). This particular feature of precatalyst 9 , that is, the ability to induce a reversible α‐H elimination/α‐H addition reaction, is attributed to the unique role of the 6‐[2‐(diethylboryl)phenyl]pyrid‐2‐yl ligand. Accordingly, a model precatalyst lacking this ligand does not have the ability to induce α‐H elimination/α‐H addition reactions. The different 11 B NMR shifts of various diethylborylphenylpyrid‐2‐ylamines and ‐amides permit a ranking of the strengths of the BN bonds in these compounds. This strength of the BN bond is correlated with the propensity of 9 /MAO to produce poly(NBE) ROMP ‐ co ‐poly(NBE) VIP ‐ co ‐poly(E) at different temperatures.